<p>To more efficiently process the large sample numbers for quantitative determination of ammonium (NH<sub>4</sub><sup>+</sup>) and phosphate (orthophosphate, PO<sub>4</sub><sup>3-</sup>) generated during comprehensive growth experiments with the marine <i>Roseobacter</i> group member<i> Phaeobacter inhibens</i> DSM 17395, specific colorimetric assays employing a microplate reader (MPR) were established. The NH<sub>4</sub><sup>+</sup> assay is based on the reaction of NH<sub>4</sub><sup>+</sup> with hypochlorite and salicylate, yielding a limit of detection of 14 µM, a limit of quantitation of 36 µM, and a linear range for quantitative determination up to 200 µM. The PO<sub>4</sub><sup>3-</sup>assay is based on the complex formation of PO<sub>4</sub><sup>3-</sup> with ammonium molybdate in the presence of ascorbate and zinc acetate, yielding a limit of detection of 13 µM, a limit of quantitation of 50 µM, and a linear range for quantitative determination up to 1 mM.
Both MPR-based assays allowed for fast (significantly lower than 1 h)
analysis of 21 samples plus standards for calibration (all measured in
triplicates) and showed only low variation across a large collection of
biological samples.</p
