Automatable on-line generation of calibration curves and standard additions in solution-cathode glow discharge optical emission spectrometry

Two methods are described that enable on-line generation of calibration standards and standard additions in solution-cathode glow discharge optical emission spectrometry (SCGD-OES). The first method employs a gradient high-performance liquid chromatography pump to perform on-line mixing and delivery of a stock standard, sample solution, and diluent to achieve a desired solution composition. The second method makes use of a simpler system of three peristaltic pumps to perform the same function of on-line solution mixing. Both methods can be computer-controlled and automated, and thereby enable both simple and standard-addition calibrations to be rapidly performed on-line. Performance of the on-line approaches is shown to be comparable to that of traditional methods of sample preparation, in terms of calibration curves, signal stability, accuracy, and limits of detection. Potential drawbacks to the on-line procedures include signal lag between changes in solution composition and pump-induced multiplicative noise. Though the new on-line methods were applied here to SCGD-OES to improve sample throughput, they are not limited in application to only SCGD-OES—any instrument that samples from flowing solution streams (flame atomic absorption spectrometry, ICP-OES, ICP-mass spectrometry, etc.) could benefit from them. - Highlights: • Describes rapid, on-line generation of calibration standards and standard additions • These methods enhance the ease of analysis and sample throughput with SCGD-OES. • On-line methods produce results comparable or superior to traditional calibration. • Possible alternative, null-point-based methods of calibration are described. • Methods are applicable to any system that samples from flowing liquid streams