Introduction

Environmental Ion Chromatography (IC) has traditionally been applied to the analysis of anions in Drinking Water. Recently IC has been gaining acceptance for wastewater analysis. Typical anions analyzed by IC are: F, Cl, NO2, Br, NO3, HPO4, and SO4. We cannot argue that IC is a superior method compared to flow for the routine determinations of Chloride and Sulfate in multiple samples of relatively consistent or clean matrices such as drinking water, low solids ground waters, and select industrial discharges. With additional columns and detectors IC can also be used for the analysis of Ammonia, Cations, and trace metals such as Chromium VI.

Detection limits for IC are about 0.1 mg/l for clean samples such as drinking water. Once samples begin to contain high dissolved solids, dissolved organics, or an over abundance of on anion in relation to the others detection limits begin to suffer. This is caused by the dilutions necessary to eliminate interferences.

Interferences

The interferences that are common with IC rarely cause problems with flow chemistry methods. For instance:

The accurate analysis of low level Chloride in SWEX leachates by IC is prevented by the high dilutions necessary to dilute the Copper, Aluminum, and Iron Sulfates to levels that would not destroy the IC column. The flow chemistry method, however, is able to analyze the solution direct without dilution.

High Chloride concentrations interfere with the determination of trace amounts of Nitrite.

Chloride does not interfere with the flow methods.

Samples for Nitrate cannot be preserved because, even if adjusted to neutral prior to analysis, the high sulfate levels require sample dilution. Because preserved samples cannot be analyzed by IC, Nitrate samples must be tested within 48 hours. Sulfuric acid (added at appropriate levels) does not interfere with the flow methods.

Fluoride is not recommended for determination by IC at levels below about 1.0 mg/l. Although there are adjustments to overcome this problem, they require deviations from the normal procedure.

Orthophosphate methods by IC are very pH specific and plagued with interferences from trace metals. The undiluted detection limit of 0.1 mg/l suffers from any required sample dilutions. Total P cannot be determined. Flow chemistry methods for P are very sensitive and interferences are rarely present. Flow chemistry can determine all forms of P in solution.

Low level sulfate is difficult to determine in high chloride brine solutions because of dilutions necessary to bring responses on scale. If samples are analyzed without dilutions the high salt content typically causes retention time shifts causing sulfate to be identified by data systems as phosphate.

IC is an excellent method for CrVI, however, this analysis requires a separate column and detector than used for anions. Flow chemistry methods utilize the same type of detector as all other color methods.

Cyanide can be determined by IC using the same CrVI column, however, CN determinations require another detector.

Ammonia can be determined by IC, however, it is separated using different column, and different reagents as anions.

Conclusion

Ion chromatography provides an unsurpassed method for the determination of anions in drinking water, and other low TDS solutions. Flow chemistry uniquely allows automated analysis of difficult sample matrices for anions, as well as trace non metals, and non metals. Flow chemistry also allows the automation of distillations, digestions, extractions, and matrix cleanup.