Micro sequential injection: environmental monitoring of nitrogen and phosphate in water using a "Lab-on-Valve" system furnished with a microcolumn.
A "Lab-on-Valve" manifold operated in the micro sequential injection (microSI) mode was adopted to accommodate EPA-approved methods for spectrophotometric determinations of nitrate, nitrite and orthophosphate in the ppb (N or P) concentration range. A computer programmable microSI protocol, utilizing stopped-flow within a copperized Cd-foil filled microcolumn was developed for nitrate reduction to nitrite with subsequent colorimetric measurement, yielding concentration ranges for nitrate of 100.0-4000.0 ppb (N) and for nitrite of 30.0-4000.0 ppb (N) and linear calibration responses of r2 = 0.9999 for nitrate and 0.9995 for nitrite. Using a stopped-flow reaction rate measurement, phosphate was determined in the range 1.0-30.0 ppb (P) with a calibration response of r2 = 0.9997. The technical improvement of this methodology, apart from micro miniaturization, is the use of the stopped-flow technique, that resulted in improved detection limits and allowed reagent consumption to be reduced 1500-fold compared with conventional procedure while the amount of metallic cadmium was reduced 20-fold compared with the EPA-approved continuous-flow assay.
Wu
C H
CH
Department of Chemistry, University of Washington, Seattle 98195-1700, USA.
Ruzicka
J
J
D017022:Flow Injection Analysis / Q000295:instrumentation / Q000379:methods; D009584:Nitrogen / Q000032:analysis*; D010710:Phosphates / Q000032:analysis*; D013053:Spectrophotometry; D013501:Surface-Active Agents; D014874:Water Pollutants, Chemical / Q000032:analysis*
D010710:Phosphates; D013501:Surface-Active Agents; D014874:Water Pollutants, Chemical; D009584:Nitrogen