Anal. Chem. 1986, 58, 2602-2606
2602
The aluminum LOD was 2 orders of magnitude worse than that for electrothermal atomic absorption spectrometry. Part of the reason was due to the closeness of the excitation and fluorescence wavelengths as previously discussed. Another problem with A1 was that it has a low volatility. The AA detection limits were carried out in a tube furnace, which provided much better atomization conditions, because of the semienclosed design. The fluorescence detection limits could have been improved if the atomization had been carried out in an enclosed furnace. In all of these cases, the detection limits may be improved by use of an enclosed cuvette. Dittrich and Stark (9) found an improvement in sensitivity of 1-3 orders of magnitude with a carbon tube rather than a carbon cup; this improvement was a result of the higher temperatures inside the carbon tube as well as to the confinement of the atomic vapor within the region of excitation. Also, more laser shots would occur while the atoms were present, resulting in amount of analyte.
a
larger signal for
a
(5) Bolshov, M. A.; Zybin, A. V.; Smirenkina, I. I. Spectrochim. Acta, Part B 1981, 36B, 1143. (6) Human, H. G. C.; Omenetto, N.; Cavalli, P.; Rossi, G. Spectrochim. Acta, Part B 1984, 39B, 1345. (7) Tilch, J.; Falk, H.; Paetzold, H. J.; Mon, P. G.; Schmidt, K. P. Colloquium Spectroscopium Internationale XXIV, FRG, Sept 15-21, 1985. (8) Arkhangelsky, B. V.; Gonchakov, A. S.; Grazhulene, S. S. Colloquium Spectroscopium Internationale XXIV, FRG, Sept 15-21, 1985. (9) Dittrich, K.; Stark, H. J. Colloquium Spectroscopium Internationale XXIV, FRG, Sept 15-21, 1985. (10) Massmann, H. Spectrochim. Acta, Part B 1968, 23B, 215. (11) L’vov, B. V. Spectrochim. Acta, Part B 1969, 24B, 53. (12) Manning, D. C.; Ediger, R. D. At. Absorpt. News/. 1976, 15 , 421. (13) Sturgeon, R. E.; Chakrabartl, C. L. Anal. Chem. 1977, 49, 90. (14) Zatka, V. J. Anal. Chem. 1978, 50, 538. (15) Manning, D. C.; Slavin, W. Anal. Chem. 1978, 50, 1234. (16) Renshaw, G. D. At. Absorpt. Newsl. 1973, 12, 158. (17) L'vov, B. V.; Pelleva, L. A. Can. J. Spectrosc. 1978, 23, 1. (18) Gregoire, D. C.; Chakrabartl, C. L. Spectrochim. Acta, Part B 1982,
37B, 11.
(19) Bratzel, . P.; Dagnall, R. M.; Winefordner, J. D. Anal. Chim. Acta 1989, 48, 197. (20) Cantle, J. E.; West, T. S. Talanta 1973, 20, 459. (21) Amos, M. D.; Bennet, P. A.; Brodie, K. G.; Lung, P. W, Y.; Matousek, J. P. Anal. Chem. 1971, 43, 211. (22) Pan, C. L; Prodan, J. V.; Falrbank, W. M„ Jr.; She, C. Y. Opt. Lett. 1980, 5, 459. (23) Greenlees, G. W.; Clark, D. L.; Kaufman, S. L.; Lewis, D. A.; Tonn, J. F.; Broadhurst, J. H. Opt. Commun. 1977, 23, 236. (24) Smith, B. W.; Parsons, M. L. J. Chem. Educ. 1973, 50, 679. (25) L'vov, B. V. Atomic Absorption Spectrochemlcai Analysis·, translated by Dixon, J. K; Adam Hllger, Ltd.: London, 1970. (26) Rayson, G. D.; Holcombe, J. A. Anal. Chim. Acta 1982, 136, 249. (27) Sturgeon, R. E.; Chakrabartl, C. L. Prog. Anal. At. Spectrosc. 1978,
given
Registry No. Pb, 7439-92-1; Cu, 7440-50-8; Mn, 7439-96-5; Sn, 7440-31-5; Al, 7429-90-5; In, 7440-74-6; Li, 7439-93-2; Pt, 7440-06-4; Ta, 7440-25-7; tantalum carbide, 51680-51-4; graphite, 7782-42-5; steel, 12597-69-2.
LITERATURE CITED (1) (2)
(3) (4)
1, 11.
(28) Winefordner, J. D. J. Chem. Educ. 1978, 55, 72.
Neumann, S.; Kriese, M. Spectrochim. Acta, Part B 1974, 29B, 127, Bolshov, . A.; Zybin, Z. V.; Zyblna, L. A.; Koloshnlkov, V. G. Majorov, I. A. Spectrochim. Acta, Part B 1976, 31B, 493. Hohimer, J. P.; Hargis, P. J., Jr. Appl. Phys. Lett. 1977, 30, 344. Bolshov, . A.; Zybin, A. V.; Koloshnlkov, V. G.; Vasnetsov, . V. Spectrochim. Acta, Part B 1981, 36B, 345.
Received for review November 18,1985. Resubmitted June 9,1986. Accepted June 26,1986. This research was supported by AFOSR-86-0015.
Determination of Chromium(III), Titanium, Vanadium, Iron(III), and Aluminum by Inductively Coupled Plasma Atomic Emission Spectrometry with an On-Line Preconcentrating Ion-Exchange Column Shizuko Hirata,* Yoshimi Umezaki, and Masahiko Ikeda1 Department of Environmental Chemistry, Government Industrial Research Institute, Chugoku, 15000 Hiro-machi, Kure 737-01, Japan
Inductively coupled plasma atomic emission spectrometry (ICP-AES) is widely used for the determination of trace metals in environmental samples. Although it is very sensitive, it sometimes suffers from the lack of sensitivity for the determination of trace metals. Recently on-line ion-exchange preconcentrating methods for flame atomic absorption spectrometry (AAS) (1-6) or ICP-AES (7-10) have been reported, and they are capable of improving the detection limit by 1 or 2 orders of magnitude, with the additional advantage of being rapid and separating the analyte from an interfering
A method utilizing a miniature Ion-exchange column of Muromac A-1 (Muromachl Chemicals, Tokyo) has been developed to Increase the sensitivity for aluminum, chromlum( III), fron(III), titanium, and vanadium measurements by Inductively coupled plasma atomic emission spectrometry (ICPAES). A sample (pH 3.8) is pumped through the column at 6.0 mL min"1, mixing with the buffer solution, and sequentially eluted directly to the nebulizer of the I CP with 2 M nitric acid at 3.0 mL min"1 by using a flow Injection analysis (FIA) system. This FIA-ICP method gave signal enhancements
matrix.
that were 34-113 times better than for a conventional continuously aspirated system for the metals studied here. A precision of the technique is better than 5% relative standard deviation at the 10 pg L"1 level for aqueous standards, and the sampling rate is 17 samples tv1. Present address: Horiba Co., Ltd., oin, Minami-ku, Kyoto 601, Japan. 1
2
Olsen et al. (1) and Hartenstein et al. (7) report the reaction of heavy metals with Chelex-100 chelate resin in the pH 9-10 region. However, when a sample solution obtained by decomposition with strong acids is adjusted to pH 9-10, chromium (III), titanium, iron (III), and aluminum form hydroxides and are precipitated, even if much buffer solution is added. Also, when a sample solution adjusted to pH 10 with ammonium hydroxide was aspirated continuously, the argon
Miyanohigashi-cho, Kish-
0003-2700/86/0358-2602Í01.50/0
©
1986 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 58, NO. 13, NOVEMBER 1986
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Table I. Operating Conditions for ICP and FIA ICP System coolant argon flow rate plasma argon flow rate carrier argon flow rate rf incident power rf reflected power nebulizer observation height above load coil
carrier flow
10.5 L min"1 1.5 L min"1 1.0 L min'1
1.3-1.4 kW ·
Figure 5. Response of (a) 10 µg L"1, (b) 20 µg L'1, and (c) 50 µg L"1 chromium(III) and titanium standards for 40-s column load times.
tinuous recorded signals by a conventional continuous aspiration method (Figure 6), where signals of both 1.0 Mg L'1 chromium(III), iron(III), titanium, and vanadium and 10 Mg L"1 aluminum are shown compared with signals for 50 Mg L"1 and 100 µg L"1 standards using conventional continuous aspiration. This figure also illustrates the reproducibility of the responses with the column operating at a sampling rate of 15 samples h'1. From the pH-dependence data of vanadium, it is expected that vanadium is concentrated in the wide pH region of the samples, but aluminum, chromium(III), iron(III), and titanium are concentrated in acidic pH regions better than in neutral and alkaline pH regions. Hartenstein et al. (7) reported that aluminum showed no signal enhancement even though it was retained at 55% efficiency by Chelex-100 resin (the stability constant of aluminum iminodiacetate is log Kx = 8.16 (16)). A portion of chelated aluminum was eluted slightly by 2 M nitric acid, and even with 6 M nitric acid chelated aluminum was not eluted reversibly. As a result, the obtained enhancement factor for aluminum was only 38-fold compared to conventional continuous aspiration methods. Although the stability constant of chromium(III) iminodiacetate complex is not known well, from the obtained enhancement factor of 133-fold for chromium(III), it is considered that chromium(III) chelates the iminodiacetate with weak affinity compared to aluminum and iron(III) and is released from the resin easily. In this study, the enhancement factor for iron(III) was obtained in the acidic pH region and the value of 52-fold is similar to the data obtained in the alkaline pH region by Hartenstein et al. (7). Calculated detection limits are listed in Table III and are compared with conventional continuous aspiration ICP (17) and a system using an electrothermal atomizer sample introduction (EA-ICP) (18). The signal enhancement of the
ANALYTICAL CHEMISTRY, VOL. 58, NO. 13, NOVEMBER 1986
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Table IV. Interference0 of Inorganic Ions with Determination of Chromium(III) foreign ion
concn, mg L"1
rel intei 100 88.2 89.3 107.9 92.5 112.6 58.7 83.6 148.4 162.6 127.2 129.4 93.0 100.2 108.0 90.9 103.8 107.3 62.7 91.9 103.8
none
Na+
K+ Ca2+
Mg2+
Fed)
i
50 mV
Mn2+ Fe2+ Co2+
Ni2+ Cu2+ Zn2+ Pb2+ Al3+ Fe3+
50mV
NO3" NO2C032" S042" P043" 0
10000 1000 100 1000 100 1000 100 1000 100 10 10 10 10 10 10 10 10 10 10
100
95.8 111.0 95.9 106.9
10
100 100 100
Interferences were examined by 180-s sample loading.
a 10
µg L'1
Cr(III) solution
with
Time
-
Al response for (a) 10 µ L~1 standard and Cr(III), Ti, Fe(III), and V responses for (b) 1 µ L"1 standards using Muromac A-1 column (2 mm l.d., 8 mm) with preconcentrating FIA-ICP system for 210-s column loading times and both (c) 50 µ L~1 and (d) 100 µ L"1 standards using conventional continuous aspiration ICP.
Figure 6.
Table III.
element
Al
Cr(III) Fe(III) Ti V 0
Detection Limits, µß L~l analytical
precon-
wavelength, nm
centrating FIA-ICP
tional ICP (17)
396.15 267.72 259.94 334.94 311.07
1.5 0.21 0.11 0.08 0.15
45 7.1 6.2 3.8
conven-
EA-ICP (18) 60 20 70
10
on 99.7% (3
