The analyst would like to have both elements present in the calibrations samples as well as make accurate Cd determinations in unknown samples. In this example, the analysts is attempting to determine the feasibility of measuring Cd in the 0.05 to 100 µg/mL range with 100 µg/mL As present. Again, a linear fit was used.įor purposes of demonstration the interference of the As 228.812 nm line upon the Cd 228.802 nm lime will be used. Here, background points must be taken equal distance from the peak center in order to make an accurate correction. If the instrument only allows for selection of background points then intensities are taken at set wavelengths, averaged and subtracted from the peak intensity. Figure 8.2 demonstrates that care was taken to avoid The Re line on the long wavelength side of the Zn 213.856 nm line and that a straight line that accurately determines the background intensity in the peak area is obtained.įigure 8.3 shows a sloping but linear background. For flat backgrounds the distance of each point from the peak intensity is not important provided there is no interference from other lines in that vicinity. In this case the instrument allows for the selection of background regions thereby improving the accuracy of the estimated background radiation. The 'algorithm' or 'correction mode' depends upon the curvature of the background, as is illustrated below.įigure 8.2 shows a flat background where correction was made on both sides of the line. The correction for background radiation is typically made by first selecting background points or regions and then a correction mode or algorithm. However, the problems with matrix matching are obvious and may offset any advantage gained when you don't make them. It would follow that the precision of the measurement would be better (lower) and for some instruments the measurement time will be shorter. It can be argued that matrix-matched standards and samples will eliminate the need for background correction where the analyst only has to measure the peak intensity. It can be seen that the highly concentrated Ca matrix contributes some to the background radiation but there are greater contributions from other sources independent of the sample matrix. Although background radiation can be lowered somewhat by adjusting instrumental parameters, it cannot be eliminated and corrections are typically necessary. The background radiation intensity for the nitric acid blank is ~ 110,000 counts at 300 nm whereas the background radiation for the Ca containing solution is ~ 170,000 counts at the same wavelength.
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