Standard Test Method for Anions in Water by Suppressed Ion Chromatography
5.1 Ion chromatography provides for both qualitative and quantitative determination of seven common anions, F−, Cl−, NO2−, HPO4 −2, Br−, NO3−, and SO4−2, in the milligram per litre range from a single analytical operation requiring only a few millilitres of sample and taking approximately 10 to 15 min for completion. Additional anions, such as carboxylic acids, can also be quantified.
Note 2: This test method may be used to determine fluoride if its peak is in the water dip by adding 1 mL of eluent (at 100× the concentration in 8.3) to all 100-mL volumes of samples and standards to negate the effect of the water dip. (See 6.3, and also see 6.4.) The quantitation of unretained peaks should be avoided. Anions such as low molecular weight organic acids (formate, acetate, propionate, etc.) that are conductive coelute with fluoride and would bias fluoride quantitation in some drinking waters and most wastewaters. The water dip can be further minimized if measures are taken to remove carbonic acid which remain in the eluent after suppression using carbonate based eluents. There is no water dip if hydroxide eluents are used.
5.2 Anion combinations such as Cl−/Br − and NO2−/NO3−, which may be difficult to distinguish by other analytical methods, are readily separated by ion chromatography.
1.1 This test method2,3 covers the sequential determination of fluoride, chloride, nitrite, ortho-phosphate, bromide, nitrate, and sulfate ions in water by suppressed ion chromatography.
Note 1: Order of elution is dependent upon the column used; see Fig. 1.
1.3 It is the user's responsibility to ensure the validity of this test method for other matrices.
1.4 Concentrations as low as 0.01 mg/L were determined depending upon the anions to be quantified, in single laboratory work. Utilizing a 50-μL sample volume loop and a sensitivity of 3000 μS/cm full scale, the approximate detection limits shown in Table 1 can be achieved. Lower detection limits have been observed with newer instrumentation, column technology and eluents. The analyst must assure optimum instrument performance to maintain a stable baseline at more sensitive conductivity full-scale settings.
1.5 The upper limit of this test method is dependent upon total anion concentration and may be determined experimentally as described in Annex A1. These limits may be extended by appropriate dilution or by use of a smaller injection volume.
1.6 Using alternate separator column and eluents may permit additional anions such as acetate, formate, or citrate to be determined. This is not the subject of this test method.
1.7 This test method update approves the use of electrolytically generated eluent, electrolytically regenerated eluent, electrolytic suppression (not autozeroing), and electrolytic trap columns also known as reagent-free ion chromatography. This approval is based on acceptance by the U.S. EPA as referenced in Appendix X2.
1.8 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.10 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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