| Summary: | 碩士 === 國立臺灣大學 === 海洋研究所 === 97 === An automated flow analyzer for the simultaneous determination of phosphate and silicate has been developed. The system in principle is similar to that of the previous Trident-223 system, but improvements are made on the Si-channel which does not involve the addition of a masking reagent. The results for silicate are compensated for the phosphate interference according to the results measurement from the other P-channel. In a manual procedure, the raw absorbance (at 410nm) obtained for silicate should comprise of both silicate and phosphate signals:
AbsSi+P = eSi*b*[Si]*Vs/Vf + eP*b*[P]*Vs/Vf
Where eSi and eP are molar extinction coefficients of silicomolybdic acid and phosphomolybdic acid at a wavelength of 410 nm, b the path length, [Si] and [P] the concentrations for silicate and phosphate, respectively. Symbols Vs and Vf represent the sample volume and the final volume. The actual silicate concentration should be:
[Si] = (AbsSi+P-eP*b*[P]*Vs/Vf)/(eSi*b*Vs/Vf)
The process looks easy but it was found that eSi and eP are not constant but subject to change at different salinities. The latter is also affected by temperature. Empirical equations have been proposed for quick estimation:
eSi (S) = -2.28*S +1800, 0<Salinity (S)<35
eP (T, S) = (0.00108*S^2 - 0.0981*S + 16.47)*T + (0.266*S^2 - 17.823*S + 506)
15℃<Temperature (T)<40℃, 0<Salinity (S)<35
With the new flow system, the analysis throughput has been reduced from 3 min to less than 60 s. With 5 cm long cuvettes, the detection limits are 0.1 uM for silicate and 0.01 uM for phosphate. Linear ranges are 0-150 uM for silicate and 0-20 uM for phosphate.
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