Background correction pixel

Figure 5.2 Model of an averaged intensity spectrum, including a pixel error and a selection of background correction pixels (BCP) analyte wavelength position dashed line...

There are two possibilities to eliminate the continuous background absorption part. The first is based on the selection of so-called background correction pixels (BCP). The intensities of these particular pixels are summed and used for the correction by calculating the ratio of the sum intensities (/bcp and /Bcpscan) of the BCP in the averaged reference spectrum 7 (refer to Figure 5.2) and in each individual analyte intensity spectrum respectively. This gives a correction factor ascan for the individual scan ... 

In HR-CS AAS it is only necessary to select two reference pixels, the so-called background correction pixels (BCP), as discribed in Section 5.2.1, symmetrically at both sides of the arsenic wavelength in order to correct for this spectral interference, as shown in Figure 8.51. 

Figure 8.51 Selection of two background correction pixels (BCP) in order to correct for the background absorption of 2 /rg A1 in the vicinity of the arsenic line at 193.696 nm (dashed line) atomization temperature 2300 °C (a) without correction (b) with BCP correction...

IS2 = Intensity of a pixel at a point in the background corrected SAMPLE IMAGE S2 long... 

Figure 2.29 A schematic diagram of a subarray with adjacent pixels of 30 gm x 30 pm on a solid state detector. These detectors have the ability to detect before, during and after the signal so that background corrections are carried out. (Copyright 1999-2008, all rights reserved, PerkinElmer, Inc.)...

Only 1-3 pixels are used for registering the analyte absorption, so all the remaining pixels are available for correction purposes. Both fluctuations in lamp emission and transmission of the atomizer are accounted for, making the system a simultaneous double-beam system of high precision with simultaneous background correction. 

A trapezoidal intensity profile of the CS spectrum is generated resulting from the convolution process, induced by the small entrance and the wider intermediate slit. At each wavelength the broadness of the intensity profile can be filled to the detector dimension by motor-controlled adjustment of the intermediate slit width. The adequate profile position on the detector is permanently checked and, when necessary, shifted by prism rotation. Figure 3.7 shows an example of a typical continuum intensity profile. It is sloped due to the echelle blaze profile since Ihe aclual diffraction angle differs from the blaze maximum. The contour of the sharp Hg absorption line at 253.652 nm is located in the middle of the profile symmetrical to the center pixel, often surrounded by additional atomic lines or molecular structures. Based on this simultaneously detected spectrum interval the unique HR-CS AAS background correction algorithm is applied as described in detail in Section 5.2. 

The molecule correction factors Uscan,. which are a measure of the strength of the different reference absorbance spectra for the corresponding scan, are obtained by omission of the pixel at the analyte wavelength position and its neighbors, since the actual analyte absorption may not influence the background correction procedure. 

Figure 8.47 Absorbance over time recorded at the center pixel of the nickel absorption line at 232.003 nm for a Brazilian crude oil sample as oil-in-water emulsion, without (dashed line) and with (sohd line) background correction, using a pyrolysis temperature of 400 °C, and an atomization temperature of 2400 °C...

Fig. 87. Time-resolved absorption spectrum of NH4H2PO4. Observation interval 120 pixels, a human urine sample in the vicinity of the As linear dispersion 1.6 pm/pixel 110 scans 193.696 nm line, (A) before, and (B) after integration time 48 ms per scan. (Reproduced molecular background correction with with permission from Ref. [291].)...

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