Correction for background absorption

Instrumental correction for background absorption using a double beam instrument or a continuum source has already been discussed (p. 325). An alternative is to assess the background absorption on a non-resonance line two or three band-passes away from the analytical line and to correct the sample absorption accordingly. This method assumes the molecular absorption to be constant over several band passes. The elimination of spectral interference from the emission of radiation by the heated sample and matrix has been discussed on page 324 et seq. 

The initial single beam dispersive spectrometers that did not, at the time, produce digitised spectra (this would have allowed for baseline correction) were soon replaced by double beam spectrometers. This more complex arrangement can directly yield the spectrum corrected for background absorption. The use of two distinct but similar optical paths, one as a reference and the other for measurement, allows the alternate measurement of the transmitted intensity ratios at each wavelength. 

Correction for background absorption with the deuterium lamp technique... 

Because atomic absorption enables direct analysis without the need of a concentration step it held promise for metals ranging from 0.1 to 1 ppm. Table 8.6 shows the absorbances obtained for nickel in a synthetic unknown prepared from Boscan crude by the method of Slavin and Trent. An air-acetylene flame afforded convenient combustion, and absorption at the 2316 non-absorbing line was subtracted from the sample absorbance observations to correct for background absorption. The observations were made at the 100 average mode using the Nixie tube digital readout. 

Quantitative elemental analysis Raw data corrected for background, absorption, fluorescence and atomic number effects to produce quantitative results with accuracy of 2-3% relative to the amount present. 

Quantitative analysis Raw data is corrected for background, absorption,... 

In order to correct for background absorption by the eluent, background subtraction often can be carried out quite reliably. Provided that isocratic LC is used, the analytes are present in a constant matrix (eluent) and IR bandshifts due to changes in environment are absent. In addition, FTIR allows the acquisition of spectral data on a precise wave number scale. However, one must be aware of ghost bands or spikes in the region where the eluent is completely opaque leading to the faulty interpretation that there is analyte absorption. 

The effect of random deviations on the determination of the population mean can be eliminated by increasing the number of samples or the sample size. As a result the observed mean approaches more and more the true mean of the population. The effect of systematic deviations is independent of the number of samples or the sample size, and can only be eliminated by taking away the cause (the correct suppository mold) or in case of the UV-determination by correction for background absorption. 

All data obtained from the proportional counters were corrected for background, absorption, counter dead time and nonlinearity, fluorescence, and atomic number. In this case the counter dead time, fluorescence, and atomic number corrections are negligible and the background can be accounted for by a simple subtraction. The absorption, however, requires more careful consideration. Detailed procedure and mass absorption coefficients were taken from Smith ( ). 

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