WO1990005913A1 - Procede de determination chromatographique de cations - Google Patents

Procede de determination chromatographique de cations Download PDF

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Publication number
WO1990005913A1
WO1990005913A1 PCT/EP1989/001395 EP8901395W WO9005913A1 WO 1990005913 A1 WO1990005913 A1 WO 1990005913A1 EP 8901395 W EP8901395 W EP 8901395W WO 9005913 A1 WO9005913 A1 WO 9005913A1
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Prior art keywords
column
acid
polybasic carboxylic
carboxylic acid
solution
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PCT/EP1989/001395
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German (de)
English (en)
Inventor
Hans-Heinrich Schaper
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Schaper Hans Heinrich
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Publication of WO1990005913A1 publication Critical patent/WO1990005913A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/96—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation using ion-exchange
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/02—Food
    • G01N33/14—Beverages
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/96—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation using ion-exchange
    • G01N2030/965—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation using ion-exchange suppressor columns

Definitions

  • the invention relates to a method for the chromatographic determination of mono- and polyvalent cations, in particular for the simultaneous determination of alkali and alkaline earth ions in wine or mineral water.
  • Hydrochloric acid is not sufficient for elution of these ions.
  • Polyvalent cations were separated using the previously known methods with complexing organic compounds which compete with the column material as chelating ligands and with ethylenediamine, which in its protonated form competes with the cations adsorbed on the column.
  • the high elution power of these eluent components causes the monovalent cations, in particular the alkali cations, to be eluted as a common fraction in or shortly after the dead volume of the respective chromatography columns.
  • ion pair chromatography a non-polar material based on silica gel or on a polymer is used as the stationary phase.
  • eluent are organic at least partially contain hydrophobic and ionic molecules that adsorb to the reverse phase column material.
  • Aliphatic sulfonic acids have hitherto been used as the elution reagent, that is to say as the counter ion for the cations to be separated.
  • the object of the invention is to propose a method and a column material with which a simultaneous separation of mono- and multivalent cations, in particular also alkali and alkaline earth ions, is possible.
  • a so-called reversed-phase column is at least partially covered with at least one polybasic carboxylic acid which has a hydrophobic residue, in that the substance which contains cations is applied to the column and then eluted.
  • Alkyl or cycloalkyldicarboxylic acids are particularly suitable here.
  • aromatic dicarboxylic acids can also be used, especially if a non-polar polymer-based material, such as the PRP-1 column, is used as the stationary phase.
  • the invention relates generally to the use of polybasic carboxylic acids and not only to the use of dicarboxylic acids, although the discussion below relies essentially on examples in which dicarboxylic acids are used as polybasic carboxylic acids.
  • carboxylic acids examples include alkyl and aryl derivatives of malonic acid and succinic acid as well as 1,2-dicarboxyl-5-alkylcyclohexanes, 1,2-dicarboxyl-alkylcyclopentanes, alkyl derivatives of phthalic acid and alkylnaphthalenedicarboxylic acids.
  • a particularly good interaction of the hydrophobic part of the carboxylic acid with the column material results with aromatic, dibasic and polybasic carboxylic acids, such as naphthalene -di -, - tri- and -tetracarboxylic acids, since charge-transfer complexes can form here with the aromatic components of the column material.
  • the decisive factor in the selection of the corresponding polybasic carboxylic acid is on the one hand the interaction of the hydrophobic residue with the non-polar column material and on the other hand the complex formation constant with the mono- and polyvalent cations to be separated.
  • the complex formation constant it has been found that particularly favorable values are achieved when the chelate complexes of the polybasic carboxylic acids form a six- or seven-membered ring together with the cation.
  • the complex formation constant is generally too small.
  • kylreste with four to sixteen carbon atoms, but especially with six to 10 carbon atoms.
  • Hexylmalonic acid and hexylsuccinic acid can be named as examples.
  • Aromatic, polybasic carboxylic acids can also be adsorbed onto the non-polar column material via appropriate alkyl chains.
  • alkyl chains are used as the hydrophobic residues of the polybasic carboxylic acids which have more than ten carbon atoms, then these carboxylic acids are very well anchored to the column material, so that the separation mechanism of the column shifts from ion pair chromatography more towards ion exchange chromatography.
  • substituents are in particular the nitro group or halogen radicals, here in particular bromine radicals.
  • the polybasic carboxylic acid is expediently applied to the column in a polar solvent, in particular in an alcoholic solution. Again, the use of a methanolic solution is particularly recommended.
  • the elution is then preferably carried out with the aid of a mono- or dicarboxylic acid in the eluent, the pK S value or first pK S value of which is less than 3, preferably less than 2.
  • the pK S value or first pK S value of which is less than 3, preferably less than 2.
  • the polybasic carboxylic acid will have to be added to the eluent.
  • the elution effect can be improved by adding so-called elution enhancers, which can be formed in particular by a diamine, to the elution solution.
  • the diamines are in the pH range in which the column according to the invention is usually used in protonated form and thus compete with the cations adsorbed on the column.
  • One of the preferred diamines is the 1,7-diaminoheptane.
  • the column is used according to the ion-pair chromatography method, in which the shorter-chain hydrophobic residues of the polybasic carboxylic acid are used in particular, it is advisable to ensure the eluent the polybasic carboxylic acid in order to ensure constant loading of the column with the polybasic carboxylic acid to add and to cover the acid with the polybasic carboxylic acid already with the eluent. It is then expedient to coat the column with the same solution and carry out the elution.
  • the column is coated with a solution of hexylsuccinic acid and oxalic acid in water, whereupon the substance which is to be analyzed for the cation content is applied to the column and then the elution is carried out with the solution used to load the column.
  • Concentrations between 1 and 4 mmol and with respect to succinic acid 0, 5 and 4 mmol oxalic acid have proven to be particularly advantageous with respect to hexylsuccinic acid.
  • a content of approx. 2 mmol hexylsuccinic acid and approx. 1 mmol oxalic acid is recommended.
  • a reversed-phase column is preferably used as the column material in the process, the stationary phase of which is a non-polar material based on silica gel, to which alkyl groups, such as RP 4 , RP 8 and RP 18 , are bound.
  • a reversed-phase column can be used, the stationary phase of which is formed by a non-polar polymer-based material, such as, for example, PRP-1.
  • the second aspect of the invention relates to the creation of a modified reversed-phase material, in particular a column, which is suitable for the chromatographic determination of mono- and polyvalent cations, in particular for the simultaneous determination of alkali and alkaline earth metal ions, in wine or mineral waters.
  • this column material is characterized in that it is at least partially at least one polybasic carboxylic acid, which has a hydrophobic residue, is occupied. The hydrophobic residue is held on the reversed phase material by non-covalent forces.
  • Non-polar materials based on silica gel which has alkyl groups, such as, for example, the RP 4 , RP 8 and RP 18 materials, are particularly suitable as reversed phase material.
  • the reversed phase material will preferably be coated with an alkyl or cycloalkyl dicarboxylic acid.
  • Column material which is especially prepared for the analysis of mineral waters and wines, preferably has an occupancy with alkyl succinic acid, in particular hexyl succinic acid.
  • Preferred solutions for covering and eluting reversed-phase material in the chromatographic determination of mono- and polyvalent cations comprise at least one polybasic carboxylic acid which has a hydrophobic residue, and a mono- or dicarboxylic acid, the pK S value or first pK S value of which is less than 3.
  • the solvent of the solution will preferably be a polar solvent.
  • the polybasic carboxylic acid here is preferably an alkyl or cycloalkyl dicarboxylic acid, it also being possible to use aromatic derivatives of dicarboxylic acids or aromatic dicarboxylic acids themselves.
  • One of the preferred solutions contains hexylsuccinic acid and oxalic acid in water, the concentrations of which are particularly useful for problematic analysis of wine and mineral water
  • Hexylsuccinic acid is approximately 2 mmol and the concentration of oxalic acid is approximately 1 mmol in water.
  • the size of the chelate rings formed by the polybasic carboxylic acid with the cations is of importance in relation to the separation properties of the system.
  • a grouping (1,4-dicarboxylic acid) is formed which can obviously complex metal ions better than, for example, the corresponding bases of monoalkylcarboxylic acids.
  • a possible coordination of two carboxylic acid groups of a monocarboxylic acid to the respective metal ion does not appear to change that much, although it must also be taken into account that the dissociation of the carboxylic acid is suppressed with increasing concentration.
  • the chelate complexes of 1,3-dicarboxylic acids for example of alkylmalonic acids, also have satisfactory complex formation constants.
  • complexes can form for calcium and magnesium by complexing with the carboxylic acid exchange groups, which can differ in the coordination numbers and complex stabilities. This is one of the reasons for the selectivity of this exchange material. For the sake of simplicity, the existing aquo complexes and the complexes of the cations with organic acids are not taken into account in this consideration.
  • R 1 , R 2 Residues of the copolymer, alkyl residues or hydrogen It follows from these explanations that the ion pair reagents should have at least two carboxy exchange groups in order to be able to form the relatively stable chelate rings, preferably 6- and 7-rings, together with the cations. At the same time, a hydrophobic residue is necessary so that interactions with the non-polar column material are possible.
  • the demands placed on the ion pair reagents are met, for example, by alkyl succinic acids.
  • a synthetic route starting from n-alcohol is used, which is outlined in the diagram of FIG. 1.
  • the melting points are determined in open glass capillaries using a melting point apparatus with a paraffin oil bath.
  • the 1 H-NMR spectra are recorded with a Bruker WP 80 (80 MHz) with tetramethylsilane (TMS) as the internal standard.
  • a Metrohm 670 tritroprocessor is used to determine the pK S values.
  • the measurement is carried out for hexylsuccinic acid in water, for dodecyl- or hexadecylsuccinic acid in 80 or 90% methanol.
  • the influence of the methanol concentration is negligible.
  • a reversed-phase material based on silica gel proves to be sufficient here, which has significantly lower costs than a polymer material.
  • the LiChrospher RP 18 with spherical 5 ⁇ material proves to be the most suitable. A further reduction in particle size in the Superspher RP 18 does not result in better separation performance. The irregular material also tested in the LiChrosorb RP 18 and the spherical Nucleosil RP 18 follow a poorer separation yourself. As described above, the hexylsuccinic acid can form seven rings with the respective cations, two or more groups also being possible.
  • the conductivity detection is the suitable detection system for the developed system because it can detect mono- and bivalent cations equally.
  • the conductivity detectors from Bischoff and Waters used here electronically suppress the basic conductivity. This more recent development is to be seen as an alternative to the suppressor method, where an anion exchange results in a "chemical" suppression of the basic conductivity.
  • the tartaric acid previously used in the eluent did not result in a separation of the bivalent cations in the ion pair system to be developed, hexylsuccinic acid initially being used as the ion pair reagent.
  • the tartaric acid has only a negligible complexing effect, so that the selectivity for the separation of the bivalent ions from the cation exchange material comes, which is underlined by comparative tests with hydrochloric, formic and acetic acid.
  • the following two conditions are to be used for the ion pair system organic acids linked: low pK values, so that a complexing action with respect to the alkaline earth metal ions may be present; Different complex stabilities with calcium and magnesium so that the retention of the bivalent cations is different.
  • Polycarboxylic acids such as maleic acid or polybasic inorganic acids such as phosphoric acid, which only have the first pK s stage in the pH range around 2.0, also prove to be less useful.
  • Organic acids are preferably used, which Substituents with predominantly or -I -M effects have to the pK s - values decrease.
  • Nitrophthalic acids include Nitrophthalic acids, various nitrosalicylic acids, sulfosalicylic acid as well as mono- and dihalogenated succinic acids.
  • oxalic acid and trifluoroacetic acid have good complexing properties, especially also in the pH range 2.6-3.5.
  • oxalic acid a better separation of the alkaline earth ions is achieved, so that it is particularly suitable for the ion pair system.
  • the optimal concentration range of the oxalic acid in the eluent is approximately 1 mmol in the present example. Smaller concentrations lead to too long retention times of the alkaline earth ions, because on the one hand the elution power of the eluent is reduced and on the other hand the capacity of the exchange groups is increased by a higher degree of dissociation. Larger concentrations of oxalic acid reduce the degree of dissociation and at the same time increase the elution power; A sufficient separation may then no longer exist. In processes as are carried out according to the prior art, 5-10 mmol of an alkyl sulfonic acid are usually used as the ion pair reagent.
  • the developed separation system is designed in such a way that it is also possible to determine sodium and potassium in their unfavorable conditions in wine and mineral water. At the same time, the bivalent cations should be determinable with acceptable retention times. If the conditions are not so unfavorable or if the excess component is determined, the elution power of the eluent, as already mentioned, should not be increased by the oxalic acid concentration.
  • the elution power of the eluent can be regulated by adjusting the pH.
  • the alkali and alkaline earth hydroxides are not well suited for this, since these cations can then no longer be detected with sufficient sensitivity.
  • Divalent cations such as ethylenediammonium should now be used, because diethanolamine or other monovalent amines, for example, first have a greater influence on the alkali ions and secondly they increase the capacity of the exchanger, because increasing the pH value means that more exchange groups are dissociated, so that retention times increase.
  • ethylenediamine is practically a dication in the pH range below about 6.
  • EN ethylenediamine
  • compounds such as 1,3-diaminopropane to 1,7-diaminoheptane are used. These have pK s values shifted even further into the "alkaline", so that they are also present in the "acidic” form as a dication. If the non-polar portion of the diamines becomes larger, the interactions with the RP 18 column material increase, which is documented by shorter retention times.
  • ion exchange chromatography can be viewed as a limiting case of ion pair chromatography.
  • dodecyl and hexadecyl succinic acid have been produced.
  • the greater hydrophobic fraction compared to hexylsuccinic acid means that these compounds are almost no longer water-soluble and have a comparatively stronger interaction with the non-polar column material.
  • HPLC column used by the column with a flow of 1.0 ml / min. is rinsed for about 1 hour.
  • Table 2 summarizes the pK a values of the three acids listed.
  • the capacity of the separation column is therefore too low to separate the bivalent ions as well as the monovalent ones.
  • Fig. 4 shows the sodium determination, which is possible with this system in contrast to the Schomburg column and other single column systems even without a so-called suppressor system.
  • the chromatogram of the calcium and magnesium determination in mineral water is shown in FIG. 5 and that of the potassium and lithium determination in FIG. 6.
  • the specified Na 2 S 2 O 3 addition and the heating time must be observed, since smaller additions and shorter times result in poor results.
  • the carbon dioxide and hydrogen carbonate contained in mineral water must be removed before injecting, otherwise the column packing can be damaged.
  • the range around ⁇ 0.1 ppm sodium should be avoided for the determination, since contaminated results can result from contamination of the glass devices used. Contamination is negligible in the area used here.
  • the samples are diluted 1: 5 to 1: 1000 for mineral water samples and 1:20 to 1: 1500 for wine samples.
  • Atomic absorption spectrometry is used as the reference method for the analyzed ions.
  • Tables 4 and 5 show the contents of the wine and mineral water samples examined in comparison with the AAS values.
  • the IC When determining sodium, the IC provides up to 11% higher values, which presumably result from organic components in the wine.
  • Table 7 shows the ratios of IC to AAS for the sodium, potassium, lithium, calcium and magnesium determination in mineral water. There is also a good agreement here.
  • the system according to the invention has crystallized out as a further possibility for simultaneously determining alkali and alkaline earth ions.
  • the separation system is also much cheaper and more universal, as shown above.
  • the ion pair reagent is removed by rinsing with 20% methanol, so that the column is also available for other separations.
  • alkyl succinic acids are synthesized that have this important group (1,4-dicarboxylic acid). They also have a non-polar alkyl residue, which allows their use as ion pair reagents in ion pair chromatography.
  • Oxalic acid has been found to be optimal acid, because it has the one hand, low pK values and on the other hand, still sufficient in the "acid" Differences in the complex stabilities to the divalent cations. Many organic acids tested only meet the first condition and are therefore less suitable.
  • the pH value of the eluent plays a decisive role: firstly, it determines the capacity of the column via the degree of dissociation of the carboxylic acid groups of hexylsuccinic acid, and secondly, it controls the elution power of the eluent via the increasing or decreasing complexing properties of oxalic acid.
  • the longer-chain alkyl succinic acids which were also tested, can be well and permanently adsorbed after rinsing the column with the methanolic solutions. However, they do not possess the required for bivalent cations selectivity, which is due to shifted to the "Alkaline" pK values. This shift also means that the capacity is much smaller. It is not possible to adjust the pH to pH ranges favorable for these acids, since the sensitivity of the conductivity detection used here drastically decreases. However, this problem can be avoided with post-column drainage.
  • the system described can be used in mineral water and wine analysis despite the unfavorable ratios of sodium and potassium and is therefore more universal and also cheaper than the Schomburg column mentioned.
  • the method according to the invention is not limited to mineral water or wine analysis, but rather lets are generally used for a cation analysis, especially for the simultaneous determination of mono- and polyvalent cations next to each other.
  • ashes can of course also be analyzed, which have been prepared in the usual way for ion chromatography.
  • Fig. 1 Synthetic route of the n-alkyl succinic acids
  • Fig. 2 The simultaneous determination of mono- and
  • Lithium peak 62 ppb Li

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Abstract

Procédé de détermination chromatographique de cations monovalents ou polyvalents, en particulier pour la détermination simultanée d'ions de bases et de bases alcalinoterreuses dans le vin ou l'eau minérale. On applique au moins un acide carboxylique polybasique comportant un résidu hydrophobe sur une colonne à inversion de phase de manière à ce qu'au moins une partie de la phase stationnaire de cette colonne soit recouverte d'acide carboxylique. On applique ensuite la substance qui contient les cations à déterminer sur la colonne et on procède enfin à l'élution des cations de la colonne à l'aide d'un éluant. On recouvre de préférence la colonne avec au moins un acide succinique d'alkyle. Les acides carboniques polybasiques utilisés pour recouvrir la colonne peuvent être substitués en position α pour les groupes carboxyles avec un substituant qui présente un effet - I ou - M. La présente invention porte en outre sur un matériau à inversion de phase recouvert avec l'acide carboxylique polyvalent et sur une solution particulièrement avantageuse pour recouvrir et éluer les matériaux à inversion de phase.
PCT/EP1989/001395 1988-11-18 1989-11-18 Procede de determination chromatographique de cations WO1990005913A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19883839035 DE3839035A1 (de) 1988-11-18 1988-11-18 Verfahren zur chromatographischen bestimmung von kationen
DEP3839035.3 1988-11-18

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WO1990005913A1 true WO1990005913A1 (fr) 1990-05-31

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2629541A1 (de) * 1974-08-05 1978-01-12 Riedel De Haen Ag Verfahren zur abtrennung von spurenelementen mittels ionenaustauschern auf cellulosebasis
DE3108924A1 (de) * 1980-03-10 1982-02-18 Dionex Corp., 94086 Sunnyvale, Calif. Verfahren und einrichtung zur chromatographischen trennung und quantitativen analyse ionischer spezies
US4455233A (en) * 1983-08-12 1984-06-19 Dionex Corporation Method and apparatus for ion analysis and detection using reverse mode suppression
EP0215432A2 (fr) * 1985-09-13 1987-03-25 Shimadzu Corporation Procédé et dispositif d'analyse des composants de lupuline

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2629541A1 (de) * 1974-08-05 1978-01-12 Riedel De Haen Ag Verfahren zur abtrennung von spurenelementen mittels ionenaustauschern auf cellulosebasis
DE3108924A1 (de) * 1980-03-10 1982-02-18 Dionex Corp., 94086 Sunnyvale, Calif. Verfahren und einrichtung zur chromatographischen trennung und quantitativen analyse ionischer spezies
US4455233A (en) * 1983-08-12 1984-06-19 Dionex Corporation Method and apparatus for ion analysis and detection using reverse mode suppression
EP0215432A2 (fr) * 1985-09-13 1987-03-25 Shimadzu Corporation Procédé et dispositif d'analyse des composants de lupuline

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