Background subtraction manual

Example In the partial TIC obtained by GC-EI-MS of an unknown mixture on a HP-5 column the chromatographic peak at 32.6 min is rather weak (Fig. 12.7). Scan 2045 extracted from its maximum yields a spectrum that is mainly due to background ions from column bleed as demonstrated by comparison to the average of scans 2068 2082. Finally, manual background subtraction ((2035 2052)-(2013 2020)) delivers a spectmm of reasonable quality, although some background signals are not completely erased. 

PUF. Each of the three 2.0-mL PUF extracts was subjected to GC-MS analyses. All analyses were conducted with a Finnigan OWA 1020 GC-MS system fitted with an SE-54 fused-silica capillary column. All spectra were collected in the total ion mode. Component spectra, both raw and background subtracted, were manually compared against USEPA-NIH library spectra to permit component identifications. Quantitative data were again provided by using dio-anthracene as the internal standard. 

Under the best of circumstances, some arbitrariness and variation is introduced by this manual method of background subtraction. For our case, we tested our choices of anchor points by choosing alternate points and found only minor changes in the final results. 

For infrared spectroscopy, this requires proper subtraction of the background moisture and carbon dioxide to get a good approximation of solvent (in the cell). These can then be used to obtain a good approximation of solute A, followed by solute B etc. This process can be done manually by trial and error,or it can be automated for optimal subtraction. The output is a set of n reference spectra. 

Three orders of the 1010 reflection were measmed. Peak-to-background ratio was 100 or more for the first peak so a computer routine was used to create a polynomial fit to the background. For peaks of second and third order, the peak-to-background ratio was less than 3 so the data were smoothed manually and then the background was subtracted. ... 

Now a correction for the non-ideal character of the multiphase topology must be performed. In the classical analysis this is a manual evaluation step which results in the subtraction of a slowly varying background [46, 72, 73]. Here the background determination is replaced by the result of a low-pass Alter, applied to the scattering image at the present state of evaluation [74],... 

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