Reagent for the determination of ammonium ions in aqueous solution

Description

Technical area

[0001] The invention relates to a solid reagent for the determination of ammonium ions (NH 4 +< , ammonium cation) in aqueous solution, a process for its preparation, a process for the qualitative detection of ammonium ions in aqueous solution and a process for the quantitative determination of ammonium ions in aqueous solution using the solid reagent. Background of the invention

[0002] Determining the ammonium ion content of an aqueous solution has become an important routine task in environmental and water analysis. Determining the concentration of ammonium ions using the Berthelot reaction is particularly reliable due to its high detection sensitivity, high selectivity, and relatively low susceptibility to interference. The application areas are diverse. It is possible to reliably determine the ammonium ion concentration in water, food, soil extracts, or biological materials.

[0003] The Berthelot reaction, also known as the indophenol reaction, is the name given to the reaction between ammonium ions and a phenol, which under suitable oxidizing conditions leads to the formation of an indophenol dye (which exhibits strong absorption between 630 and 720 nm). The reaction mechanism is complex and not yet fully understood. However, it is assumed that in the first step, the ammonium ions are deprotonated by increasing the pH value to form ammonia, which reacts with the hypohalite (shown below as an example for hypochlorite). in situThe generated monochloramine is then reacted with two molecules of a phenol compound (shown below as an example of phenol) using a catalyst (e.g., sodium nitroprusside (NPN)) to form an indophenol dye (oxidative dehydrogenation process). To ensure a successful reaction, a relatively high pH value (pH > 10.5) must be maintained. The reaction steps mentioned are shown in the following reaction scheme: State of the art

[0004] EP 707210 relates to agents and methods for determining ammonium ions in aqueous solutions based on the Berthelot reaction. In this reaction, a support impregnated with a phenol derivative is brought into contact for a certain period of time with hypochlorite, hypobromite, or a sample solution containing a hypohalite-forming agent and made alkaline with sodium hydroxide solution. The discoloration of the support indicates the presence of ammonium ions. In addition to the phenol derivative, the support also contains catalysts and buffer substances, and the sample solution may also be mixed with buffer substances.

[0005] EP 1840566 relates to a setup or arrangement for determining the ammonium ion content of a liquid sample. This arrangement comprises an indicator element comprising an indicator mixture of ammonium chloride and a pH indicator. The described indicator mixture is isolated from the surrounding atmosphere, so that atmospheric gas cannot penetrate the indicator mixture. The arrangement has a gas-permeable membrane between the pH indicator mixture and the liquid sample. The color change is determined by a photometer directed at the indicator element. The operation of the arrangement is described as follows: " At the beginning of a measurement, water vapor from the liquid sample diffuses through the gas-permeable membrane into the indicator mixture, dissolving the indicator mixture until its vapor pressure equals that of the liquid sample. After that, the water content in the indicator mixture remains constant. The ammonia gas diffusing through the gas-permeable membrane into the indicator mixture shifts the pH of the ammonium chloride solution.

[0006] WO 2018 / 054797 relates to a method for determining ammonium or ammonia in aqueous samples using a two-component system for the Berthelot reaction. For quantitative and qualitative evaluation, the blue color of the resulting indophenol is measured photometrically. In addition to the measurement result of a single measurement, the described method is intended to provide direct information on the plausibility of this measurement result by measuring the absorbance in the absorption range of the blue indole dye formed in the sample and also measuring the absorbance in the absorption range of the nitroprusside used as a catalyst.

[0007] EP 1566632 relates to a test strip with which in one step (so-called " dip and read") the ammonium ion concentration in aqueous solutions can be determined and in which all necessary reagents are contained in a single pad. Detection is carried out by means of color change of pH indicators.

[0008] DIN ISO 15923-1:2013 concerns the determination of ammonium in aqueous solutions using the Berthelot reaction with subsequent photometric detection. Two reagents are provided for this purpose, which are mixed with the sample solution. The sodium nitroprusside reagent is an aqueous solution of sodium salicylate, sodium citrate (" to mask interference from cations such as calcium or magnesium ions") and sodium nitroprusside. The second reagent is an aqueous solution of sodium hydroxide and sodium dichloroisocyanurate (dichloroisocyanurate reagent or DIC reagent). Both reagents are mixed in one volume each with up to 10 volumes of the sample solution and incubated at 30 to 40 °C for at least 480 seconds before the absorbance is measured at 660 nm. The calibration range for this standardized method is 0.05 to 2.0 mg / L. Task

[0009] Conventional methods known in the prior art for determining ammonium ions in aqueous solution, including the aforementioned DIN standard based on the Berthelot reaction, use at least two different reagents. However, this results in these methods requiring numerous steps. Therefore, there is a need for an improved method for determining the ammonium ion concentration in aqueous solution that reduces both labor and material requirements.

[0010] With common "ready-to-use" test kits, the interference of the sample matrix must also be considered. Another problem with the determination of ammonium ions in aqueous solution using the Berthelot reaction is that this reaction is highly dependent on the concentration of the chlorine donor. Therefore, it is usually added at the end to ensure complete chlorination of NH3 to monochloramine. If too high a concentration of the chlorine donor is used, the indophenol dye is oxidized, leading to under-determined results. "Ready-to-use" test kits are subject to aging, which can lead to under-determined results, but also to over-determined results.

[0011] According to the invention, it was found that the problem underlying the invention is solved by combining all substances required for the Berthelot reaction in a single solid reagent (one-component system). However, it was observed that the substances commonly used in the Berthelot reaction cannot be combined as solids. The choice of base proved to be particularly critical for the stability of the reagent. It was experimentally determined that a variety of criteria must be considered when selecting a suitable base and that the base used according to the invention should be a strong base that is not only slightly hygroscopic under standard storage conditions but also resistant to oxidation by the hypohalite source present in the mixture. Brief description of the invention

[0012] The problem underlying the invention was solved by the features of independent claims 1, and 11 to 14.

[0013] The first aspect of the invention relates to a solid reagent for the determination of ammonium ions in aqueous solution comprising or essentially consisting of a mixture of the following components: (i) catalyst, (ii) base, (iii) hypohalite source, and (iv) phenol compound, wherein the catalyst is sodium nitroprusside or sodium hexacyanoferrate; wherein the base has a pK B value of -2 to 4, with the proviso that the base is not a hydroxide; and wherein the phenol compound is an ortho- and / or meta-substituted phenol according to the following structure: wherein the substituents R', R" and R‴ are independently selected from the group consisting of H, alkyl, aryl, CO 2 H, CO 2 Li, CO 2 Na, CO 2 K, CO, C(O)NAlkyl 2 , C(O)NH 2 , C(S)OAlkyl, C(O)SAlkyl, CO 2 Alkyl, OAlkyl, SAlkyl, CH(OAlkyl) 2 , CH(OAlkyl)(SAlkyl), CH(SAlkyl) 2 , F, Cl, Br, I, OH and SH; wherein alkyl is a hydrocarbon group of the general formula C n H 2n+1, where "n" corresponds to the number of carbon atoms and is an integer value in the range of 1 to 18; and aryl is an aromatic carbon group having 5 to 10 carbons.

[0014] In one embodiment of the solid reagent described above, the catalyst is sodium nitroprusside.

[0015] In a further embodiment of the solid reagent described above, the base is selected from the group consisting of alkali and / or alkaline earth metal phosphates, alkali and / or alkaline earth metal carbonates and alkali and / or alkaline earth metal oxides.

[0016] In a further embodiment of the solid reagent described above, the base is selected from the group consisting of alkali metal phosphates, alkali metal carbonates and alkaline earth metal oxides.

[0017] In a further embodiment of the solid reagent described above, the hypohalite source is selected from the group consisting of dichloroisocyanuric acid, trichlorocyanuric acid and / or their salts.

[0018] In a further embodiment of the solid reagent described above, the phenol compound is selected from the group consisting of phenol, thymol, salicylic acid and / or its salts, α-naphthol, guaiacol, o-phenylphenol, o-chlorophenol, 2-methyl-5-hydroxyquinoline and m-cresol.

[0019] In a further embodiment of the solid reagent described above, the solid reagent comprises at least 2 wt.% of base with respect to the total weight of the dried reagent and / or at least 2 wt.% of phenol compound with respect to the total weight of the dried reagent.

[0020] In a further embodiment of the solid reagent described above, the solid reagent comprises up to 1 wt.% of (i), up to 2.5 wt.% of (ii), up to 1 wt.% of (iii) and up to 25 wt.% of (iv) with respect to the total weight of the dried reagent, up to 1 wt.% of (i), up to 5 wt.% of (ii), up to 1 wt.% of (iii) and up to 25 wt.% of (iv) with respect to the total weight of the dried reagent, up to 0.5 wt.% of (i), up to 55 wt.% of (ii), up to 0.5 wt.% of (iii) and up to 15 wt.% of (iv) with respect to the total weight of the dried reagent, or up to 1 wt.% of (i), up to 20 wt.% of (ii), up to 0.75 wt.% of (iii) and up to 20 wt.% of (iv) with respect to the total weight of the dried reagent, with the remainder consisting of additives.

[0021] In a further embodiment of the solid reagent described above, the reagent is free of water.

[0022] In a further embodiment of the solid reagent described above, the reagent is in the form of a powder cushion.

[0023] The solid reagent can be in tablet form.

[0024] The second aspect of the invention relates to a test kit for the determination of ammonium ions in aqueous solution comprising the solid reagent according to the first aspect of the invention.

[0025] The third aspect of the invention relates to a method for the qualitative detection of ammonium ions in aqueous solution comprising the following steps: a) Providing a sample solution; b) Adding the solid reagent according to the first aspect of the invention to the sample solution provided or providing the solid reagent and then adding the sample solution; c) Stirring the resulting solution; d) Incubating under normal conditions for 30 min or until the solution changes color.

[0026] In a preferred embodiment of this method for the qualitative detection of ammonium ions in aqueous solution, 10 to 40 mg and preferably 15 to 30 mg of the solid reagent are used per milliliter of sample solution.

[0027] The fourth aspect of the invention relates to a method for the quantitative determination of ammonium ions in aqueous solution comprising the following steps: a) Providing a sample solution; b) Pipetting the sample solution into a cuvette; c) Adding the solid reagent according to the first aspect of the invention to the sample solution; d) Completely or partially dissolving the added solid reagent; e) Incubating under normal conditions for 30 min; f) Photometrically determining the absorbance of the solution at a wavelength of 680 nm.

[0028] In a preferred embodiment of this method for the qualitative detection of ammonium ions in aqueous solution, 10 to 40 mg and preferably 15 to 30 mg of the solid reagent are used per milliliter of sample solution.

[0029] The fifth aspect of the invention relates to the use of the solid reagent according to the first aspect of the invention for the qualitative detection and / or quantitative determination of ammonium ions in aqueous solution.

[0030] The reagent according to the invention offers a number of advantages. Among other things, the reagent according to the invention enables a rapid and uncomplicated analytical method for the determination of ammonium ions in aqueous solution by eliminating the need for multiple solutions, as is common in prior art methods for the determination of ammonium ions in aqueous solution. This improvement also reduces the material requirements. The reagent exhibits high storage stability, which is characterized by the fact that even during long storage periods (even under stressful conditions), the detection limit and the quantification limit of the analytical method based on the Berthelot reaction do not deteriorate. Description of the characters

[0031] Figure 1 shows a calibration for the quantitative determination of ammonium ion concentration using Reagent 1. The inventive method for the quantitative determination of ammonium ions in aqueous solution was applied to samples of known ammonium ion concentrations (0.1, 0.2, 0.3, 0.4, and 0.5 mg / L, see corresponding points). The dotted line shows the calibration curve, and the corresponding fit function is also shown. Figure 2 shows the evaluation of a storage test for Reagent 1 under stress conditions. The dashed line corresponds to the nominal value of the standard solution of 0.5 mg / L, which was analyzed at regular intervals using the inventive method for the quantitative determination of ammonium ions. The dotted lines indicate the error tolerance of ± 0.05 mg / L. Figure 3 shows an extinction spectrum of indophenol blue obtained by the Berthelot reaction with salicylic acid as the phenol compound.Figure 4 shows a calibration for the quantitative determination of the ammonium ion concentration using reagent 2. The method according to the invention for the quantitative determination of ammonium ions in aqueous solution was applied to samples of known ammonium ion concentration. The measurement points, the calibration curve, and the corresponding fit function are shown. Figure 5 shows the evaluation of a storage test for reagent 3 under stress conditions. The dashed line corresponds to the target value of the standard solution of 0.5 mg / L, which was analyzed at regular intervals using the method according to the invention for the quantitative determination of ammonium ions. The dotted lines indicate the error tolerance of ± 0.05 mg / L. Figure 6 shows the evaluation of a storage test for reagent 4 under stress conditions.The dashed line corresponds to the nominal value of the standard solution of 0.5 mg / L, which was analyzed at regular intervals using the method according to the invention for the quantitative determination of ammonium ions. The dotted lines indicate the error tolerance of ± 0.05 mg / L. Figure 7 shows a calibration for the quantitative determination of the ammonium ion concentration using reagent 5. The method according to the invention for the quantitative determination of ammonium ions in aqueous solution was applied to samples of known ammonium ion concentration. The measurement points, the calibration curve, and the associated fit function are shown. Figure 8 shows a calibration for the quantitative determination of the ammonium ion concentration using reagent 6. The method according to the invention for the quantitative determination of ammonium ions in aqueous solution was applied to samples of known ammonium ion concentration.The measurement points, the calibration curve, and the corresponding fit function are shown. Figure 9 shows a calibration for the quantitative determination of the ammonium ion concentration using reagent 7. The inventive method for the quantitative determination of ammonium ions in aqueous solution was applied to samples with known ammonium ion concentrations. The measurement points, the calibration curve, and the corresponding fit function are shown. Definitions of terms

[0032] The ammonium ion (with the synonyms: NH 4 +< , ammonium, or azanium ion) is the conjugate acid to the base ammonia (NH 3 ). It is a cation that can form salts with anions.

[0033] The term "hydroxide" is restricted to metal hydroxides (alkali metal hydroxides, alkaline earth metal hydroxides, transition metal hydroxides, and the hydroxides of metals of the third main group), i.e., those compounds that contain dissociable hydroxide ions (OH -< ). This does not include acidic compounds (alcohols, carboxylic acids, etc.) that carry only one hydroxyl group.

[0034] Unless otherwise stated, all reactions and procedures (e.g. determinations or measurement methods) are carried out under standard conditions, i.e. at the standard temperature of 25 °C and the standard pressure of 101.3 kPa.

[0035] According to the present technical teaching, the term "solid" means that the substance characterized by it exists in a fixed state of aggregation, i.e., as a solid, under normal conditions. This property is independent of whether the substance in question is organic or inorganic in nature.

[0036] A salt is a solid compound consisting of an arrangement of cations and anions. A salt of an acid or base is the deprotonated acid (anion) or the protonated base (cation), which, together with a corresponding counterion, form a crystal lattice. The counterion to the deprotonated acid can be an alkali or alkaline earth metal ion; transition metal ions (e.g., cations of chromium, manganese, iron, cobalt, copper, or silver, which are stable in aqueous solution under normal conditions) are also conceivable as counterions.

[0037] "Stability" means storage stability under normal conditions.

[0038] The unit of concentration, unless otherwise stated, is [g / mL], provided that the unit of concentration for the determination range of ammonium is [mg / L].

[0039] The term "comprise," in addition to its literal meaning, also includes the expressions "consist essentially of" and "consist of." Thus, an article that "comprises" specifically listed elements may contain other elements in addition to those elements, or it may not contain any other elements in the sense of "consist of." The terms "have," "include," and "contain" do not exclude other elements or steps. The expression "consist essentially of" means that the essential components of a composition or steps of a process are listed, but the composition or process may contain other (unlisted) components or steps that do not significantly affect the basic (material) properties of the composition or process.

[0040] The use of the indefinite article does not exclude a plural.

[0041] Specificity is the ability of a method to detect a substance or a class of substances without being distorted by other components present in the sample and thus to clearly identify them.

[0042] The sensitivity of a method is the magnitude of the change in the response of a measurement signal divided by the change in the triggering variable (e.g., the target analyte concentration). The sensitivity of an analytical method corresponds to the slope of the calibration curve.

[0043] Measurement precision is a measure of the fluctuations caused by the test device or associated analytical instrument. It is determined by analyzing a standard multiple times (unless otherwise stated, the standard is analyzed six times).

[0044] Method precision is the random variation of the analytical results. It is determined by repeating the entire analysis, from weighing and sample preparation to measurement and reporting (unless otherwise stated, analyses are performed in six replicates).

[0045] The detection limit of a method is the smallest concentration of the analyte in a sample that can be detected qualitatively (but not quantitatively) (yes / no decision).

[0046] The limit of quantification of a method is the smallest concentration of the analyte in the sample that can be quantitatively determined with a given precision and accuracy.

[0047] According to the technology of the invention, the term "determination" encompasses not only qualitative detection but also quantitative determination of the analyte concentration. According to the technology of the invention, the term "detection" encompasses qualitative detection but not quantitative determination of the analyte concentration.

[0048] The phrase "several" specifies the integer number of the item to which the phrase refers, excluding 0 and 1. "Several" means that a number of 2, 3, 4, 5, 6, 7, 8, 9, or 10 to 100 of a particular item can exist.

[0049] According to the present technical teaching, the alkali metal counterion is selected from the group consisting of sodium, potassium, and lithium. The preferred alkali metal counterions are sodium or lithium. It is most preferred that sodium is the alkali metal counterion. According to the present technical teaching, the alkaline earth metal counterion is selected from the group consisting of magnesium, calcium, strontium, and barium. The preferred alkaline earth metal counterions are magnesium, calcium, or strontium. It is most preferred that the alkaline earth metal counterion is magnesium or calcium. It is especially preferred that the alkaline earth metal counterion is calcium.

[0050] According to the present technical teaching, storage under normal conditions corresponds to storage in a dry, clean, well-ventilated room at a room temperature between 15 °C and 25 °C or up to 30 °C depending on external climatic conditions.

[0051] A powder pillow is a quantity of the reagent packaged in a foil or film (e.g. in an aluminum bag), wherein the powder pillow may comprise 13 to 17 mg, 26 to 32 mg, 52 to 64 mg, 78 to 96 mg, 104 to 128 mg, 130 to 160 mg, 156 to 192 mg or up to 600 mg of the solid reagent according to the invention. Detailed description of the invention Components of the reagent catalyst

[0052] Catalysts are a component of the reagent according to the invention. According to the present technical teaching, the catalyst is sodium hexacyanoferrate or sodium nitroprusside. According to the present technical teaching, the catalyst is preferably sodium nitroprusside.

[0053] Sodium nitroprusside has the following chemical structural formula: Na 2 [Fe(CN) 5 NO] and may contain water inclusions in the crystal lattice. Sodium nitroprusside is the most widely used catalyst for the Berthelot reaction. Although the reaction mechanism is not fully understood, it is believed, without limiting the subject matter of the invention, that the catalyst stabilizes the monochloramine and catalyzes the reaction between monochloramine and the phenol compound, i.e., the oxidative dehydrogenation process. base

[0054] According to the present technical teaching, the base can have a pK B value of -2 to 4, provided that the base is not a hydroxide. In a preferred embodiment, the base has a pK B value of 0.35 to 3.75.

[0055] According to the present technical teaching, the base is little or not hygroscopic when stored under normal conditions.

[0056] According to the present technical teaching, the base is selected from the group consisting of alkali and / or alkaline earth metal phosphates, alkali and / or alkaline earth metal carbonates, and alkali and / or alkaline earth metal oxides. According to the present technical teaching, the base is preferably selected from the group consisting of alkali metal phosphates, alkali metal carbonates, and alkaline earth metal oxides.

[0057] According to the present technical teaching, the alkali metal counterion is selected from the group consisting of sodium, potassium, and lithium. The preferred alkali metal counterions are sodium or lithium. It is most preferred that sodium is the alkali metal counterion. According to the present technical teaching, the alkaline earth metal counterion is selected from the group consisting of magnesium, calcium, strontium, and barium. The preferred alkaline earth metal counterions are magnesium, calcium, or strontium. It is most preferred that the alkaline earth metal counterion is magnesium or calcium. It is especially preferred that the alkaline earth metal counterion is calcium.

[0058] According to the present technical teaching, the base is particularly preferably selected from the group consisting of potassium phosphate, sodium carbonate and calcium oxide, with potassium phosphate and / or calcium oxide being further preferred. Hypohalite source

[0059] As previously described, the formation of monochloro- or monobromoamine represents the first step in the Berthelot reaction mechanism and is usually achieved in the presence of hypochlorite or hypobromite. Hypochlorite or hypobromite are in situ formed from solid organochlorine or organobromine compounds, which preferably undergo quantitative hydrolysis to the corresponding hypohalides. The hypohalide source according to the invention is dichloroisocyanuric acid, trichlorocyanuric acid, and / or their salts. Preferred hypohalite sources are dichloroisocyanuric acid and its alkali or alkaline earth metal salts, with an alkali metal salt, such as a sodium or potassium salt of dichloroisocyanuric acid, being particularly preferred. Phenol compound

[0060] The phenol compound according to the present technical teaching has an unsubstituted para-position which is also sterically unhindered or it is a phenol with a halogen-substituted para-position.

[0061] The phenol compound according to the present technical teaching is an ortho- and / or meta-substituted phenol according to the following structure: wherein the substituents R', R" and R‴ are independently selected from H, alkyl, aryl, CO 2 H, CO 2 Li, CO 2 Na, CO 2 K, CO, C(O)NAlkyl 2 , C(O)NH 2 , C(S)OAlkyl, C(O)SAlkyl, CO 2 Alkyl, OAlkyl, SAlkyl, CH(OAlkyl) 2 , CH(OAlkyl)(SAlkyl), CH(SAlkyl) 2 , F, Cl, Br, I, OH and SH. R' and R" can be attached to the in Figure 3 shown structure form a fused aromatic ring, thus forming a bi- or tricyclic ring system. It is preferred that the substituents R', R" and R‴ are independently selected from H, alkyl, aryl, CO 2 H, Oalkyl and Cl.

[0062] Alkyl is a hydrocarbon group of the general formula C n H 2n+1 , where "n" corresponds to the number of carbon atoms and can assume an integer value in the range of 1 to 18, 1 to 10, 1 to 5, or 1 to 3. It is preferred that n corresponds to 1, 2, or 3. It is most preferred that n corresponds to 1 or 3. If n corresponds to a value of 3 or more, the alkyl group can be linear or branched.

[0063] Aryl is an aromatic carbon group having 5 to 10 carbon atoms. Aromatic C5 or C6 rings are preferred, which may have C1-C6 alkyl, carboxy, and / or hydroxy groups as substituents. Aryl is particularly preferably an aromatic C6 ring, which may be substituted by C1-C6 alkyl, carboxy, and / or hydroxy groups.

[0064] The phenol compound can be selected from the group consisting of phenol, thymol, salicylic acid and / or its salts, α-naphthol, guaiacol, o-phenylphenol, o-chlorophenol, 2-methyl-5-hydroxyquinoline, and m-cresol. Preferred phenol compounds are thymol and sodium salicylate. Sodium salicylate is particularly preferred as the phenol compound. Composition of the reagent Embodiments

[0065] According to the present technical teaching, the solid reagent may comprise calcium oxide, sodium salicylate, dichloroisocyanuric acid and sodium nitroprusside.

[0066] According to the present technical teaching, the solid reagent may comprise sodium carbonate, sodium salicylate, dichloroisocyanuric acid and sodium nitroprusside.

[0067] According to the present technical teaching, the solid reagent may comprise lithium carbonate, sodium salicylate, dichloroisocyanuric acid and sodium nitroprusside.

[0068] According to the present technical teaching, the solid reagent may comprise potassium phosphate, sodium salicylate, dichloroisocyanuric acid and sodium nitroprusside.

[0069] According to the present technical teaching, the solid reagent may comprise calcium oxide, sodium salicylate, dichloroisocyanuric acid, sodium nitroprusside and sodium chloride.

[0070] According to the present technical teaching, the solid reagent may comprise sodium carbonate, sodium salicylate, dichloroisocyanuric acid, sodium nitroprusside and sodium chloride.

[0071] According to the present technical teaching, the solid reagent may comprise lithium carbonate, sodium salicylate, dichloroisocyanuric acid, sodium nitroprusside and sodium chloride.

[0072] According to the present technical teaching, the solid reagent may comprise potassium phosphate, sodium salicylate, dichloroisocyanuric acid, sodium nitroprusside and sodium chloride.

[0073] According to the present technical teaching, the solid reagent may comprise calcium oxide, sodium salicylate, dichloroisocyanuric acid, sodium nitroprusside, citric acid and sodium chloride.

[0074] According to the present technical teaching, the solid reagent may comprise sodium carbonate, sodium salicylate, dichloroisocyanuric acid, sodium nitroprusside, citric acid and sodium chloride.

[0075] According to the present technical teaching, the solid reagent may comprise lithium carbonate, sodium salicylate, dichloroisocyanuric acid, sodium nitroprusside, citric acid and sodium chloride.

[0076] According to the present technical teaching, the solid reagent may comprise potassium phosphate, sodium salicylate, dichloroisocyanuric acid, sodium nitroprusside, citric acid and sodium chloride.

[0077] According to the present technical teaching, the solid reagent may comprise calcium oxide, sodium salicylate, sodium dichloroisocyanurate and sodium nitroprusside.

[0078] According to the present technical teaching, the solid reagent may comprise sodium carbonate, sodium salicylate, sodium dichloroisocyanurate and sodium nitroprusside.

[0079] According to the present technical teaching, the solid reagent may comprise lithium carbonate, sodium salicylate, sodium dichloroisocyanurate and sodium nitroprusside.

[0080] According to the present technical teaching, the solid reagent may comprise potassium phosphate, sodium salicylate, sodium dichloroisocyanurate and sodium nitroprusside.

[0081] According to the present technical teaching, the solid reagent may comprise calcium oxide, sodium salicylate, sodium dichloroisocyanurate, sodium nitroprusside and sodium chloride.

[0082] According to the present technical teaching, the solid reagent may comprise sodium carbonate, sodium salicylate, sodium dichloroisocyanurate, sodium nitroprusside and sodium chloride.

[0083] According to the present technical teaching, the solid reagent may comprise lithium carbonate, sodium salicylate, sodium dichloroisocyanurate, sodium nitroprusside and sodium chloride.

[0084] According to the present technical teaching, the solid reagent may comprise potassium phosphate, sodium salicylate, sodium dichloroisocyanurate, sodium nitroprusside and sodium chloride.

[0085] According to the present technical teaching, the solid reagent may comprise calcium oxide, sodium salicylate, sodium dichloroisocyanurate, sodium nitroprusside, citric acid and sodium chloride.

[0086] According to the present technical teaching, the solid reagent may comprise sodium carbonate, sodium salicylate, sodium dichloroisocyanurate, sodium nitroprusside, citric acid and sodium chloride.

[0087] According to the present technical teaching, the solid reagent may comprise lithium carbonate, sodium salicylate, sodium dichloroisocyanurate, sodium nitroprusside, citric acid and sodium chloride.

[0088] According to the present technical teaching, the solid reagent may comprise potassium phosphate, sodium salicylate, sodium dichloroisocyanurate, sodium nitroprusside, citric acid and sodium chloride. Ratio of components

[0089] In the Berthelot reaction, there is a complex relationship between the concentration of the reactants and the reaction intermediates, making the choice of optimal concentrations difficult.

[0090] According to the present technical teaching, the solid reagent may comprise up to 2.5% or up to 5% of the catalyst (expressed as weight percent with respect to the total weight of the dried reagent).

[0091] According to the present technical teaching, the solid reagent may comprise at least 1%, at least 1.5%, or at least 2%, or from 1% to 94%, from 1% to 70%, from 1.5% to 55%, from 5% to 40%, or from 10 to 30% of the base (expressed as weight percent relative to the total weight of the dried reagent). It is also conceivable for the solid reagent to comprise 1%, 1.5%, 5%, 10%, 30%, 40%, 55%, or 70% to 94% of the base (expressed as weight percent relative to the total weight of the dried reagent).

[0092] According to the present technical teaching, it is preferred that the solid reagent comprises the base in an amount which ensures that when the reagent is added to the aqueous solution (to be analyzed / determined), the solubility of the base in water under normal conditions (material constant) is not exceeded.

[0093] According to the present technical teaching, the solid reagent may comprise up to 2.5% or up to 5% of the hypohalite source (expressed as a weight percentage relative to the total weight of the dried reagent).

[0094] According to the present technical teaching, the solid reagent may comprise from 1% to 94%, from 5% to 70%, from 5% to 50%, from 5% to 40%, from 10% to 30%, or from 10% to 25% of the phenol (expressed as weight percent relative to the total weight of the dried reagent). The solid reagent preferably comprises from 10 to 25% by weight of the phenol relative to the total weight of the dried reagent.

[0095] According to the present technical teaching, the solid reagent may comprise any proportion of additives, which is determined only by the proportion of the remaining components using the following formula:

[0096] The components of the reagent according to the invention are, unless otherwise stated herein, given in weight percent based on the total weight of the dried reagent.

[0097] The components (catalyst:base:hypohalite source:phenol compound:additives - normalized to the proportion of base) can be present in one of the following ratios: up to 0.40:1: up to 0.34: up to 9.27: up to 30.00; up to 0.50:1: up to 0.43: up to 11.62: up to 37.61; up to 0.01:1: up to 0.01: up to 0.23: up to 0.75; or up to 0.05:1: up to 0.04: up to 1.16: up to 3.74. Additive

[0098] According to the present technical teaching, each embodiment may contain additives.

[0099] According to the present technical teaching, the reagent may contain from 0.01 to 0.5, 0.1, 0.05, or 0.02 wt.%, up to 0.1 wt.%, up to 0.05 wt.%, or up to 0.02 wt.% water. It is preferred that the reagent according to the invention be free of water.

[0100] According to the present technical teaching, the additives are selected from the group consisting of one or more chelating agents, fillers and combinations thereof.

[0101] The one or more chelating agents that can be used according to the present technical teachings are selected from the group consisting of alkali and alkaline earth metal salts of ethylenediaminetetraacetic acid (EDTA), citric acid, tartaric acid, and combinations thereof. Preferred chelating agents are alkali metal salts of EDTA, citric acid, and / or tartaric acid.

[0102] According to the present technical teaching, the alkali metal counterion is selected from the group consisting of sodium, potassium, and lithium. The preferred alkali metal counterions are sodium or potassium. It is most preferred that sodium is the alkali metal counterion. According to the present technical teaching, the alkaline earth metal counterion is selected from the group consisting of magnesium, calcium, strontium, and barium. The preferred alkaline earth metal counterions are magnesium, calcium, or strontium. It is most preferred that the alkaline earth metal counterion is magnesium or calcium. It is especially preferred that the alkaline earth metal counterion is calcium.

[0103] Particularly preferred chelating agents are trisodium citrate and / or disodium tartrate.

[0104] Fillers that can be used according to the present technical teaching are selected from sodium chloride, mannitol, sodium sulfate and calcium chloride.

[0105] The solid reagent according to the invention may contain from 0.01 to 0.5 wt% water, based on the total weight of the reagent, or may be free of water.

[0106] The solid reagent according to the invention can be in powder form or as a powder cushion. It is preferred that the powder cushion contains 600 mg or less of the solid reagent according to the invention, and in particular 13 to 17 mg, 26 to 32 mg, 52 to 64 mg, 78 to 96 mg, 104 to 128 mg, 130 to 160 mg, or 156 to 192 mg of the solid reagent according to the invention.

[0107] Furthermore, the solid reagent can be in tablet form. Measurement methods Qualitative evidence

[0108] The procedure for the qualitative detection of ammonium ions in aqueous solution comprises the following steps: a) Providing a sample solution; b) Adding the solid reagent according to the present technical teaching, wherein the amount of added reagent depends on the volume of the sample solution; c) Completely or partially dissolving the added solid reagent; d) Incubating under normal conditions for 30 minutes or until discoloration of the reaction solution has occurred.

[0109] It should be noted that although the Berthelot reaction produces a blue dye, the objectively and visually detected coloration depends on the components of the reagent (coloration here refers to the formation of a mixed color between the color of the solution and the resulting blue dye). For example, if sodium hexacyanoferrate is used as the catalyst, the reaction solution appears green due to the formation of a mixed color, because sodium hexacyanoferrate, as a decahydrate, is a yellow solid. Quantitative determination

[0110] The method for the quantitative determination of ammonium ions in aqueous solution comprises the following steps: a) Providing a sample solution; b) Pipetting the sample solution into a cuvette; c) Adding the solid reagent according to the present technical teaching, wherein the amount of added reagent depends on the volume of the sample solution; d) Completely or partially dissolving the added solid reagent; e) Incubating under standard conditions for 30 min; f) Photometrically determining the absorbance of the solution at a wavelength of 680 nm.

[0111] In the described methods (quantitative detection and qualitative determination), 10 to 40 mg and preferably 15 to 30 mg of the solid reagent are added for 1 mL of sample solution. Experiments

[0112] Conventional competitor products that utilize the indophenol blue method (Berthelot reaction) use at least two different reagents. For example, HACH's reagents contain a "salicylate reagent" and a "cyanuric acid reagent" (Table 1, Entry 1), in which the above-listed reagents are divided into two so-called powder pads. In the LCK 304 ammonium cuvette test, sodium salicylates and dichloroisocyanuric acid are also separated by the reagent in the test tube and the Dosicap (Table 1, Entry 2). A third product from HACH, "AmVer," also separates the individual components into two reagents (Table 1, Entry 3). In an ammonium test from Merck, which can be evaluated using a color card, the individual components of the reaction are even divided into three different reagents (Table 1, Entry 4).Further examples of multicomponent systems from Merck, Lovibond and MACHEREY-NAGEL are listed (Table 1, entries 5 to 7). Table 1 Comparison of commercially available (usual) systems and the reagent according to the invention entry test kit Phenol compound base catalyst Hypohalite source 1 Salicylate reagent 2653299 Sodium salicylate Sodium nitroprusside Cyanurate reagent 2653199 Disodium tartrate LiOH Dichloroisocyanuric acid 2 LCK 304 round cuvette Sodium salicylate Trisodium citrate NaOH LCK 304 Dosicap Sodium nitroprusside Dichloroisocyanuric acid 3 HACH AmVer 2604545 Salicylate reagent Sodium salicylates Trisodium citrate Disodium tartrate Sodium nitroprusside HACH AmVer 2604545 Cyanurate reagent Trisodium citrate Disodium tartrate LiOH Dichloroisocyanuric acid 4 MQuant 114428 Ammonium Test (Merck) Reagent 1 NaOH MQuant 114428 Ammonium test (Merck) Reagent 2 Dichloroisocyanuric acid MQuant 114428 Ammonium test (Merck) Reagent 3 Thymol Sodium nitroprusside 5 MACHEREY NAGEL 985003 Reagent 1 Sodium salicylate Trisodium citrate NaOH MACHEREY NAGEL 985003 Reagent 2 (Nanofix) Sodium nitroprusside Dichloroisocyanuric acid 6 Ammonium with tablet No. 1 Lovibond 00512581 Salicylic acid Sodium nitroprusside Ammonium with tablet No. 2 Lovibond 00512591 LiOH Dichloroisocyanuric acid 7 Ammonium with Vario Powder Packet Salicylate Reagent Sodium salicylate Sodium nitroprusside Ammonium with Vario Powder Packet Cyanurate Reagent LiOH Dichloroisocyanuric acid 8a Powder Pillow Ammonium with CaO Sodium salicylate CaO Sodium nitroprusside Dichloroisocyanuric acid 8b Powder Pillow Ammonium with K3PO4 Sodium salicylate K3PO4 Sodium nitroprusside Dichloroisocyanuric acid 8c Powder Pillow Ammonium with Na2CO3 Sodium salicylate Na2CO3 Sodium nitroprusside Dichloroisocyanuric acid

[0113] The use of CaO has proven to be advantageous. The powder mixture provides good measurement results in the range of 0.05 - 0.50 mg / L ammonium ( Entry 8a ). The storage test in the form of powder pillows showed a shelf life of 2 years. Tripotassium phosphate also provides good measurement results as a base in the range of 0.05 - 0.50 mg / L ammonium ( Entry 8b ) . Samples Chemicals used:

[0114] Sodium nitroprusside (CAS: 13755-38-9; from Merck, Catalog No.: 1065410500) Sodium salicylate (CAS: 54-21-7; from Bernd Kraft, Catalog No.: BK17418.3600) NaCl (CAS: 7647-14-5; from Merck, Catalog No.: 106404) Sodium dichloroisocyanurate (CAS: 52671-45-1; from Acros, Catalog No.: 11300290) CaO (CAS: 1305-78-8; from Acros, Catalog No.: AC422830010) Na 2 CO 3 (CAS: 497-19-8, from Merck, Catalog No.: 106392) Li 2 CO 3 (CAS: 554-13-2, from Sigma-Aldrich, Catalog No.: 255823) K 3 PO 4 •3H 2 O (CAS: 22763-03-7, from Merck, Catalog No.: 1.05102)

[0115] The following reagents were tested: Reagent 1 (APP019):

[0116] 11,6 g Sodium nitroprusside 272 g Sodium salicylate 880 g NaCl 10 g Sodium dichloroisocyanurate 29,33 g CaO Reagent 2 (APP020):

[0117] 11,6 g Sodium nitroprusside 272 g Sodium salicylate 880 g NaCl 10 g Sodium dichloroisocyanurate 23,4 g CaO Reagent 3 (APP011):

[0118] 11,6 g Sodium nitroprusside 272 g Sodium salicylate 880 g NaCl 10 g Sodium dichloroisocyanurate 1175 g Na2CO3 Reagent 4 (APP010):

[0119] 11,6 g Sodium nitroprusside 272 g Sodium salicylate 880 g NaCl 10 g Sodium dichloroisocyanurate 235 g Na2CO3 Reagent 5 (APP009):

[0120] 11,6 g Sodium nitroprusside 272 g Sodium salicylate 880 g NaCl 10 g Sodium dichloroisocyanurate 1173,6 g Li2CO3 Reagent 6 (APP008):

[0121] 11,6 g Sodium nitroprusside 272 g Sodium salicylate 880 g NaCl 10 g Sodium dichloroisocyanurate 235 g Li2CO3 Reagent 7 (APP006):

[0122] 11,6 g Sodium nitroprusside 272 g Sodium salicylate 880 g NaCl 10 g Sodium dichloroisocyanurate 1175 g K 3 PO 4 •3H 2 O Calibration functions

[0123] Calibration series were recorded for the reagents using 5 or 10 standard solutions of equidistant concentrations. The test procedure is as follows: 1) Add 1 gram measuring spoon (approx. 130-160 mg) of the reagent according to the invention to 5 mL of sample solution in a 14 mm round cuvette. 2) Close the round cuvette with the screw cap and shake. 3) Incubate for 30 minutes under normal conditions. 4) Clean the outside of the round cuvette. 5) Determine the absorbance at 680 nm in a VIS II spectrophotometer (MACHEREY-NAGEL). 6) Create the calibration function using the obtained pairs of values.

[0124] Figures 1 , 4 , 7, 8 and 9 show such calibration series using the calibration series recorded for reagents 1, 2, 5, 6 and 7 as examples. Process characteristics

[0125] The following process characteristics were recorded for Reagent 2: Table 2 Performance data for Reagent 2. Process characteristics Standard deviation 0.005 mE Procedural standard deviation 0.004 mg / L gradient 1287.68 mU / (mg / L) Ordinate section 35.2 mE Detection limit (estimated value) 0.015 mg / L Limit of quantification (estimated value) 0.046 mg / L Process variation coefficient Vx,o 0,96 %

[0126] The unit [mE] is the milliextinction according to: E = log I 0 / I 1 where I 0 corresponds to the intensity of the incident (radiated) light and I 1 corresponds to the intensity of the transmitted light. Long-term storage test

[0127] A subsequent storage test in a commercially available drying oven from Memmert (universal oven UF160plus) at 50 °C allows an assessment and extrapolation of the storage life of the powder mixture (see Figures 2 , 5 and 6The influence of stress conditions during storage was quantified by applying the inventive method for the quantitative determination of ammonium ions in aqueous solution to a sample of known ammonium ion concentration (target value = 0.5 mg / L, see dashed line) at regular intervals. The calibration function obtained as described above was used for this purpose. The absorbance measurement was performed at 680 nm in a VIS II spectrophotometer (MACHEREY-NAGEL). From this storage test, the shelf life of the powder mixture can be reliably extrapolated for approximately 3 years.

[0128] The reagents provide good results in calibration and storage tests. No deviations beyond the error tolerance (10% error tolerance, corresponding to ±0.05 mg / L at a target value of 0.5 mg / L, see dotted lines) were observed for the reagent according to the invention. Influence of the amount of reagent

[0129] The series of experiments, the results of which are summarized in Table 3, was carried out using the following steps: a) Place the solid reagent 2 in a round cuvette with an outer diameter of 16 mm; b) Add 5 mL of sample solution with a nominal ammonium concentration of 0.5 mg / L; b) Close and shake the round cuvette; c) Incubate under standard conditions for 30 min; d) Photometric determination of the absorbance of the solution at a wavelength of 680 nm. Table 3 Dependence of the measurement result on the amount of reagent 2 remark Reagent quantity Reagent amount per mL sample volume Measured concentration Deviation from the target value 12.5 mg 2.5 mg / mL 0.05 mg / mL -90 % 25.0 mg 5.0 mg / mL 0.34 mg / mL -32 % 50.0 mg 10.0 mg / mL 0.45 mg / mL -10 % 75.0 mg 15.0 mg / mL 0.49 mg / mL -2 % 100.0 mg 20.0 mg / mL 0.50 mg / mL 0 % 150.0 mg 30.0 mg / mL 0.52 mg / mL 4 % 200.0 mg 40.0 mg / mL 0.53 mg / mL 6 % cloudy 300.0 mg 60.0 mg / mL 0.63 mg / mL 26 % cloudy 400.0 mg 80.0 mg / mL 0.68 mg / mL 36 % cloudy 500.0 mg 100.0 mg / mL 0.67 mg / mL 34 %

[0130] Table 3 shows the dependence of the measurement result on the reagent quantity. Reagent quantities of 10 to 40 mg per milliliter of sample volume provide particularly high measurement precision. Short-term storage stability

[0131] To investigate the storage stability of the solid reagent according to the invention and that of mixtures containing hydroxides as base, the compositions summarized in Table 4 were prepared. For this purpose, the catalyst, base, hypohalite source, and phenolic compound were mixed and homogenized in a mortar. In all examples, sodium nitroprusside, dichloroisocyanuric acid (DCI), and sodium salicylate were used as the catalyst, hypohalite source, and phenolic compound, with sodium chloride used as the filler (sodium chloride accounts for the remaining wt.% relative to the total weight of the dried composition). These compositions were stored for 2 days under normal conditions, initially being examined hourly and then daily for external changes.

[0132] In this way, the bases of the invention (CaO, Na 2 CO 3 , and K 3 PO 4 ) could be directly compared with the hydroxides used in commercially available multicomponent systems. In this context, the influence of the amount of base in the composition (relative to the total weight of the dried composition) on storage stability was also investigated. Table 4 Compositions tested for short-term storage stability # base Percentage in wt.% catalyst Percentage in wt.% Hypohalite source Percentage in wt.% Phenol compound Percentage in wt.% 1 CaO 5 NPN 0,94 DCI 0,81 Sodium salicylate 22 2 Na2CO3 10 NPN 0,89 DCI 0,77 Sodium salicylate 21 3 K 3 PO 4 •3H 2 O 10 NPN 0,89 DCI 0,77 Sodium salicylate 21 4 LiOH 2 NPN 0,97 DCI 0,84 Sodium salicylate 23 5 LiOH 5 NPN 0,94 DCI 0,81 Sodium salicylate 22 6 LiOH 10 NPN 0,89 DCI 0,77 Sodium salicylate 21 7 NaOH 2 NPN 0,97 DCI 0,84 Sodium salicylate 23 8 NaOH 5 NPN 0,94 DCI 0,81 Sodium salicylate 22 9 NaOH 10 NPN 0,89 DCI 0,77 Sodium salicylate 21 10 KOH 2 NPN 0,97 DCI 0,84 Sodium salicylate 23 11 KOH 5 NPN 0,94 DCI 0,81 Sodium salicylate 22

[0133] After just a few hours, a yellowish discoloration of compositions 7 to 11 was objectively (visually) noticeable. Compositions 4 to 6 showed a slight yellowing after one day. Furthermore, clumping was observed for compositions 4 to 11. These effects increased with increasing proportion of hydroxide in the composition. The compositions according to the invention, in contrast, remained finely powdered (no clumping) and showed no discoloration.

Claims

1. A solid-state reagent for assaying ammonium ions in aqueous solution, comprising, or essentially consisting of, a mixture of the following components: (i) a catalyst, (ii) a base, (iii) a hypohalite source, and (iv) a phenol compound, wherein said catalyst is sodium nitroprusside or sodium hexacyanoferrate, wherein said base has a pKB value of from -2 to +4, with the proviso that the base is not a hydroxide, and wherein the phenol compound is an ortho- and / or meta-substituted phenol according to the following structure: wherein the substituents R', R" and R‴ are independently selected from the group consisting of H, alkyl, aryl, CO2H, CO2Li, CO2Na, CO2K, CO, C(O)Nalkyl2, C(O)NH2, C(S)Oalkyl, C(O)Salkyl, CO2alkyl, Oalkyl, Salkyl, CH(Oalkyl)2, CH(Oalkyl)(Salkyl), CH(Salkyl)2, F, Cl, Br, I, OH and SH; wherein alkyl is a hydrocarbyl group of general formula CnH2n+1, in which "n" is the number of carbon atoms and is an integer within a range from 1 to 18; and aryl is an aromatic hydrocarbyl group with 5 to 10 carbon atoms.

2. The solid-state reagent according to claim 1, characterized in that said catalyst is sodium nitroprusside.

3. The solid-state reagent according to one or more of the preceding claims, characterized in that said base is selected from the group consisting of alkali and / or alkaline earth metal phosphates, alkali and / or alkaline earth metal carbonates, and alkali and / or alkaline earth metal oxides.

4. The solid-state reagent according to one or more of the preceding claims, characterized in that said base is selected from the group consisting of alkali metal phosphates, alkali metal carbonates, or alkaline earth metal oxides.

5. The solid-state reagent according to one or more of the preceding claims, characterized in that said hypohalite source is selected from the group consisting of dichloroisocyanuric acid, trichlorocyanuric acid, and / or their salts.

6. The solid-state reagent according to one or more of the preceding claims, characterized in that said phenol compound is selected from the group consisting of phenol, thymol, salicylic acid and / or its salts, α-naphthol, guajacol, o-phenylphenol, o-chlorophenol, 2-methyl-5-hydroxyquinoline, and m-cresol.

7. The solid-state reagent according to one or more of the preceding claims, characterized in that said solid-state reagent comprises at least 2% by weight of base, based on the total weight of the dried reagent, and / or at least 2% by weight of phenol compound, based on the total weight of the dried reagent.

8. The solid-state reagent according to one or more of the preceding claims, characterized in that said solid-state reagent comprises up to 1% by weight of (i), up to 2.5% by weight of (ii), up to 1% by weight of (iii), and up to 25% by weight of (iv), based on the total weight of the dried reagent, the remainder consisting of additives; comprises up to 1% by weight of (i), up to 5% by weight of (ii), up to 1% by weight of (iii), and up to 25% by weight of (iv), based on the total weight of the dried reagent, the remainder consisting of additives; comprises up to 0.5% by weight of (i), up to 55% by weight of (ii), up to 0.5% by weight of (iii), and up to 15% by weight of (iv), based on the total weight of the dried reagent, the remainder consisting of additives; or comprises up to 1% by weight of (i), up to 20% by weight of (ii), up to 0.75% by weight of (iii), and up to 20% by weight of (iv), based on the total weight of the dried reagent, the remainder consisting of additives.

9. The solid-state reagent according to one or more of the preceding claims, characterized in that the reagent is free of water.

10. The solid-state reagent according to one or more of the preceding claims, wherein (i) said reagent is in the form of a powder pad; or (ii) said reagent is in tablet form.

11. A test kit for assaying ammonium ions in aqueous solution, comprising the solid-state reagent according to one or more of the preceding claims.

12. Use of the solid-state reagent according to one or more of claims 1 to 10 for the qualitative detection and / or the quantitative determination of ammonium ions in aqueous solution.

13. A method for the qualitative detection of ammonium ions in aqueous solution comprising the following steps: a) providing a sample solution; b) adding the solid-state reagent according to one or more of claims 1 to 10 to the provided sample solution, or providing the solid-state reagent and then adding the sample solution; c) stirring the solution obtained; d) incubating under normal conditions for 30 min, or until a discoloration of the solution has occurred.

14. A method for the quantitative determination of ammonium ions in aqueous solution comprising the following steps: a) providing a sample solution; b) pipetting said sample solution into a cuvette; c) adding the solid-state reagent according to one or more of claims 1 to 10 to the sample solution; d) completely or partially dissolving the added solid-state reagent; e) incubating under normal conditions for 30 min; f) photometric determination of the absorbance of the solution at a wavelength of 680 nm.

15. The method according to claim 13 or 14, characterized in that 10 to 40 mg and preferably 15 to 30 mg of the solid-state reagent is used per milliliter of the sample solution.