780
Anal. Chem. 1985, 57, 780-782
J
-----+-
Flgure 3. Pyrogram of 10 nmol of phenylalanine on a cross-linked OV-1701 capillary column with zero sample split ratio and 0.59 mLlmin column flow. Column oven temperature was held at 0 OC for 2 min, then ramped at 15 OC/min to 220 'C.
temperature. This peak also tails due to slow transfer into the column. Such peak broadening and tailing may make it difficult to separate early eluting components of more complex pyrograms and may also make the accurate determination of peak areas difficult. Pyrogram 2B was obtained by using the modified interface system. The early eluting peak is narrower and more symmetric because of the reduced mixing volume of the interface. Later eluting components of the pyrograms are cold trapped on the column and therefore exhibit narrow and symmetric peaks in both pyrograms. In Figure 2A with the commercial interface, the peak eluting a t about 23 min is diminished in height and area (in comparison to the peak in pyrogram 2B), indicating that the less volatile components are being con-
densed at cold spots in the system. Heating the interface-GC injection port transfer line often eliminates such a problem. The modified interface, with the probe inserted in the GC injection port itself, does not suffer from the problem of cold spots as long as the injection port is kept at an adequately high temperature. As a final note, repeated pyrolysis of polystyrene on both systems indicated that peak heights and areas are much more reproducible using the modified interface (2% relative standard deviation) in comparison to the externally mounted interface (7-9% relative standard deviation). Figure 3 illustrates a pyrogram of phenylalanine obtained using the modified interface with zero split flow and cyrogenic oven temperature programming. These experimental conditions provide maximum sensitivity for all pyrolysates in addition to enhanced resolution for the early eluting components. This combination of experimental techniques may permit structural elucidation by analytical pyrolysis on samples in the nanogram to microgram range.
ACKNOWLEDGMENT The authors thank Matt Przybyciel for preparation of the OV-1701 column. Registry No. Polystyrene, 9003-53-6;phenylalanine, 63-91-2. LITERATURE CITED (1) Levy, R. L. In "Chromatographic Reviews"; Lederer, M., Ed.; Elsevier: Amsterdam, 1966; Vol. 8,pp 48-89. (2) Berezkin, V. G. CRCCrit. Rev. Anal. Chem. 1981, 1 1 , 1-18. (3) Jacques, C. A.; Morgan, S. L. J . Chromatogr. Sci. 1080, 18, 6 7 9-6 83. (4) Simon, W.; Glacobbo, H. Angew. Chem., I n t . Ed. Engl. 1965, 4 , 936-943. (5) Levy, R. L. J . Gas Chromatogr. 1967, 5 , 107-113. (6) Irwin, W. J. "Analytical Pyrolysis, A Comprehenslve Guide"; Marcel Dekker: New York, 1982; p 50. (7) Morgan, S. L.; Jacques, C. A. Ana/. Chem. 1982, 5 4 , 741-747. (8) Hudson, J. R.; Morgan, S. L.; Fox, A. Anal. Biochem. 1982, 120, 59-65.
RECEIVEDfor review September 10,1984. Accepted November 5,1984. This work was supported in part by NIH Grant No. 27135. The donation of a gas chromatographic instrument by Hewlett-Packard (Palo Alto, CA) is gratefully acknowledged.
Anion Contamination of Environmental Water Samples Introduced by Filter Media P.C. Jay Environmental Research Branch, Atomic Energy of Canada Limited, Chalk River Nuclear Laboratories, Chalk River, Ontario, Canada KOJ 1JO During measurement of the anion content of surface water and groundwater, contamination can occur from leachable anions present in membrane-type filter media used in the process of filtering samples. Cation contamination of environmental water samples, due to filtration, is well established in the literature. Robertson ( 1 ) has shown that many types of filter materials contain significant levels of metallic impurities that can contaminate solutions during the filtration process. Apart from C1-, he did not report on other anion impurities in these materials. Kosta (2) in an otherwise extensive review of contamination as a limiting parameter, reports only that major contaminants such as chloride and sodium may exceed the 1 Pg/cm2 level in filters based on cellulose esters (Millipore). Other workers ( 3 , 4 )have shown C1-, Br-, NO;, and SO-: contamination from specific filters
but there is no report that surveys the leachable anion content of those membrane-type filters commonly used in water analyses. The work reported here shows that filters from several manufacturers contain considerable amounts of leachable anions and that if such filters are used without careful prewashing, inaccurate data will result.
EXPERIMENTAL SECTION An ion chromatograph with eluent suppression [ICES] coupled to a Hewlett-Packard HP3390A reporting integrator was used to determine the content ofleachates obtained from deionized distilled water (DDW) washesof types of membrane filters. The ICES system was an extensively modified Dionex 10 ion chromatograph with a hollow-fiber suppressor (5). A 0.003 M NaHC03/0.0024 M Na2C03eluent and a 0.050 M H2S04regenerant was used throughout this work. With a 100 p L sample
0003-2700/85/0357-0780$01.50/0 Published 1985 by the American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985
Table I. Leachable Anion Content of Membrane Filters” filter type
F-
C1-
Millipore SSWP 3 pm, 47 mm Millipore RAWP 1.2 pm, 47 mm Millipore HAWP 0.45 pm, 47 mm Millipore VCWP 100 pm, 47 mm Millipore GSWP 0.22 pm, 47 mm Millipore SCWP, 8 pm, 47 mm Gelman GA-8 0.2 pm, 47 mm Gelman GA-6 0.45 pm, 47 mm Gelman GA-3 1.2 pm, 47 mm Gelman GA-1 5.0 pm, 47 mm Gelman Tuffryn HT-100 0.1 pm, 25 mm Gelman Tuffryn Glass Fibre A-E 47 mm Gelman Tuffryn GN-6 0.45 pm, 47 mm Whatman GF/F microfibre 1.6 pm, 47 mm Nucleopore Membra-fil 0.45 pm, 25 mm Nuclepore Polycarbonate 0.4 pm, 25 mm 0.2 pm, 25 mm 0.1 pm, 25 mm DDW
1.0
11.2
1.0 21.7
8.7
4.6
8.8
