ASTM D5996 Measuring Anionic Contaminants in Water by On-Line Ion Chromatography

Introduction

ASTM D5996 determines the analysis of high-purity water by Ion Chromatography (IC). This technique measures the concentration of acetate, formate, chloride, fluoride, phosphate, nitrate, and sulfate in a continuously flowing sample. The values stated in SI units are to be regarded as standard.

Scope

This test method describes on-line analysis by ion chromatography of high-purity water. It determines a range of anionic impurities in high-purity water. It usually operates within a 0.01-100 μg/L concentration range. The acetate, formate, chloride, fluoride, phosphate, nitrate, and sulfate are measured using a continuously flowing water sample. This technique’s accuracy depends on the reagent water quality used for preparing standards. Preparation of accurate standards at low concentration values (<1.0 μg/L) becomes difficult; therefore, special care will be taken in their preparation. The sample may have to be conditioned from higher pressures and temperatures to amenable conditions for on-line analysis.

Apparatus used in ASTM D5996

The apparatus used in ASTM D5996 is as follows:

Test Procedure

In ASTM D5996, a continuously flowing sample is injected into the instrument through a sample injection valve. The sample is pumped through a concentrator column where the anions of interest are collected on an ion-exchange resin. After a suitable sample volume has been passed through the concentrator column, sample flow is diverted, and the eluent is pumped through the concentrator column to remove the trapped anions. This eluant then flows through an analytical column set where the anions are separated based on the retention characteristic of each anion relative to the eluent used. The eluant stream containing the anions of interest passes through a suppressor device where the cations from the eluent are exchanged for hydrogen ions, converting the anions to their acid form. After using the suppressor device, the eluent solution is passed through a conductivity detector to detect the separated anions. Detection limits for the anions are enhanced because the anions are in the acid form rather than the salt. The anions are identified based on the retention time compared to known standards. The anions can be quantified by measuring peak height or area and comparing the detector response to known standards.

Test Specimen

The sample size can vary depending on the instrument setup and the concentration of the measured contaminants. However, the temperature control should be at ± 0.5°C or better. Anion contaminants should be at less than 0.02 μg/L.

Result

ASTM D5996 measures the concentration of several types of anionic contaminants, including acetate, formate, chloride, fluoride, phosphate, nitrate, and sulfate, with concentration values ranging from 0.01 to 100 μg/L in high-purity water. It improves sensitivity by converting the anions into their acid forms to measure the peak heights or areas relative to known standards.

Conclusion

ASTM D5996 is used to determine and analyze high-purity water using ion chromatography. This technique measures the concentration of acetate, formate, chloride, fluoride, phosphate, nitrate, and sulfate anionic impurities in a continuously flowing sample. Measuring these contaminants with quantitative accuracy helps assure water quality in the industry by using stringent standards to protect against potential damage from some equipment and contamination and inefficiency in running operations. This analysis is vital in most industries, especially semiconductor and pharmaceutical production and power generation, where pure water is essential for product quality and system performance. It also facilitates concerns about regulatory compliance and optimal production processes.

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