Segmented continuous-flow analyses of nutrient in seawater: intralaboratory comparison of Technicon AutoAnalyzer II and Bran plus Luebbe Continuous Flow AutoAnalyzer III

The analytical performance of the Technicon AutoAnalyzer II (AA II) and the Bran+Luebbe (R) Continuous-Flow AutoAnalyzer III (AA3) for nitrate+nitrite, orthophosphate and silicic acid analyses in seawater is evaluated. Both auto analyzers had quite similar design; the differences were only in the application of modern technologies by the Bran+Luebbe (flow cell, digital colorimeters, and fiber optics) and in the data acquisition and analysis software. All critical analytical parameters were comparable to the current recognized oceanographic community standards. A t-test for the standard deviation of pooled data (=0.01) showed that instrument precisions and accuracies for the specific nutrient analyses were not significantly different at the 99% confidence level. Both auto analyzers demonstrated the trend of decreasing accuracy with decreasing of nutrient concentrations. The AA3 showed lower detection limit for all channels compared to the AA II: 0.018 M for o-phosphate, 0.009 M for nitrate+nitrite, and 0.012 M for silicic acid. In all ranges of tested low nutrient standards, the AA3 was more precise and more accurate than the AA II. Comparison of results for analyses of the North Pacific deep samples (1200-4800 m) showed that the precision for all nutrient analyses was 1%; the F-test illustrated that differences in nutrient concentrations acquired by two analyzers were not significant at the 99% confidence level. Our conclusion is that both auto analyzers demonstrate compatible analytical performance with the better one attributable to the AA3 for lower nutrient concentrations.