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Analyte Signal (analyte + signal)
Selected AbstractsTheory of net analyte signal vectors in inverse regressionJOURNAL OF CHEMOMETRICS, Issue 12 2003Rasmus Bro Abstract The net analyte signal and the net analyte signal vector are useful measures in building and optimizing multivariate calibration models. In this paper a theory for their use in inverse regression is developed. The theory of net analyte signal was originally derived from classical least squares in spectral calibration where the responses of all pure analytes and interferents are assumed to be known. However, in chemometrics, inverse calibration models such as partial least squares regression are more abundant and several tools for calculating the net analyte signal in inverse regression models have been proposed. These methods yield different results and most do not provide results that are in accordance with the chosen calibration model. In this paper a thorough development of a calibration-specific net analyte signal vector is given. This definition turns out to be almost identical to the one recently suggested by Faber (Anal. Chem. 1998; 70: 5108,5110). A required correction of the net analyte signal in situations with negative predicted responses is also discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source] Generalization of rank reduction problems with Wedderburn's formulaJOURNAL OF CHEMOMETRICS, Issue 11 2003Joan Ferré Abstract In first- and second-order calibration methods based on spectroscopic data, the calculation of the space spanned by the spectra of the interferences has been an important research subject for, among many other applications, calculating the net analyte signal and obtaining figures of merit. Recently, many different calculation methods have been introduced. We show that the calculation of this space can be interpreted from a unified point of view, namely from the rank-one downdating Wedderburn formula. This formula enables one to better understand the properties of the calculation methods currently available. A number of recently introduced signal-preprocessing methods also fit into the proposed framework. Copyright © 2004 John Wiley & Sons, Ltd. [source] Improved calculation of the net analyte signal in inverse multivariate calibrationJOURNAL OF CHEMOMETRICS, Issue 6 2001Joan Ferré Abstract The net analyte signal (NAS) is the part of the measured signal that a calibration model relates to the property of interest (e.g. analyte concentration). Accurate values of the NAS are required in multivariate calibration to calculate analytical figures of merit such as sensitivity, selectivity, signal-to-noise ratio and limit of detection. This paper presents an improved version of the calculation method for the NAS in inverse models proposed by Lorber et al. (Anal. Chem. 1997; 69: 1620). Model coefficients and predictions calculated with the improved NAS are the same as those from the common equations of principal component regression (PCR) and partial least squares (PLS) regression. The necessary alterations to the calculations of sensitivity, selectivity and the pseudounivariate presentation of the model are also provided. Copyright © 2001 John Wiley & Sons, Ltd. [source] Infrared laser desorption and ionization of polypeptides from a polyacrylamide gelJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 3 2002Michelle Baltz-Knorr Abstract We observed direct desorption and ionization of angiotensin II and bovine insulin from a frozen polyacrylamide gel without the addition of an exogenous matrix, using picosecond pulses from a tunable, mid-infrared free-electron laser tuned to strong absorption bands of the gel. At 5.7, 5.9, 6.1 and 6.3 µm we were able to desorb and ionize both analyte molecules, with the strongest analyte signal generated at 5.9 µm. However, no analyte signal was observed at 5.5 µm. Consistent with a previous report, we did not observe ions of either polypeptide at 2.9 µm, in spite of strong overall absorption. We discuss the implications of this wavelength-dependent ionization, including possible ablation mechanisms and energy partitioning between competing vibrational modes. Copyright © 2002 John Wiley & Sons, Ltd. [source] Desorption sonic spray ionization for (high) voltage-free ambient mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2006Renato Haddad Sonic spray ionization is shown to create a supersonic cloud of charged droplets able to promote efficient desorption and ionization of drugs directly from the surfaces of commercial drug tablets at ambient conditions. Compared with desorption electrospray ionization (DESI), desorption sonic spray ionization (DeSSI) is advantageous since it uses neither heating nor high voltages at the spray capillary. DeSSI therefore provides a more friendly environment in which to perform ambient mass spectrometry (MS). DeSSI-MS is herein evaluated for the analysis of drug tablets, and found to be, in general, as sensitive as DESI-MS. The (high) voltage-free DeSSI method provides, however, cleaner mass spectra with less abundant solvent cluster ions and with enough abundant analyte signal for tandem mass spectrometry (MS/MS). These features may therefore facilitate the DeSSI-MS detection of low molar mass components or impurities, or both. The higher-velocity supersonic DeSSI spray also facilitates matrix penetration thus providing more homogenous sampling and longer lasting ion signals. Copyright © 2006 John Wiley & Sons, Ltd. [source] Segmented post-column analyte addition; a concept for continuous response control of liquid chromatography/mass spectrometry peaks affected by signal suppression/enhancementRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2005Anton Kaufmann A novel technique, "segmented post-column analyte addition", is proposed to visualize and compensate signal suppression/enhancement effects in electrospray ionization tandem mass spectrometry (ESI-MS/MS). Instead of delivering a constant flow of analyte solution between the liquid chromatography (LC) column exit and the ESI interface into the eluent resulting from LC separation of analyte-free matrix in order to determine retention time widows in which suppression/enhancement is unimportant (King et al., J. Am. Soc. Mass Spectrom. 2000; 11: 942), segmented packets of analyte-containing solvent and analyte-free solvent were infused into an LC eluent resulting from separation of an analyte-containing sample. The obtained, superimposed, periodic spikes are much narrower than the analyte peak eluting from the column. The height of the spikes is affected by signal suppression phenomena to the same extent as the analyte signal, and hence variations of the spike height can be used to correct the peak area of analyte peaks affected by signal suppression/enhancement. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||