Flow injection sample-to-standard additions method. Spectrophotometric determination of hydrochloric acid and orthophosphate

Conventional flow injection (Fl) has been utilised for the development of the sample-to-standard additions method as an alternative to the reverse Fl standard additions method. An equation has been derived for the proposed method, allowing the calculation of sample concentration from two transient signals obtained from the injection of the sample solution and the blank, which must possess matched matrix composition. For these conditions the sample-to-standard additions method was as effective as the standard additions method. Two conventional Fl methods for the determination of hydrochloric acid and orthophosphate in phosphate rock digests were examined by the sample-to-standard additions method. Satisfactorily accurate and precise results were demonstrated. Because the proposed method was operated in the conventional Fl mode, an autosampler was incorporated to obtain a throughput of 80–100 samples h–1.