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

Solid-sample Technique The apparatus (Fig. 1.) based on the combination of arc and flame developed by Professors Kantor and Pungor [2] at our Department and produced by the MOMHungarian Optical Works, was applied in the solid-sample technique. The sample is placed in the hole or terminal surface of a graphite electrode, which is placed in the arc chamber. Then the arc is ignited by the depression and release of the upper elelctrode. The spray produced is flushed with a 9+1 ratio nitrogen-air stream into the mixing chamber of the SPEKTROMOM 190 A equipment (and then into the flame), through the cyclone and the ejector. The cyclone separates the coarse fraction of the graphite particles produced, the ejector ensuring an adequate streaming of the spray. The electrodes were made of 5 mm diameter graphite pieces (type SU—103). A DC current are of 10 A was applied in the evaporation of the samples. The solutions were portioned out by 5pl Eppendorf pipettes. The optimum conditions of test were established by the application of 5 ul of 20 ppm lead solution on the anode, and measuring the absorbance after arcing. The optimum conditions were in agreement with those found in the conventional atomic absorption technique. The absorption signals obtained were recorded (Fig. 2.). As will be seen in the Figure, signals of different peak heights were obtained in testing a given quantity of lead. However, the quantity of lead added is proportional to the area under the peak, not to the peak height. Thus in cooperation between our Department and MOM, an electronic integrator was developed operating along the principle of pulse counting (after a voltage-to-frequency conversion). The integrator is also marketed by the MOM—Hungarian Optical Works. The Figure shows the measurement values provided by the integrator, which exhibit only a narrow deviation. Preparation of Samples The anode is formed as a „cup" of 4 mm inside diameter and 8 mm depth. The 25 mm diameter filter paper was cut into four equal parts which were folded up and placed into the anode ,,cup". In this way, 4 parallel tests could be performed with each sample. It was found that the clean filter paper did not contain lead in a measurable quantity. When this was done, a lead solution of known concentration was applied on each filter paper, and the calibration curve was recorded (Fig. 3.). The curve is linear in the range of low concentrations, exhibiting a curvature at a higher concentrations. It is evident from the Figure that the average values (obtained with reference to peak height/differ considerably from the calibration curve obtained by integration: the material introduced into the light absorption field exhibits an irregular distribution in time.