Speciation of Arsenic and Cadmium Compounds by Reversed-Phase Ion-Pair LC with Single-Wavelength Inductively Coupled Plasma Detection

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Abstract
Inductively coupled plasma (ICP) is one of the most popular plasma sources for spectrochemical analysis involving both single-element and multielement determinations. The occurrence of spectral overlap interferences has been a problem with some samples in complex matrices. The selection of appropriate analytical lines may require some compromise between optimum detection limits and the least spectral interference from major concomitants. However, if potential interfering substances are separated in time, their determination within a single-wavelength window (channel) should be possible. The applicability of ICP detection combined with high pressure liquid chromatography (HPLC) for speciation plus time resolution appears to be an attractive and potentially valuable analytical tool. The use of single-channel detection with reversed-phase ion-pair LC to separate Cd and As compounds has been investigated in this work. Complex samples containing sodium arsenite, sodium arsenate, cadmium ethylenediaminetetraacetate, and cadmium nitrilotriacetate were separated by reversed-phase ion-pair LC and detected in the single-channel mode at 228.812 nm, one of the useful “arsenic” emission wavelengths. This enables Cd (228.802 nm) and As speciation and detection at one wavelength setting because, within this bandpass, emission from both Cd and As can be detected. The separation efficiency has been improved through development of suitable column materials and mobile phases. The present experiment also shows the advantage of the ICP as an element-specific and -selective detector when compared to a conventional UV detector. Discussion of the advantages and applicability of this single-channel technique is given in terms of simplicity, sensitivity, precision, and detection limits.