ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2007, том 62, № 1, с. 66-70
^=ОРИГИНАЛЬНЫЕ СТАТЬИ =
УДК 543
DETERMINATION OF PALLADIUM, PLATINUM AND RHODIUM BY HPLC WITH ON-LINE COLUMN ENRICHMENT USING 4-CARBOXYLPHENYL-THIORHODANINE AS PRE-COLUMN DERIVATIZATION REAGENT
© 2007 r. Haitao Lin*, Zhang Jie Huang*, Qiufen Hu*, Guangyu Yang*, Gan Zhang**
*Department of Chemistry, Yunnan University Kunming 650091, P R. China **Guangzhou Institute of Geochemistry, China Academy of Sciences Guangzhou 510640, PR. China Received 16.03.2005; in final form 19.06.2006
In the present work, 4-carboxylphenyl-thiorhodanine (CPTR) was synthesized. A new method for the simultaneous determination of palladium, platinum and rhodium ions as metal-CPTR chelates was developed using a rapid column high performance liquid chromatography equipped with on-line enrichment technique. Palladium, platinum and rhodium ions were pre-column derivatized with CPTR to form colored chelates. The Pd-CPTR, Pt-CPTR and Rh-CPTR chelates can absorbed onto the front of the enrichment column [ZORBAX Stable Bound, 4.6 x 10 mm, 1.8 |im] when they are injected with a buffer solution of 0.05 M sodium acetate-acetic acid (pH3.5) as mobile phase. After the enrichment had finished, by switching the six ports switching valve, the retained chelates were back-flushed by mobile phase and moved towards the analytical column. The chelate separation on the analytical column [ZORBAX Stable Bound, 4.6 x 50 mm, 1.8 urn] was achieved with 46% acetonitrile (containing 0.05 M of pH3.5 sodium acetate-acetic acid buffer and 0.01M TritonX-100) as mobile phase. Palladium, platinum and rhodium were separated completely within 2 min. The detection limits (S/N = 3) of palladium, platinum and rhodium are 1.4 ng/L, 1.6 ng/L and 2.0 ng/L, respectively. The method was applied to the determination of palladium, platinum and rhodium in water, urine and soil samples with good results.
Environmental contamination by the platinum group elements (PGEs), mainly related to automotive catalytic converters, is exponentially increasing and the reliable, and accurate quantification is a mandatory task [1-4]. The wide use of palladium, platinum and rhodium not only in automotive catalytic converters but as a drug (Pt) and in food production (Pd) [5] has led to a more uncontrolled release of those metals in the environment, with respect to the traditional chemical industry. Moreover, the platinum group elements derived from automotive catalytic converters are released as nanocrystallites (particles less than 3 ^m in diameter) due to thermal cracking of the catalyser structure and to mechanical abrasion [6-7]. These particles are not blocked by the upper respiratory system and can deeply interact with the lungs. Although the bioavailability and toxicology of PGEs is still an open question, the determination of basal concentrations of these metals has a key role because of an increase of their level [8, 9]. The heterogeneous composition of samples and the low concentration levels of palladium, platinum and rhodium involved make the direct measurement of analytes really difficult. Several analytical techniques have been employed in recent years and most of advantages and
drawbacks have been reviewed [10-20]. In previous work, a high performance liquid chromatography method for the determination of platinum group metals has been reported. The method has been proved to be a favorable and reliable technique [17-23]. However, the routine chromatographic methods need a long separation time (more then 10 min is needed).
In this paper, a new reagent, 4-carboxylphenyl-thiorhodanine (CPTR), was first synthesized and used as pre-column derivatization regent for palladium, platinum and rhodium, and a ZORBAX Stable Bound rapid analysis column (4.6 x 50 mm, 1.8 ^m) was used for the separation of Pd-CPTR, Pt-CPTR and Rh-CPTR chelates on a high performance liquid chromatograph equipped with on-line enrichment technique. Palladium, platinum and rhodium can form stable color chelates with CPTR at room temperature rapidly, and the metal chelates were separated completely within 2.0 min. The separation time was greatly shortened compared to the routine chromatographic methods. This method can be applied to the determination ^g/L level of palladium, platinum and rhodium ions in water, human urine and soil samples with good results.
EXPERIMENTAL
Apparatus. On line column enrichment system used is shown in Figure 1. This system includes Waters 2690 Alliance quadripump, Waters 515 pump, Waters 996 photodiode array detector, six ports switching valve, large volume injector (can containing 10.0 mL samples) and column. The enrichment column is ZOR-BAX Stable Bound pre-column (4.6 x 10 mm, 1.8 |m) and the analytical column is ZORBAX Stable Bound rapid column (4.6 x 50 mm, 1.8 |m). The pH value was determined with a Beckman $-200 pH meter.
Synthesis of CPTR. CPTR was synthesized using following procedure: 50 mL of acetic acid was added to the sample of 1.5 g of thiorhodanine and 1.9 g of 4-car-boxylbenzaldehyde, and the mixture was heated gently to dissolve the thiorhodanine and 1.9 g of 4-carboxyl-benzaldehyde completely. The solution was refluxed for about 1.0 h, and 0.5 mL of concentrated sulfuric acid was added dropwise during refluxing. After the color of the solution turned red, the refluxing was stopped and the sample was poured into 150 mL of dustilled water. To the solution, a small amount of aqueous ammonia was added. Thereafter, the precipitants were separated by filtration, and were recrystallized twice with absolute alcohol. The yield is 52%. The structure of CPTR was verified by elemental analysis, IR, *HNMR and MS. Elemental analysis: CnHvNO2S3, calculated (found), 46.95(46.89%) C, 2.51 (2.64%) H, 4.98 (4.91%) N, 34.19 (34.13%) S. IR (KBr) (cm-1): 35202540 (v-COOH); 3060, 3030 (v=C-H); 1660 (8n-h); 1566, 1548, 1515 (v-C=C); 1292 (v-C-N); 1171, 1215 (v-C=S); 825 (5-Ar-H); 806 (5-C=C-H). XHNMR (solvent: DMSO-d6) (5, ppm): 10.94 (1H, s, -COOH, H 3); 8.02 (2 H, d, Ar-H, H 2 and H 4); 7.58 (2 H, d, Ar-H, H 1 and H 5); 6.35 (1 H, s, -C=C-H, H 6). MS (EI) (m/z): 281 (M+). All this shows that CPTR has the following structure.
2 1 H H
4 5 II
S
Chemicals. All of the solutions were prepared with ultra-pure water obtained from a Milli-Q50 SP Reagent Water System (Millipore Corporation, USA). Palladium, platinum and rhodium standard solution (1.0 mg/mL) was obtained from Chinese Standards Center. A working solution of 0.2 |g/mL was prepared by diluting this standard solution. HPLC grade acetonitrile (Fisher Corporation, USA), and sodium acetate-acetic acid buffer solution (0.5M, pH 3.5) were used. CPTR solution (2.0 x 10-4 M) was prepared by dissolving CPTR with 95% ethanol. Mobile phase A: 0.05 M pH 3.5 sodium acetate-acetic acid buffer solution. Mobile phase B: 46% acetonitrile (containing 0.05 M of pH 3.5 sodi-
Fig. 1. On-line enrichment system using the valve-switching technique Pump A, Waters 515 Pump. Pump B, Waters 2690 Alliance quadripump. Injector can contain 10 mL of sample. Six ports switching valve (Waters Corporation). Enrichment Column, ZORBAX (4.6 x 10 mm, 1.8 |m). Analytical column, ZORBAX (4.6 x 50 mm, 1.8 |m). Detector, Waters 996 photodiode array detector. MP A, 0.05 M of pH 3.5 sodium acetate-acetic acid buffer solution MP B, 46% acetonitrile (contains 0.05 M sodium acetate-acetic acid buffer pH 3.5 and 0.01 M TritonX-100).
um acetate-acetic acid buffer salt and 0.01 M of Triton X-100). All other reagents used were of analytical reagent grade. The glass and Teflon ware used were soaked in 5% of nitric acid for at least 2 h, and then thoroughly wash with pure water.
Standard Procedure. A 0-15 mL of 0.2 |g/mL standard or sample solution were transferred into a 25 mL of volumetric flask. 4.0 mL of 1.0 x 10-4 M CPTR solution, 3.0 mL of 0.5 M sodium acetate-acetic acid buffer solution (pH 3.5) and 1.0 mL of 1% TritonX-100 solution were added. The solution was diluted to volume with water and mixed well. After 10 min, 10.0 mL of solution were introduced into injector and sent to enrichment column with mobile phase A at flow rate of 2.0 mL/min. When the enrichment had finished, by switching the valve of six ports switching valve, the metal-CPTR chelates, which absorbed onto the fore-side of enrichment column, were eluted by mobile phase B at the flow rate of 2.0 mL/min in reverse direction and moved towards the analytical column. The chelates were separated on the analytical column. A tridimensional (X axis: retention time, Y axis: wavelength, Z axis: absorbance) chromatogram was recorded at 400~650 nm n with photodiode array detector and the chromatogram of 5 10 nm is shown in Figure 2.
RESULTS AND DISCUSSION
Precolumn Derivation. The optimal pH value for the CPTR reaction with metal ions is 2.3-5.8 for palladium, 2.1-4.6 for platinum, and 1.2-4.2 for rhodium, so 0.5 M (pH 3.5) sodium acetate-acetic acid buffer solution was recommended to control pH.
It was found that 1.0 mL of 1.0 x 10-4 M CPTR solution was sufficient to complex 5.0 |g of palladium, plat-
Au
0 0.6 1.2 1.8 2.4
Minute
Fig. 2. Chromatogram of the standard sample (a) and occu-pationally exposed human urine sample (b). The concentration of palladium, platinum and rhodium is 1.0 jg/L in the standard sample.
inum and rhodium, However, in real samples the foreign ions, such as Hg2+, Pb2+, Cu2+, Ag+ etc, form complex with CPTR. Therefore, the amount of CPTR must be in excess. In this experiment, 4.0 mL of 1.0 x 10-4 M CPTR solution wre recommended.
The experiments show that in the nonionic surfactant or cationic surfactant medium, the sensitivity of the metal-CPTR chelates was increased markedly. Various nonionic surfactants and cationic surfactants enhance the absorbance in the following sequence: TritonX-100 > > Tween-80 > Tween-20 > CTMAB > CPB. Therefore, TritonX-100 was selected as additive in this experiment. The use of 0.5-1.5 mL of TritonX
Для дальнейшего прочтения статьи необходимо приобрести полный текст. Статьи высылаются в формате PDF на указанную при оплате почту. Время доставки составляет менее 10 минут. Стоимость одной статьи — 150 рублей.