Development of an Automatic pH Adjustment Instrument for the Preparation of Analytical Samples Prior to Solid Phase Extraction.

An automatic pH adjustment instrument was developed for the preparation of analytical samples prior to solid phase extraction, which is widely used as a pretreatment technique for the separation of sample matrixes and preconcentration of elements for analysis. Real-time monitoring of the sample pH condition was performed by observing the light signal intensity of the pH-sensitive wavelength of the pH indicating reagent. A light of pH-insensitive wavelength was selected as the reference light to cancel the signal intensity variation of the pH-sensitive light due to the difference of pH indicating reagent concentration, possible difference in transparency of sample vessels, and minute fluctuation of the light source.