An Autonomous Nutrient Analyzer for Oceanic Long-term in situ biogeochemical monitoring,
Thouron, D., Vuillemin, R., Philippon X., Lourenço A., Provost C., Cruzado, A., and Garçon, V.,
Analytical Chemistry, 75, 11, 2601-2609.
ANAIS (Autonomous Nutrient Analyzer In Situ) has been developed to monitor nitrate, silicate and phosphate concentrations while deployed at sea at pressure (down to 1000 m). Detection is made by spectrophotometry. The instrument uses solenoid-driven diaphragm pumps to propel the sample, the standards, and the reagents through a microconduit, flow-injection style thermostated manifold. The analyzers are placed in an equipressure container filled with oil. Figures of merit in the laboratory include an accuracy of 1, 1 and 3% for nitrate, silicate and phosphate, respectively; a perfect linearity for calibration curves in the concentrations ranges found in the open ocean and an excellent comparison with Technicon Auto-Analyzer II determinations. The measurement protocol includes three steps over 13 minutes: rinsing with the sample stream, reagents introduction, and absorbance detection. Field tests comprise ANAIS nitrate, silicate and phosphate testing alone in the surface ocean. Phosphate results are not yet fully satisfactory. The instrument implemented on top of a YOYO vertical eulerian profiler was then deployed successfully in the Northwestern Mediterranean Sea acquiring thirty nitrate profiles between 200 and 1100 m over a 15 day period. This chemical analyzer can be a valuable observing asset adapted on any type of oceanographic platform.