Calibration of Flameless Atomic Absorption Instruments With the advent of a variety of flameless atomic absorption instruments on the market, the method of sample introduction has taken a somewhat different course in that a carefully measured quantity of either a solid or a solution can be introduced into the flameless excitation compartment. The tedious preparation of a series of five or six standard solutions for instrument calibration can be neglected and a single standard solution employed for the calibration. We have found that a good calibration curve can be constructed by altering the volume of the solution injected into the excitation chamber. The measured absorbance is dependent on the absolute quantity of element introduced into the chamber, e.g., one might inject 10, 15, 20, 25, 30, pl of a 0.1 ppm solution into the chamber. We have even been successful with 5 pl quantities. The volume of the sample can then be varied until the absorbance value lies in the middle of the calibration curve. Computation a t first sight leads to chaos as one attempts to calculate the sample value with respect t o two different solutions and six different injection volumes. Since most solutions can he prepared in ppm and the quantity most suited to sample injection is the pl, I have adopted the unit "ppm rl" for the absolute quantity of material introduced into the chamber. Le., 20 pl of a 0.1 ppm copper solution contain 2 ppm pl copper. The unknown solution will then yield a ppm pl value from the calibration curve, division of which with the quantity injected immediately yields the sought concentration. Conveniently enough, 1ppm pl is equivalent to one nanogram.
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396 /Journal of Chemical Education
J. C. Bast
