Analy tica Chimica Acta, 82 (1976) 321-327

0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

A RAPID METHOD FOR THE DETERMINATION OF MERCURY IN AIR BY FLAMELESS ATOMIC ABSORPTION SPECTROMETRY

DORIS GARDNER*

Oceanography Department, University of Liverpool, P-0. Box 147. Liverpool L69 3BX (England)

(Received 17th September 1975)

ABSTRACT

A rapid method for the determination of total gaseous mercury in the atmosphere is described. A simple, inexpensive sampling device is used; the collection time for mercury levels above 5 ng m -’ is less than 25 min; less than 10 min is then needed to determine the mercury by flameless atomic absorption. For subnanogram levels longer sampling periods are used, but air polluted with mercury can be monitored in a few minutes. Data obtained for different samples are presented_

Since the first mercury pollution disaster [l] scientists have become increasingly aware of the need for accurate monitoring of environmental samples for this metal. Because mercury vapour is rapidly adsorbed into the blood stream from the lungs, and some early signs of poisoning are apparent long before they become medically evident [2], atmospheric contamination by mercury is of particular concern. The concentration of mercury in the atmosphere is extremely variable and is controlled by physical and geographi- cal factors such as altitude, barometric pressure, and proximity to mercury sources such as ore bodies. Values reported range from l-20 - lo5 ng mW3 Hg in mercury mines at Idria, Yugoslavia, and 0.6-9.7 - lo5 ng me3 in a mercury processing plant [3], to O-20 ng mm3 in samples from non-mineral- ized, non-polluted areas [4, 5]_

Most methods for the determination of atmospheric mercury employ elaborate and expensive equipment [6--101 or require lengthy periods to trap detectable quantities of mercury 16, 7,11-151. However, many of these methods are restricted to heavily polluted environments such as mines and processing plants. Because the ambient mercury concentrations of environmental air samples may fall to very low levels, a method having a detection level of < 2 ng mm3 is desirable, and as these levels also vary greatly over small intervals of time, the analysis must be completed in a short period. This paper describes a rapid, simple and efficient technique that fulfills these conditions.

*Present address: CSIRO Division of Fisheries & Oceanography, P-0. Box 21, Cronulla, N.S.W. 2230 (Australia).

EXPERIMENTAL

Apparatus

The mercury trapping system is shown in Fig. 1. The all-glass absorption trap A consists of a tube containing the absorbant (25 ml) surmounted by the splash bulbs (250 ml). The deep lip at each joint prevents loss of the absorbant at the high flow rates required, while the sinter (porosity 0) ensures maximal contact between air and reagent. To prevent excessive evaporation of the absorbant on hot, dry days, the tube may be immersed in an ice bath G and be preceded in the line by an air saturation bottle B which contains dilute tin(II) chloride solution. The diaphragm pump C (William & James Model G2353) draws air through the system and is protected from occasional reagent splashes by the trap D. The flow is controlled at 40 1 min-’ by a needle valve and measured with a GEC Elliot 1100 rotameter E. To prevent large particles entering the system the inlet is protected by a 15 cm plug of glass-wool F (a glass fibre filter pad may be used if it is necessary to sample the particulates).

The trapped mercury was measured with a Unicam SP 90A, Series 2 atomic absorption spectrophotometer using a cold-vapour technique I163 _ The equipment was set up as shown in Fig. 2. The mercury vapour, liberated by adding tin(I1) chloride to the 25-ml measuring cylinder A, is pumped through a short drying column B of magnesium perchlorate into the X-cm fused silica cell C in the light path of the atomic absorption spectrophoto- meter by means of a peristaltic pump D (flow-rate, 130 ml mm-‘) _ Dead space was kept to a minimum by making all connecting tubing as short and narrow as possible.

Fig. 1. The mercury trapping apparatus.

323

Hq Lamp

Fig. 2. The mercury detecting apparatus.

Reagents

Reagents were prepared with mercury-free water obtained by all-glass distillation followed by passage through a cation-exchange resin (Dowex AG50-W-X8) in its hydrogen form. Analytical-grade chemicals were employed, and were tested for mercury contamination before use.

Absorbant. This solution was prepared daily by mixing 25 ml of 4 7% potassium perrnanganate solution with 25 ml of 10 70 sulphuric acid and diluting to 100 ml with distilled water.

Hydroxyammonium chloride solution. A 20 % (w/v) solution was purified by repeated extraction with 0.05 ‘3% dithizone in redistilled carbon tetrachloride.

Tin(H) chloride reagent. Tin(I1) chloride dihydrate (30 g) was dissolved in 30 ml of 5 M HCl which had been purified by passage through a column of Deacidite FF anion-exchange resin (500-100 mesh). The solution was then diluted to 50 ml with distilled water, and purified by bubbling nitrogen through it to remove mercury. The reagent was prepared fresh daily.

Standard mercury solution

A lo6 ng ml-’ stock solution was prepared by dissolving 0.1354 g of mercury(I1) chloride in 100 ml of 5 M HCl. A standard solution of lo2 ng ml-’ was prepared daily by dilution.

324

Glassware

All glassware was cleaned with a mixture of concentrated nitric and hydrochloric acids (1:l) and rinsed with mercury-free water before use.

h%UIETHOD

Set up the trapping system shown in Fig. 1 and add 25 ml of the absorbant to the mercury absorption trap. Using the vacuum pump, draw air at 40 1 min-’ through the trap for 25 min. Disconnect the pump, allow the trap to drain, then transfer the contents to a 25-ml stoppered measuring cylinder. Wash the trap with 1 ml of 20 % hydroxyammonium chloride solution, then with distilled water, and add the washings to the cylinder. Adjust the volume to 24 ml with water. Immediately before analysis by atomic absorption qectrophotometer, add a further 1 ml of hydroxy- ammonium chloride solution and mis until colourless. Add 1 ml of 30 % tin(II) chloride solution, fit the bubbling head on the cylinder immediately, then pass air through the closed circuit by means of the peristaltic pump, and measure the maximum absorbance at 253.7 nm. A steady state should be attained after 30 s. Measure a blank value for the reagents and prepare a calibration graph for standard mercury solutions.

RESULTS AND DISCUSSION

Experiments were performed to devise an efficient trapping system for mercury. The type and concentration of the absorbing reagent for mercury, and the flow rate of the sample through this reagent, are important. For these experiments ‘031-Ig was used for convenience; in the final stages, natural mercury was used to test the method under optimum conditions. Known mercury- concentrations were released, from a gas wash bottle upstream of the trapping systems, by 30 % SnC12 in 5 M HCl.

Low flow rates for long periods gave mercury losses of up to 7 % as a result of adsorption onto the walls of the trapping system. Since the 2mHg could only be recovered completely by rinsing the trap with concentrated nitric acid, it was preferable to use higher flow rates for shorter periods; a mixture (1:1:2) of 10 % (v/v) HzS0,:4 % (w/v) KMnO,:H,O was used. Figure 3 shows the recovery of ‘03Hg from the absorption tubes of two traps arranged in series, as the mixed reagent concentration is increased.

These conditions have been used in the standard method outlined above to monitor atmospheric samples in which the concentration of mercury can vary greatly, depending on the area under investigation. It has also been used to monitor laboratory air samples and both land-based and shipboard environmental studies which will be discussed elsewhere. Under normal conditions mercury from 1 m3 of air was collected: after rainstorms, however, mercury levels were so low that it was necessary to pass at least 2 m3 of air

325

Fig. 3. Mercury trapped vs. concentration of trapping reagent,

through the absorbing solution. Smaller sample volumes of air were required in polarographic laboratories as the calibration graph obtained with the standard samples was not linear above 500 ng of mercury.

Published methods for mercury analysis in air report standard dtiviations on replicate samples ranging from 1% t6 ] to 20 5% [ 111 _ It is not known if these reflect experimental errors (the majority = 10 %) or changes in the atmospheric concentration during prolonged sampling periods. During this series of experiments, however, it was found that unless a common inlet was used for replicate sampfe analyses run in paraIfe1, the standard deviation could be up to 30 95, because of large variations in the mercury concentration over short periods and over small areas. The use of a common inlet gave variations of less than 1% (P. D_ Jones, personal communication).

With this sampling equipment secured to a portable frame, and aliquots of fresh reagent mixed ready in stoppered measuring cylinders, this technique gives a fast, cheap and accurate method of measuring the ambient mercury concentrations in any locality_ Table 1 indicates the enormous range of ambient mercury levels found in different environments; potentially dangerous working areas e.g., polarographic laboratories and processing plants etc., can be monitored frequently. Although the maximum permissibIe concentration allowable for public exposure in the U.S.A. is l - 103 ng mm3 Cl.?] threshold Iimit values from 5 - lo3 ng rnw3 for a.IkyI mercury to 1 - 10’ ng rnp3 for metahic mercury in working environments are tolerated in other countries. When more than 5 - lo3 ng Hg me3 was found in and around an unvented polarographic laboratory, an extractor fan reduced that concentra- tion quickly to tolerable Ievefs. The concentrations found outdoors ranged from 0 to 70 ng rnM3* but tended to be much higher on misty and foggy days;

326

TABLE 1

Mercury concentrations in various environments under differing conditions

Place and time Mercury (ng m?

Comment

OUTDOOR (Liverpool)

INDOOR

March 02.00 March 09.30 March 16.45 March 20.11 June 10.00 June 16.30

Research Laboratory 1

Research Laboratory 2 Polarographic Laboratory

Outside Polarographic Laboratory Library

Polarographic Laboratory

Offices away from laboratories

0 62

150 1.2 9

10

350

148 >5000

4900

510

178

70

Raining Fine Misty Raining Wind-Drizzle Fine

Broken thermo.- meter found -

Unvented, large volumes of Hg used -

Situated above Polarographic Lab. Vented for 10 min with extraction fan -

levels of 18 - lo3 ng me3 _ m smog in the vicinity of busy highways 1201 have been recorded.

The author wishes to thank Professor J. P. Riley, and NERC for financial support for this work_

REFERENCES

1 2

3 4 5

6

7 8 9

10

11

K. h-ukayama, Advan. Water Pollut. Res., 3 (1966) 153. D. B. Sbaffin, D. B. Dinman, J. M. Miller, R. G. Smith and D. H. Zoltine, Final Report - N.I.O.S.H. contact, 1973.

. .

G. A. Neville, Can. Chem. Educ., 3 (1967) 4. Y. A_ Sergeev, fnt. Geol. Rev., 3 (1961) 93. J. H. McCathy, Jr., W-W. Vaughan, R.E. Learned and J-L. Meuschke, U.S., Geol. Surv. Circ., (1969) 609. G. L. Carte, R. S. Thomas, L. Dubois and J. L. Monkman, Sci. Total Environ., 2 (1973) 251. S. J. Long, D- R. Scott and R. J. Thompson, Anal. Chem., 45 (1973) 2227. D. A. Church and T. Hadeishi, Appl. Phys. Lett., 24 (1974) 185. D. Siemer, J. Lech and R. Woodriff, Appl. Spectrosc., 28 (1974) 68. T. Hadeishi, D. A. Church, R. D. McLaughlin, B. D. Zak, M. Nakamura and B. Chang, Science, 187 (1975) 348. P. F. Svistov and Yu. L Turkin, Anal. Metody Geokhim Issled Mater Geokhim Konf. 4th 1970 (1972) 77.

327

12 J_ Panek, Cesk. Hyg., 18 (1973) 244. 13 A. Sugimae, Bunseki Kagaku, 22 (1973) 1350. 14 F. P. Scaringelli, J. C. Puzak, B. I. Bennett and L. D. Robert. Anal. Chem., 46 (1974)

278. 15 J. Scullman and G. Widmark, Int. J. Environ. Anal. Chem., 2 (1972) 29. 16 D. Gardner and J. P. Riley, J. Cons. Int. Exp. Mer., 35 (1974) 202. 17 Anon, Environ. Protect. Agen. Pub. AP’I’D 0753, Dec. 1971. 18 A. V. Roschin and L. A. ‘Iimofeevskaya, Ambio, 4 (1975) 30. 19 M. Winell, Ambio, 4 (1975) 34. 20 Y. Fujimura, Jap. J. Hyg., Series No. 7, 2nd Report, 18 (1974) 10.