DE10016545A1 - Quantitative determination of organophosphorus compounds by replacing the cations in solution with hydrogen ions, concentrating the solution, decomposing the compounds to orthophosphate and measuring orthophosphate content - Google Patents

Abstract

Organophosphorus compounds are quantitatively determined by replacing the cations in a sample solution with hydrogen ions; concentrating the solution to remove hydrochloric acid; decomposing the compounds to orthophosphate by adding peroxodisulfate; and measuring the orthophosphate content.

Description

The present invention relates to a new method for the quantitative determination of organophosphorus compounds in highly dilute aqueous solutions using ion exchangers, which can also be used in aqueous solutions with chloride of <2000 mg Cl ^⊖ / l.

Phosphonates and phosphinates are used to a considerable extent in water action (mainly for stone and corrosion inhibition in cooling and process water) and cleaning processes (mainly to inhibit incrustation and sequestration in industrial, institutional and household Cleaners). During the use concentrations at the Wasserbe often only a few mg / l, some can be found in industrial cleaners Reach 100 mg / l.

For the analytical determination of phosphonates and phosphinates in refrigeration and Various processes are known for process waters. An identification of the Phosphonate or the phosphinate at the same time with a content determination is over ion chromatography possible. Despite this ideal statement for the user Ability of the method have been due to the high cost of this equipment Methodology enforced other procedures in practice. The Phosphonates or phosphinates converted to orthophosphate by oxidative degradation converts that then using known methods, e.g. B. the "molybdenum blue method", is determined quantitatively (see e.g. DIN 38 405, part 11. German standard procedure for water, waste water and sludge analysis, anions (group D), Be tuning of phosphorus compounds (D11), Beuth Verlag GmbH, Berlin 30, March 1988).  

The use of salts as an oxidizing agent has been used for the oxidative degradation peroxodisulfuric acid (potassium or ammonium salt) has proven itself. The degradation reak tion can by heating or UV radiation or z. B. also by the addition "activated" by silver ions (U.S. Pat. 4,544,639); H. greatly accelerated.

We have now found that the good practice outlined above by the DIN 38 405 for the analysis of phosphonic acids under certain conditions gives wrong results.

In water with a relatively high content of chlorides starting at approx. 2000 mg Cl ^⊖ / l, see Comparative ^Example 2, as well as at much lower bromide concentrations, the concentrations of phosphonic acid contained in the solutions are not approximated.

The object of the present invention was therefore the development of an analysis ver driving for organophosphorus compounds in very dilute aqueous solutions, as they are used in cooling and process water, the above Does not have disadvantages.

The invention and thus the solution to the problem relates to a method for analytical determination of organophosphorus compounds, which can also be used in aqueous solutions with chloride ^contents of <2000 mg Cl ^⊖ / l, characterized in that

• a) exchanges the cations in the sample solution with an ion exchange resin for H ⁺ ,
• b) the exchanged solution is concentrated while removing hydrochloric acid,
• c) the organophosphorus compound in the acidic pH range by peroxide sulfate additive oxidatively degrades to orthophosphate and  
• d) the orthophosphate content for calculating the initial concentration of the Organophosphorus compound determined.

In spite of increased chloride contents, the process according to the invention has a new aspect Finding rate for the organophosphorus compounds as orthophosphate of over 90% on.

In a preferred embodiment, the sample to be analyzed is diluted to a maximum cation content of approximately C (eq ⁺ ) = 300 mmol / l by adding demineralized water before starting with process step a).

In a further preferred embodiment and if the sample to be analyzed contains bromide ions, step b) is followed by step

• 1. b ') Concentrate the sample about 5%, based on the original sample volume nitric acid added and evaporated to dryness.

If necessary, process step b ') is repeated again, but with the addition of concentrated hydrochloric acid (about 5 to 50% of the original sample volume) instead of the nitric acid and with further concentration or evaporation, if necessary to dryness. The concentration of the hydrochloric acid solution is carried out to such an extent that the chloride content of the test solution in process step c) does not exceed 5 g / l, preferably 2 g / l. The cation exchange in process step a) is preferably over 90%. Lewatit®S100 in the H ⁺ form is preferably used as the ion exchange resin.

According to the present method, in step b) the analysis is carried out rende solution preferably to dryness or to small residual volumes of about a maximum of 20% of the original sample volume is concentrated.  

The analysis method according to the invention preferably allows the analysis of
2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC)
1-hydroxyethane-1,1-di-phosphonic acid (HEDP)
Amino-tris-methylene-phosphonic (AMP)
but also phosphinocarboxylic acids.

With the method according to the invention, the ge above can particularly preferably called organophosphoric acids in concentrations of 0.2 to 200 mg / l analyzed become.

The method according to the invention is particularly suitable for analyzing 2- Phosphonobutane-1,2,4-tricarboxylic acid (PBTC).

By diluting the sample before process step a), the prerequisites are to be set so that an extensive exchange is achieved in the subsequent exchange of the cations for H ⁺ a). With the Lewatit®S 100 cation exchange resin chosen by us in the present application in the H ⁺ form, this exchange took place to such an extent when the sample was diluted to about C (eq ⁺ ) = 200 mmol / l that no disturbances occurred in the subsequent steps . In contrast, this exchange was so incomplete when using a double-concentrated solution that during the subsequent evaporation b) of the combined processes, salts crystallized out, which caused the solution to "spray".

The original sample contains such low salt levels that it is largely Cation exchange can already take place in the undiluted sample is a ver Thinning before process step a) is not necessary. On the other hand, it is possible in process step a) itself a stronger one than is necessary for the ion exchange Perform dilution; it is disadvantageous, however, that during evaporation b) more water needs to be evaporated.  

Steps c) and d) are carried out in a manner known per se.

Any bromide present in the starting solution must be reached before reaching Ver step c) (by writing step b ') are removed. That can on best done by adding an oxidizing agent, causing the bromide to Bromine is oxidized. Because of its volatility, bromine is easily removable. As Oxidizing agents can be used nitric acid. Excess oxidation medium such as B. excess nitric acid or degradation products of nitric acid should be removed as completely as possible by smoking, before in Step c) the oxidative degradation of the organophosphorus compounds or before the ortho phosphate determination d) is carried out.

The following examples illustrate the process. Comparative examples show the poor results of processes according to the state of the art or of alternative methods not according to the invention.  

Examples Example 1 Composition of the test solution

233.8 g NaCl / l
2.5 mg PBTC / l

Carrying out the determination 1. Dilution of the sample and cation exchange

20 ml of the sample was diluted to about 1 liter with demineralized water. This diluted solution was passed over an ion exchange column containing 100 ml of freshly regenerated Lewatit®S 100 exchange resin in the H ⁺ form. Column data: inner diameter 20 mm, length 500 mm. After 1 h, the exchange was complete and washing was carried out with demineralized water (100 ml, 15 min.).

2. Concentration and (partial) removal of chloride

The combined column drains were in the hood on a hot plate Normal pressure first in a 2 liter beaker, finally in a 250 ml Beaker, tall form, almost dry (residual volume approx. 0.2 ml) steams. With 2.5 ml of sulfuric acid (concentration: 2.5 mol / l) Residue was taken up and demineralized water was added to 50 ml replenished.  

3. Oxidative degradation of the phosphonic acid to orthophosphate

5 ml of an aqueous solution of Ammonium peroxodisulfate (concentration: 2 wt .-%) added, then 15 min. heated to weak boiling. After cooling, the procedure was under Add the ammonium peroxodisulfate solution and then heat repeated. The solution volume was increased by occasional addition kept from water to over 25 ml.

4. Determination of the orthophosphate content

The solution was cooled and washed with sodium hydroxide solution (concentration: 45% by weight) neutralized; the orthophosphate content was determined by method DiN 38 405-D11-1 analyzes: Orthophosphate ions form in acidic solution complex with molybdate ions in the presence of antimony ions is reduced to molybdenum blue by ascorbic acid. The color intensity that the orthophosphate concentration is proportional, is in the photometer at 880 nm measured. Via one using potassium dihydrogenphos calibration curve set up phat was finally evaluated.

A brine which contained only 233.8 g NaCl / l and which was used as a comparison the test sample had been treated.

5. Result

Based on the starting solution, a content of 0.92 mg PO ₄ / l ≘ 2.6 mg PBTC / l was found.

Example 2 Composition of the test solution

683.1 g MgCl ₂

× 6 H ₂

Oil
100.0 g CaCl ₂

× 2 H ₂

Oil
14.4 g NaBr / l
2.5 mg PBTC / l

Carrying out the determination 1. Dilution of the sample and cation exchange

20 ml of the sample was diluted to about 1 liter with demineralized water. This diluted solution was passed through an ion exchange column containing 100 ml of freshly regenerated Lewatit®S100 exchange resin in the H ⁺ form. Column data: inner diameter 20 mm, length 500 mm. After 1 h, the exchange was complete and washing was carried out with demineralized water (100 ml, 15 min.).

2. Concentration and (partial) removal of chloride as well as complete Bromide removal

The combined solutions were in the hood on a hot plate at normal Print in beakers, most recently in a 250 ml beaker, tall form evaporated approx. 10 ml. After cooling, 1 ml of concentrated salpe tersic acid slowly added dropwise with stirring. At the boiling point bromine and nitrous gases are expelled and the solution is almost dry steams. After adding 5 ml of concentrated hydrochloric acid, the mixture was again bis almost evaporated to dryness. With 2.5 ml of sulfuric acid (concentration:  2.5 mol / l) the residue was taken up and demineralized Make up water to 50 ml.

3. Oxidative degradation of the phosphonic acid to orthophosphate

5 ml of a solution of ammonium per oxodisulfate (concentration: 2 wt .-%) added, then 15 min. to the black boiling. After cooling, the procedure was adding the ammonium peroxodisulfate solution and then heating again get. The solution volume was determined by occasionally adding Water kept above 25 ml.

4. Determination of the orthophosphate content

The solution was cooled and neutralized; the orthophosphate content was analyzed according to method Din 38 405-D11-1: orthophosphate ions form in acidic solution with molybdate ions in the presence of antimony Ions a complex that is reduced to molybdenum blue by ascorbic acid becomes. The color intensity, which is proportional to the orthophosphate concentration, is measured in the photometer at 880 nm. About one using Potassium dihydrogen phosphate calibration curve was evaluated.

5. Result

Based on the starting solution, a content of 0.93 mg PO ₄ / ≘ 2.6 mg PBTC / l was found.

Example 3

In an experiment carried out analogously to Example 2, the instead of 2.5 mg PBTC / l only 1.0 mg PBTC / l had been added in two experiments 1.0 mg PBTC / l and 1.1 mg PBTC / l recovered.

Example 4 Composition of the test solution

233.8 g NaCl / l
2.0 mg HEDP / l

The determination was carried out analogously to Example 1, but 20 ml of sample vol diluted to a final volume of 2 l before the solution passes over the ion exchanger would give.

Result

Based on the starting solution, 2.06 mg HEDP / l were found.

Example 5 Composition of the test solution

683.1 g MgCl ₂

× 6 H ₂

Oil
100.0 g CaCl ₂

× 2 H ₂

Oil
14.4 g NaBr / l
2.5 mg PBTC / l

Carrying out the determination 1. Dilution of the sample and cation exchange

100 ml of the sample was diluted to about 5 l with demineralized water. This diluted solution was passed through an ion exchange column containing 800 ml of freshly regenerated Lewatit®S100 exchange resin in the H ⁺ form. Column data: inner diameter 60 mm, length 700 mm. After approx. 120 min. the exchange was finished and it was washed with 0.5 l demineralized water (duration: approx. 30 min.).

2. Concentration and partial removal of chloride as well as complete Bromide removal

The combined solutions were concentrated in a rotary evaporator and then set to exactly 500 ml.

Four concentrated samples containing 100 ml each were mixed in 250 ml Beaker, tall shape, on the hot plate until about 10 ml of residual volume steamed. After each addition of 1 ml of concentrated nitric acid further evaporated to dryness before using sulfuric acid and Water was made up to 50 ml each. Three of the samples were processed as follows described, worked up. The processing of the fourth sample was as described in Comparative Example 1.

3. Oxidative degradation of the phosphonic acid to orthophosphate

In the three samples the oxidative degradation and the orthophosphate be mood as described in example 2 points 3.) and 4.).  

Result

PBTC concentrations of 2.5, 2.6 and 2.8 mg / l, based on the starting solution, found.  

Comparative examples Comparative Example 1 (not according to the invention)

The sample from Example 5, point 2, which was not the oxide, was used as the starting material tive degradation had been supplied by acid digestion with peroxodisulfate. In her the proportion of orthophosphate determined by the previous work up tion process, in particular by evaporating the hydrochloric acid column drain and the subsequent addition of concentrated nitric acid, by breaking down the Phosphonic acid had arisen.

Result

Based on the starting solution, only a content of 1.0 mg PBTC / l ge found, this corresponds to only 40% of the PBTC concentration contained in the sample tion.

Comparative Example 2 (prior art) Composition of the examined solutions

The solutions each contained 2.5 mg PBTC / l and different concentrations of sodium chloride:

• a) 47.5 g Cl ^⊖ / l
• b) 9.5 g Cl ^⊖ / l
• c) 4.75 g Cl ^⊖ / l
• d) 2.375 g Cl ^⊖ / l

Implementation of the determination:
Without prior ion exchange, the oxidative degradation of the phosphonic acid to orthophosphate was carried out analogously to Example 1 point 3.) and then the orthophosphate content was determined analogously to Example 1 point 4.).

The evaluation showed the following contents of the starting solutions:

• a) 0.34 mg PO ₄ / l ≘ 0.97 mg PBTC / l ≘ 39% of the "true" content
• b) 0.55 mg PO ₄ / l ≘ 1.56 mg PBTC / l ≘ 62% of the "true" content
• c) 0.67 mg PO ₄ / l ≘ 1.90 mg PBTC / l ≘ 76% of the "true" content.
• d) 0.77 mg PO ₄ / l ≘ 2.19 mg PBTC / l ≘ 88% of the "true" content.

In a further comparison test, solutions of the following composition were analyzed:

• a) 77.9 g NaCl / l
  2.5 mg PO ₄ / l
• b) 39.0 g NaCl / l
  2.5 mg PO ₄ / l
• c) 19.5 g NaCl / l
  2.5 mg PO ₄ / l

The orthosphate concentration was adjusted by dissolving KH ₂ PO ₄ .

The following values were found by analyzing the solutions according to Example 1 point 4):

• a) 2.35 mg PO ₄ / l
• b) 2.40 mg PO ₄ / l, and
• c) 2.45 mg PO ₄ / l

This shows that high chloride concentrations are particularly negative hardly affect the oxidative degradation of the phosphonic acids to orthophosphate but on the orthophosphate determination.

Claims (10)

1. A method for the quantitative determination of organophosphorus compounds in aqueous solution, characterized in that

• a) exchanges the cations in the sample solution with an ion exchange resin for H ⁺ ,
• b) the exchanged solution is concentrated while removing hydrochloric acid,
• c) oxidatively degrades the organophosphorus compound to orthophosphate in the acidic pH range by adding peroxodisulfate and
• d) the orthophosphate content for calculating the initial concentration of the organophosphorus compound is determined.

2. The method according to claim 1, characterized in that the starting solution is diluted to a cation concentration of at most C (eq ⁺ ) = 300 mmol / l before the ion exchange. 3. The method according to claim 1, characterized in that the exchange of the cations for H ⁺ takes place to over 90%. 4. The method according to claim 1, characterized in that the constriction the hydrochloric acid solution is driven so far that the chloride content of the test solution solution in process step c) does not exceed 5 g / l. 5. The method according to claim 1, characterized in that in the method step b) the solution to be analyzed except for small residual volumes of approximately a maximum of 20% of the original sample volume is concentrated.   6. The method according to claims 1 to 5, characterized in that the Organophosphorus compounds phosphonocarboxylic acids, 1-hydroxyethane-1,1- diphosphonic acid, amino-tris-methylenephosphonic acid and phosphinocar are acids. 7. The method according to claims 1 to 5, characterized in that the Organophosphorus compound is 2-phosphonobutane-1,2,4-tricarboxylic acid. 8. The method according to claims 1 to 7, characterized in that the organophosphorus compounds to be determined in concentrations of 0.2 up to 200 mg / l. 9. The method according to claims 1 to 8, characterized in that any bromide in the starting solution by using a Oxidizing agent and evaporation of the bromine formed before reaching of process step c) is removed. 10. The method according to claims 1 to 9, characterized in that it can be used in solutions with chloride ^contents of <2000 mg Cl ^⊖ /.