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High‐frequency measurement of seawater chemistry: Flow‐injection analysis of macronutrients
Author(s) -
Hales Burke,
Geen Alexander,
Takahashi Taro
Publication year - 2004
Publication title -
limnology and oceanography: methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.898
H-Index - 72
ISSN - 1541-5856
DOI - 10.4319/lom.2004.2.91
Subject(s) - seawater , nitrate , volumetric flow rate , chemistry , silicate , phosphate , mineralogy , volume (thermodynamics) , analytical chemistry (journal) , sea salt , autoanalyzer , environmental chemistry , chromatography , geology , oceanography , physics , aerosol , organic chemistry , quantum mechanics
We adapted a commercially available flow‐injection autoanalyzer (Lachat Quik‐Chem 8000) to measure seawater nitrate concentrations at a rate of nearly 0.1 Hz and phosphate and silicate concentrations at a rate half that. Several minor improvements, including reduced sample‐loop size, high sample flushing rate, modified carrier chemistry, and use of peak height rather than peak area as a proxy for nutrient concentration aided in the increase in sampling rate. The most significant improvement, however, was the construction of a copperized cadmium NO 3 − reduction column that had a high surface area to volume ratio and a stable packing geometry. Preliminary results from a cruise in the Ross Sea in austral spring of 1997 are shown. Precision of all three analyses is better than 1%. Comparison of the nutrient concentrations determined by the rapid analysis method described here with traditional discrete analyses shows that nitrate and silicate determined by the two approaches are within a few percent of each other, but that the phosphate concentrations determined by the rapid analysis are as much as 10% lower than those determined by the discrete analyses.