Anal. Chem. 1984, 56,1037-1039
al-SCR chelates and the color changes with freed SCR at the spots would become obscured. Such concentration limits of metal ions measured with chloride anions are shown in Table I1 for detecting EDTA and NTA. Only Na(1) ions did not disturb the detections up to 0.8 M within our experimental limit, but chloride counterions of more than 0.2 M caused tailing of the spots for EDTA from NTA. Similar tailing effects were also found for sulfate and nitrate anions of more than 0.2 M each and for oxalate anions of more than 0.05 M. Because of such probable tailings, Fitzgerald's addition of HCI to HCOOH to resolve DTPA from EDTA and NTA (1) was somewhat questionable. We could do this without HC1 as mentioned. Some other analytical applications of the proposed Cu(11)-SCR system have been under study in our laboratory (4, 5 ) and will be reported.
1037
ACKNOWLEDGMENT We thank Y. Yokoyama for his drawings of all the figures in this paper. Registry No. IDA, 142-73-4;NTA, 139-13-9;HEDTA, 489678-0; EDTA, 60-00-4; GEDTA, 67-42-5; CyDTA, 13291-61-7; DTPA, 67-43-6.
LITERATURE CITED (1) Fltzgerald, E. A. Anal. Chem. 1975, 4 7 , 356-357. (2) Matsuo, T.; Shida, J.; Sato, S. Jpn. Anal. 1971, 20,693-697. (3) Korbl, J.; Svoboda, V.; Terzljski, D.; Pribll. R. Chem. Ind. (DuesseldOH) 1957, 1624-1625. (4) Matsuoka, S. Master's Thesis, Faculty of Engineering, Yokohama National University, 1982. (5) Momoki, K.; Kaneko, T., unpublished work.
RECEIVED for review November 16,1983. Accepted January 30, 1984.
Analysis of Atmospheric Aerosols by Nonsuppressed Ion Chromatography M. J. Willison and A. G. Clarke* Department of Fuel and Energy, Leeds University, Leeds LS2.9JT, United Kingdom Ion chromatography has become the standard method of analysis for simple inorganic anions in many types of environmental sample. Common examples include river waters, precipitation, and atmospheric particulate matter collected by filtration. The value of ion chromatography for the analysis of atmospheric aerosols was first demonstrated by Mulik et al. (I) and was discussed in several of the papers presented at the second symposium on Ion Chromatographic Analysis of Environmental Pollutants (2). By use of Hi-Vol samplers relatively large amounts of collected aerosol are available for analysis. However with the more recent dichotomous samplers, with flow rates of about 1m3/h, the mass of collected aerosol may be only a few hundred micrograms. In terms of the mass of sulfate, nitrate, and chloride the range may be from over 100 pg to less than 10 pg per filter and after extraction the concentrations may be as low as 1ppm. While larger laboratories can justify the investment in the commercially available systems (e.g., Dionex) there is a strong incentive for smaller laboratories to adapt already available HPLC instrumentation as a low cost alternative for ion chromatography. This paper summarizes the performance of one such system developed of necessity when wet chemical methods became inadequate for the required analyses. The experimental system utilizes a Vydac 302 I.C. column with low conductivity buffered eluents. No suppressor column is needed with this approach as with the carbonate/bicarbonate eluents used in the Dionex system. The characteristics of the Vydac column have been fairly well established from previous studies (3, 4 ) and its use for the analysis of aqueous samples has been discussed in other recent publications (5, 6). Although nonsuppressed ion chromatography may be slightly poorer in detection limits than the suppressed approach, it is adequate for many applications and has proved perfectly satisfactory for aerosol analyses. To date nearly 1500 filter samples have been analyzed for sulfate, nitrate, and chloride levels forming one of the largest sets of data yet obtained for aerosol composition in the U.K. Details of this
survey are presented elsewhere (7).
EXPERIMENTAL SECTION Sampling. Aerosol samples were collected on dried and preweighed polypropylene-backed Teflon filters by using Sierra Model 245 automatic dichotomous samplers. These samplers fractionate the aerosol according to size, into fine (C2.5 pm) and coarse (2.5-15 pm) fractions. Daily 24-h samples were taken simultaneously at an urban (University rooftop) and a rural site (7 km west of Harrogate and 20 km north of Leeds, Yorkshire, U.K.). Analysis. Apparatus. The chromatographic system comprises a guard column (Vydac SC 30-40 pm pellicular packing, 5 cm X 2.5 mm i.d., Separations Group), a low capacity silica pellicular anion exchange column (Vydac 302 IC, 25 cm X 4.6 mm i.d., Separations Group), and a conductivity detector (Laboratory Data Control, Model 701). Eluent is pumped at 2 mL/min through the system by a Beckman llOA pump fitted with a pulse dampener. Samples (100 pL) are injected onto the column via a sample loop and Rheodyne 7125 injection value. The output from the detecter is fed simultaneously to a chart recorder and an integrator. Since the electrical conductivity of the solutions is strongly temperature dependent, good temperature stability is essential. Rather than establish positive temperature control at, for example, 30 "C as has been done by some authors (4),the system has been maintained at room temperature (20 "C). The injection valve, columns, and detector head are all mounted in a well-insulated, draft-proof Perspex box. This minimizes base line noise due to rapid temperature fluctuations but does not prevent an overall base line drift if the temperature of the room changes markedly. The detector was operated in the absolute mode in which temperature compensation at 2.5% per OC is made automatically. An alternative differential mode is available with the L.D.C. instrument using pure eluent in a reference conductivity cell adjacent to the sample cell. Temperature compensation should be achieved with this arrangement and in principle a higher detector response to small conductivity changes is possible. In practice poor base line stability was found in the differential mode and it was not used for any of the experiments described in this article. Reagents. All chemicals were analytical reagent grade (BDH Anal&) unless otherwise stated. All solutions were prepared with
0003-2700/64/0356-1037$01.50/00 1984 American Chemical Society
1038
ANALYTICAL CHEMISTRY, VOL. 56, NO. 6, MAY 1984 150-
Table I. Effect of Eluent p H on Retention Time (min) PH
c1-
NO 3-
so,>-
5 5.5 6
4.1
6.0 5.2 5.0
19.4
,E..
13.3
-100-
10.9
tI
3.7 3.4
E
2 W
I Y
2
50-
n
I
5
10 15 C O N C E N T R A T I O N (pprn)
20
Figure 2. Concentration (ppm) vs. peak height (mm) for CI-, NO3-, and
so42-.
C O N C E N T R A T I O N (pprn)
Figure 1. Concentration (ppm) vs. peak area (arbitrary units) for Cl-, NO,-, and SO:-. Milli R/Q (Millipore Corp.) purified water. Eluent. Stock phthalic acid solution (0.02 M, BDH general purpose reagent) was diluted and the appropriate volume of 0.1 N sodium tetraborate solution added to give the required pH. The eluent was degassed under vacuum immediately prior to use. The retention time is inversely proportional to the eluent concentration so a balance must be struck between good resolution of the earlier peaks (Cl-, NO;) and an unduly long retention time M phthalate was found to be for sulfate. In practice 1 X satisfactory. The alternative eluents sometimes used in single column ion chromatography are benzoic acid or benzoates (8). However the monobasic benzoate ion is not effective in displacing strongly bound ions such as sulfate from the resin and gives unacceptably long retention times. Although there is a theoretical improvement in detection limits in using benzoic acid rather than phthalic acid it is of no value for sulfate analyses. Standards. All reagents (NaC1, NaN03, Na2S04,NaN02,Nal3r) were dried under vacuum before use. Stock solutions of standards were diluted with eluent immediately before use to give the appropriate concentration. Filter Extracts. Filters were extracted with eluent (10 mL) by sonication for ca. 45 min. Analysis was carried out as soon as possible after extraction. Where this was not possible, samples were stored at 4 "C. The extraction of the filters with eluent rather than with pure water is necessary to avoid the interference of the "solvent" peak with the chloride peak as discussed later.
RESULTS AND DISCUSSION Choice of pH. The effective eluting species is the doubly charged phthalate anion and increasing the pH raises the concentration of this ion hence reducing the retention time. Optimum conditions The effect is most marked for Sod2-. for the analysis were found with eluent concentration 1 X lo-' M and pH 5. The effect of pH is shown in Table I. As well as affecting retention times the pH was found to affect the shape of the solvent peak. This peak, occurring shortly after injection, consists of eluent anions displaced from the resin by sample anions plus sample cations. A positive peak is obtained at high sample concentrations while the injection of pure water results in a negative peak due to the effect of dilution on the background conductivity. The extraction of filters with eluent always results in a positive peak irrespective of the aerosol concentration. Extraction of the filter with water sometimes results in a pronounced negative solvent peak which interferes with the resolution of the chloride peak. This generally occurs with low aerosol con-
I
I
I
100
I
I
200
!
I
300
N U M B E R OF SAMPLES
Figure 3. Retention time of CI-, NO3-, and SO.,'- vs. the number of samples through the column. centrations. The quantitative interpretation of the solvent peak has been dealt with by Herschovitz et al. (9). Calibration. Calibration was undertaken with mixed C1-, NO3-, and S042-standards. Good linearity was obtained between peak area and concentration over the range 0-20 ppm (Figure 1). Correlation coefficients were >0.99. Good linearity was also obtained with peak height for NO3- and S042(correlation coefficients >0.99) but with C1- (Figure 2) a quadratic fit was more appropriate. Column Degradation. Column degradation is evidenced by a gradual reduction in retention time as shown in Figure 3. The sulfate retention time decreased by 10 min after 300 samples, nitrate by 6-7 min, and chloride by ca. 1min. The reduction in retention time is not important for sulfate, indeed it means a shorter analysis time. However, chloride and nitrate become less well resolved with column age. With a new column it is convenient to use a slightly higher eluent pH of 5.5 to speed up the analysis later switching to pH 5 to maintain adequate resolution. By careful choice of pH it is possible to obtain ca. 600 injections during the lifetime of a column. Attempts have been made to regenerate the column with the intention of improving this separation of the early peaks. Washing the column with M formic acid had no effect. Addition of 2 X M n-tetrabutylammonium hydroxide to the formic acid solution and rewashing the column also had little effect. In fact it resulted in broadening of the nitrate peak. This broadening of the nitrate peak also occurs when n-tetrabutylammonium hydroxide and phoshate eluents are used in the reversed-phase mode (10). Filter Results. A typical chromatogram of a filter extract is shown in Figure 4. All samples contain chloride, nitrate, and sulfate as major components but it is sometimes possible to detect minor peaks attributable to nitrite and bromide. Bromide has its origins in traffic emissions due to the for-
Anal. Chem. 1984, 56, 1039-1041
3
Br-
O.2ppm
4
NO;
12.2ppm
5
50-:
22.5ppm
volume this equates to a detection limit of 1 pg on the filter. This is more than adequate for the concentration of ionic species present in atmospheric aerosols which occur at the two sampling sites even on the least polluted days. Detection limits could be improved if necessary by increasing the injection volume or decreasing the extraction volume. Repeated analysis of a single coarse particle filter sample gave the results shown in (Table 11) in terms of solution concentration (ppm). This indicates that the precision of the analysis is of the order of f2-3%. In conclusion, with a relatively small investment in a conductivity detector and appropriate columns, existing HPLC equipment was adapted to provide a satisfactory ion chromatography system. Application to the analysis of atmospheric aerosols collected on filters requires extraction of the sample with the eluent solution and choice of a suitable pH to give adequate C1-, NO3- resolution while not giving too long a retention time for Sod2-.pH 5 was M phthalate eluent. generally found to be suitable with a The detection limit was about 0.1 ppm or 1 pg of C1-, NOS-, or Sod2on the filter. Registry No. C1-, 16887-00-6; NO3-, 14797-55-8; Sod2-, 14808-79-8.
1
5
I
I
1
I
20
15
10
5
1
0
TIME(rninutes1
Figure 4.
LITERATURE CITED
Chromatogram of fine aerosol filter extract at pH 5.5.
Table 11. Analysis of a Single Coarse Particle Filter Sample
max min mean(N = 10)
1.99 1.86 1.91
NO;, ppm 4.82 4.39 4.59
std dev
0.05
0.14
Cl-, ppm
1039
SO,'-, PP m
0.15
7.30 6.83
7.08
mulation of lead antiknock additives. It seems unlikely that the nitrite originates in the aerosol since analysis of a clean filter from a freshly opened box shows a similar peak corresponding to about 5 wg of N02-/filter. For a 1OO-wL sample and use of the optimum operating conditions, 0.1 ppm can be readily detected. This is equivalent to injecting 10 ng onto the column. For a 10-mL extraction
(1) Mulik, J. D.; Puckett, R.; Wllilams, D.; Sawlcki, E. Anal. Lett. 1976, 9, 653. (2) Sawicki, E., Mulik, J. D., Wittgenstein, E., Eds. "Ion Chromatographic Analysis of Environmental Pollutants"; Ann Arbor Science Publishers: Ann Arbor, MI, 1978; Vol. 1. (3) Harrison, K. and Burge, D.,Paper presented at the Pittsburgh Conference on Applied Spectroscopy; Cleveland, OH, March 1979; Paper 301. (4) Glatz, J. A.; Girard, J. E. J. Chromatogr. Sci. 1982, 2 0 , 266. (5) Dogan, S.; Haerdi, W. Chimia 1981, 35, 339. (6) Girard, J. E.; Glatz, J. A. Am. Lab. (Fairfield, Conn.) 1981, 13 (lo), 26. (7) Clarke, A. G.; Willison, M. J., submitted to Atmos. Envlron. (6) Gjerde, D.J.; Fritz, J. S. Anal. Chem. 1981, 53, 2324. (9) Herschovitz, H.; Yarnltzky, Ch.; Schmuckler, G. J. Chromafogr. 1962, 244, 217. (10) Molnar, I.; Knauer, H.; Wilk, D. J. Cbromatogr. 1980, 201, 225-240.
RECEIVED for review August 25,1983. Resubmitted November 17, 1983. Accepted January 9, 1984. Financial support for this work was provided by the Science and Engineering Research Council in the form of a research grant and a fellowship to M. J. Willison.
Mounting Assembly for Preparation of Electrodes from Totally Insoluble Conducting Polymers Andrzej Czerwinski,' J o h n R. Schrader, a n d H a r r y B. Mark, Jr.* Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221 In the past few years, there has been an increasing interest in the study of surface-modified (1) and polymer electrodes (2). Such exotic electrode materials have significant fundamental properties and have considerable potential for practical applications in electrocatalysis. Very recently, several papers have reported the application of various conducting polymers as electrodes (2). In our laboratory we have been synthesizing a variety of substituted polyacetylenes and polythienylenes for study as electrode materials (3, 4 ) . In cases where the polymer material either is soluble in a nonaqueous solvent or can be obtained in a high density nonporous form, preparing it as an electrode is relatively simple. In the first case, a drop leave from the University of Warsaw, Warsaw, Poland.
of the dissolved polymer solution is placed on a platinum, carbon, or other conducting substrate and the solvent is evaporated (1). In the second case, the polymer material is glued to a metal wire with a silver conducting epoxy cement and the contact area masked with an inert epoxy cement such as Torr Seal (5-7). However, most of the new conducting polymers that have been synthesized in our laboratory are amorphous, highly porous, and totally insoluble in all solvents. Although these materials can be pressed into a pellet, this has presented a major problem in the construction of an electrode for the study of these materials. For example, poly(p-nitrophenylacetylene) is produced as totally insoluble, highly porous hard grains (8). They are easily connected to a metal wire with a conducting silver epoxy and the connection is well
0003-2700/84/0356-1039$01.50/00 1984 American Chemical Society
