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.

Survey of bottled waters for perchlorate by electrospray ionization mass spectrometry (ESI-MS) and ion chromatography (IC)

“…Capillary electrophoresis or Raman scattering spectrometry 24,25 may one day play a similar role, but these techniques are currently not sensitive enough without pre-concentration (eg with an anion exchange resin or sample stacking). ESI-MS may be applied to a variety of drinking water matrices as a con®rmatory technique to support identi®cations made by IC.…”

Iodate and Perchlorate in Bottled Water

“…This was the first analytical method reported to be capable of submilligram per liter perchlorate measurements (detection limit approximately 700 g/l). In 1995, a report showed that preconcentration followed by Raman spectroscopy resulted in a detection limit of 1000 g/l (Kowalchyk et al, 1995). Raman spectroscopy was applied to the analysis of perchlorate in 1980; however, the technique was quite insensitive (milligram per liter detection limits) (Miller and Macklin, 1980;Urbansky, 2000b).…”

“…Raman spectroscopy was applied to the analysis of perchlorate in 1980; however, the technique was quite insensitive (milligram per liter detection limits) (Miller and Macklin, 1980;Urbansky, 2000b). The initial paper describes a custom-built suppressed conductivity detector that was capable of "minimum detection limits Iodate and Perchlorate in Bottled Water 289 Kowalchyk et al, (1995) 1996 Despite the publication of methods with detection capabilities as low as 700 g/l, these spectroscopic methods did not become widely used.…”

Detection of hexamethonium‐perchlorate association complexes using NACE‐MS

“…CE with indirect UV detection was applied to the forensic analysis of perchlorate and other chlorine oxide anions [16] and for the analysis of perchlorate in semiconductor washes [17]. Early CE work also made use of ionic conductivity [18], Raman spectroscopy [19], and specific ion electrode [20] detectors for perchlorate, but these experimental systems are not readily available. Other physical properties of perchlorate (soft polarizable anionic character, weak hydration, high solubility in nonaqueous solvents) facilitate its electrophoretic resolution in volatile fluids that readily lend themselves to electrospray MS detection.…”