Signal/background ratio

Therefore the signal/background ratio and the detection limits improve significantiy, generally by a factor of 2 or 3. 

For improved sensitivity and selectivity, GC/MS/MS in the ion trap meets the criteria for obtaining low detection Umits. MS/MS enhances selectivity by separating the target compound from the chemical background (due to the matrix), and, in essence, the matrix is virtually ehminated. The result is a better signal/background ratio (and lower detection limits). CoUision induced dissociation (CID) of isolated ion species in an ion trap has thus become a powerful technique. 

One fairly simple solution is to surround the small sample with material in which implanted muons are quickly depolarized or in which muonium is formed, whose precession frequency (especially if sizable transverse fields are applied) is well beyond the time resolution of the spectrometer. Powdered high-quality Y-Fe203 is a material of choice. Still, this leads to a poor signal/background ratio in the p,SR spectra and hence to a severe loss in data accuracy. 

Sample preparation must also be compatible with the chromatographic separation and detection method. The analyte concentration in the extract is one obvious example of this since it must be sufficiently large that the analytical measurement can provide sufficient signal to permit acceptable levels of accuracy and precision. Demands on signal background ratio also arise here since the extract must be sufficiently free of matrix components that might cause matrix interferences and/or matrix effects such as ionization suppression, but this aspect can only be... 

Figure 9.9 A chromatogram obtained from the analysis of a plasma extract showing a signal background ratio (S/B) of approximately 10 1.

In the low resolving power spectrum of an extracted adult urine sample the ions due to the glycosides are detectable above the background ions. The signal-background ratio is sufficient to allow the measurement of both steroids in the urine of adult patients. A more sensitive technique is required, however, for samples from paediatric patients where much lower concentrations of glycoside are involved. 

Comparison of Sensitivity and Signal/Background Ratios for Two Analyte Masses— Fe —Using A Conventional Cross-Flow Nebulizer and A USN Fitted with A Membrane Desolvation System... 

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