Sequential Injection-On-line Dilution Micro-sample Introduction Technique and Its Application to Automatic Photometric Determination of Nitrite in Water Samples

By applying the sequential injection technique,an automatic intelligent on-line dilution micro-sample introduction system(SIA system) was proposed.Operation mode and analytical characteristic of this system was studied by its application to the photometric determination of NO-2 in water samples.The analog voltage signal output of the spectrophotometer in the course of measurement were fed back to the sequential injector,to judge whether dilution is needed or not.If the value of voltage is smaller than 305 mV(corresponding to the absorbance value of 0.8),the SIA system will proceed to the dilution program,otherwise,proceed to the direct determination program,both of which will perform automatically.Linearity ranges of the calibration curves were found ranged from 1 to 50 μmol·L-1 of NO-2 without dilution,and from 50 to 500 μmol·L-1 of NO-2 with dilution.Values of RSD′s(n=11) obtained were 0.7%(at concentration level of 10 μmol·L-1),and 1.0%(at concentration level of 200 μmol·L-1).The SIA system proposed was found to be feasible for automatic analytical process where large variation of concentration of analyte is encountered and on-line dilution is necessary.