programmable calculator such as the Hewlett-Packard 65 ( 5 ) . If Q p -t Qr 6 0.05, the results satisfy the desired criterion. Applying the 95% confidence criterion to the results reported by McFarren, Lishka, and Parker ( 1 ) produced 23 changes in classification in 192 sets of results. Examples of changes from McFarren et a1.k classification are shown in Table I1 for each analytical method in which they occurred. Farrell (6) calculated T for results for the determination of pesticides in vegetable matter by gas chromatography; 8 out of 32 sets of results change classification when a strict 95% confidence limit is applied, compared with 2 out of 16 sets of results reported by McFarren et al. ( I ) for pesticides in water. One of the reasons for this difference is that the total errors for the latter results are generally so large that the accuracy of the criterion does not matter. Reassessment of the published results shows that if the original criterion, or any similar one with different limits, is to be used to discriminate between methods, it is important that the test applied should correspond to the desired confi-
dence level, as otherwise a considerable proportion of results may be rejected unnecessarily.
LITERATURE CITED (1) E. F. McFarren, R. J. Lishka, and J. H. Parker, Anal. Chern., 42, 358 (1970). (2) K. Eckschlager, Anal. Chern., 44, 878 (1972). (3) D. V. Lindley and J. C. P. Miller, "Cambridge Elementary Statistical Tables", Cambridge University Press, Cambridge, England, 1962. (4) "Handbook of Chemistry and Physics", 45th ed., The Chemical Rubber Company, Cleveland, Ohio, 1964. (5) "HP-65 STAT-PAC l", Programs STAT 1-10Ai and 1 - 1 0 ~ 2 Hewlett-Packard , Company, Cupertino, Calif., 1974. (6) T. J. Farrell, Anal. Chern., 43, 156 (1971).
Derek Midgley Central Electricity Research Laboratories Kelvin Avenue, Leatherhead Surrey KT22 7SE, England
RECEIVEDfor review September 10, 1976. Accepted November 29,1976.
In Situ Decomposition Product Isolated from Tenax GC While Sampling Stack Gases Sir: Tenax GC has been found to be very useful as an adsorbent for collecting organic vapors from the atmosphere, and its use has been reported by several investigators (1-3). It has been used for several years by our laboratory for collection of organic materials from power plant stack gases, in combination with a filter to remove particulate matter ( 3 ) . In many stack gas samples collected by Battelle, there has been a small but variable amount of an amorphous yellow or orange crystalline substance. At first it was thought that this material was part of the collected sample, and was tentatively identified as a conjugated quinone or ketone in earlier reports to EPA ( 4 ) .Since these were either EPA Level 1analyses ( 5 ) or GC/MS analyses for polycyclic organic materials (POM's) ( 3 ) ,identification was not the aim of the studies. However, the consistency with which this material occurred was so unexpected that a concerted effort was made to identify it. One LC fraction of an EPA Level 1 analysis carried out on a power plant effluent sample yielded beautiful orange crystals, and therefore it was felt that the fraction might be pure. Infrared and NMR spectra were obtained on this fraction; the infrared spectrum matched a reference spectrum of 2,6-diphenyl-pquinone (DPQ) and the NMR spectrum supported this structure. Tenax GC is an aromatic polyether, a polymer of 2,6-diphenylhydroquinone,made by oxidative coupling of 2,6-diphenyl phenol. Power plant stack gases usually contain small amounts of sulfuric acid and excess air and, because of the high water vapor of stack gases, the sampler adsorbent bed is always run a t 55-80 "C to keep it above the dew point of the water in the stack gases. It seems reasonable that these conditions could lead to formation of 2,6-diphenyl-p -quinone, through the interaction between sulfuric acid and Tenax GC under oxidizing conditions. Although PDQ is the only compound which we have observed, the formation of other products from a complex decomposition process cannot be precluded. A recently concluded study of the variables affecting the performance of the Battelle Adsorbent Sampler (6) additionally provided an authoritative explanation of the formation of 2,6-diphenyl-p -quinone. In this study, five variables were examined, listed in Table I. The SO2 and NO were metered into a stream of air heated to 450 "C in a tube furnace; HzO was added using a syringe 512
ANALYTICAL CHEMISTRY, VOL. 49, NO. 3, MARCH 1977
pump, injecting it directly into the hot portion of the furnace. The experiments involving collection of organic materials are not directly pertinent to this cdmmunication, except for the observation that small and varying amounts of DPQ were found in all experiments. Preliminary experiments showed that DPQ occurred even in the total absence of organic material. In an attempt to establish the exact cause of formation of DPQ, experiments were run using sulfur dioxide (3000 ppm) and sulfuric acid (30 ppm), which represent approximately the highest levels found in power plant stack gases. No DPQ was formed, even when the sulfuric acid level was raised to about 300 ppm; however, when nitric oxide was added, even without sulfur dioxide and sulfuric acid, DPQ was always formed even when the sampler was operated at 25 "C. The amount of DPQ was not absolutely quantified, but the amount formed appeared to be greater a t high sampler temperatures and high nitric oxide concentrations. Approximately 10 to 15 mg of DPQ was formed under the most adverse conditions. Part of the nitric oxide is oxidized to higher oxides, probably even forming some nitric acid, since the simulated stack gas which contains nitric oxide, water vapor, and air is heated. In any case, it is not sulfuric acid, but nitrogen oxide or nitric acid which is responsible for formation of DPQ from Tenax. The amount of DPQ formed is always very small compared to the amount of Tenax GC in a sampler. However, the formation of DPQ raises questions about its effect on the performance of Tenax GC in a vapor sampling system, since the DPQ must either come from chain scission, or removal of an end group. I t was beyond the scope of our program to undertake extensive polymer characterization studies. Therefore the effect on Tenax GC of the polymer degradation that leads to formation of DPQ was investigated by comparing the performance of Tenax GC as a gas chromatographic column material. For this study a quantity of Tenax GC was thoroughly extracted (24 hours in a Soxhlet extractor) with pentane and then methanol. This Tenax GC was then dried and "activated" overnight at 200 "C and a portion was then subjected to the most severe sampling conditions observed for formation of DPQ (1500 ppm NO, 3000 ppm S02, 8% HzQ, sampler temperature 82 "C) for 2 hours (twice the usual sampling
Table I. Variables Studied in Evaluation of Battelle Adsorbent Sampler Variable
so2
Level 200 and 3000 ppm
NO
150,500,and 1500 ppm
H20
2 , 4 , and 8% by volume 55,68, and 82 "C 10 and 50 pg of each
Temperature Organic compound levela
a A mixture of several organic materials was vaporized and collected under the various conditions.
Battelle Adsorbent Sampler for a wide range of organic materials in stack gases, while highlighting the great versatility of such sampling systems, have indicated potential shortcomings, the likes of which have been largely ignored to date by most workers in the field. The dangers of an empirical approach to sampling complex industrial emission samples cannot be overemphasized; it is strongly recommended that other stack gas sampling systems utilizing various adsorbents and sampling parameters should undergo rigorous validation studies, similar to the program from which the data for this communication were taken. ACKNOWLEDGMENT
time). The Tenax GC from the Battelle Adsorbent Sampler was then extracted for 24 hours with pentane and dried. Two glass GC columns (2-mm i.d. X 10-ft long) were packed with Tenax GC, one with the cleaned "untreated" material and one with the material subjected to stack sampling conditions which form DPQ. Gas chromatograms of a mixture of several organic compounds were run on the two columns. There was no significant difference between the chromatogram obtained using the Tenax used in the sampling experiment, and that of the untreated control, as measured from comparison of chromatographic efficiencies of the two columns. The latter parameter was determined from a consideration of retention times and peak widths (at half peak height) for the GC peaks for each of seven organic compounds chromatographed on the two columns. We have concluded that degradation of Tenax GC does not affect the efficiency or capacity of a sampling system, such as the Battelle Adsorbent Sampler, which may utilize this adsorbent. Simple analytical schemes which are carried out on extracts of such sampling systems, such as the EPA Level-1 organic analysis ( 4 ) ,should be implemented with care in view of potential interference from DPQ; however, more sophisticated analytical schemes such as EPA Level-2 ( 4 )and selective methods for POM analysis ( 3 )are well capable of taking such interference into consideration. Last, the results of our overall study on the validation of the
We thank R. J. Jakobsen for the IR identification, P. A. Clarke for the NMR confirmation of the structure of DPQ, and P. J. Perry for technical assistance in the program. LITERATURE CITED (1) E. D. Pelllzari, J. E. Bunch, R. E. Beckley, and J. McRae, "Determination of Trace Hazardous Organic Vapor Pollutants in Ambient Atmospheres by Gas Chromatography/MassSpectrometry/Computer", Anal. Chem., 48, 803-7 (1976). (2) W. Bertsch, A. Zlakis, H. M. Liebich, and H. J. Schneider, "Concentration and Analysis of Organic Volatiles in Skylab 4", J. Chromatogr., 99, 673-87 (1974). (3) P. W. Jones, R. D. Giammar, P. E. Strup. and T. B. Stanford, "Efficient Collection of Polycyclic Organic Compounds frm Combustion Effluents", Environ. Sci. Techno/., IO, 806-10 (1976). (4) P. W. Jones and R. J. Jakobsen. Interim Report to EPA on Contract No. 68-02-1409, Task 41, January 9, 1976. (5)P. W. Jones, A. P. Graffeo, P. A. Clarke, R. Detrick, and R. J. Jakobsen, "Technical Manual for Measurement of Organic Materials in Process Streams", €PA Publication No. 600/2-76-072. (6) Electric Power Research Institute Contract No. RP 383-2, Final Report in preparation.
Maynard B. Neher* Peter W. J o n e s Battelle Columbus Laboratories 505 King Avenue Columbus, Ohio 43201
RECEIVEDfor review October 26,1976. Accepted December 10, 1976.
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