Method for detecting phosphate ester in lubricant

Abstract

The invention relates to the technical field of lubricants, and discloses a method for detecting phosphate in a lubricant. The method comprises the following steps: (1) obtaining a standard chromatogram of phosphate; (2) mixing a lubricant sample to be detected, an adsorbent and an extraction reagent to obtain an upper-layer extracting solution containing phosphate, and obtaining a chromatogram of the upper-layer extracting solution; and (3) comparing the standard chromatogram with the chromatogram of the upper-layer extracting solution to obtain the type and the content of the phosphate ester in the lubricant sample. The method is low in detection limit, high in recovery rate, small in error, accurate in qualitation and quantification, good in sensitivity and repeatability, suitable for analysis and detection of phosphate in the whole life cycle process of the lubricant, applicable to various lubricants and high in universality.

Description

Technical Field

[0001] The invention relates to the technical field of lubricants, and in particular to a method for detecting phosphate ester in a lubricant. Background Art

[0002] Lubricating oil is widely used in today's society. Especially with the renewal and transformation of engine parts, the working conditions of mechanical equipment have become more and more harsh, and the requirements of mechanical parts for lubricating oil are getting higher and higher, requiring oil products to reduce wear and friction between parts under boundary lubrication conditions. As an important component of lubricating oil, phosphate ester extreme pressure anti-wear agent is a class of organic compounds with strong chemical activity. Its mechanism of action is: when the contact pressure of the friction surface of the mechanical part is high, the concave and convex points on the friction metal surface mesh with each other, generating local high temperature and high pressure. The extreme pressure anti-wear agent can react chemically with the metal surface, and then produce a solid protective film of sulfurized, phosphated or chlorinated metal with low shear strength, which separates the friction metal surface, thereby preventing metal wear and sintering.

[0003] According to relevant data, the losses caused by friction and wear are as high as trillions of yuan each year. Therefore, it is necessary to develop an analytical detection method for analyzing and determining the phosphate compounds contained in lubricating grease samples. However, the existing sample preparation methods for phosphate esters mainly focus on samples such as food and plastics, and the operation process mainly includes: organic solvent extraction, centrifugal separation, and solid phase extraction (SPE) purification and impurity removal. Among them, organic solvent extraction is time-consuming and labor-intensive, and the sample capacity of the solid phase extraction column used is limited, and the column is prone to clogging. The elution and washing process is time-consuming, and the recovery rate of the target component is low. If the lubricating grease sample is subjected to the above-mentioned extraction method in the field of food or plastics, emulsification is prone to occur, and centrifugal separation is difficult to achieve. In addition, the viscosity of the lubricating grease sample is high, and the conventional solid phase extraction purification process is time-consuming. Moreover, the grease sample is very easy to clog the extraction purification column, which brings great trouble to the analysis and detection.

[0004] Therefore, it is urgent to establish a simple and efficient analytical detection method to extract and separate the target phosphate components in lubricant samples to the maximum extent, reduce the measurement error, and then realize the qualitative and quantitative analysis of phosphate compounds in lubricant samples, and provide necessary data support for oil monitoring and analysis of lubricants. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art and to provide a method for detecting phosphate esters in lubricants. The method has a low detection limit, a high recovery rate, a small error, accurate qualitative and quantitative analysis, good sensitivity and repeatability, is suitable for the analysis and detection of phosphate esters during the entire life cycle of lubricants, is applicable to a variety of lubricants, and has strong universality.

[0006] In order to achieve the above object, the present invention provides a method for detecting phosphate ester in a lubricant, the method comprising:

[0007] (1) obtaining a standard chromatogram of phosphate;

[0008] (2) mixing the lubricant sample to be tested, the adsorbent and the extraction reagent to obtain an upper extract containing phosphate ester, and obtaining a chromatogram of the upper extract;

[0009] The adsorbent includes a first adsorbent and a second adsorbent, the hydrophilic-hydrophobic partition coefficient of the first adsorbent LogP≥4, and the hydrophilic-hydrophobic partition coefficient of the second adsorbent LogP≤-1;

[0010] The extraction reagent contains an organic reagent, and the solubility parameter of the organic reagent is δ≥9 (cal / cm 3 ) 0.5 , and the hydrophilic-hydrophobic partition coefficient LogP of the organic reagent satisfies -1≤LogP≤4; (3) comparing the above standard chromatogram with the chromatogram of the above upper layer extract to obtain the type and content of the phosphate ester in the lubricant sample.

[0011] The method provided by the present invention has high sensitivity, low detection limit, good repeatability, and is suitable for the analysis and detection of phosphate esters during the entire life cycle of lubricants. The method can fully purify and remove components other than phosphate esters, has a high recovery rate, a small error, is applicable to a variety of lubricants, and has strong universality. The method can also achieve purification and extraction at the same time, is simple and efficient, and can also purify and extract multiple lubricants at the same time. In addition, when using gas chromatography, there are no special requirements for the chromatograph itself, and it is suitable for various types of gas chromatograph analysis and detection. DETAILED DESCRIPTION

[0012] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0013] The present invention provides a method for detecting phosphate ester in a lubricant, the method comprising:

[0014] (1) obtaining a standard chromatogram of phosphate;

[0015] (2) mixing the lubricant sample to be tested, the adsorbent and the extraction reagent to obtain an upper extract containing phosphate ester, and obtaining a chromatogram of the upper extract;

[0016] The adsorbent includes a first adsorbent and a second adsorbent, the hydrophilic-hydrophobic partition coefficient of the first adsorbent LogP≥4, and the hydrophilic-hydrophobic partition coefficient of the second adsorbent LogP≤-1;

[0017] The extraction reagent contains an organic reagent, and the solubility parameter of the organic reagent is δ≥9 (cal / cm 3 ) 0.5 , and the hydrophilic-hydrophobic partition coefficient LogP of the organic agent satisfies -1≤LogP≤4 (for example, LogP can be -1, -0.8, -0.5, -0.3, 0.1, 0.3, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, and the range formed by any two of the above values ​​and the values ​​within the range);

[0018] (3) Compare the standard chromatogram with the chromatogram of the upper extract to obtain the type and content of the phosphate ester in the lubricant sample.

[0019] Among them, the hydrophilic and hydrophobic partition coefficient of the organic reagent, the first adsorbent or the second adsorbent refers to the logarithmic value of the ratio of the partition coefficient of the substance in n-octane and water, which is determined according to the method in the literature (Wang Liansheng et al. "Determination of the partition coefficient of several alkyl benzyl ethers in n-octane / water system." Environmental Chemistry 04 (1985): 27-29.). The solubility parameter of the organic reagent is the sum of all the attractive forces radiated by the molecule. Numerically, it is the square of the cohesive energy per gram molecule per unit volume, which is obtained according to the method in the literature (Christopher D. Vaughan. The use of solubility parameters [J]. Global Technology Daily Chemicals Science, 1998 (5): 8-11). Among them, (cal / cm 3 ) 0.5 It is the unit of solubility parameter, i.e. (cal / cm 3 ) to the power of 0.5.

[0020] The inventor of the present invention has found in the research that by adopting the above steps, after the lubricant sample to be tested is treated with the above adsorbent and extraction reagent, the phosphate ester in the lubricant sample to be tested can be fully extracted into the extraction reagent phase, and other components in the lubricant such as base oil and other non-target detection components are adsorbed on the adsorbent. The first adsorbent, the second adsorbent and the extraction reagent that meet the above properties defined by the present invention can be selected to achieve full separation of the phosphate ester and other components, and the type and content of the phosphate ester can be confirmed by using a chromatogram, which can fully ensure that the method has high sensitivity and recovery rate. The method has a small error and a low detection limit, and is suitable for the analysis and detection of phosphate esters during the entire life cycle of the lubricant. The method is applicable to a variety of lubricants and has strong universality. The method of the present invention can achieve purification and extraction at the same time, which is simple and efficient.

[0021] Furthermore, it is understood that the organic reagent is not miscible with the lubricant, otherwise the purpose of extracting the components cannot be achieved, for example, ethyl acetate is miscible with the lubricant. The above is common knowledge in the art.

[0022] According to a particularly preferred embodiment of the present invention, the hydrophilic-hydrophobic partition coefficient of the first adsorbent is 4≤LogP≤10 (for example, LogP may be 4, 5, 6, 7, 8, 9, 10, and a range formed by any two of the above values, and a value within the range).

[0023] According to a particularly preferred embodiment of the present invention, the hydrophilic-hydrophobic partition coefficient of the second adsorbent is -2≤LogP≤-1 (for example, LogP may be -2, -1.8, -1.5, -1.3, -1, and a range formed by any two of the above values, and a value within the range).

[0024] According to a particularly preferred embodiment of the present invention, the solubility parameter of the organic agent is 9≤δ≤18 (for example, it can be 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 16, 17, 18 and the range formed by any two of the above values ​​and the value within the range) (cal / cm 3 ) 0.5 .

[0025] According to the present invention, preferably, the chromatogram is a gas chromatography. A gas chromatography-flame ionization detector (GC-FID) can be used to obtain a gas chromatogram. The specific operating conditions of the gas chromatography-flame ionization detector (GC-FID) can be conventional conditions in the art, for example: the operating conditions of the gas chromatograph (GC) can be as follows: the injection port temperature is 325°C, the injection volume is 1μL, the split ratio is 10:1, the constant flow is 2mL / min, the column temperature of the chromatographic column is maintained at 100°C for 1min, then increased to 325°C at 20°C / min, and maintained for 3min; the chromatographic column model is Aglient HP-5 capillary column (300×0.25mm, film thickness 0.25μm); flame ionization detector (FID): the detector temperature is 350°C.

[0026] It is understandable that in the field of lubricants, those skilled in the art are aware of the specific types of phosphate esters, and their standard chromatograms can also be obtained through standard product testing or reference.

[0027] In some cases, when a lubricant sample to be tested is obtained, the specific type of phosphate ester contained therein can be known based on the product label thereon, and the standard chromatogram can also be obtained by self-determination.

[0028] Among them, the external standard method or standard addition method commonly used in the field of chromatography can be used to obtain a standard chromatogram. The external standard method is to dissolve the target substance to be tested in an organic solvent to obtain solutions of different concentrations, and then perform chromatographic injection measurement to obtain a standard chromatogram; the standard addition method is to add a quantitative target substance to a sample matrix (for the solution of the present invention, that is, a lubricant matrix) that does not contain the target substance to be tested, and treat it in the same way as the lubricant sample to be tested (also perform the treatment of step (2)), and then perform chromatographic injection measurement to obtain a standard chromatogram. The present invention preferably adopts the standard addition method, so that it can ensure that the standard chromatogram and the chromatogram of the lubricant sample to be tested have fewer operational differences and are more comparable.

[0029] A standard curve can be constructed based on the peak area and concentration according to the standard chromatogram of phosphate esters. Different types of phosphate esters need to have their own standard curves.

[0030] Even if the specific type of phosphate ester contained in the lubricant sample to be tested is not known in advance, the specific type of phosphate ester can be confirmed by the retention time by comparing the chromatogram of the upper extract with the standard chromatograms of various phosphate esters. Then, the concentration of phosphate ester in the lubricant to be tested is determined by the standard curve of the specific phosphate ester and the peak area of ​​the chromatogram of the upper extract. In this way, qualitative and quantitative analysis is achieved. Therefore, the specific type of phosphate ester contained in the lubricant can also be qualitatively determined first.

[0031] Preferably, the method for obtaining a standard chromatogram of a phosphate ester comprises: preparing standard solutions of different concentrations containing a known phosphate ester, and obtaining a standard chromatogram and a standard curve corresponding to the phosphate ester.

[0032] According to the present invention, preferably, the lubricant includes lubricating oil and / or lubricating grease.

[0033] According to the present invention, preferably, the lubricating oil is selected from at least one of diesel engine oil, gasoline engine oil, hydraulic oil, transmission oil and gear oil.

[0034] According to the present invention, preferably, the lubricating grease is selected from at least one of bearing grease, gear grease and chain grease.

[0035] The method provided by the present invention is applicable to the above different types of lubricants and has strong universality. Moreover, the method of the present invention is not limited to the specific composition of the lubricant. However, preferably, the base oil in the lubricant is selected from at least one of Class I oil, Class II oil, Class III oil, Class IV oil and Class V oil. Wherein Class I oil refers to the base oil produced by conventional solvent refining method, Class II oil is the base oil produced by catalyst hydrocracking, Class III oil is the base oil produced by hydroisomerization, Class IV oil refers to the base oil produced by linear alpha olefin polymerization reaction, and Class V oil refers to other synthetic base oils, mainly including esters and alkylated aromatic base oils. The base oil can be composed of one or more of the above.

[0036] In addition, other additives in the lubricant are not particularly limited. Other additives may include detergents (which may be organic metal sulfonates, alkylphenols, sulfurized alkylphenols, salicylates, etc.), dispersants (which may be succinimides, succinates, phenolic amine condensates, etc.), viscosity modifiers (which may be polymethacrylates, ethylene-propylene copolymers, polyisobutylenes, etc.), pour point depressants (which may be alkylnaphthalene, poly-alpha-olefins, etc.), antioxidants (which may be di-tert-butylparacresol, alkylated diphenylamine, etc.), anti-foaming agents (which may be dimethyl silicone oil, polyacrylates, etc.) and at least one of rust and corrosion inhibitors (which may be alkylphenols, fatty acids, sulfonates, etc.). Furthermore, the content of the above components is not particularly limited and may be conventional in the art. For example, based on the total weight of the lubricant, the weight content of each component is: the base oil may be 70-99wt%, the detergent may be 4-7wt%, the dispersant may be 2.5-5wt%; the viscosity index agent may be 1.8-3.2wt%; the pour point depressant may be 0.1-1.5wt%; the antioxidant may be 1.0-6.5wt%; the antifoaming agent may be 0.01-0.05wt%; and the rust and corrosion inhibitor may be 0.1-1wt%.

[0037] According to the present invention, preferably, the lubricant contains one or more phosphates. Different specific types have different retention times during chromatographic analysis, which can be used to distinguish the types, and the respective contents are then determined by the peak areas of the corresponding standard curves.

[0038] According to the present invention, preferably, the phosphate ester is selected from at least one of triethyl phosphate, tripropyl phosphate, tributyl phosphate and triphenyl phosphate.

[0039] According to the present invention, preferably, the content of phosphate ester in the lubricant is not less than 0.00001wt%, preferably not less than 0.00003wt%. It can be understood that the lubricant may contain one or more phosphate esters, and the above-mentioned "the content of phosphate ester is not less than 0.00001wt%" means that the content of any one phosphate ester is not less than the above-mentioned 0.00001wt%, rather than the total sum of all phosphate esters in the lubricant. The inventors of the present invention have found in their research that when the content of phosphate ester is not less than 0.00001wt%, the phosphate ester can be sensitively detected; when the content of phosphate ester is not less than 0.00003wt%, the content of phosphate ester can be more accurately determined.

[0040] According to the present invention, preferably, the mass ratio of the first adsorbent to the second adsorbent is (0.5-8):1, more preferably (1-5):1 (for example, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 and the ratio range formed by any two of the above ratios and the ratio within the range). The inventors of the present invention further found in the study that when the above ratio is met, it can further ensure that the other components in the lubricant except the phosphate ester are fully adsorbed on the adsorbent.

[0041] According to the present invention, preferably, the first adsorbent is selected from lipophilic organic polymer adsorbents and / or silica gel adsorbents bonded with non-polar groups; the lipophilic organic polymer adsorbent is preferably a styrene-divinylbenzene copolymer adsorbent, and the non-polar group is a C8-C20 alkyl group, preferably at least one of (n-) octyl, (n-) decyl, (n-) dodecyl, (n-) tetradecyl, (n-) hexadecyl and (n-) octadecyl.

[0042] According to the present invention, preferably, the second adsorbent is selected from an inorganic adsorbent or a silica gel solid phase adsorbent with a polar organic group bonded to the surface; the inorganic adsorbent is preferably at least one of alumina, silica and silicate, more preferably at least one of alumina, diatomaceous earth, fluorosilicic acid, montmorillonite and inorganic silica gel adsorbent; the polar organic group is selected from at least one of amino, cyano and diol (i.e., two hydroxyl groups). According to the present invention, preferably, the mass ratio of the lubricant sample to be tested and the adsorbent is (2-10):1 (for example, it can be 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 and the ratio range formed by any two of the above ratios and the ratio within the range). This can further ensure that the other components in the lubricant except the phosphate ester are fully adsorbed on the adsorbent.

[0043] According to the present invention, preferably, the volume ratio of the lubricant to the extraction agent is 1:(0.9-8), more preferably 1:(1-5) (for example, it can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5 and the ratio range formed by any two of the above ratios and the ratio within the range). It can be understood that the density of the lubricant is generally about 0.8-0.9 g / ml.

[0044] According to the present invention, preferably, the organic reagent is selected from at least one of methanol, ethanol, acetonitrile, acetone, chloroform and dichloromethane.

[0045] According to a preferred embodiment of the present invention, the extraction reagent is an organic reagent as described above.

[0046] According to another preferred embodiment of the present invention, the extraction reagent further contains water, and the content of the organic reagent in the extraction reagent is ≥ 60 volume %.

[0047] The inventors of the present invention have further found in their research that when the extraction reagent is the above-mentioned, it can further ensure that the phosphate ester in the lubricant is fully extracted into the extraction reagent phase, and the recovery rate is higher.

[0048] According to the present invention, preferably, in step (2), the lubricant sample to be tested is sequentially mixed with an adsorbent and an extraction reagent, and then the mixed materials are sequentially vortexed and centrifuged to obtain an upper layer extract containing phosphate ester. After the lubricant sample is uniformly mixed with the adsorbent, it is then mixed with the extraction reagent.

[0049] It can be understood that after the lubricant sample to be tested, the adsorbent and the extraction reagent are mixed, the mixed system will be more fully stratified by the above-mentioned vortex and centrifugation, and the phosphate ester will be fully extracted into the extraction reagent phase to obtain the upper extract, while the adsorbent that adsorbs other components in the lubricant will exist in the lower layer of the mixed system.

[0050] According to the present invention, preferably, the vortex conditions include: vortexing for 0.5-5min (for example, 0.5min, 1min, 2min, 3min, 4min, 5min and the value within the range formed by any two of the above values) r / min. It can be understood that vortexing is a rapid mixing operation that can enhance the contact between materials in a short time and achieve rapid and efficient extraction.

[0051] According to the present invention, preferably, the centrifugal conditions include: centrifugation at 1000-6000 (for example, it can be 1000, 1200, 1500, 1800, 2000, 2200, 2500, 2800, 3000, 3200, 3500, 3800, 4000, 4300, 4500, 4800, 5000, 5300, 5500, 5800, 6000 and the value within the range formed by any two of the above values ​​and the value within the range) r / min for 0.5-5 min (for example, it can be 0.5 min, 1 min, 2 min, 3 min, 4 min, 5 min and the value within the range formed by any two of the above values ​​and the value within the range).

[0052] Under the above conditions, the recovery rate of phosphate ester can be further improved.

[0053] The present invention will be described in detail below through examples.

[0054] In the following examples, C8 adsorbent refers to a silica gel adsorbent with n-octyl groups bonded to the surface, purchased from Agilent Technologies, with a catalog number of 12213009;

[0055] C18 adsorbent refers to a silica gel adsorbent with n-octadecyl bonded on the surface, purchased from Agilent Technologies, catalog number 12213012;

[0056] C2 adsorbent refers to a silica gel adsorbent with ethyl groups bonded to the surface, purchased from Agilent Technologies, catalog number 12213006;

[0057] Styrene-divinylbenzene copolymer adsorbent was purchased from Beijing Wokai Biotechnology Co., Ltd., catalog number 217484;

[0058] Montmorillonite was purchased from Shanghai Yuanye Biotechnology Co., Ltd., product number S42017;

[0059] Diatomaceous earth, purchased from Beijing Bailingwei Technology Co., Ltd., catalog number 227605;

[0060] Amino adsorbent refers to a silica adsorbent with organic groups including amino groups bonded to the surface, purchased from Agilent Technologies, catalog number 5982-1882;

[0061] The cyano adsorbent refers to a silica gel adsorbent with organic groups including cyano groups bonded on the surface, which was purchased from Beijing Bailingwei Technology Co., Ltd. with a product number of 9207740.

[0062] In the following examples, a gas chromatograph-flame ionization detector (GC-FID) was purchased from Agilent Instrument Co., Ltd., model 7890B; the operating conditions of the gas chromatograph (GC) were as follows: the injection port temperature was 325° C., the injection volume was 1 μL, the split ratio was 10:1, the constant flow was 2 mL / min, the column temperature was maintained at 100° C. for 1 min, then increased to 325° C. at 20° C. / min and maintained for 3 min; the chromatographic column model was Aglient HP-5 capillary column (300×0.25 mm, film thickness 0.25 μm); the flame ionization detector (FID): the detector temperature was 350° C.

[0063] The standard addition method was used to obtain the standard curves of triethyl phosphate, tripropyl phosphate, tributyl phosphate and triphenyl phosphate. Taking tributyl phosphate as an example, the standard addition method is as follows:

[0064] (1) Take 6 blank diesel engine oil samples (i.e., those that do not contain phosphate additives) and place them in 6 centrifuge tubes, 10 g each. The base oil in the blank diesel engine oil is a mixture of Class I oil and Class IV oil. Other additives include detergent (salicylate), dispersant (succinimide), viscosity modifier (polymethacrylate), and pour point depressant (alkyl naphthalene). Based on the total weight of the diesel engine oil, the base oil accounts for 90 wt%, the detergent accounts for 3.5 wt%, the dispersant accounts for 3.2 wt%, the viscosity modifier accounts for 2.3 wt%, and the pour point depressant accounts for 1 wt%.

[0065] Tributyl phosphate was added thereto respectively to obtain 7 lubricating oil samples containing different phosphate concentrations. Relative to the total weight of the lubricating oil to be tested, the actual concentrations of tributyl phosphate were 0.0001wt%, 0.0005wt%, 0.001wt%, 0.005wt%, 0.01wt%, 0.05wt% and 0.1wt%, respectively.

[0066] (2) The 7 samples of lubricating oil to be tested were processed as follows:

[0067] Take 1g of sample and mix it with 0.2g of adsorbent (0.1gC8 adsorbent + 0.1g alumina). After mixing evenly, add 2mL of methanol to extract, then vortex at 1500r / min for 2min, and then centrifuge at 3000r / min for 1min to obtain the upper extract.

[0068] (3) The upper extract is subjected to GC-FID to obtain a standard gas chromatogram and obtain the peak area. A standard curve is constructed based on the peak area and concentration.

[0069] The standard curves of other phosphate compounds were obtained in the same way as above.

[0070] According to the above gas chromatograms, as well as their respective concentrations and peak areas, standard curves of triethyl phosphate, tripropyl phosphate, tributyl phosphate and triphenyl phosphate were obtained. The expressions and correlation coefficients of the standard curves are shown in Table 1. Where x is the mass percentage of the target component, in g / g, and y is the response peak area, in μV·s. The method for determining the detection limit and the quantification limit is as follows: record the signal-to-noise ratio X (peak height to baseline noise ratio), and the concentration when the lubricating oil sample to be tested is diluted to X / 3 times is the detection limit; dilute the lubricating oil sample to be tested to X / 10 times, and the concentration at this time is the quantification limit (this method is a commonly used method for determining the detection limit and quantification limit in this field).

[0071] Table 1

[0072] Compound Linear correlation Correlation coefficient Limit of Quantitation (LOQ) Limit of Detection (LOD) Triethyl phosphate y=7186.9x+9.03 0.9979 0.00005wt% 0.000015wt% Tripropyl phosphate y=7979.2x+10.91 0.9978 0.00003wt% 0.00001wt% Tributyl phosphate y=10675x+13.33 0.9978 0.00003wt% 0.00001wt% Triphenyl phosphate y=12011x+2.20 0.9981 0.0001wt% 0.00003wt%

[0073] In the following examples, the above standard curve is used.

[0074] In the following examples, recovery rate = measured concentration / actual concentration × 100%.

[0075] Example 1

[0076] (1) Take 4 portions of blank hydraulic oil (i.e., no target phosphate compound) and place them in four centrifuge tubes, 5 g each. The base oil in the blank hydraulic oil is Class II oil, and the other additive is a pour point depressant (alkyl naphthalene). Based on the total weight of the hydraulic oil, the content of the base oil is 99.2 wt%, and the pour point depressant is 0.8 wt%.

[0077] Triethyl phosphate, tripropyl phosphate, tributyl phosphate and triphenyl phosphate were added thereto to obtain three samples to be tested. The actual concentration of the four phosphates in sample 1 was 0.001 wt %; the actual concentration of the four phosphates in sample 2 was 0.01 wt %; and the actual concentration of the four phosphates in sample 3 was 0.05 wt %.

[0078] (2) For the above three samples to be tested, perform the following treatments respectively:

[0079] Take 0.8g of the sample to be tested, add 0.2g of mixed adsorbent (0.15g C8 adsorbent (LogP≈5.18) + 0.05g inorganic silica gel adsorbent (LogP≈-1.4)), mix well, and add 2mL acetonitrile (δ=14.5(cal / cm 3 ) 0.5 , LogP=-0.45), then vortexed at 2000r / min for 3min, and centrifuged at 3500r / min for 1min to obtain the upper extract.

[0080] (3) Take the upper extract and use GC-FID to obtain the gas chromatogram of the sample. Identify each substance by retention time, as well as the corresponding peak and peak area.

[0081] The standard curve of each substance and the peak area of ​​the gas chromatogram obtained in step (3) were compared to obtain the concentration of each phosphate ester in each sample, and then converted to obtain the actual concentration of each phosphate ester in the lubricating oil sample to be tested. The results are shown in Table 2.

[0082] Example 2

[0083] (1) Take 6 g of blank transmission oil (the base oil is a mixture of Class II oil, Class III oil and Class IV oil, and other additives mainly include detergent (alkyl phenol calcium), dispersant (succinate) and rust and corrosion inhibitor (fatty acid), wherein, based on the total weight of the transmission oil, the content of the base oil is 92.4 wt%, the detergent is 3.6 wt%, the dispersant is 2.8 wt%, the extreme pressure anti-wear agent is 0.8 wt%, and the rust and corrosion inhibitor is 0.4 wt%) in a centrifuge tube. Add tributyl phosphate thereto to obtain a lubricating oil sample to be tested having a tributyl phosphate concentration of 0.01 wt%.

[0084] (2) Take 0.9 g of the above sample, add 0.25 g of adsorbent (0.2 g of styrene-divinylbenzene copolymer adsorbent (LogP≈5.0) + 0.05 g of montmorillonite adsorbent (LogP≈-1.3)), and after mixing evenly, add 2 mL of acetone (δ=9.8 (cal / cm 3 ) 0.5 , LogP=-0.16), and then vortexed at 2500r / min for 2min, followed by centrifugation at 3000r / min for 0.5min to obtain the upper extract.

[0085] (3) Taking the upper extract, using GC-FID to obtain a gas chromatogram of the sample, identifying that the sample contains tributyl phosphate through the retention time, and obtaining the corresponding peak area.

[0086] The standard curve of tributyl phosphate and the peak area of ​​the gas chromatogram obtained in step (3) are compared to obtain the concentration of tributyl phosphate, and then the actual concentration of tributyl phosphate in the lubricating oil sample to be tested is calculated. The results are shown in Table 2.

[0087] Example 3

[0088] The lubricating oil sample to be tested was prepared and tested according to the method in Example 2, except that acetone was replaced by acetone-water solution (wherein the volume fraction of acetone was 60%). The results are shown in Table 2.

[0089] Example 4

[0090] (1) Take 5 g of blank bearing grease (i.e., it does not contain phosphate compounds) in a centrifuge tube, the base oil in the blank bearing grease is a mixture of Class I oil and Class II oil, and other additives are antioxidants (specifically di-tert-butyl-p-cresol) and rust and corrosion inhibitors (specifically petroleum sulfonates), wherein, based on the total weight of the grease, the content of the base oil is 98.4 wt%, the antioxidant is 1.3 wt%, and the rust inhibitor is 0.3 wt%.

[0091] Triphenyl phosphate was added thereto to obtain a lubricating ester sample to be tested, wherein the actual concentration of triphenyl phosphate was 0.04 wt %.

[0092] (2) Take 1.2 g of the above-mentioned lubricating ester sample to be tested, add 0.30 g of adsorbent (0.25 g of C18 adsorbent (LogP≈9.2) + 0.05 g of diatomaceous earth (LogP≈-1.5)), mix well, and add 3 mL of chloroform (δ=9.4 (cal / cm 3 ) 0.5 , LogP=1.75), vortex at 2500r / min for 1min, centrifuge at 2000r / min for 1min to obtain the upper extract;

[0093] (3) Take the upper extract and use GC-FID to obtain a gas chromatogram of the sample. According to the retention time, it can be determined that the phosphate contained therein is triphenyl phosphate. According to the peak area and the standard curve, the concentration of triphenyl phosphate in the lubricating ester sample to be tested is determined to be 0.046wt%.

[0094] Comparative Example 1

[0095] Take the blank hydraulic oil in Example 1, add tributyl phosphate thereto, and obtain a sample with a tributyl phosphate concentration of 0.01 wt %.

[0096] The concentration of 0.8 g of the sample was measured according to the steps (2) to (3) in Example 1, except that acetonitrile was replaced by acetonitrile-water solution (wherein the volume fraction of acetonitrile was 30%). The results are shown in Table 2.

[0097] Comparative Example 2

[0098] Take the blank hydraulic oil in Example 1, add tributyl phosphate thereto, and obtain a sample with a tributyl phosphate concentration of 0.01 wt %.

[0099] The concentration of 0.8 g of the sample was determined according to the steps (2) to (3) in Example 1, except that acetonitrile was replaced by carbon tetrachloride (δ = 8.6 (cal / cm 3 ) 0.5 , LogP=2.86). The results are shown in Table 2.

[0100] Comparative Example 3

[0101] Take the blank hydraulic oil in Example 1, add tributyl phosphate thereto, and obtain a sample with a tributyl phosphate concentration of 0.01 wt %.

[0102] The concentration of 0.8 g of the sample was measured according to the steps (2) to (3) in Example 1, except that the first adsorbent was not used and the mass of the second adsorbent was 0.2 g. The results are shown in Table 2.

[0103] Comparative Example 4

[0104] Take the blank hydraulic oil in Example 1, add tributyl phosphate thereto, and obtain a sample with a tributyl phosphate concentration of 0.01 wt %.

[0105] The concentration of 0.8 g of the sample was measured according to the steps (2) to (3) in Example 1, except that the second adsorbent was not used and the mass of the first adsorbent was 0.2 g. The results are shown in Table 2.

[0106] Comparative Example 5

[0107] Take the blank hydraulic oil in Example 1, add tributyl phosphate thereto, and obtain a sample with a tributyl phosphate concentration of 0.01 wt %.

[0108] The concentration of 0.8 g of the sample was measured according to the steps (2) to (3) in Example 1, except that the second adsorbent remained unchanged and the first adsorbent was replaced with C2 adsorbent (LogP≈1.8). The results are shown in Table 2.

[0109] Comparative Example 6

[0110] Take the blank hydraulic oil in Example 1, add tributyl phosphate thereto, and obtain a sample with a tributyl phosphate concentration of 0.01 wt %.

[0111] 0.8 g of the sample was treated according to (2)-(3) in Example 1, except that no adsorbent was added.

[0112] Table 2

[0113]

[0114]

[0115] As can be seen from the above, the method provided by the present invention has a high recovery rate and a small error (it is generally believed in the art that for trace analysis, a recovery rate between 80-120% is acceptable), and can accurately reflect the concentration of different phosphates and different concentrations, and has good repeatability and quantitative accuracy. In addition, the method provided by the present invention is more suitable for detecting triethyl phosphate, tributyl phosphate and triphenyl phosphate in lubricants. For the above three phosphates, a higher recovery rate can be obtained at a lower concentration.

[0116] Example 5

[0117] This example uses a standard curve to determine the content of phosphate compounds in the entire life cycle of the internal combustion engine oil.

[0118] The same blank diesel engine oil as that used to obtain the standard curve of phosphate esters was taken, and triphenyl phosphate was added to make the concentration of triphenyl phosphate 0.1 wt % to obtain simulated internal combustion engine oil.

[0119] A laboratory simulation bench test was carried out on the simulated internal combustion engine oil, and the required oil samples were obtained at 0, 5, 15, 30, 60, 100 and 150 hours respectively.

[0120] The method of sampling and analysis at different times is:

[0121] Take 0.8g oil sample, add 0.25g adsorbent (0.20g C8 adsorbent (LogP≈5.2) + 0.05g amino adsorbent (LogP≈-1.4)), mix well, add 2mL dichloromethane (δ=9.8(cal / cm 3 ) 0.5 , LogP=1.19), then vortexed at 2500r / min for 1min, and centrifuged at 4000r / min for 1min to obtain the upper extract.

[0122] The upper extract was taken and GC-FID was used to obtain the gas chromatogram of the sample, as well as the corresponding peaks and peak areas, and compared with the standard curve of triphenyl phosphate to obtain the actual concentrations. See Table 3.

[0123] Table 3

[0124] Use time (h) 0 5 15 30 60 100 150 Content (wt%) 0.1 0.1 0.087 0.058 0.04 0.007 0.0002

[0125] The data changes in Table 3 are consistent with the consumption trend of phosphate esters in the lubricant field, and the results are relatively accurate, indicating that the method provided by the present invention is suitable for monitoring the content of various phosphate ester compounds throughout the life cycle of lubricating oil.

[0126] Example 6

[0127] Used to illustrate the application of the method of the present invention in determining the type and content of unknown phosphate compounds

[0128] 1.5 g of a gasoline engine oil (purchased from Sinopec Great Wall Lubricant Company) was placed in a centrifuge tube, and 0.4 g of adsorbent (0.30 g of C18 adsorbent (LogP≈9.2) + 0.10 g of cyano adsorbent (LogP≈-1.5)) was added thereto. After mixing evenly, 3 mL of methanol (δ=14.8 (cal / cm 3 ) 0.5 , LogP=-0.72), then vortexed at 2500r / min for 1min, and centrifuged at 2500r / min for 1min to obtain the upper extract.

[0129] The upper extract was taken and GC-FID was used to obtain a gas chromatogram of the sample. The phosphate compound contained therein was identified as tributyl phosphate by retention time. According to the peak area and the standard curve corresponding to tributyl phosphate, the concentration of tributyl phosphate in the diesel was 0.040wt%.

[0130] Example 7

[0131] Take the blank hydraulic oil in Example 1, add tributyl phosphate thereto, and obtain a sample with a tributyl phosphate concentration of 0.01 wt %.

[0132] The concentration of 0.8 g of the sample was measured according to the steps (2)-(3) in Example 1, except that the mass ratio of the first adsorbent to the second adsorbent was 0.5:1, the total mass was still 0.2 g, and other conditions were kept unchanged. The measured concentration was 0.0072 wt % and the recovery rate was 72.0 %.

[0133] Example 8

[0134] Take the blank hydraulic oil in Example 1, add tributyl phosphate thereto, and obtain a sample with a tributyl phosphate concentration of 0.01 wt %.

[0135] For 0.8 g of the sample, the concentration was measured according to the steps (2)-(3) in Example 1, except that the total mass of the first adsorbent and the second adsorbent was 0.6 g, the mass ratio of the first adsorbent to the second adsorbent was still 3:1, and other conditions were kept unchanged. The measured concentration was 0.0068 wt %, and the recovery rate was 68.0%.

[0136] Example 9

[0137] Take the blank hydraulic oil in Example 1, add tributyl phosphate thereto, and obtain a sample with a tributyl phosphate concentration of 0.01 wt %.

[0138] The concentration of 0.8 g of the sample was determined according to the steps (2)-(3) in Example 1, except that the volume of the extraction reagent was 0.5 mL and other conditions were kept constant. The measured concentration was 0.0069 wt % and the recovery rate was 69.0 %.

[0139] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for detecting phosphate ester in a lubricant, characterized in that: The method includes: (1) obtaining a standard chromatogram of phosphate; (2) mixing the lubricant sample to be tested, the adsorbent and the extraction reagent to obtain an upper extract containing phosphate ester, and obtaining a chromatogram of the upper extract; The adsorbent includes a first adsorbent and a second adsorbent, the hydrophilic-hydrophobic partition coefficient of the first adsorbent LogP≥4, and the hydrophilic-hydrophobic partition coefficient of the second adsorbent LogP≤-1; The extraction reagent contains an organic reagent, and the solubility parameter of the organic reagent is δ≥9 (cal / cm 3 ) 0 . 5 , and the hydrophilic-hydrophobic partition coefficient LogP of the organic reagent satisfies -1≤LogP≤4; (3) Compare the standard chromatogram with the chromatogram of the upper extract to obtain the type and content of the phosphate ester in the lubricant sample.

2. The method according to claim 1, wherein: The chromatogram is a gas chromatography; And / or, the method for obtaining a standard chromatogram of a phosphate ester includes: preparing standard solutions of different concentrations containing a known phosphate ester, and obtaining a standard chromatogram and a standard curve corresponding to the phosphate ester.

3. The method according to claim 1, wherein: Lubricants include lubricating oils and / or lubricating greases.

4. The method according to claim 3, wherein: The lubricating oil is selected from at least one of diesel engine oil, gasoline engine oil, hydraulic oil, transmission oil and gear oil; Preferably, the lubricating grease is selected from at least one of bearing grease, gear grease and chain grease; Preferably, the base oil in the lubricant is selected from at least one of Group I oil, Group II oil, Group III oil, Group IV oil and Group V oil.

5. The method according to claim 1, wherein: The lubricant contains one or more phosphate esters; Preferably, the phosphate ester is at least one selected from triethyl phosphate, tripropyl phosphate, tributyl phosphate and triphenyl phosphate.

6. The method according to claim 1 or 5, wherein: The content of the phosphoric acid ester in the lubricant is not less than 0.00001 wt %, preferably not less than 0.00003 wt %.

7. The method according to claim 1, wherein: The mass ratio of the first adsorbent to the second adsorbent is (0.5-8):1, preferably (1-5):1; And / or, the first adsorbent is selected from a lipophilic organic polymer adsorbent and / or a silica gel adsorbent bonded with a non-polar group; the lipophilic organic polymer adsorbent is preferably a styrene-divinylbenzene copolymer adsorbent, and the non-polar group is a C8-C20 alkyl group, preferably at least one of an octyl group, a decyl group, a dodecyl group, a tetradecyl group, a hexadecyl group and an octadecyl group; And / or, the second adsorbent is selected from an inorganic adsorbent or a silica gel solid phase adsorbent with a polar organic group bonded to the surface; the inorganic adsorbent is preferably at least one of aluminum oxide, silicon oxide and silicate, more preferably at least one of aluminum oxide, diatomaceous earth, fluorosilicic acid, montmorillonite and inorganic silica gel adsorbent; the polar organic group is selected from at least one of an amino group, a cyano group and a diol group.

8. The method according to claim 1 or 7, wherein: The mass ratio of the lubricant sample to be tested and the adsorbent is (2-10):

1.

9. The method according to claim 1 or 3, wherein: The volume ratio of lubricant to extraction agent is 1:(0.9-8), preferably 1:(1-5).

10. The method according to claim 1 or 5, wherein: The organic reagent is selected from at least one of methanol, ethanol, acetonitrile, acetone, chloroform and dichloromethane; And / or, the extraction reagent further contains water, and the content of the organic reagent in the extraction reagent is ≥ 60 volume %.

11. The method according to claim 1 or 7, wherein: In step (2), the lubricant sample to be tested is mixed with an adsorbent and an extraction reagent in sequence, and then the mixed materials are vortexed and centrifuged in sequence to obtain an upper layer extract containing phosphate ester.

12. The method according to claim 11, wherein: The vortexing conditions include: vortexing at 1000-3000 r / min for 0.5-5 min; Preferably, the centrifugal conditions include: centrifugation at 1000-6000 r / min for 0.5-5 min.

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