Standard in the rinse

Abstract

Standard in the rinse (SIR) is a novel calibration method where a calibration curve is prepared by introducing a sample into an instrument, then “rinsing” the instrument with a standard solution containing all analytes. The method completely bypasses the need to prepare a calibration curve of individual standard solutions of known concentration: samples are loaded into an autosampler, and the measurement is performed while the sample is flushed from the system by the spiked rinse. Two “timestamp” internal standards are employed (one in the sample and the second in the rinse) to allow determination of the relative sample to standard ratio being measured by the instrument at a given time. Proof-of-concept for SIR was obtained using ICP-OES, but the technique could be applied to any measurement technique that accepts samples in a flowing liquid stream. Incorporation of a traditional internal standard into both the sample and standard corrected for sample matrix effects, even though the sample and rinse are not matrix matched. SIR was evaluated through spike recovery experiments into complex sample matrices. The method was further validated using four certified reference materials. Analyte percent recoveries across all tested sample matrices and CRMs ranged from 88 to 120 %, with relative standard deviations on the order of a few percent. Limits of detection were on the order of single digit μg L−1, typical for ICP-OES measurements. One standard concentration of 0.500 mg L−1 could determine analytes in the sample ranging from LOD to values approaching 50.0 mg L−1, covering four orders of magnitude.