Solid-phase extraction method for improved removal of phospholipids from biological samples

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 62 / 609,262, filed December 21, 2017 and entitled "SOLID PHASE EXTRACTION METHODS FOR ENHANCED REMOVAL OF PHOSPHOLIPIDS FROM BIOLOGICAL SAMPLES.BACKGROUND

[0002] The present disclosure relates to methods and kits for the enhanced removal of phospholipids from biological samples by Solid Phase Extraction (SPE). Biological samples frequently contain phospholipids which can interfere with sample analyses, including liquid chromatography-mass spectrometry (LC-MS) analysis, commonly resulting in signal suppression or enhancement. Phospholipids may also lead to column and instrument fouling during LC-MS analysis. Removing phospholipids is beneficial to improve signal-to-noise ratios and data reproducibility.

[0003] ISMAIEL et al. "Investigation of endogenous blood plasma phospholipids, cholesterol and glycerides that contribute to matrix effects in bioanalysis by liquid chromatography / mass spectrometry", JOURNAL OF CHROMATOGRAPHY B: BIOMEDICAL SCIENCES & APPLICATIONS, vol. 878, no. 31, 1 December 2010 (2010-12-01), pages 3303-3316 discloses a sample enrichment procedure employing different sorbents.SUMMARY

[0004] The invention relates to a method of performing a sample enrichment procedure as defined in the claims. In various aspects, the present disclosure not encompassed by the wording of the claims pertains to methods of performing sample enrichment procedures, which comprise: adding a sample fluid that comprises at least one phospholipid and at least one target analyte to a sorbent that comprises a hydrophobic component and a cation exchange component (e.g., a sorbent comprising a copolymer that comprises a hydrophobic organic monomer, an organic monomer comprising a cation-exchange group, and optionally a hydrophilic organic monomer, among other possibilities), thereby resulting in sorbent with bound phospholipid and bound target analyte; adding an aqueous solution comprising an acidic compound and a salt (e.g., by adding the aqueous solution to the sample fluid prior to addition of the sample fluid to the sorbent and / or by adding the aqueous solution to the sorbent after addition of the sample fluid to the sorbent); adding an organic solution to the sorbent thereby desorbing at least a portion of the bound phospholipid from the sorbent; and adding an elution solution to the sorbent, thereby desorbing at least a portion of the bound target analyte from the sorbent and forming a solution of the target analyte in the elution solution.

[0005] For example, the present disclosure not encompassed by the wording of the claims is directed to methods of performing sample enrichment procedures that comprise: adding a sample fluid that comprises at least one phospholipid and at least one target analyte to a sorbent comprising an organic copolymer that comprises a hydrophobic organic monomer, a hydrophilic organic monomer and an organic monomer comprising a cation-exchange group thereby yielding sorbent with adsorbed phospholipid and adsorbed target analyte; adding an aqueous solution comprising an acidic compound and a first salt species (e.g., by adding the aqueous solution to the sample fluid prior to addition of the sample fluid to the sorbent and / or or by adding the aqueous solution to the sorbent after addition of the sample fluid to the sorbent); adding an organic solution comprising a first organic solvent species to the sorbent thereby desorbing at least a portion of the phospholipid from the sorbent: adding an elution solution that comprises (a) a basic compound or a second salt species (which may be the same as or different from the first salt species) and (b) a second organic solvent species (which may be the same as or different from the first organic solvent species) to the sorbent, thereby desorbing at least a portion of the target analyte from the sorbent and forming a solution of the target analyte in the elution solution.

[0006] As another example, the present disclosure not encompassed by the wording of the claims is directed to methods of performing a sample enrichment procedure, the method comprising: adding an aqueous solution comprising an acidic compound and a first salt species to a sample fluid that comprises at least one phospholipid and at least one target analyte, thereby forming a pretreated sample: adding the pretreated sample to a sorbent, thereby resulting in sorbent with adsorbed phospholipid and adsorbed target analyte, wherein the sorbent comprises a hydrophobic component and a cation exchange component (e.g., a sorbent comprising a copolymer that comprises a hydrophobic organic monomer, an organic monomer comprising a cation-exchange group, and optionally a hydrophilic organic monomer, among other possibilities); washing the sorbent in a single washing step wherein an organic solution comprising a first organic solvent species is added to the sorbent thereby desorbing at least a portion of the phospholipid from the sorbent; and adding an elution solution that comprises (a) a basic compound or a second salt species (which may be the same as or different from the first salt species) and (b) a second organic solvent species (which may be the same as or different from the first organic solvent species) to the sorbent, thereby desorbing at least a portion of the target analyte from the sorbent and forming a solution of the target analyte in the elution solution.

[0007] In some embodiments, the target analyte may be a base with a pK a of at least 5.

[0008] In some embodiments, which can be used in conjunction with any of the above aspects and embodiments, the aqueous solution may comprise the acidic compound in an amount sufficient to provide the aqueous solution with a pH that is at least two pH units below a lowest pK a of the target analyte.

[0009] In some embodiments, the acidic compound may be selected from an organic acid. phosphoric acid, hydrochloric acid, or carbonic acid.

[0010] In some embodiments, the solutions of the first and second salt species may comprise the salt in an amount corresponding to an ionic strength ranging from 10-250 mM.

[0011] In some embodiments. the first and second salt species may be salts that dissociate into an organic acid anion or an inorganic anion and a cation selected from a Group I metal cation, a Group II metal cation, an ammonium cation, and an amine cation. The organic acid anion may be selected, for example, from formate, acetate, propionate, butyrate, oxalate, malonate, succinate, maleate, glutarate, glycolate, lactate, malate, citrate and gluconate, among others.

[0012] In some embodiments, the first and second organic solvent species may be selected from methanol, ethanol, 1-propanol, 2-propanol, acetonitrile, acetone, ethyl acetate, methyl ethyl ketone, tetrahydrofuran and blends thereof.

[0013] In some embodiments, the elution solution may comprise the basic compound in an amount sufficient to provide the elution solution with a pH that is at least two pH units above a highest pK a of the target analyte.

[0014] In some embodiments, the sample fluid may comprise a biological sample selected from a whole blood sample, a plasma sample, a serum sample, a food sample, and a food extract sample.

[0015] In other aspects, the present disclosure not encompassed by the wording of the claims pertains to kits which may be useful, for example, in conjunction with any of the above methods, the kits comprising (a) a sorbent comprising a hydrophobic moiety and a cation exchange moiety; (b) an aqueous solution comprising an acidic compound and a first salt species: and (c) optionally, one or more of the following components: (i) a first organic solution (which may be used, for example, as the organic solution in the preceding methods) that comprises a first organic solvent species. (ii) a second organic solution (which may be used, for example, as the elution solution in the preceding methods) that comprises (iia) a second organic solvent species (which may be the same as or different from the first organic solvent species) and (iib) a basic compound or a second salt species (which may be the same as or different from the first salt species), (iii) a collection plate or collection vials, (i) a cap mat, (v) calibration and reference standards. (vi) identification tagging for each component, and (vii) instructions for use.

[0016] In various aspects, the present invention pertains to methods of performing sample enrichment procedures, which comprise: (a) adding a sample fluid that comprises at least one phospholipid and at least one target analyte to a sorbent that comprises a hydrophobic component and a cation exchange component that comprises a counter-ion that is ammonium (e.g., a sorbent comprising a copolymer that comprises a hydrophobic organic monomer, an organic monomer comprising a cation-exchange group that comprises a counter-ion that is ammonium, and optionally a hydrophilic organic monomer, among other possibilities), thereby resulting in sorbent with adsorbed phospholipid and adsorbed target analyte; (b) adding a first organic solution comprising a first organic solvent to remove at least a portion of the adsorbed phospholipid; and (c) adding an elution solution that comprises (i) a basic compound or a salt species and (ii) a second organic solvent species to the sorbent, wherein the second organic solvent species may be the same as or different from the first organic solvent species, thereby desorbing at least a portion of the target analyte from the sorbent and forming a solution of the target analyte in the elution solution.

[0017] In some embodiments, which may be used in conjunction with any of the above aspects and embodiments, the cation exchange group comprises a sulfonate moiety.

[0018] In some embodiments, which may be used in conjunction with any of the above aspects and embodiments, the first and second organic solvent species are selected from methanol, ethanol, 1-propanol, 2-propanol, acetonitrile, acetone, ethyl acetate, methyl ethyl ketone, tetrahydrofuran and blends thereof.

[0019] In some embodiments, which may be used in conjunction with any of the above aspects and embodiments, the elution solution comprises the basic compound. For example, the the basic compound may be provided in an amount sufficient to provide the elution solution with a pH that is at least two pH units above a highest pK a of the target analyte.

[0020] In some embodiments, which may be used in conjunction with any of the above aspects and embodiments, the elution solution comprises the salt species. In certain of these embodiments, the salt species may be one that dissociates into (a) an organic acid anion (e.g., formate, acetate, propionate, butyrate, oxalate, malonate, succinate, maleate, glutarate, glycolate, lactate, malate, citrate, gluconate, etc.) or an inorganic anion (e.g., chloride, fluoride, bromide, hydroxide, nitrate, nitrite, sulfate,. phosphate, etc.) and (b) a cation selected from a Group I metal cation, a Group II metal cation, an ammonium cation, and an amine cation. In certain of these embodiments, the elution solution that comprises the salt species comprises the salt species in an amount corresponding to an ionic strength ranging from 10-250 mM.

[0021] In some embodiments, which may be used in conjunction with any of the above aspects and embodiments, the methods further comprise adding an aqueous solution to the sorbent (e.g. after adding the sample fluid and before adding the first organic solution). In some of these embodiments, the aqueous solution comprises an organic acid. In some of these embodiments, the aqueous solution comprises one or more acids selected from the following: formic acid, acetic acid, propionic acid, butyric acid, oxalic acid, malonic acid, succinic acid maleic acid, glycolic acid, lactic acid, tartaric acid, malic acid, citric acid and gluconic acid, phosphoric acid, hydrochloric acid and carbonic acid.

[0022] In some embodiments, which may be used in conjunction with any of the above aspects and embodiments, the target analyte is a base with a pK a of at least 5.

[0023] In some embodiments, which may be used in conjunction with any of the above aspects and embodiments, the sample fluid comprises a biological sample selected from a whole blood sample, a plasma sample, a serum sample, a food sample, and a food extract sample.

[0024] These and numerous other aspects and embodiments will now be described in the Detailed Description and Claims to follow.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Fig. 1 shows a comparison of the elute fraction analyte % recoveries for the Existing Oasis MCX Protocol and the New Protocol 1. Fig. 2 shows a comparison of the elute fraction phosphatidylcholine peak areas for the Existing Oasis MCX Protocol and the New Protocol 1. Fig. 3 shows a comparison of the elute step analyte % recoveries for the New Protocol 1, New Protocol 2a and New Protocol 2b. Fig. 4 shows a comparison of the elute fraction phosphatidylcholine peak areas for the New Protocol 1, New Protocol 2a and New Protocol 2b. Fig. 5 shows a comparison of phosphatidylcholine level and analyte recovery using varying amounts of ammonium formate in the methanol wash step for new protocol 3. DETAILED DESCRIPTION

[0026] The present disclosure pertains to methods for enhanced removal of phospholipids from biological samples and to sorbents, devices and kits beneficial in performing such methods.

[0027] In some aspects, the present disclosure not encompassed by the wording of the claims pertains to methods of performing sample enrichment that comprise: (a) adding a sample fluid that comprises at least one phospholipid and at least one target analyte to a sorbent, wherein the sorbent comprises a hydrophobic component and a cation exchange component; (b) either (i) adding an aqueous solution comprising an acidic compound and a first salt species to the sample fluid prior to adding the sample fluid to the sorbent or (ii) adding an aqueous solution comprising an acidic compound and a salt to the sorbent after loading the sorbent with the sample fluid; (c) adding a washing solution that comprises a first organic solvent species to the sorbent thereby desorbing at least a portion of the phospholipid from the sorbent; and (d) adding an elution solution that comprises (i) a basic compound or a second salt species, which may be the same as or different from the first salt species, and (ii) a second organic solvent species, which may be the same as or different from the first organic solvent species, to the sorbent, thereby desorbing at least a portion of the target analyte from the sorbent and forming a solution of the target analyte in the elution solution.

[0028] In some aspects, the present disclosure not encompassed by the wording of the claims pertains to methods of performing sample enrichment that comprise: (a) adding a sample fluid that comprises at least one phospholipid and at least one target analyte to a sorbent comprising a hydrophobic component and a cation exchange component comprising a counter-ion that is not H +< , thereby resulting in sorbent with adsorbed phospholipid and adsorbed target analyte; (b) adding a washing solution that comprises a first organic solvent species to remove at least a portion of the adsorbed phospholipid; and (c) adding an elution solution that comprises (i) a basic compound or a salt species and (ii) a second organic solvent species to the sorbent, wherein the second organic solvent species may be the same as or different from the first organic solvent species, thereby desorbing at least a portion of the target analyte from the sorbent and forming a solution of the target analyte in the elution solution. Optionally, the sample fluid is or is derived from a biological sample. Exemplary biological samples include any biological sample that contains phospholipids, such as biological fluids (e.g., whole blood samples, blood plasma samples, serum samples, etc.), biological tissues, biological matrices, cells (e.g., one or more types of cells), and cell culture supernatants, and foods that contain phospholipids (e.g., meats, whole grains, legumes, eggs, etc.), food extracts.

[0029] As indicated above, the methods of performing sample enrichment described herein include a step where a sample fluid that comprises at least one phospholipid and at least one target analyte is added to a sorbent (suitable sorbents are described in more detail below).

[0030] Such a process frequently referred to as a "loading" process, and commonly involves passing the sample fluid through a device that contains the sorbent (such devices are described in more detail below). During loading, the one or more target analytes, along with various non-target substances, including one or more phospholipids, are adsorbed onto the sorbent. Contact time and / or flow rate may be optimized for proper diffusion kinetics and binding of the one or more target analytes and the one or more phospholipids to the sorbent. If desired the sample fluid may be passed multiple times through the device.

[0031] In certain embodiments, for example, where the sorbent is not readily water-wettable, conditioning and equilibrating steps may optionally be performed prior to sample loading. For example, in an exemplary embodiment, the conditioning may be performed with methanol, ethanol, propanol, isopropyl alcohol, water and a mixture thereof, among other possibilities. For example, in an exemplary embodiment, the equilibrating solution may have an appropriate pH and solvent strength to provide equilibrated partitioning environments in the sorbent when the sample fluid is loaded. Exemplary equilibrating solution / solvent include, for example, water, an aqueous solution such as a buffer solution (e.g., a phosphate buffer solution), a water-miscible organic solvent solution and the like.

[0032] In certain embodiments, for example, where the sorbent is sufficiently water-wettable, conditioning and equilibrating may be omitted before sample loading.

[0033] In certain methods of performing sample enrichment described herein, including methods that employ a sorbent comprising a cation exchange component that comprises H +< as a counter ion, which is not according to the invention, prior to adding a washing solution that comprises a first organic solvent species, an aqueous solution comprising an acidic compound and a first salt species may be either (a) added to the sample fluid prior to adding the sample fluid to the sorbent or (b) added to the sorbent after loading the sorbent with the sample fluid.

[0034] In either of these intermediate steps, the acidic compound in the aqueous solution may be selected from a variety of acidic compounds, including one or more of the following: organic acids such as formic acid, acetic acid, propionic acid, butyric acid, oxalic acid, malonic acid, succinic acid and maleic acid, among others and including organic hydroxyacids such as glycolic acid, lactic acid, tartaric acid, malic acid, citric acid and gluconic acid, among others; and inorganic acids such as phosphoric acid, hydrochloric acid, or carbonic acid, among others.

[0035] The amount of acid in the aqueous solution may vary but is beneficially provided in an amount sufficient to provide the aqueous solution with a pH that is at least two pH units below a lowest pK a of the target analyte.

[0036] Salt species for using in conjunction with the present disclosure, including the first salt species in the aqueous solution, may be selected from a variety of salts, including salts that comprise (a) an anion selected from organic anions (those based on organic acids), such as formate, acetate, propionate, butyrate, oxalate, malonate, succinate, maleate, or glutarate, glycolate, lactate, malate, citrate, and gluconate, and other anionic species such as halides, nitrate, phosphate, sulfate, and sulfonates, among others and (b) a cation selected from ammonium cations, Group I metal cations, Group II metal cations, and cations based on amines (also referred to herein as an amine cation), such as methyl amine (methyl ammonium), methane diamine (methyl diammonium), ethyl amine (ethyl ammonium), ethyl diamine (ethyl diammonium), diethylamine (diethyl ammonium), diethanolamine (diethanol ammonium), tromethamine, choline, pyrrolidine (pyrrolidinium), pyrrole (pyrrolium), piperazine (piperazinium), or pyridine (pyridinium), among others. In certain embodiments, the salt is ammonium formate.

[0037] The amount of salt in the aqueous solution may vary widely. In certain embodiments, the salt may be provided in an amount that produces an ionic strength ranging from 10-250 mM, where ionic strength is expressed by the equation, I = 1 2 ∑ i c i z i 2 , where c i is the molar concentration of any ion in solution, and z i is its valence. For salts consisting of an anion having a valence of 1 and a cation having a valence of 1, the ionic strength of the solution is equal to the molar concentration of the dissolved salt.

[0038] After either of these intermediate steps, the washing solution that comprises the first organic solvent species is contacted with the sorbent thereby desorbing at least a portion of the at least one phospholipid from the sorbent. In this way, non-target substances, including the one or more phospholipids are separated from the one or more target analytes, which are bound to the sorbent, thereby resulting in the elution of the non-target substances, while allowing the one or more target analytes to remain retained on the sorbent.

[0039] In certain other methods of performing sample enrichment not encompassed by the wording of the claims described herein, including methods that employ a sorbent comprising a cation exchange component comprising a counter-ion that is not H +< (e.g., counter-ion selected from a Group I metal cation, a Group II metal cation, an ammonium cation, and an amine cation), the washing solution that comprises the first organic solvent species may be contacted with the sorbent, without an intermediate step employing an aqueous solution comprising an acidic compound and a first salt species as described above. As above, the washing solution that comprises the first organic solvent species desorbs at least a portion of the at least one phospholipid from the sorbent, thereby separating non-target substances, including the one or more phospholipids, from the one or more target analytes, which are bound to the sorbent, resulting in the elution of the non-target substances, while allowing the one or more target analytes to remain retained on the sorbent.

[0040] A variety of organic solvent species may be used in the washing solutions of the present disclosure, including one or more of the following, among others: methanol, ethanol, 1-propanol, 2-propanol, acetonitrile, acetone, ethyl acetate, methyl ethyl ketone, and tetrahydrofuran. In certain beneficial embodiments, the organic solvent species is methanol.

[0041] After separating the washing solution from the sorbent, an elution solution that comprises (a) a basic compound or a salt species (also referred to herein as a second salt species in some embodiments), which may be the same as or different from the first salt species described above, and (b) an organic solvent species (also referred to herein as a second organic solvent species), which may be the same as or different from the first organic solvent species described above, is contacted with the sorbent, thereby desorbing at least a portion of the at least one target analyte from the sorbent and forming a solution of the target analyte in the elution solution.

[0042] The base in the elution solution may be selected from a variety of bases. The amount of base in the elution solution may vary but is beneficially provided in an amount sufficient to provide the elution solution with a pH that is at least two pH units above a highest pK a of the target analyte. Examples of bases may be selected from one or more of the following, among others: ammonium hydroxide (NH 4 OH), alkali metal hydroxides (e.g., LiOH, NaOH, KOH, RbOH, etc.), alkaline earth metal hydroxides (e.g., Mg(OH) 2 , Ca(OH) 2 , Sr(OH) 2 , etc.), organic bases (e.g., triethylamine), and combinations thereof. In certain beneficial embodiments, a volatile base such as ammonium hydroxide is particularly beneficial.

[0043] The second salt species in the elution solution may be selected from a variety of salts, including salts that comprise (a) an anion selected from organic anions (those based on organic acids), such as formate, acetate, propionate, butyrate, oxalate, malonate, succinate, maleate, or glutarate, glycolate, lactate, malate, citrate, and gluconate, among others and (b) a cation selected from ammonium cations, and cations based on amines, such as methyl amine (methyl ammonium), methane diamine (methyl diammonium), ethyl amine (ethyl ammonium), ethyl diamine (ethyl diammonium), diethylamine (diethyl ammonium), diethanolamine (diethanol ammonium), tromethamine, choline, pyrrolidine (pyrrolidinium), pyrrole (pyrrolium), piperazine (piperazinium), or pyridine (pyridinium), among others. In certain embodiments, the salt is ammonium formate. The amount of salt in the elution solution may vary but is beneficially provided in an amount sufficient to effectively elute the analyte.

[0044] A variety of second organic solvent species may be used in the elution solutions of the present disclosure, which solvent species may be same as or different from those of the washing solution (also referred to as the first organic solvent species)_and include one or more of the following, among others: methanol, ethanol, 1-propanol, 2-propanol, acetonitrile, acetone, ethyl acetate, methyl ethyl ketone, and tetrahydrofuran. In certain beneficial embodiments, the organic solvent species is methanol.

[0045] In particular beneficial embodiments, the elution solution comprises 2-10 vol% concentrated NH 4 OH and 90-98 vol% methanol

[0046] After being eluted from the sorbent, further processing of the one or more target analytes may include, for example, identifying, quantifying, or otherwise processing the one or more target analytes.

[0047] In various embodiments, methods described herein may further comprise analyzing samples using analytical instruments and / or techniques, for example, liquid chromatography (LC), including high performance liquid chromatography (HPLC) and ultra-high performance liquid chromatography (UHPLC ), mass spectrometry (MS), including electrospray ionization mass spectrometry (ESI-MS), or a combination thereof. For instance, in some embodiments, the processed samples may be analyzed using liquid chromatography, such as HPLC or UHPLC, in combination with mass spectrometry, such as ESI-MS, examples of which include liquid chromatography-mass spectrometry (LC-MS) techniques and liquid chromatography-mass spectrometry / mass spectrometry (LC-MS / MS) techniques. In certain cases, analytical samples may be evaporated to dryness, and then reconstituted in another solution before being injected into a liquid chromatography system.

[0048] As noted above, sorbents for use in the present disclosure include sorbents having a hydrophobic component and a cation exchange component In some embodiments, the sorbents comprise an organic polymer having a hydrophobic component and a cation exchange component.

[0049] As used herein, "hydrophobic" means lacking an affinity for, repelling, or failing to adsorb or absorb water, whereas "hydrophilic" means having an affinity for, attracting, adsorbing or absorbing water,

[0050] As used herein, "organic polymers" are organic molecules containing multiple copies (e.g., from 5 to 10 to 25 to 50 to 100 to 250 to 500 to 1000 or more copies) of one or more constitutional units, commonly referred to as organic monomers. As used herein, "organic monomers" may refer to free monomers and to those incorporated into polymers, with the distinction being clear from the context in which the term is used. As a specific example, the following monomer, , and the following incorporated monomer, (where n is 1), may each be referred to herein as "a styrene sulfonate monomer." It is noted that incorporated monomers are named independently of the monomer that was polymerized to form the polymer. For instance, in the preceding example, the incorporated styrene sulfonate monomer may, in theory, be formed from a free styrene sulfonate monomer or from a styrene monomer that is first polymerized and later subjected to a sulfonation process. In either case, the incorporated organic monomer is referred to herein as a styrene sulfonate monomer.

[0051] Organic polymers may take on a number of configurations, which may be selected, for example, from linear, cyclic and branched configurations, among others. Branched configurations include star-shaped configurations (e.g.. configurations in which three or more chains emanate from a single branch point), comb configurations (e.g., configurations having a polymer backbone and a plurality of side chains, also referred to as "graft" configurations), dendritic configurations (e.g., arborescent and hyperbranched poly mers), networked (e.g., crosslinked) configurations and so forth.

[0052] As used herein, "organic homopolymers" are polymers that contain multiple copies of a single organic monomer. As used herein, "organic copolymers" are organic polymers that contain multiple copies of at least two dissimilar organic monomers, examples of which include random, statistical, gradient, periodic (e.g.. alternating) and block copolymers.

[0053] In some embodiments, the organic polymer having a hydrophobic component and a cation exchange component, may be, for example, an organic copolymer comprising a hydrophobic organic monomer and an organic monomer having a cation-exchange group. In some embodiments, the organic copolymer comprising the hydrophobic organic monomer and the organic monomer having the cation-exchange group may further comprise a hydrophilic organic monomer, thereby improving the water wettability of the copolymer. Exemplary examples are described in U.S. Patent Nos. 7,232,520 and 7,442,299.

[0054] In certain embodiments, the hydrophobic monomer may be selected from alkene monomers (e.g., butadiene), monomers having a straight chain C2-C18-alkyl group. monomers having a branched chain C3-C18-alkyl group, monomers having a C6-C18 monocyclic or multicyclic, saturated, unsaturated or aromatic carbocyclic group. e.g., a phenyl group, or a phenylene group. Specific examples of hydrophobic monomers include, for example, divinylbenzene, styrene, or ethylvinylbenzene.

[0055] In certain embodiments, the organic monomer having the cation-exchange group may be selected from organic monomers that comprise one or more sulfonate groups. In particular embodiments, the organic monomer having the cation-exchange group may be a divinylbenzene monomer that comprises one or more sulfonate groups. In certain embodiments, the cation-exchange group comprises H +< as a counter-ion. In certain embodiments, the cation-exchange group comprises a counter-ion that is not H +< (e.g., a Group I metal cation, a Group II metal cation, an ammonium cation, an amine cation, etc.).

[0056] In certain embodiments, the hydrophilic monomer may be selected from monomers having an amide group, monomers having an ester group, monomers having a carbonate group, monomers having a carbamate group, monomers having a urea group, monomers having a hydroxyl group, and monomers having a nitrogen-containing heterocyclic group, e.g., a saturated, unsaturated or aromatic heterocyclic group. Specific examples include, for example, 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, N-vinylpyrrolidone, N-vinyl-piperidone, N-vinyl caprolactam, alkyl acrylates (e.g., methyl acrylate, ethyl acrylate, etc ), alkyl methacrylates (e.g , methyl methacrylate, ethyl methacrylate, etc.), vinyl acetate, acrylamide, or methacrylamide.

[0057] Typically, the organic copolymer will comprise a multifunctional hydrophobic monomer such as divinylbenzene and / or a multifunctional hydrophilic monomer such as ethylene glycol dimethacrylate, methylene bisacrylamide or allyl methacrylate to provide crosslinks in the copolymer.

[0058] Instead of, or in addition to, sorbents that comprise an organic poly mer having a hydrophobic component and a cation exchange component as described above, in some embodiments, a sorbent may be employed that is based on inorganic materials such as silica-based materials, alumina-based materials, titania-based materials, and zirconia-based materials. For example, such materials may be surface modified to include both a hydrophobic component (e.g., a C4 to C30 alkyl or aromatic component) and a cation exchange component (e.g., an alkylsulfonate, an aromatic sulfonate or an alkylphosphate).

[0059] Sorbents for use in the present disclosure may comprise sorbent particles, which may vary widely in size and may range, for example, from about 5 to about 100 µm in diameter, among other possible particle sizes. Sorbent particles for use in conjunction with the present disclosure may be porous or non-porous.

[0060] Devices in accordance with the present disclosure commonly include sorbents such as those described herein in a packed sorbent bed.

[0061] Devices in accordance with the present disclosure commonly include a housing having a chamber for accepting and holding sorbent. In various embodiments, the housing may be provided an inlet and an outlet.

[0062] The construction materials for the housing include inorganic materials, for instance, metals such as stainless steel and ceramics such as glass, as well as synthetic polymeric materials such as polyethylene, polypropylene, polyether ether ketone (PEEK), and polytetrafluoroethylene, among others.

[0063] Optionally, the device may include one or more filters which act to hold the sorbent in a housing. Exemplary filters may be, for example, in a form of membrane, screen, frit or spherical porous filter.

[0064] Optionally, a solution received in the housing may flow into the sorbent spontaneously, for example, capillary action. Alternatively, the flow may be generated through the sorbent by external forces, such as gravity or centrifugation, or by applying a vacuum to an outlet of the housing or positive pressure to an inlet of the housing.

[0065] Specific examples of housings for use in the present disclosure include, for example, a syringe, an injection cartridge, a column (e.g., a microbore column, capillary column or nanocolumn), a multi-well device such as a 4 to 8- well rack, a 4 to 8-well strip, a 48 to 96-well plate, a 96 to 384-well micro-elution plate, micro-elution tip devices, including a 4 to 8-tip micro-elution strip, a 96 to 384-micro-elution tip array, a single micro-elution pipet tip, a thin layer plate, a microtiter plate, a spin tube or a spin container.

[0066] Multi-well formats are commonly used with robotic fluid dispensing systems. Typical multi-well formats include 48-, 96-, and 384-well standard plate formats, although other formats are clearly possible.

[0067] Kits may also be provided which comprise a sorbent as described elsewhere herein and one or more of any of the following: (a) an aqueous solution that comprises an acidic compound and a first salt species as described elsewhere herein, (b) an organic solution comprising a first organic solvent species as described elsewhere herein, (c) an elution solution that comprises (i) a basic compound or a second salt species and (ii) a second organic solvent species as described elsewhere herein, (d) a collection plate or collection vial, (e) a cap mat, (f) calibration and reference standards, and (g) instructions for use. The sorbent may be disposed in a housing, for example, in a column, a single-use cartridge, a multi-well strip, a multi-well plate, or other housing as described elsewhere herein.Example 1 (not according to the invention)

[0068] A comparison of an existing Oasis MCX SPE protocol (Oasis Cartridge and 96-Well Plate Care and Use Manual, #716001391EN, section VII, Waters Corp., USA) and a protocol in accordance with the present disclosure (New Protocol 1) was carried out using 1 cc cartridges containing 30 mg of a 30 µm mixed mode reversed phase / strong cation exchange copolymer sorbent. The sorbent was prepared as described in US patents 7,232,520 and 7,442,299. The sample was a solution of a phospholipid standard (L-α-phosphatidylcholine from egg yolk, Sigma catalog number P3556) dissolved in acetonitrile / methanol / water (80 / 1 / 19 v / v / v). The two protocols are shown in Table 1. Table 1 Step New Protocol 1Oasis MCX Existing Protocol Load1 mL of 1 mg / mL L- a - phosphatidylcholine in acetonitrile / methanol / water 80 / 1 / 19 v / v / v1 mL of 1 mg / mL L- α-phosphatidylcholine in acetonitrile / methanol / water 80 / 1 / 19 v / v / vWash 11 mL of 100 mM Ammonium Formate in 2% Formic Acid (aq)1 mL of 2% Formic Acid (aq)Wash 21 mL of methanol1 mL of methanolElute1 mL of methanol + 5% NH 4 OH1 mL of methanol + 5% NH 4 OH

[0069] 100 mM ammonium formate in 2% aqueous formic acid is a solution prepared from ammonium formate and 98 / 2 v / v water / formic acid. 2% formic acid is a solution prepare by 98 / 2 v / v water / formic acid. 5% ammonium hydroxide in methanol is a solution containing 95 / 5 (v / v) methanol / concentrated NH 4 OH. The solutions from each stage of the SPE protocol were analyzed using UPLC with UV detection, employing the conditions given in Table 2, which shows chromatographic conditions for phosphatidylcholine quantification and Table 3, which shows gradient conditions for phosphatidylcholine quantification.

[0070] The eluted solutions were neutralized by adding 35 µL of 98% formic acid (aq) before analyzing them, to avoid hydrolysis of the phosphatidylcholine catalyzed by the presence of ammonium hydroxide (NH 4 OH). The relative concentrations of phosphatidylcholine in each fraction were determined by comparing the integrated peak areas to the sum of the areas for all four fractions. Eight replicates were carried out, and the average results were calculated. Table 2 InstrumentACQUITY UPLC System / ACQUITY I-Class SystemWaters Corporation, Milford MA, USAColumnACQUITY UPLC BEH C 8 1.7 µm 2.1 × 50 mmWaters Corporation, Milford MA, USAColumn Temperature60°CTUV200 nm (L-α-phosphatidylcholine Removal)214 nm (Analyte Recovery)Loop Size2 µLInjection TypePartial loop with needle overfillInjection Volume1.4 µLStrong Wash Solvent Volume150 µLWeak Wash Solvent Volume500 µLSample Temperature22°CSampling Rate40 (pts / sec)Mobile Phase A1 (L-α-phosphatidylcholine Removal)100% waterMobile Phase B1(L-α-phosphatidylcholine Removal)100% acetonitrileMobile Phase A2 (Analyte Recovery)0.1% Trifluoroacetic acid in 100% waterMobile Phase B2 (Analyte Recovery)0.075% Trifluoroacetic acid in 100% acetonitrileStrong Needle Wash0.075% Trifluoroacetic acid in 100% acetonitrileWeak Needle Wash10% acetonitrile / 90% water v / vSeal wash10% acetonitrile / 90% water v / v Table 3 Time (min)Flow (mL / min)%A1 / %A2%B1 / %B2CurveInitial0.599.90.1Initial0.50.599.90.167.00.5406068.00.559569.50.559569.80.599.90.1610.50.599.90.16

[0071] Table 4 shows the results of the phosphatidylcholine removal test (% of total phosphatidylcholine found in each fraction) using the two SPE protocols. The results show that with the existing Oasis MCX protocol, most of the phosphatidylcholine (84.5%) was found in the elute fraction. Most of the remainder (11.9%) was found in the load fraction, with very little found in the wash fractions. In contrast, with the New Protocol 1, most of the phosphatidylcholine (88.7%) was found in the wash 2 fraction. The load fraction contained 10.3% and the elute fraction only contained 0.8%. This demonstrates that the new protocol results in a 105-fold reduction in the phosphatidylcholine content of the elute fraction. This is the fraction that is typically analyzed using LC / MS / MS, where phosphatidylcholine may result in signal suppression or enhancement as well as column and instrument fouling. Table 4 FractionNew Protocol 1Existing Oasis MCX ProtocolLoad10.3%11.9%Wash 10.2%0.3%Wash 288.7%3.3%Elute0.8%84.5% Example 2 (not according to the invention)

[0072] A comparison of the existing Oasis MCX SPE protocol and New Protocol 1 was carried out where the sample was rat plasma (from Bioreclamation IVT, Westbury, NY, USA catalog number RATPLEDTA2) containing endogenous phospholipids and spiked with basic analytes (approximately 30 ng / well of each analyte). The SPE device was a 96-well SPE plate containing 10 mg per well of a 30 µm mixed mode reversed phase / strong cation exchange copolymer sorbent. The sorbent was prepared as described in US patents 7,232,520 and 7,442,299. The protocols are shown in Table 5. 4% aq H 3 PO 4 is a solution of 96 / 4 (v / v) water / concentrated H 3 PO 4 . Table 5 Step New Protocol 1 Existing Oasis MCX Protocol Load100 µL of rat plasma plus 100 µL of 4% aq H 3 PO 4 100 µL of rat plasma plus 100 µL of 4% aq H 3 PO 4 Wash 1500 µL of 100 mM ammonium formate in 2% aq. formic acid500 µL of 2% aq. formic acidWash 2500 µL methanol500 µL methanolElute2 x 150 µL 5% ammonium hydroxide in methanol2 x 150 µL 5% ammonium hydroxide in methanol

[0073] The elute fractions were diluted 1:1 (v / v) with 50:50 methanol / water and analyzed using UPLC with MS / MS detection, employing the conditions given in Table 6, which shows system and method conditions for LC-MS / MS analyses, Table 7, which shows MRM conditions and transitions for basic analytes, and Table 8, which shows MRM conditions and transitions for the phosphatidylcholine class phospholipids (note: phosphatidylcholine quantitation used the TIC generated from all MRM transitions). Table 6 LC-MS / MS System:ACQUITY I-Class UPLC with Xevo TQ-S Mass Spectrometer (MS / MS)Waters Corporation, Milford MA, USAColumn:ACQUITY UPLC BEH C 18 , 1.7 µm, 2.1 x 100 mmWaters Corporation, Milford MA, USAColumn Temperature:40°CInjection Volume:2.0 µLMobile Phases:A1: 0.1% Formic Acid in WaterB1: 0.1% Formic Acid in AcetonitrileNeedle Wash:Strong- 2% Formic Acid in 1:1:1:1Acetonitrile: Methanol: Isopropanol: Water (v / v)Weak- 90:10 Water: Acetonitrile (v / v)Flow Rate:0.6 mL / minGradient:Initial conditions: 2% B1. Hold for 1 min at 2% B1, linear ramp to 70% B1 over 3 minutes, linear ramp to 95% B1 over 0.1 min. Hold at 95% B1 for 2.9 min, return to initial conditions in 0.5 min, hold at 2% B1 for 0.5 min.Run Time:8.0 minutesMass Spectrometer:Xevo TQ-SCapillary Voltage:1.0 kVCone Voltage:See Table 7 and 8Desolvation Temperature:500 °CDesolvation Gas Flow:1000 L / hrCone Gas Flow:150 L / hr Table 7 Analyte Cone Voltage (V) Precurs or Ion (m / z) Product Ions (m / z) Collision Energy (V) Caffeine20195.16106.0430Oxymorphone20302.17198.2444Procainamide20236.10120.2530Methamphetamine20150.2491.0415Oxycodone20316.10241.0830Codeine20300.20165.10303,4-Methylenedioxy-methamphetamine (MDMA)20194.21105.1822Clonidine20230.09159.9430Risperidone20411.32110.1750Propranolol20260.26116.2318Amitriptyline20278.2391.1924Verapamil20455.44150.1744Phencyclidine (PCP)20244.1786.0210 Table 8 Precursor Ion (m / z) Product Ion (m / z) Cone Voltage (V) Collision Energy (V) 496.40184.103530520.40184.103530522.40184.103530524.40184.103530704.40184.103530758.40184.103530760.40184.103530784.40184.103530786.40184.103530806.40184.103530808.40184.103530

[0074] Recoveries were calculated from the ratio of pre-spiked to post-spiked peak areas. For each protocol, replicates were run (n = 4 for analytes, n = 8 for phosphatidylcholine). The average analyte recoveries and phosphatidylcholine amounts by peak area in the Elute fraction are reported here.

[0075] The results are summarized in Fig. 1, which is a comparison of the elute fraction analyte % recoveries for the Existing Oasis MCX Protocol and the New Protocol 1, and Fig. 2, which is a comparison of the elute fraction phosphatidylcholine peak areas for the Existing Oasis MCX Protocol and the New Protocol 1. As seen in these figures, New Protocol 1 gives over a 5-fold decrease in the amount of phosphatidylcholine present in the Elute fraction relative to the Existing Oasis MCX Protocol, while providing equivalent analyte recoveries, compared to the existing protocol.Example 3 (not according to the invention)

[0076] A comparison of the New Protocol 1, New Protocol 2a and New Protocol 2b was carried out where the sample was rat plasma (from Bioreclamation IVT, catalog number RATPLEDTA2) containing endogenous phospholipids and spiked with basic analytes (approximately 30 ng / well of each analyte). The SPE device was a 96-well SPE plate containing 10 mg per well of a 30 µm mixed mode reversed phase / strong cation exchange copolymer sorbent. The sorbent was prepared as described in US patents 7,232,520 and 7,442,299. The protocols are shown in Table 9. Table 9 Step New Protocol 1 New Protocol 2a New Protocol 2b Load100 µL of rat plasma plus 100 µL of 4% aq H 3 PO 4 100 µL of rat plasma plus 100 µL of 200 mM ammonium formate in 4% aq H 3 PO 4 100 µL of rat plasma plus 100 µL of 200 mM ammonium formate in 4% Formic AcidWash 1500 µL of 100 mM ammonium formate in 2% aq. formic acid(not applicable)(not applicable)Wash 2500 µL methanol500 µL methanol500 µL methanolElute2 x 150 µL 5% ammonium hydroxide in methanol2 x 150 µL 5% ammonium hydroxide in methanol2 x 150 µL 5% ammonium hydroxide in methanol

[0077] The elute fractions were diluted 1:1 (v / v) with 50:50 methanol / water and analyzed by UPLC with MS / MS detection, using the conditions given in Tables 6, 7 and 8 (above). Recoveries were calculated from the ratio of pre-spiked to post-spiked peak areas. For each protocol, replicates were run (n = 4 for analytes, n = 8 for phosphatidylcholine). The average analyte recoveries and phosphatidylcholine amounts by peak area in the elute fraction are reported here.

[0078] The results are summarized in Fig. 3, which shows a comparison of the elute step analyte % recoveries for the New Protocol 1, New Protocol 2a and New Protocol 2b, and Fig. 4, which shows a comparison of the elute fraction phosphatidylcholine peak areas for the New Protocol 1, New Protocol 2a and New Protocol 2b.

[0079] Regarding the phosphatidylcholine levels, New Protocol 2a gave results similar to New Protocol 1 while New Protocol 2b gave a level that was lower by a factor of approximately two. For the analyte recoveries, New Protocol 2a and 2b gave equivalent results to New Protocol 1.Example 4 (not according to the invention)

[0080] In New Protocol 3, a salt is added to the methanol wash solution. A series of experiments were carried out to determine the ammonium formate concentrations that are best for removing phosphatidylcholine while retaining the analytes. The protocols are described in Table 10. Table 10 Step Oasis MCX Existing Protocol New Protocol 3 Load1 mL of sample1 mL of sampleWash 11 mL of 2% Formic Acid (aq)1 mL of 2% Formic Acid (aq)Wash 21 mL of methanol1 mL of methanol + Ammonium Formate (10 to 100 mM)Elute1 mL of methanol + 5% NH 4 OH1 mL of methanol + 5% NH 4 OH

[0081] For the phosphatidylcholine level tests, the sample was a solution of L-α-phosphatidylcholine from egg yolk (Sigma catalog number P3556) dissolved in acetonitrile / methanol / water (80 / 1 / 19 v / v / v). The elute solutions were neutralized by adding 35 µL of 98% formic acid (aq) before analyzing them, to avoid hydrolysis of the phosphatidylcholine catalyzed by the presence of ammonium hydroxide (NH 4 OH). The concentrations of phosphatidylcholine in each fraction were determined by comparing the integrated peak areas to those of 1 mg / mL L-α-phosphatidylcholine in acetonitrile / methanol / water 80 / 1 / 19 v / v / v. For the analyte recovery tests, the sample was isotonic saline diluted 1:1 v / v with 4% H 3 PO 4 (aq) spiked with 5.5 µg / mL amphetamine, 5.9 µg / mL metoprolol and 3.3 µg / mL amitriptyline. Recoveries were calculated from the ratio of pre-spiked to post-spiked peak areas. For each protocol, 4 replicates were run. The elute fractions were analyzed using UPLC with UV detection, with the separation conditions described in Tables 2 and 3 (see above).

[0082] Fig. 5 shows a comparison of phosphatidylcholine level and analyte recovery using varying amounts of ammonium formate in the methanol wash step for New Protocol 3. As seen from this figure, the results reveal that 30 mM is a pivotal concentration for both phosphatidylcholine removal and analyte recovery. An ammonium formate concentration of 30 mM was found to achieve a low level of phosphatidylcholine in the elute fraction. However, analyte recovery decreases as the ammonium formate concentration is increased beyond this level.Example 5

[0083] A 2 gram batch of modified Oasis MCX (Oasis MCX-NH 4 +< ) sorbent was prepared as follows. Oasis MCX 30 µm (Waters Corporation) was suspended in 200 mL of 1 molar ammonium formate, pH 3 for 1.5 to 2 hours, then filtered through a 10 µm filter and washed 2X using 250 mL of DI water. The material was allowed to air dry for 72 hours in a hood.

[0084] An initial experiment was carried out using the 30 µm Oasis MCX - NH 4 +< sorbent in 1 cc / 30 mg cartridge format. The sample was a solution of a phospholipid standard (L-α-phosphatidylcholine from egg yolk, Sigma catalog number P3556) dissolved in acetonitrile / methanol / water (80 / 1 / 19 v / v / v).

[0085] Three protocols are shown in Table 11. The solutions from each stage of the SPE protocol were analyzed using UPLC with UV detection, employing the conditions given in Tables 12 and 13. The elute solutions were neutralized by adding 35 µL of 98% formic acid before analyzing them, to avoid hydrolysis of the phosphatidylcholine (PC) catalyzed by the presence of ammonium hydroxide (NH 4 OH). The concentrations of phosphatidylcholine in each fraction were determined by comparing the integrated peak areas to the sum of the total area.

[0086] The results (see Table 11) show that with all three protocols, most of the phosphatidylcholine (> 55%) was found in the load fraction. In the 4-Step method, the 2% formic acid aqueous wash appears to result in the PC being bound on the sorbent by ionexchange, preventing it from being effectively removed by wash 2 (methanol). As a result, a significant amount of PC is present in the elute step using 5% concentrated ammonium hydroxide in methanol. In the 3-Step method, no acidic aqueous wash was used, allowing the bulk of the remaining PC to be removed in the methanol wash step, and the remaining PC (9.1%) was removed in the elute step using 5% concentrated ammonium hydroxide in methanol. The 2-Step method did not have an aqueous or organic wash step and the bulk of the PC that was not in the load fraction was found in the elute fraction (33.8%). Table 11: SPE Protocols and % Phosphatidylcholine in Each Fraction using 1 cc / 30 mg Oasis MCX-NH 4 +< Cartridges Step 4-Step 3-Step 2-Step Load1 mL of 1 mg / mL L- a -phosphatidylcholine in acetonitrile / methanol / water 80 / 1 / 19 v / v / vWash 11 mL of 2% Formic Acid (aq)No WASH UsedNo WASH usedWash 21 mL of methanol1 mL of methanolNo WASH usedElute1 mL of methanol + 5% NH 4 OHResults % Phosphatidylcholine in Each Fraction Load58.3%57.6%66.2%Wash 16.5%No WASH UsedNo WASH UsedWash 28.7%33.3%No WASH UsedElute26.5%9.1%33.8% Table 12. Chromatographic Conditions for Phosphatidylcholine Quantification InstrumentACQUITY UPLC System / ACQUITY I-Class SystemColumnACQUITY UPLC BEH C 8 1.7 µm 2.1 × 50 mmColumn Temperature60°CTUV200 nmLoop Size2 µLInjection TypePartial loop with needle overfillInjection Volume1.4 µLStrong Wash Solvent Volume150 µLWeak Wash Solvent Volume500 µLSample Temperature22°CSampling Rate:40 (pts / sec)Mobile Phase A1:100% waterMobile Phase B1:100% acetonitrileStrong Needle Wash:0.075% Trifluoroacetic acid in 100% acetonitrileWeak Needle Wash:10% acetonitrile / 90% water v / vSeal wash10% acetonitrile / 90% water v / v Table 13. Gradient Conditions for Phosphatidylcholine Quantification Time (min)Flow (mL / min)%A1%B1CurveInitial0.599.90.1Initial0.50.599.90.167.00.5406068.00.559569.50.559569.80.599.90.1610.50.599.90.16 Example 6

[0087] Four batches of modified Oasis MCX (Oasis MCX-NH 4 +< ) sorbent were prepared using the conditions shown in Table 14.

[0088] The 4-Step protocol (see Table 11) was used to evaluate each batch. The solutions from each stage of the SPE protocol were analyzed using UPLC with UV detection, employing the conditions given in Tables 12 and 13. The elute solutions were neutralized by adding 35 µL of 98% formic acid before analyzing them, to avoid hydrolysis of the phosphatidylcholine (PC) catalyzed by the presence of ammonium hydroxide (NH 4 OH). The concentrations of phosphatidylcholine in each fraction were determined by comparing the integrated peak areas to the sum of the total area.

[0089] The results (see Table 15) show that with the 4-Step protocol, the four batches of Oasis MCX-NH 4 +< sorbent performed equivalently. Most of the phosphatidylcholine (> 80%) was found in the load fraction. Very little was found in the aqueous wash fraction (< 2.5%) or methanol wash fraction (< 4.5%), and ca 10-12% was found in the elute fraction. % Recovery of basic analytes on the Oasis MCX-NH 4 +< sorbent was determined on a single cartridge and the peak areas in the elute solution were compared to the post-spike solution to determine the % recovery. The goal of the experiment was to initially assess if the analytes are retained by the Oasis MCX- NH 4 +< sorbent. Recoveries of 100% or greater were achieved with the cartridges prepared using the Oasis MCX- NH 4 +< sorbent. Table 14. Preparation Conditions for Four Batches of Oasis MCX- NH 4 +< Batch ~ 2 gramsBatch 01Batch 02Batch 03Batch 04Step 1Pre-wash with 4% H 3 PO 4 (aq) 100 mL / gram material; ~ 1 hourNO Pre-washPre-wash with 4% H 3 PO 4 (aq) 100 mL / gram material; ~ 1 hourNO Pre-washStep 2Filter off the fluid using a 10 µm filterMaterial will be dryFilter off the fluid using a 10 µm filterMaterial will be dryStep 3Put material in 250 mL bottleStep 4Suspend material in 100 mM Ammonium Formate, pH 3; 100 mL / gram material; ~ 1 hoursSuspend material in 100 mM Ammonium Formate, pH 3; 100 mL / gram material; ~ 1 hoursSuspend material in 100 mM Ammonium Hydroxide; 100 mL / gram material; ~ 1 hoursSuspend material in 100 mM Ammonium Hydroxide; 100 mL / gram material; ~ 1 hoursStep 5Filter off the fluid using a 10 µm filterStep 6Suspend material in 100 mM Ammonium Formate, pH 3; 100 mL / gram material; overnightSuspend material in 100 mM Ammonium Formate, pH 3; 100 mL / gram material; overnightSuspend material in 100 mM Ammonium Hydroxide; 100 mL / gram material; overnightSuspend material in 100 mM Ammonium Hydroxide; 100 mL / gram material; overnightStep 7Filter off the fluid using a 10 µm filterStep 8Wash with 100% methanol; 100 mL / gram material; pull dry and repeatStep 9Let dry in hood Table 15: % Phosphatidylcholine in Each Fraction of the 4-Step SPE Protocol using Oasis MCX-NH 4 +< Batches FractionBatch 01Batch 02Batch 03Batch 04Load81.182.483.683.8Wash 12.42.22.52.4Wash 24.44.14.43.9Elute12.111.39.69.9 % Recovery of Basic Analytes using Oasis MCX-NH 4 +< Batches 02 and 04 D-Amphetamine--114--112(+)-Metoprolol--107--107Amitriptyline HCl--115--113

Claims

1. A method of performing a sample enrichment procedure, the method comprising: adding a sample fluid that comprises at least one phospholipid and at least one target analyte to an ammonium-modified sorbent comprising a hydrophobic component and a cation exchange component, wherein the cation of the cation exchange component is an ammonium cation, thereby resulting in the ammonium-modified sorbent adsorbed with phospholipid and adsorbed with target analyte; optionally, adding an aqueous solution comprising an acidic compound selected from an organic acid, phosphoric acid, hydrochloric acid, and carbonic acid to the ammonium-modified sorbent; adding an organic solution comprising a first organic solvent species to the ammonium-modified sorbent thereby desorbing at least a portion of the phospholipid from the ammonium-modified sorbent; and adding an elution solution that comprises: (i) a basic compound or salt species; and (ii) a second organic solvent species to the ammonium-modified sorbent thereby desorbing at least a portion of the target analyte from the ammonium-modified sorbent and forming a solution of the target analyte in the elution solution, wherein the second organic solvent species may be the same or different from the first organic solvent species.

2. The method of claim 1, wherein the target analyte is a base with a pKa of at least 5.

3. The method of claim 1, wherein the aqueous solution comprises the acidic compound in an amount sufficient to provide the aqueous solution with a pH that is at least two pH units below a lowest pKa of the target analyte.

4. The method of claim 1, wherein the acidic compound is formic acid.

5. The method of claim 1, wherein the elution solution comprises the salt species in an amount corresponding to an ionic strength ranging from 10-250 mM.

6. The method of claim 1, wherein the first organic solvent species and the second organic solvent species are selected from methanol, ethanol, 1-propanol, 2-propanol, acetonitrile, acetone, ethyl acetate, methyl ethyl ketone, tetrahydrofuran and blends thereof.

7. The method of claim 1, wherein the elution solution comprises the basic compound in an amount sufficient to provide the elution solution with a pH that is at least two pH units above a highest pKa of the target analyte.

8. The method of claim 1, wherein the sample fluid comprises a biological sample selected from a whole blood sample, a plasma sample, a serum sample, a food sample, and a food extract sample.

9. The method of claim 1, wherein the method does not comprise adding the aqueous solution comprising the acidic compound to the ammonium-modified sorbent.

10. The method of claim 1, the method comprising adding the aqueous solution comprising the acidic compound to the ammonium-modified sorbent and adding the organic solution comprising the first organic solvent species to the ammonium-modified sorbent thereby desorbing at least a portion of the phospholipid from the ammonium-modified sorbent.