Rapid Normal Raman Spectroscopy of Sub-Ppm Oxy-Anion Solutions: The Role of Electrophoretic Preconcentration

Abstract

Normal Raman spectroscopy is used as an on-line detector for capillary electrophoresis (CE) to detect sub-ppm mixtures of nitrate and perchlorate in water. Field-amplified injection, a form of sample stacking, into a running electrolyte of 0.1 M KCl increases the analyte concentration at the detection window by up to 1800 times its starting value. Raman bands of nitrate (1047 cm⁻¹) and perchlorate (934 cm⁻¹) are measured in a total separation time of less than 3 min, with only 1-s integration times. The Raman spectroscopy of solutions originally 1 × 10⁻⁵ M nitrate (620 ppb) and perchlorate (1 ppm) is demonstrated.