Analysis of wastewater for anionic and cationic nutrients by ion chromatography in a single run with sequential flow injection analysis.
To prevent nutrient enrichment and, hence the undesirable ecological impacts, the nutrients monitored in wastewater samples include two anionic species, i.e., nitrate and orthophosphate, and a cationic species, ammonium. Ion chromatography (IC) is one of the popularly used techniques for determinations of nitrate and phosphate in these samples, whereas determination of ammonium in wastewater samples is typically done using manual or automated wet chemistry, e.g., flow injection analysis (FIA). We have developed a sequential IC-FIA method, using Lachat's QC8000 IC system, which allows determinations of nitrate, phosphate and ammonia in a single injection. In this system, a QuickChem Small Suppressor cartridge is regenerated in between the samples. A sample is injected while leaving the suppressor off-line. Ammonium, a cation, elutes in the void volume of an anion-exchange column. The unsuppressed column effluent, exiting the conductivity flow cell, up to this point is used for FIA determination of ammonia. When ammonia exits the conductivity flow cell, a fully regenerated suppressor is brought in-line for conductometric detection of the anions. Analog data are simultaneously acquired from colorimetric and conductometric detectors, for the cationic and anionic nutrients, respectively. The method is accurate with spike recoveries in wastewater samples ranging from 91% for nitrate to 114% for chloride. It is precise with RSD values, for replicate analyses (n = 7) of a mid-range standard, ranging from 0.4% for phosphate to 1% for nitrate.
Karmarkar
S V
SV
Zellweger Analytics, Lachat Instruments Division, Milwaukee, WI 53218, USA. shree.karmarkar@zelana.com
D000641:Ammonia / Q000032:analysis; D000838:Anions / Q000032:analysis*; D002412:Cations / Q000032:analysis*; D002852:Chromatography, Ion Exchange / Q000379:methods*; D004553:Electric Conductivity; D017022:Flow Injection Analysis / Q000379:methods*; D012722:Sewage; D014867:Water / Q000737:chemistry
D000838:Anions; D002412:Cations; D012722:Sewage; D014867:Water; D000641:Ammonia