3.2.5.1. Principle and Flow Programming of SSSC
The flow protocol for SSS Calibration (A) comprises five steps where the dispensed volume by P2 is the only variable controlling concentration of series of thus generated standard solutions. The dispensed volume increases from step 1 when Single Standard is (almost) undiluted through steps 2 to 4 whereby SS is diluted to 1/2, 1/4 and 1/8 to step 5 – where BLANK value is obtained by monitoring carrier stream of deionized water (DI). Thus, the calibration range will comprise five points in micro molar range when SS=4.0 µM is used (column 2) and in nanomolar range when SS= 500 nM N is used (column 3).
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The semiautomatic protocol for assay of nitrite using SS calibration (B) generates three absorbance values for each concentration point during three cycles. The volume and flow rate for P2 as well the associated standard concentration must be typed in at the beginning of each calibration run. While semiautomatic, this approach has advantage of versatility of since dilution ratios can be typed in any sequence or multiple runs.
Absorbance values, collected from calibration runs (C,E), during stop flow period (WIN), were applied to construct graphs (D,F). By using 4.0 µM N standard, the calibration line covers micro molar range by using 500 nM N standard, calibration covers nano molar range. Reproducibility of determination is similar in both ranges.
