Light elements are hard to quantify by X-ray fluorescence (XRF) spectrometry because, after a photoelectric excitation, they predominantly relax emitting Auger electrons, greatly reducing the fluorescence count thus limiting the signal-to-noise ratios (SNR) observed. Low SNR values have deleterious outcomes in model building. Notable in ordinary least squares (OLS) regression based on peak height, they also affect more robust regression methods, such as partial least squares regression. While low SNR can also be observed with low concentrations of heavier elements, this paper focuses on boron.To overcome the low SNR hurdle, curve-fitting regression (CFR), a novel method elaborated in this paper, seeks to fit full scans with summed Gaussian curves. The methodology was illustrated with pressed microcrystalline cellulose spiked with sodium tetraborate decahydrate (borax) powder samples. The calibration set ranged from 0% to 21.5% m / m boron, and a PANalytical Axios wavelength dispersive X-ray fluorescence system with rhodium source was used to perform the tests. A calibration curve with determination coefficient (R
In quantitative PCR (qPCR), replicates can minimize the impact of intra-assay variation; however, inter-assay variations must be minimized to obtain a robust quantification method. The method proposed in this study uses Savitzky-Golay smoothing and differentiation (SGSD) to identify a derivative-maximum-based cycle of quantification. It does not rely on curve modeling, as is the case with many existing techniques. PCR fluorescence data sets challenged for inter-assay variations (different thermocycler units, different reagents batches, different operators, different standard curves, and different labs) were used for the evaluation. The algorithm was compared with a four-parameter logistic model (4PLM) method, the C0 method, and the threshold method. The SGSD method compared favourably with all methods in terms of inter-assay variation. SGSD was statistically different from the 4PLM (P = 0.03), C0 (P = 0.05), and threshold (P = 0.004) methods on relative error comparison basis. For intra-assay variations, SGSD outperformed the threshold method (P = 0.005) and equalled the 4PLM and C0 methods (P > 0.05) on relative error basis. Our results demonstrate that the SGSD method could potentially be an alternative to sigmoid modeling based methods (4PLM and C0) when PCR data are challenged for inter-assay variations.
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