There are no good alternate wavelengths to 213.8 nm to reduce the sensitivity of the zinc AA measurement so that the measurement will fall in the linear range. The technician must turn the burner head perpendicular to the optical path shown above, so that the pathlength of the measurement is reduced by approximately 20 times. This is required since the upper limit of the linear range for zinc determined using the conventional (i.e., parallel to the optical path) configuration at 213.8 nm is approximately 1 ppm. Turning the burner head should reduce measurement sensitivity enough to keep measurements around 20 ppm Zn in the linear range. The technician should prepare standards that contain the exact concentrations of acid that are in the samples. Furthermore, he should prepare standards that bracket the suspected concentrations of the samples. With a suspected concentration of 20 ppm Zn, standards of 5, 10, 20, 30, and 40 ppm should be satisfactory, as well as a reagent blank containing only the acids. Standards of 5 and 10 ppm are to establish the linear range and standards of 30 and 40 ppm are to accomodate any samples of higher zinc concentration as well as to allow the use of curve-correction algorithms to quantitate those samples. The samples and standards are measured and a blank solution containing only distilled water is introduced into the flame between each sample or standard.

Unfortunately, the technician finds that while the baseline is very stable when the distilled water is measured, a very significant baseline drift (to higher absorbances ... see the chart recording in the figure ... absorbance is the vertical axis and increasing time on the horizontal axis) is observed when a sample, a standard, or the reagent blank is measured? What's going on and what can he do about it?

Click here to see the correct answer.