Van T. Lieu, A. Connon, and W. E. Huddleston California state"niversitv Long Beach, 90840
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A Non-Flame Atomic Adsorption Attachment for Trace Mercury Determination
Since the discovery of mercury pollution in the Great Lakes in 1970. much effort has been expanded in the determination of mercury in our environmh.. In a continuing effort to keep our analytical chemistry course instmctive, interesting t o students, and relevantto current interest, an experiment which involves the use of an inexpensive and simply constructed non-flame atomic absorption attachment has been devised for the determination of trace amounts of mercury. In the experiment, the student sees for himself the importance of trace analysis on samples from the environment and biological systems and experiences first hand the extent to which mercury pollution has affected the student as an individual. Apparatus The non-flame atomic absorotion attachment used in this experiment can be easily and simply constructed or he adapted from inexpensive and easily accessible glassware and equipment. The absorption cell is constructed from a 250-mm Liebig type demountable condenser with the inner tuhe removed. The ends of the condenser are cut off a t the two side arms and ground flat with sand paper. Two quartz windows which are of the same size as the outside diameter of the condenser are then glued on the two ends with a small amount of contact cement. The two ends of the condenser of the two side arms can be readily cut by employing the following procedure. Obtain a piece of thin card and wrap the card around the condenser so that the straight edge of the card lies in the position of the required cut. Using the straight edge of the card as a guide for a glass cutting knife, make a cut around the condenser. Heat the condenser with a small flame with a blow pipe, rotating the condenser slowly with the cut-mark directly in the path of the flame. This should cause the glass to crack along the cut. The end of the condenser can be separated by a slight pull. The desiccant flask is adapted from a 250-ml filtering flask and packed with glass wool and anhydrous calcium chloride. A 110-V, 6.5-W aquarium air pump is used as the
source of sweeping air and can be obtained from tropical fish and supplies shops. The reaction tuhe is a Pyrex test tube (25 x 200 mm) with the side arm fitted with a fritted disk with a gas dispersion tuhe. The non-flame atomic absorption attachment is assembled as shown in Figure 1 and is used in conjunction with a Perkin-Elmer Model 303 atomic absorption spectrophotometer equipped with a Heathkit 10-in. chart recorder. All components are connected with Tygon tubing. The air flow rate is adjusted with the use of a screw clamp hetween the pump and the reaction tube. The absorption cell is held in place in the light beam with the use of a utility clamp and ringstand and can he adjusted vertically and horizontally to give maximum transmittance. Reagents The reagents used are Stannous Chloride (SnC12.2Hz0), 40% (w/v) solution in 1 M hydrochloric acid. Standard Mercury Solution, 1000 pg/ml. It is prepared by dissolving 0.1354 g of mercuric chloride in 100 ml of 1 N sulfuric acid. From this solution prepare by dilution a 0.1 pg/ml mercury solution in 1 N sulfuric acid. The diluted mercury solution should be prepared fresh daily. Sulfuric Acid, 3 M. Hydroxylamine Hydrochloride, 1.5%(wjv) in deionized water. Potassium Permanganate, 5% (w/v) in deionized water. Oetyl Alcohol.
Figure 2. Recorder trace of various quantities of mercury.
From Pump
(c) to E~houst
Figure 1. Schematic representation of non-flame atomic absorption attachment l a ) reaction tube (25 X 200 Pyrex test tube with side arm). ib) desiccant flask (250-ml filtering flask). 1cJ absorption cell (constructed from outer tube of 250-mm Liebig type demountable condenser).
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/ Journal of Chemical Education
Mercury, ng Figure 3. Relative recorder peak height as a function of quantity of mercury.
Experiment
Standard mercury samples ranging in size from 10-4GU ng of mercury may be used for the preparation of the calibration curve. To the reaction tube are added 20 ml of deionized water and 5 ml of stannous chloride. The reaction tube is attached to the aeration apparatus. The pump is turned on and the recorder adjusted to read zero after purging the system with air for several minutes. The reaction tube is removed, the standard mercury sample added and the reaction tube immediately reattached to the aeration apparatus. A peak is obtained on the recorder within 2-3 min. A typical recorder trace with various quantities of mercury is shown in Figure 2. The calibration curve is prepared by plotting relative peak height versus quantity of mercury (Fig. 3). It can he seen, by varying sample size, that linearity is main-
tained torover a rangeupto l5Ong. Each student ir to determine the mercury content in his o n n urine. Pariral ur 24-hr urine samples can he used Hecause contents of mercury in urine can he variable, a preliminary run should he made to determine order of magnitude of the mercury concentration. An aliquot of urine sample (5-25 ml) is pipetted and placed in a 100-ml beaker. One milliliter of 3 M sulfuric acid and 5 ml of potassium permanganate are added and the solution boiled gently for a few minutea. Any excess potassium permanganate is destroyed by drop-wise addition of hydroxylamine hydrochloride until the disappearance of permanganate color. A drop of octyl alcohol is added to prevent excessive foaming during the aeration process. The sample solution is transferred quantitatively to the reaction tube and the mercury content determined according to the procedure as described for the standards.
Volume 51. Number 1 1 . November 1974
1 753
