Abstract
A new flow injection analysis technique was developed for determining nitrogen, carbon, or sulfite species in varieties of complex matrixes. The method is based on the use of a bulk acoustic wave detector in combination with gas diffusion separation. Samples were injected into a carrier stream of water, merged with a reagent stream of an appropriate pH where the analyte was converted into a gaseous species, and diffused across a Teflon microporous membrane into a recipient stream. Then the trapped ionic compound in the recipient stream was monitored on-line with a bulk acoustic wave detector on the basis of sensitive response to changes of the solution conductance. The method is applied successfully for determining ammonium in Kjeldahl digest obtained from amino acids and blood proteins; total carbon, total inorganic carbon, and total organic carbon in waste and river waters; sulfite in wines and fruit juices; nitrate, nitrite, ammonium, and total inorganic nitrogen in natural waters; and total ammonia and total carbon dioxide in blood. The throughput, detection limit, and precision of the proposed method varied from 20 to 78 samples/h, 1 to 10 μM, and 0.6 to 1.8%, respectively. The method was validated by comparison with conventional procedure such as titration, spectrophotometry, or gas-sensing electrode. Theoretical background, the potential interference, and influencing factors, including composition of the acceptor and donor streams, flow injection parameters, cell constant and operating voltage of the sensor, and temperature are also discussed in detail.
Flow injection analysis with membrane separation; Determination of ammonia in blood and urine.