1974
Anal. Chem. 1980, 52, 1974-1977
acetic acid on the joints prior to assembly will suffice to seal them and its use will prevent “creeping” of the grease throughout the entire system. Higher and more reproducible results were obtained in this laboratory by using the tall form cylinders (instead of flasks) for collecting the hydrogen sulfide and the method of reagent addition specified in the Procedure section of this paper rather than with Gustafsson’s recommended methodology ( 3 , 4 ) . It is very important that the trapping solution, once it has been acidified with the amino reagent, not be violently mixed or even allowed to stand for long before the addition of the ferric chloride reagent. The overall time for the analysis of a single solution sample is on the order of 10 min including the delay for color development. Solid samples require 2 or 3 min more. The
relative standard deviations obtained on finely ground solid calcined nuclear waste containing from 0.1 to 10% sulfur as sulfate are typically on the order of 3-5%.
LITERATURE CITED St. Lorant, I. Hoppe-Seyler’s 2. Physiol. Cbem. 1929, 85, 245. Johnson, C. M.; Nishita, H. Anal. Cbem. 1952, 24,736-742. Gustafsson, L. Talanta 1960, 4 , 227-235. Gustafsson, L. Talanta 1960, 4 , 236-243. Annu. Book ASTM Stand. 1979, Part 45, C698, 312-314. Thorn, L. E.; Bryan, R. G.; Waterbury, G. R. Report LA-5884; Los Alamos Scientific Laboratory: Los Alamos. NM, June 1975. (7) Sinclair, A.; Hall, R. D.; Burns, D. T.; Hayes, W. P. Talanta 1971, 76. 972-976.
(1) (2) (3) (4) (5) (6)
RECEIVED for review February 19, 1980. Accepted July 14, 1980.
Sampling of Tetraalkyllead Compounds in Air for Determination by Gas Chromatography-Atomic Absorption Spectrometry Waiter R. A. De Jonghe, Dipankar Chakraborti,’ and Fred C. Adams’ Department of Chemistry, University of Antwerp (U.I.A.), E-26 70 WiIrQk,Belgium
Cantuti and Cartoni first described a procedure for the direct collection of tetraethyllead from polluted air and its chromatographic determination at ppm levels by using electron capture detection ( I ) . Their technique was later modified and improved in order to apply it to the analysis of city air (2). In this way detection limits of about 0.05 and 0.5 pg/m3 were reported for the determination of tetraethyllead and tetramethyllead. Since both methods use electron capture detection, they lack the specificity required for environmental samples, as these contain a variety of other compounds with high electron affinity. By use of cooled gas chromatographic column packing material for the collection, the tetraalkyllead compounds (TML = tetramethyllead, TMEL = trimethylethyllead, DMDEL = dimethyldiethyllead, MTEL = methyltriethyllead, and T E L = tetraethyllead) have also been determined with gas chromatography/atomic absorption spectrometry (GC/ AAS). This method was first reported by Chau et al. ( 3 ) . However, the low analytical sensitivity combined with a very slow air sampling rate (13Ck150 mL/min) made this procedure unsuitable for the analysis of ambient air ( 4 ) . In later modifications, the sensitivity was greatly improved ( 5 , 6) but the determination of tetraalkyllead compounds in street air still required collection times of 16 h or more. Other reports also mentioned the possibilities of the GC/AAS technique for the analysis of tetraalkyllead compounds in the air, without entering into details about the method used for sampling (7) or analysis (8, 9). In the latter work only samples of polluted atmospheres with organic lead concentrations of 0.1 pg/m3 or higher were adequate in order to separate the different alkyllead components. Reamer et al. (10) developed a method using a gas chromatograph/microwave plasma detector, by which the trapped tetraalkyllead compounds (TAL) were not directly eluted into the gas chromatograph but removed from the adsorbent by a freeze-drying technique. The limit of detection for an individual organolead species was quoted as about 0.5 ng/m3 P r e s e n t address: D e p a r t m e n t of C h e m i s t r y , J a d a v p u r U n i v e r India.
sity, Calcutta-32,
0003-2700/80/0352-1974$01 .OO/O
for a 2-h sample. Despite the high sensitivity, this method is not practical for pollution-control measurements in view of the lengthy period (more than 1 2 h) required for the analysis of a single sample. With the exception of the work of Laveskog ( I I ) , no method published so far is able to monitor alkyllead species in ambient air within a reasonably short time. Laveskog’s method, however, involved gas chromatographic/mass spectrometric instrumentation, which is not readily available to most workers. Atomic absorption spectrometry, being sensitive, relatively free of interferences, and widely available in trace metal laboratories, appears to be more suitable as the detection system (12),provided it is used in conjunction with a sampling technique other than sample collection on tubes filled with a GC adsorbent. This report describes the development and utilization of a suitable sampling system for the analysis by GC/AAS. Sampling periods of 1 h or less proved to be sufficient, even for the determination of alkyllead species in relatively nonpolluted air. The major difficulty in collecting the compounds from air samples on GC column packing material is the condensation of moisture in the trap. Ice condensation on the column material leads to clogging of the pores and a sharp decrease in the air flow rate. The volume of air that can be sampled, is therefore limited. Several authors pass the air before it enters the adsorption tube through a predeposition trap, to condense the excess of atmospheric water. By use of sampling apparatus with an empty U-tube at -15 “C, maximal reported volumes are about 7 5 L (6),as water condensation on the adsorption tube is not completely prevented. An empty impinger held at -78 “C is still not capable of extending the sampling volumes above 200 L (9, 10). To design a more efficient water condensation trap, we investigated the use of a large U-tube filled with glass beads. In this way the predeposition of water would be much improved as a result of a better cooling efficiency of the air. From preliminary experiments it appeared that this predeposition trap was really effective, only if temperatures of about -80 “C or lower are used. However, a t these low temperatures, a substantial fraction of the tetraalkylleads is retained also, 1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 12, OCTOBER 1980 ai coilection system
Table I. Bypass of Cryogenic Trap at Various Temperatures
I
I
membrane filter
13-43
,
LL
i3
rotcmeter
% TML escaped from CrY0,g trap, C composition of cooling mixturea trapping
temp of
L A J cryogenic trap -130 "C b) desorption system
- 21 -39
v x u u r l pump
- 55
-78 -120 -196 a
wcter bath 60 "C
adsorptlon tube. -196 "C
1975
vacuum pump
cl injection system
Figure 1. Apparatus for collection (a),desorption (b), and injection (c) of tetraalkyllead compounds
especially the less volatile species, whereas at higher temperatures also a rapid obstruction of the chromatographic adsorption tube occurs. Provided the trap is cooled down to sufficiently low temperatures to retain also the more volatile species, DMDEL, TMEL, and TML, it could therefore be used for the direct collection of the lead alkyl compounds. This would allow much higher air flow rates than is possible with chromatographic adsorption tubes.
EXPERIMENTAL SECTION Apparatus. The gas chromatograph/atomic absorption spectrometer system (GC/AAS) used was identical with that reported previously (13). Air Sampling. The air to be analyzed was passed at a flow rate of about 6 L/min for 1h through a two-component collection system (Figure la). The first stage was a 47-mm Nuclepore membrane filter (0.4 r m ) to remove the lead-containing particulates. The second stage was a cryogenic sampling trap for the collection of the volatile tetraalkyllead compounds. It consists of a U-shaped Pyrex tube (50 cm long by 25 mm i.d.) filled with glass beads of 4 mm diameter and immersed in a liquid nitrogen-ethanol slush bath at -130 "C (14). After sampling is completed, the U-tube remains in the slush bath until analyzed. A DT/VT 1.5 Becker vacuum pump was used to suck the sample. Flow rate readings were measured with a GEC Elliot 1100 rotameter. Analytical Procedure. After the sample was obtained, the trapped alkyllead compounds were thermally desorbed from the large U-tube and transferred to a short adsorption tube (Figure lb) by connecting the sampling tube, still immersed in the slush bath, with a short glass column (26 cm long by 6 mm 0.d. and 2 mm i.d.) packed with 0.2 g of 3% OV-101 on 100/120 mesh Gaschrom Q and kept in liquid nitrogen. While air was passed at a flow rate of 1 L/min, the U-tube was removed from the slush bath and allowed to warm slowly in air and then in a water bath at 60 "C. With this treatment a rather constant air flow through the desorption system can be maintained, but near the end of the operation, when appreciable amounts of water start to evaporate out of the trap and condense on top of the adsorption tube, the flow rate decreases and desorption stops. The adsorption tube was then attached to the four-port valve installed between the carrier gas inlet and the injection port of
crushed ice/NaCl ( 3 / 1 ) crushed ice/CaC1,.6H20 (1.2/2) crushed ice/CaC1;6H20 (1.4/2) solid CO, liquid N,/ethanol slush liquid N,
96 105
101 7
