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Response variations

Problems with solvent flameout, hydrocarbon quenching structure-response variations for different sulfur-phosphorus-containing compounds can be partially solved by using dual-flame burner. Figure 3.14 (177-179). The lower flame... [Pg.149]

Genes involved in drug metabolism encode enzymes or receptor proteins that dictate drug response. Variations in gene structure, primarily single nucleotide... [Pg.516]

The mean-centering operation effectively removes the absolute intensity information from each of the variables, thus enabling snbsequent modeling methods to focus on the response variations about the mean. In PAT instrument calibration applications, mean-centering is almost always nsefnl, because it is almost always the case that relevant analyzer signal is represented by variation in responses at different variables, and that the absolute values of the responses at those variables are not relevant to the problem at hand. [Pg.370]

However, the PLS-DA method requires sufficient calibration samples for each class to enable effective determination of discriminant thresholds, and one must be very careful to avoid overfitting of a PLS-DA model through the use of too many PLS factors. Also, the PLS-DA method does not explicitly account for response variations within classes. Although such variations in the calibration data can be useful information for assigning and determining uncertainty in class assignments during prediction, it will be treated essentially... [Pg.395]

Abstract Internal standards play critical roles in ensuring the accuracy of reported concentrations in LC-MS bioanalysis. How do you find an appropriate internal standard so that analyte losses and experimental variations during sample preparation, chromatographic separation, and mass spectrometric detection could be corrected How is the concentration of an internal standard determined Should internal standard responses be monitored during the analysis of incurred samples What are the main causes for internal standard response variations How do they impact the quantitation Why are stable isotope labeled internal standards preferred And yet one should still have an open-mind in their usage for the analysis of incurred samples. All these questions are addressed in this chapter supported by theoretical considerations and practical examples. [Pg.1]

Internal Standard Response Variations During Incurred Sample Analysis... [Pg.14]

Typical Causes of and Solutions to Internal Standard Response Variations... [Pg.15]

Therefore, it is expected that there might be differences in matrix components for different samples because each sample is from an individual subject and collected at different sampling time. These differences could cause many different types of IS response variations. [Pg.19]

The solubility or stability of an internal standard in IS working solution could cause IS response variations. Sometimes, an issue of solubility could appear as an issue of stability [42], For example, high interbatch IS response variation was observed for a method of raloxifene glucuronides based on protein precipitation by acetonitrile containing deuterated raloxifene glucuronides. However, internal standard responses within a batch were relatively stable and no such variations in the responses of the corresponding analytes were observed. It was further noticed that the internal standard responses of a batch appeared to be correlated to the operation speed of the lab technician who performed the batch. The faster a lab technician s speed was, the higher the IS responses of his run were. [Pg.23]

Fig. 14 (a, top) Hydrophobicity (log D) vs. pH curves for penciclovir and vidarabine. (b, middle) Less internal standard response variation was observed while using vidarabine as the internal standard (CV= 13.02 %) but 43 % of the calibration standards (CS) and quality controls (QC) were rejected. Extraction MCX (mixed-mode strong cation exchange)-based solid-phase extraction, (c, bottom) More IS response variation was observed while using a deuterated internal standard, penciclovir-d4 (CV = 23.81 %) but 100 % of the CS and QC samples were accepted. Reproduced from ref. [36] with permission from Elsevier... [Pg.24]

Furthermore, sometimes a change of solvent supplier or lot could cause issues of stability for an internal standard and therefore IS response variations. For example, Napoli reported unusual IS response variation and stability problem when a different lot of acetonitrile was used for the preparation of ascomycin working solution (as the internal standard for tacrolimus, [43]). [Pg.25]

When multiple sample treatment steps are used, especially derivatization is involved, larger IS response variations are usually expected. For instance, in a method based on T.T.F. followed by derivatization and SPE, as large as fourfold difference in IS responses was observed for CS and QC samples as well as incurred samples (Fig. 16). Despite this large IS response variation, the accuracy of the concentration-known CS and QC samples was not impacted, it can be therefore concluded that the concentrations of unknown samples are also reliable. [Pg.25]

In addition to the above, there might be other less common causes for IS response variations. For example, due to mixed usage of rubber-lined caps and FIFE (polytetrafluoroethylene)-lined caps during the liquid-liquid extraction shaking (mixing) step, randomly low IS responses were observed for extracted samples, i.e.,... [Pg.25]

The Impact of Internal Standard Response Variations on Quantitation... [Pg.27]

The main purpose of troubleshooting IS response variations is to make sure that the quantitation of unknown samples has not been impacted despite the variable or abnormal IS responses observed. Unfortunately, there is no clear-cut yes or no answer to... [Pg.27]

Tan A, Hussain S, Musuku A, Masse R (2009) Internal standard response variations during incurred sample analysis by LC-MS/MS case by case trouble-shooting. J Chromatogr B 877 3201-3209... [Pg.32]

Channel-to-channel spectral response correction Normalization factors necessary to correct for channel-to-channel spectral response variations and variations in the spectral transfer effi-of the optical system, e.g., grating efficiency, can be stored in memory and thus provide the means for an automatic spectrum correction, Fig. 4. [Pg.9]

Different validation data sets should be prepared to investigate every source of expected variation in the response. For example, validation sets might be designed to study short-term or long-term variation in instrument response, variation from instrument to instrument, variation due to small changes in sample temperature, and so on. [Pg.114]

Sensitivity Ability of an analytical method to detect a response variation due... [Pg.628]

Figure 3.4. Effect of in.strument response function on relative intensities for CH2CI2. Spectrum c is corrected for response variation with wavelength and shows correct relative intensities. Figure 3.4. Effect of in.strument response function on relative intensities for CH2CI2. Spectrum c is corrected for response variation with wavelength and shows correct relative intensities.
A rigorous means for removing discontinuities between segments is the use of luminescent standards described in Section 10.3. The standard has a known emission spectrum, which is recorded with the same set of segments as the Raman spectrum of interest (34). The standard emission experiences the same response variations as the Raman scattering, so its spectrum includes the same... [Pg.208]

Figure 10.8. Schematic of procedure for correction of spectra for instrumental response variation. R represents the response function 0z. and Figure 10.8. Schematic of procedure for correction of spectra for instrumental response variation. R represents the response function 0z. and <j s are the actual output of the sample and standard (intensity vs. Raman shift) and Ss and S/, the observed spectra.

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See also in sourсe #XX -- [ Pg.300 , Pg.301 ]




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