Spectral analysis subtraction

Re-analysis with better purification should be considered if the count rate is unexpectedly high or the observed half life and radiation energies are not those of the radioanalyte. Contaminant radionuclides may be tolerated if they do not interfere with counting the radioanalyte, or can be subtracted from the count rate with only a minor increase in detection uncertainty. In spectral analysis of alpha particles and gamma rays, for example, contaminant radionuclides are tolerated in the sample if they do not interfere with counting the characteristic spectral peaks of the analyte. 

Computer software is now available or nearing completion to permit rapid collection of FT-IR spectra and a variety of digital manipulations including spectral subtractions, differentiation, deconvolution, baseline straightening, and multicomponent spectral analysis. 

The variance of the recorded fluctuations is equal to the integral of the power spectrum over the recording bandwidth and it is measured with much greater accuracy than the spectral distribution However, undesired noise contributions cannot be easily subtracted from the total variance without the help of the spectral analysis. Furthermore, the measured variance is an underestimation of the actual variance, due to bandwidth limitations (the integral of Lorentzian spectrum up to its cut-off frequency yields only 50% of the variance). 

Spectral searching and stripping in the analysis of a mixture of mannitol and cocaine hydrochloride, (a) IR spectrum for the mixture (b) Library IR spectrum of mannitol (c) Result of subtracting mannitol s IR spectrum from that of the mixture ... 

Mrad/h). Films were stored at -20° until analysis could be carried out. Oxidized films and derivatized, oxidized films were characterized by iodometry (reflux with Nal in isopropanol/acetic acid) and by transmission Fourier Transform (FT) IR (Perkin Elmer 1500), using the spectral subtraction technique (3, 14). Free radicals were measured by the electron spin resonance technique (e.s.r., Varian E4 spectrometer). 

To record a mass spectrum it is necessary to introduce a sample into the ion source of a mass spectrometer, to ionize sample molecules (to obtain positive or negative ions), to separate these ions according to their mass-to-charge ratio (m/z) and to record the quantity of ions of each m/z. A computer controls all the operations and helps to process the data. It makes it possible to get any format of a spectrum, to achieve subtraction or averaging of spectra, and to carry out a library search using spectral libraries. A principal scheme of a mass spectrometer is represented in Fig. 5.2. To resolve more complex tasks (e.g., direct analysis of a mixture) tandem mass spectrometry (see below and Chapter 3) may be applied. 

The IR methods have progressed from hand-drawn baselines and peak height or area for quantitation, to spectral subtraction, to leastsquares methods. Least-squares analysis eliminates the reliance on single peaks for quantitation and the subjectivity of spectral subtraction. However, negative concentration coefficients are a problem with least-squares analysis, since they have no physical meaning. Negative components can be omitted according to some criterion and the least-squares process iterated until only... 

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