filters as seen in Table IV. One can imagine that a difference in the trace-gas composition in the tunnel relative to the ambient air might result in the obvious greater propensity to spurious Eiulfate formation in the ambient case. We have no rationale for the other anomalies in the glass-fiber results. In some of the instances shown in Table IV, the amount of spurious sulfate renders the glass-fiber filter unacceptable not only for sulfate but even for gross mass determination. The strengthened quartz-fiber filter is as bad or worse; spurious sulfate can be seen to have been 64% as much as the true sulfate and 5% as much as the amount of gross particulate matter, by virtue of conversion of 7% of the SO2 to which the filter was exposed. The data suggest that egregious amounts of spurious sulfate are a consequence of filter alkalinity. This should be studied further, IDecause certain procedures (13) for imparting strength to glass- or quartz-fiber filters involve treatment with alkali. Thle filter types that give the most spurious sulfate (Table IV) are also the ones that give aqueous extracts that are alkaline. Summary. We find that the formation of spurious sulfate in filter sampling can be quite minimal or can be quite extensive. It has to do primarily with the filter medium and not the aerosol deposit. The amount formed depends very much on the type of filter. Of the types evaluated, poly(tetraflu0roethylene) membrane and pH-neutral qnartz fiber filters are the best. At least in the case of the latter type of filter, a saturation effect seems to exist so that, given the opportunity for a sufficiently long sampling period, the error relative to the true sulfate can be brought within bounds.
ACKNOWLEDGMENT We thank William H. Sherlock, former Executive Director, Pennsylvania Turnpike Commission, and the many members of his organization who helped us in carrying out these ex-
periments. We also thank Douglas E. McKee, of the Ford Research Staff, for his assistance with the experiments.
LITERATURE CITED (1) R. E. Lee, Jr., and J. Wagman, J. Am. lnd. Hyg. Assoc., 27, 266-271 (1966). (2) J. W. Coffer, "SO2 Oxidation to Sulfate on a High Volume Air Sampler", M.S.E. Thesis, University of Washington, 1974; J. W. Coffer, C. McJilton, and R. J. Charison, Paper No. 102, Division of Analytical Chemistry, American Chemical Society, 167th National Meeting, Los Angeles, Calif., April 3, 1974. (3) W. R. Pierson and W. W. Brachaczek. Rubber Chem. Technol.. 47, 1275-1299 (1974). (4) W. R. Pierson and W. W. Brachaczek, "Alrborne Particulate Debris from Rubber Tires", in Proceedings of Conference on Environmental Aspects of Chemical Use in Rubber Processing Operations (Akron, Ohio, March 12-14, 1975), Franklin A. Ayer, compiler, EPA-560/1-75-002 (Office of Toxic Substances, U S . Environmental Protection Agency, July 1975), pp 217-273,306-311, (5) W. R. Pierson and W. W. Brachaczek, J. Air Pollut. Control Assoc., 25, 404-405 (1975). (6) W. R. Pierson and W. W. Brachaczek, Paper 760039 presented at SAE Automotive Engineering Congress, Detroit, Mich., February 1976. (7) J. S. Fritz and S . S . Yamamura, Anal. Chem., 27, 1461 (1955). (8) R. S.Fielder and C. H. Morgan, Anal. Chim. Acta, 23, 538 (1960). (9) J. W. Butler and D. N. Locke, J. Environ. Sci. Health-€nviron. Sci. Eng., A l l , 79 (1976). (10) 0. Samuelson, "Ion Exchange Separations in Analytical Chemistry", John Wiley 8. Sons, New York, 1963, pp 247-249. (11) A. L. Cohen, Environ. Sci. Technol., 7, 60-61 (1973). (12) M. W. First, Environ. Sci. Technol., 7, 181 (1973). (13) A. L. Benson, P. L. Levins, A. A. Massucco, D. B. Sparrow, and J. R. Vaientine, J. Air Pollut. Control Assoc., 25, 274-277 (1975).
William R. Pierson* Robert H. Hammerle Wanda W. Brachaczek Ford Motor Company Research Staff P. 0. Box 2053 Dearborn, Mich. 48121 RECEIVEDfor review February 18, 1976. Accepted July 6, 1976.
Modified Buffer for Use with Fluoride-Selective Electrodes Sir: Thle addition of a total-ionic strength buffer (TISB) containing Na salts (1.9 M) to solutions when estimating Fusing a fluoride-selective electrode is now a well-established procedure (1).The purposes of this buffer are: (i) to provide a background of high-ionic strength, (ii) to adjust the pH, (iii) to release any fluoride bound to metals by the inclusion of a stronger complexing agent (trans-1,2-diaminocyclohexaneN,N,N',N'-tetraacetic acid (CDTA)). However, several workers (2-4)have measured association between Na+ and F- and their results would suggest the formation of an appreciable concentration of NaFO in TISB, thus partially negating some of the decomplexing function. The degree of association between K+ and F- is much less than with the Na salt (2) so that replacement of Na salts by K salts in TISB should be an improvement. To assess the degree of ion-pairing, measurements were made with an Orion Research Inc. fluoride-selective electrode (94-90) and double-junction reference (90-02-00) 3.5 M KC1 in outer compartment, immersed in TISB macle to the following compositions:XC1= 1.0 M, acetic acid = 0.25 M, X acetate = 0.75 M, CDTA = 0.011 M, with X = Na or E; buffers were mixed with an equal volume of NaF solutions to give concentrations 5 X 10-7-5 X 10-3 M. Other measurements were also made in solutions 5 X lod4M without buffer but containing 4 M NaCl or KC1 because it should be easier to detect ion-pairing a t these high concentrations.
For concentrations 5 X 10-5-5 X M NaF, an excellent fit to the Nernst equation was found with both buffers (see Figure 1).There was a shift between the two lines with EN^ - E K = 6.0 f 0.4 mV. A larger difference was observed between the emf's in 4 M NaCl and KC1 with EN^ - E K = 19.7 f 0.4 mV. The sign of these differences is consistent with greater ion-pairing in the Na salt solutions than in the K salt solutions. By making some reasonable assumptions about activity coefficients, the magnitude of these differences can be shown to be in agreement with previous estimates of association constant and suggest that 15-20% of total fluoride is present as NaFO in TISB prepared from Na salts. Measurements made at concentrations below 5 X 10-5 M were of lower precision because of slow equilibration of the electrode. The time to reach a slow drift (0.1 mV/5 min) often exceeded 30 min and there was no significant difference between the Na and K buffers in this respect. Omission of CDTA from the buffers did not reduce this time markedly. At concentrations below 5 X M in the Na buffer, the results deviated from the linear graph (see Figure 1).This deviation was much less for results from the K buffer. Other workers have noted a similar nonlinearity using TISB and have attributed the effect to the presence of F as an impurity in the buffer salts ( 5 , 6 ) . To estimate the impurities, measurements were made in buffers diluted with an equal volume of water not containing
ANALYTICAL CHEMISTRY, VOL. 48. NO. 12, OCTOBER 1976
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centrations, the linear region of the graph was extended down to M. Although a generalization cannot be made on the basis of results with one batch of salts, it may be noted that Mesmer ( 6 )in a similar experiment found less F in 1M KC1 than in 1 M NaCl. It follows from this comparison that in order to avoid possible complications from ion-pairing and to be consistent with the use of KF as primary standard ( 2 ) that TISB or other high-ionic strength solutions be prepared from K salts rather than Na salts. As a possible additional benefit from this change, K salts may introduce lower F impurity than Na salts resulting in an extended linear calibration and reduction in the minimum detectable concentration. LITERATURE CITED 10"
166 NaF
105 concentration m o l e w l i t r e
Flgure 1. Emf vs. log(NaF concentratlon mol/l.) for N a and K buffers All polnts from the K buffer have been dlsplaced 00 mV downward for greater M NaF for whlch clarlty. (0)Experlmental polnts; (0)points in the reglon the nomlnal concentratlons have been corrected for the presence of F lmpurlty In the buffer
intentionally-added F. By extrapolation of the linear portion of the graphs values of 4 X 10-6 and 1X 10-6 M were derived as the contributions from impurities in the Na and K buffers, respectively. When correction was made to the nominal con-
(1) J. E. Harwood, Water Res., 3,273 (1969). (2) R. A. Roblnson, W. C. Duer, and R. G. Bates, Anal. Chem., 43, 1802 (197 1)(3) W. C. Duer, R. C. Roblnson,and R. G. Bates, J. Chem. SOC.,Faraday Trans.. 7, 68, 710 (1972). (4) J. N. Butler and R. Huston, Anal. Chem., 42, 1300 (1970). (6) M. S. Frant and J. W. Ross, Anal. Chem., 40, 1189 (1988). (0) R. E. Mesmer, Anal. Chem., 40, 443 (1908).
J. Bagg Department of Industrial Science University of Melbourne Parkville, Victoria 3062 Australia
RECEIVEDfor review May 3,1976. Accepted June 30,1976.
Chromatographic Analysis of Gaseous Products from Pyrolysis of Organic Wastes with a Single Column Sir: The operation and optimization of a pilot plant at which organic wastes, such as wood shavings, solid municipal waste, or rice hulls are pyrolyzed requires a method of analysis of the gaseous products, The gases detected were Hz, Nz, CO, COz, HzO,CH4, CzH4, CzH6, C6H6, and C7Hs. Our objective was to obtain a method of determination for these gases as simply and rapidly as possible. A search of the literature failed to show a simple separation of this particular combination of gases. Hollis and Hayes (1) showed that Hz, Nz,Oz, Ar, and CO could be separated at -78 "C on a Porapak Q column. In the same paper, they indicated that the column could also separate Hz,air, CO, CH4, COz, CzH4, CzHa, and HzO in that order at room temperature. This separation was made by Cross ( 2 ) .Papic (3) later separated C1 through C4 hydrocarbons, also on a column of Porapak Q. Many people have combined columns to achieve better separations (4-7). Stufkens and Bogaard (8)made a separation of Nz, 02,COz, CzHe and heavier hydrocarbons, including and C7H8 using a Porapak R column operated between -10 "C and 230 "C. This correspondence describes a method whereby the above mentioned gases may be separated for determination employing a single column. EXPERIMENTAL Apparatus. A Hewlett-Packard 5750 gas chromatograph equipped with temperature programming and a 0.5-ml gas sampling valve was used. The dual stainless steel columns (10ft X %in.id.) were packed with 50-80 mesh Porapak QS and modified with 2% terephthalic 1812
ANALYTICAL CHEMISTRY, VOL. 48,
NO. 12,
acid. Method. The separation was carried out as follows: prior to sample injection, the oven was cooled to room temperature (-26 "C).This was best achieved by opening the oven door and leaving it open
Table I. Analytical Conditions Sample Size : Column Length: Diameter: Material : Packing : Packing size: Packing modifier: Carrier gas: Temperatures Column:
0.5 ml
10 ft l/o-in. i.d. Stainless steel Porapak QS 50-80 mesh 2% Terephthalic acid Helium
Room temperature (- 26 "C) t o 200 "C Primary isothermal period: 2 min 60 "C/min Programming rate : Final isothermal rate: Balance of analysis 230 "C Injection port: 260 "C Detector: Sample loop: Room temperature ( - 26 "C) Recorder Chart speed : 2.00 in./min for 4 min 0.25 in./min for balance Detector Type : Thermal conductivity Bridge current: 160 mA
OCTOBER 1976
