Evaluation of gradient flow analysis as calibration strategy for spectroanalytical techniques with plasma source

Abstract

Gradient flow analysis (GFA) is a novel calibration method that can improve the precision, accuracy and sample throughput for spectroanalytical instrumental techniques. The GFA method simultaneously combines the advantages of calibration by standard additions and internal standardization with the sample throughput of flow analysis. The use of GFA is simple because it does not require a series of calibration standard solutions to be prepared. Instead, only two solutions are prepared: standards + sample (1:1 v/v, solution A) and blank + sample (1:1 v/v, solution B). When solution A is introduced, the transient analytical signals for the analytes and the internal standard rise until they reach a plateau region. When solution B is mixed with solution A, the gradual dilution of the analytes and the internal standard results in signals decrease, followed by the formation of another lower intensity plateau. As the amount of sample is not changed, since both solutions contain 50% v/v of it, a matrix matching effect is obtained like in the standard additions method. By plotting the analyte-to-internal standard signal ratio (SA/SIS) in function of the inverse of the internal standard concentration (1/CIS), the analytes' concentrations can be determined by the slope-to-intercept ratio (slope / intercept) of that curve. The GFA is fast and requires no instrumental modifications or any other analytical strategy. This method can be applied to any multielement analytical technique that employs a continuous sample introduction system. In this context, this research plan proposes the evaluation of GFA for inductively coupled plasma optical emission (ICP OES) and mass spectrometry (ICP-MS). It is also proposed the evaluation of GFA in microwave induced plasma optical emission spectrometry (MIP OES) to overcome matrix interference issues.