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Anal. Chem. 1984, 56, 1035-1037
AIDS FOR ANALYTICAL CHEMISTS Copper( 11)-Sarcosine Cresol Red for Detection of Chelants after Separation by Thin-Layer Chromatography Kozo Momoki* a n d Hirokatsu Katano
Laboratory for Industrial Analytical Chemistry, Yokohama National University, Hodogaya-ku, Yokohama 240, Japan Although studies of thin-layer chromatography (TLC) of metal-chelant chelates have been attempted previously, only Fitzgerald (I) has reported direct TLC identification of chelants themselves, However, he could barely separate some chelants with varied mobile phases. We checked the technique and found that his detection system was neither simple nor sensitive. Fitzgerald found separation with DEAE-cellulose in formic acid media suitable for chelants. Fitzgerald employed decoloration of Ni(I1)-dimethylglyoxime (DMG) by the presence of chelants for the detection. Three additions of Ni(II), NH, vapor, and DMG successively to the TLC plate were tediously needed. In addition, white spots on pink background had to be observed visually but were not clearly distiguishable. Furthermore, most conditional formation constants of the Ni(I1)-chelants involved were calculated as less than that of Ni(I1)-DMG. Thus, great quantities of chelants were required for the detection. Because of the detection system, his TLC method would suffer from a reduced applicability. In this paper, we propose an improved detection system applied to the TLC separation with DEAE-cellulose in formic acid media. A simple one-shot spraying reagent which can be used sensitively in an acidic pH range in accord with the acidic separation is presented. The new reagent is Cu(I1)Sarcosine Cresol Red (2)which was 1or 2 orders of magnitude more sensitive than Ni(I1)-DMG depending on the seven chelants presently identified. The seven chelants were iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), N hydroxyethylenediamine-N,N’,N’-triaceticacid (HEDTA), ethylenediaminetetraacetic(EDTA), (glycol ether)diamineN,N,N‘,N’-tetraacetic acid (GEDTA), trans-1,2-cyclohexanediamine-N,N,N’,N’-tetraaceticacid (CyDTA), and diethylenetriamine-N,N,”,N”,”’-pentaacetic acid (DTPA). Some effects affecting the separation or the detection were also studied. EXPERIMENTAL SECTION Materials. Disodium EDTA dihydrate from Wako Pure Chem. Inds., Ltd., Osaka, IDA and GEDTA from Dojin Labs., Kumamoto, and disodium NTA, HEDTA, CyDTA, and DTPA from Tokyo Kasei Kogyo Co., Ltd., Tokyo, were purchased. DEAE-cellulose of Serva Feinbiochemica obtained through Seikagaku Kogyo Co., Ltd., Tokyo, were used throughout, Sarcosine Cresol Red (SCR), 3,3’-bis(N-methyl-N-carboxymethylaminomethyl)-o-cresolsulfonphthalein(31, was obtained from Dojin Labs., Kumamoto. Water and methanol were distilled before use. Other reagents were of analytical grade and used without further purification. TLC Plates. The DEAE-cellulose was converted to formic acid form and spread manually to 0.15-2.20 mm thickness of glass plates of 200 mm X 50 mm by using a homemade applicator. The plates were dried in an air bath at 60 O C for 2 h before use. One-Shot Spraying Solution. SCR (mol w t 606.6) and Cu(I1) sulfate in the mole ratio of 1:2 were dissolved into an aqueous solution which was then brought to pH 5.0 with the acetate buffer. Immediately before use, the solution was added with a 40% 0003-2700/84/0356-1035$0 1.50/0
Table I. Minimum Amounts and Concentrations in the Initial 1.5 p L Sample Spots of the Complexanes Suitable for TLC Detection amount,‘ complexane IDA NTA HEDTA EDTA GEDTA CyDTA DTPA
concentration %a mM
w/v
1.5 0.45 0.75 1.2 0.75 1.5 0.75
0.10 0.03 0.05
0.08 0.05 0.10 0.05
3.8 1.6 3.6 2.2 1.3 2.7 1.3
Can be compared with 60 pg and 2%, respectively, in 3 rL spots by Fitzgerald ( 1 ) . a
volume of methanol. The mixture, which was adjusted to 2.0 X M SCR, was used as the one-shot spraying solution. TLC Procedure. A 1.5-pL portion of the sample chelant solution was spotted with a 5-pL Hamilton microsyringe and developed until a mobile phase front traveled 6.0 cm from the initial spot. The mobile phase was formic acid aqueous solution. After development, the plate was dried with a hot air gun and sprayed with the above solution. R E S U L T S AND DISCUSSION The present detection is based on the dissociation of Cu(11)-SCR chelate to Cu(I1)-chelant and SCR by the presence of the chelant to be identified. Matsuo et al. (2)reported the spectrophotometric determination of copper by using Cu(11)-SCR 1:l chelate formation at pH 5.0 with the absorption maximum at 570 nm against 430 nm for SCR. Matsuoka ( 4 ) recently estimated the conditional formation constant of the chelate to be about 106.4from the mole ratio plot, although the plot seemed to contain some other chelate(s) besides 1:l. The corresponding constants calculated for the seven chelants were larger than 108,gfor Cu(I1)-NTA except for the 1O6.O for Cu(I1)-IDA. Thus, the Cu(I1)-SCR spraying solution was expected to work well for the present one-shot detection of acid separated chelant spots. In fact, the TLC became simple and sensitive. Yellow spots on purple background were clearly observed. Even IDA, expected to be difficult from the above constant values, could be detected easily when SCR and Cu(I1) were mixed in a 1:2 mole ratio in the spraying solution. Fitzgerald ( I ) spotted 3-pL portions of 2% sample solutions, giving rise to 60 hg for each chelant. We needed the most suitable 1.5-pL portions of these chelant solutions adjusted to appropriate concentrations. Thus, at the minimums, we could detect 40-130 times smaller amounts or 30-100 times smaller concentrations of the chelants than those detected by Fitzgerald, as shown in Table I. Figure 1shows the typical TLC results of the seven chelants with 0.3 M HCOOH (Figure la) and 1.5 M HCOOH (Figure lb) as the mobile phase. The separated spots with 0.3 M 0 1984 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 56, NO. 6, MAY 1984 0 1
b;*
u 3
(a)
(b)
Figure 1. Thin-layer chromatogram of seven chelants: mobile phase, (a) 0.3 M HCOOH, (b) 1.5 M HCOOH; chelants, (1)IDA, (2) HEDTA, (3)CyDTA, (4)GEDTA, (5) EDTA, (6) DTPA, (7) NTA.
-0
20
40
60
80
100
Nonchorged Species, %
Figure 3. R, vs. relative molar ratlos of noncharged species to all the species produced from each cheiant: (0)EDTA, 2.2 mM; (A)NTA, 1.6mM; (0) GEDTA, 1.3 mM; (A)CyDTA, 2.7 mM; (0)DTPA, 1.3mM: (0)HEDTA, 3.6 mM; (V)IDA, 3.8 mM.
EDTA(2,2 rnM)
0
1,o
2.0
3.0
[HCOOHI, M
Figure 2. R,vs. formic acid concentrations in the mobile phase: (0) EDTA, 2.2 mM; (A)NTA, 1.6 mM.
HCOOH are seen to be generally larger than those with 1.5 M HCOOH. Although too much broadening or tailing of the spots was seldom experienced, we preferred 1.5 M HCOOH, giving the sharper separations. The measured Rf values of IDA, HEDTA, CyDTA, GEDTA, EDTA, DTPA, and NTA were 0.74,0.72,0.52,0.22,0.20,0.13, and 0.07, respectively, with 0.3 M HCOOH and 0.94,0.95,0.91, 0.74, 0.60, 0.68, and 0.27, respectively, with 1.5 M HCOOH. These values were the average of at least five replicates. The standard deviations of the Rf values measured for EDTA and NTA from the 20 plates were within 0.02-0.03 Rf units. The above results suggested that the Rf value of each chelant would increase with increasing concentration of HCOOH in the mobile phase. Figure 2 was obtained for EDTA and NTA. Also, the resolution of R, between these two spots became better with the more concentrated HCOOH solutions as shown. The abscissa of Figure 2 could be converted simply to a scale of decreasing pH or increasing ionic strength with increasing concentrations of HCOOH. Thus, pH or ionic strength of the mobile phase can vary the Rf values as shown in Figure 2. Instead, we found that these Rf values were dependent primarily on the calculated relative mole ratios of the noncharged (fully protonated) species to all the species produced from each chelant (Figure 3). However, this result would be of natural consequence from the fact that we used DEAE-cellulose anion exchanger as the stationary phase. In the application studies, the chelants added to tap water gave almost the same TLC results as above, suggesting that slight impurities in tap water did not affect the separation nor detection. Addition of more amounts of metal chlorides slightly increased the Rf values of fixed EDTA and NTA. The increases would come mainly from the increases not of metal
I
o'21 01
0
20
40
60
80
[CI-I, mM
Figure 4. R,vs. chloride ion concentrations added as metal chlorides: (0) Na(1);(A) KU); (0) Ca(I1);(VIMg(I1); ( 0 )AI(II1); ( 0 )Mn(I1); ( + I Pb(I1).
Table 11. Maximum Concentrations of Coexisting Metal Ions Permitting Color Changes of EDTA and NTA Spots metal ion WI)
Mg( 111 Ca(11) Mn( 11)
Pb(I1) Al( 111) Fe(111)
maximum concn, M EDTA spot NTA spot 0.8 0.1
0.8 0.1
0.06 0.06 0.001 0.02 0.001
0.2 0.3 0.2 0.002 0.002
ions but of chloride anions in accord with the above anionexchange mechanism (Figure 4). However, some concomitant metal-complex formations by metal ions might also occur and affect the TLC results. Some noncharged chelates if formed with the sample chelants would move the spots further than anions did, as probably in the cases of Pb(I1) and Al(II1) in Figure 4. On the other hand, too much metal ion in the initial samples could form met-
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, i t 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-backedTeflon 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 chromatographicsystem 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 conductivitydetector (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
