Technikatörténeti szemle 10. (1978)

A MÉRÉS ÉS A MÉRTÉKEK AZ EMBER MŰVELŐDÉSÉBEN című konferencián Budapesten, 1976. április 27–30-án elhangzott előadások II. - Fodor P.–Kertai M.–Pólos L.: Atomabszorpciós méréstechnika és a környezetvédelem

Optical System The instrument has a single-beam design employing a quartz-prism as a dispersing element and a measurement range of 190 to 800 nm. The composite beam of light from the hollow-cathode lamp (the light source) is directed into the flame chamber by a quartz collector lens. The image of the cathode spot formed there is projected by a concave mirror (with the aid of additional plain mirrors) into the entry slit of the monochromator. Using a paraboloid collimator mirror of 320 mm focal length, the Littrow monochromator passes the monochromatic light through the exit slit directly to the photomultiplier. The monochromator has an accuracy of ¿2 nm at 250 nm. The entry and exit slits are arranged next to each other, forming a single unit. The curvature of the spectral lines is compensated for by an arched exit slit of bilateral operation (adjustable from 0 to 2 mm). The monochromator and the reflecting mirrors are protected by a casing against external atmospheric influences, forming an enclosed unit. The optimum conditions of the test were defined in previous experiments. They ware as specified below. Air and acetylene flow rates of 10 and 1,8 1/min respectively; with an Original Hanau lamp employed, the filament current of the lamp is 10 mA; the distance above the top of the burner head was 6 mm; optical slit, 0,1 mm; 5-fold scale expansion. Preparations of Samples The membrane filters were digested in a 3:2 mixture of concentrated nitric acid and hydrogen peroxide, over a micro-burner. After complete digestion, the mixture of the acids was evaporated, the residue was washed with deionized water into a Petri-dish and evaporated to dryness unter an infra-lamp. The dry residue was dissolved in 2 ml of 0,5 per cent tartaric acid, and the lead content was determined under the above mentioned conditions by the atomic absorption technique [3]. The set of standard solutions also contained 0,5 per cen tartaric-acid. Sensitivity and Deviation of the Technique The lead contents in the samples tested varied between 0,6 and 13 fig. With tartaric acid solutions, 0,65 ug of Pb yields an absorbance of 1 per cent—i.e. several of the tests had to be carried out in the vicinity of the detection threshold. The technique was investigated for deviation as the function of lead concentration. Using a micro-pipette, a known quantity of lead was applied to 9 membrance filters and the lead contents were tested after the preparation discussed above. The error of the determination lies between 1,5 and 5 per cent.