THE MEASUREMENT OF NITRITE, NITRATE AND PHOSPHATE WITH TEST KITS AND STANDARD PROCEDURES - A COMPARISON

Portable test kits, which are accepted as analytical techniques for me asuring dissolved inorganic nitrite, nitrate, and phosphate were compa red with standard methods in terms of analytical performance, colour s tability, chemical background of water solutions, salinity interferenc e, filtration and storage procedures. The kit detector, a Hach DR/2000 , was also compared to a laboratory spectrophotometer, a Shimadzu UV-2 100. Absorbance measurements indicated that the Hach colorimetric dete ctor is a reliable spectrophotometric sensor and compared well to the Shimadzu UV-2I00, but the former has the advantage of being more porta ble, versatile and cheaper than the latter. Detection limits for nitri te, nitrate and phosphate were 0.300, 0.657 and 0.162, and 0.048, 0.04 9 and 0.050 mu M for the kits and standard procedures, respectively. M olecular absorption coefficients achieved for phosphate were 21,600 an d 22,700 (M.cm)(-1), and for nitrate 29,900 and 47,900 (M.cm)(-1), res pectively. However, for nitrate the coefficients differed markedly [12 ,000 and 44,500 (M.cm)(-1)]. Reagent blanks from the test kits were hi gher than those from the standard techniques. Differences between filt ered and non-filtered water samples from aquaculture facilities and ot her environments were found. The full chemical reaction (colour) of th e kit reagents proved to be stable after 40 min. Information on spectr al response, kinetics, multi-point calibration curves and storage of k it reagents is also provided. The studied test kits for determining ni trite and phosphate can be used in monitoring natural waters. But for nitrate, salt interference should be taken into account.