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A high-selectivity spectrophotometric reagent for determining platinum(IV)
Talanta 53 (2001) 937 – 941 www.elsevier.com/locate/talanta
A high-selectivity spectrophotometric reagent for determining platinum(IV) Donglan Ma a,*, Ying Li a, Kuangbiao Ma a, Jianping Li a, Jianguo Chen b, Jiawei Yan b, Yulu Wang a a
Department of Chemistry, Henan Normal Uni6ersity, Major Open Laboratory in En6ironmental Engineering of Henan Pro6ince, Xinxiang, Henan 453002, P.R. China b Nanyang Higher Teacher’s College, Nanyang, Henan, 473000, P.R. China Received 16 July 1999; received in revised form 23 August 2000; accepted 28 August 2000
Abstract The new reagent N-(m-Methylphenyl)-N%-(sodium p-aminobenzenesulfonate)-thiourea (MMPT) was synthesized and its structure was confirmed by elemental analysis, IR, UV and 1HNMR spectra. The apparent molar absorptivities of usual ions were determined and the chromogenic reaction with microamounts of platinum(IV) was studied in detail. In the medium of an HAc-NaAc buffer solution, MMPT can react with platinum(IV) to form a green soluble complex. The maximum absorbance of the complex is at 754.4 nm (o754.4 = 8.58×104 L·mol − 1·cm − 1) and 332.8 nm (o332.8 =1.14×105 L·mol − 1·cm − 1). Beer’s law was obeyed for platinum concentrations in the range of 0 1.28 mg·L − 1; the correlation coefficient was r= 0.9995. At 754.4 nm, over 50 ions did not interfere with the reaction. It is one of the simplest and most selective methods available. It was convenient and rapid and has been applied to the direct determination of Pt(IV) in ores and catalysts with satisfactory results. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Spectrophotometric; N-(m-Methylphenyl)-N%-(sodium p-amino-benzenesulfonate)-thiourea (MMPT); Platinum(IV)
1. Introduction Platinum has important roles in environmental and biological fields. A platinum-based catalyst can remove 90% of the carbon monoxide, unburned hydrocarbons and nitrogen oxides in exhaust gases from vehicles, and platinum is the major component of the catalyst. Moreover, plat* Corresponding author. Fax: +86-373-3383145. E-mail address: [email protected] (D. Ma).
inum-containing compounds have found important application in treatment of cancerous tumors and rheumatoid arthritis. Numerous spectrophotometric determinations of platinum(IV) have been reported with chromogenic reagents [1–3], but high-selectivity reagents have been rarely reported. The determination of Pt(IV) is easily interfered with by other precious metals [4]. The reagent 2-(5bromo-2-pyridylazo)-5-dimethylaminoaniline (5Br-PADMA) can form a violet-red complex with
0039-9140/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 3 9 - 9 1 4 0 ( 0 0 ) 0 0 5 8 3 - X
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D. Ma et al. / Talanta 53 (2001) 937–941
platinum(IV), whose apparent molar absorptivity is 8.3 ×104 l·mol − 1·cm − 1, but the determination of platinum(IV) is seriously interfered with by Co(II) and Pd(II), which must be separated in advance [5]. In the Pt-reagent binary coloring systems, an ultra high sensitivity reagent has appeared [6], with an apparent molar absorptivity of 1.75×105 l·mol − 1 cm − 1. However, its application is time-consuming and exhibits low selectivity. The reagent MMPT we synthesized can form complexes with most metal ions with maximum absorbance about 300 nm. For determining Pt(IV), 754.4 nm was selected as the working wavelength; over 50 ions did not interfere with the measurement. The method has been successfully used for the determination of microamounts of platinum(IV) in catalysts and ores.
bath. When the temperature rose over 85°C, excess m-methylphenyl-isothiocyanate [8] alcohol solution was added, and the solution immediately became two layers. When the oil layer disappeared, the solution was allowed to stand for 1 h. Then it was cooled to room temperature. The unreacted m-methylphenyl-isothiocyanate was extracted by ether. The water-layer was concentrated and a precipitate was obtained, then filtered, and recrystallized from alcohol. A light yellow powder was obtained in 84% yield.
2.4. Structure formula of MMPT
2.5. Property of MMPT 2. Experimental
2.1. Instruments SP3-300 IR spectrophotometer (PYE-Unicam Company, UK); JEOX-FX 90Q HNMR spectrophotometer (P.E. Company, USA); PERKINELMER LAMBDA 17 UV/VIS spectrophotometer (P.E. Company); 240C elemental analyzer (P.E. Company); pHS-2 meter (Shanghai Second Instrument Factory, China)
IR(KBr, cm − 1): 3440, 3280, 3160(NH); 2920(CH3); 1600(C6H5); 1210(C= S); 1040 (NHCSNH); 1180, 1125(Ar-SO3). HNMR: d 1H(ppm), 2.44(3H, s, CH3); 7.05– 7.88(8H, m, Ar–H); 4.8(3H, br, NH, NH–NH). UV: lmax = 246.0 nm, o246.0 = 6.0× 104 -1 −1 l·mol ·cm . Elemental Analysis (%): Calculated(Found), C 44.56(44.34), H 4.24(4.53), N 11.11 (10.81).
2.6. Apparent molar absorpti6ity of MMPT-M n + complexes
2.2. Reagent All reagents were of analytical grade. Distilled water was used throughout. Stock standard platinum solution (1.0 mg·ml − 1) was prepared by dissolving 0.2654 g H2PtCl6·5H2O in distilled water and standardized in a 100 ml calibrated flask. More dilute standard solutions were prepared from this stock solution. MMPT solution: 0.05% water solution. HAc-NaAc buffer solution: pH=4.0.
2.3. Synthesis of MMPT A 4.8 g portion of p-hydrazino-phenylsulfoacid [7] was placed in a three-necked flask and the pH value was adjusted to neutral with NaOH solution. Then this solution was heated slowly in a water
In weak acidic, neutral and weak alkaline media, 37 cation complexes with MMPT were studied. The apparent molar absorptivities (o) are listed in Table 1 (oB 103 not listed).
2.7. Procedure for determining microamounts of platinum(IV) Take a known volume of Pt(IV) solution in a 25 ml standard flask, add 2.0 ml HAc-NaAc buffer solution (pH 4.0) and 3.0 ml MMPT solution, dilute to about 20 ml with distilled water, shake, heat in 90°C water bath for 3 min, remove, cool to room temperature in flowing water, dilute to mark with distilled water and mix thoroughly. Measure the absorbance at 754.4 nm against a
D. Ma et al. / Talanta 53 (2001) 937–941
939
Table 1 The apparent absorptivity of different ions Mn+
Au Hg Ce Cu Pt Fe Mg Mn W Ag Pd Co Bi Sn Be V Zn Ca La Cd Nb
pH4.0
pH7.0
pH10.0
lmax/nm
o×10−4
lmax/nm
o×10−4
lmax/nm
o×10−4
332.8 294.0 332.8 366.0 709.2 368.8 755.0 332.8 305.6 306.4 313.2 336.0 365.6 283.2 294.2
0.83 1.01 0.12 0.23 0.45 1.36 2.65 2.83 0.26 0.11 0.22 0.23 0.11 2.15 0.47
295.2
1.14
345.0
0.49
316.8 311.2 675.6 320.0 756.0 294.0 305.0
0.36 0.47 0.31 1.81 2.54 2.07 0.28
338.4 333.6 290.0
0.24 0.32 0.13
333.0 338.4 297.2
0.38 0.19 0.27
334.8 286.4 294.4 244.8 258.8 298.8 277.6
0.13 2.53 0.21 0.43 0.37 0.45 0.12
332.8 313.2 314.2 342.4 244.8 324.8 338.4 238.4 246.8 248.4 332.8 343.4
0.53 0.79 0.59 0.12 0.32 0.10 0.14 0.14 0.26 0.64 0.79 0.19
reagent blank platinum.
prepared
similarly
without
There is less interference and higher sensitivity in NaAc-HAc buffer solution than in others. So, the NaAc-HAc (pH4.0) buffer solution was considered; its dosage was 2.0 ml.
3. Results and discussion
3.1. Spectra of absorbance The maximum absorbance of MMPT solution is at 246.0 nm. The complex Pt-MMPT’ s has maxima at 332.8 nm (o332.8 =1.14× 105 l·mol − 1·cm − 1) and 754.4 nm (o754.4 =8.58× 104 l·mol − 1·cm − 1). Considering its selectivity, the determining wavelength is selected at 754.4 nm (Fig. 1).
3.2. Effect of media Several buffer solutions (HAc-NaAc, KH2PO4 – Na2HPO4 and KH2PO4 – NaOH) were tested.
Fig. 1. Absorption spectra: (1) MMPT against water; (2) Pt(IV)-MMPT against MMPT.
D. Ma et al. / Talanta 53 (2001) 937–941
940
Fig. 2. Effect of different temperatures for 5 min.
Fig. 4. Working curve Pt(IV) mg/25 ml.
PVA, SLS, AG, Triton X-100, CTMAB, CPB were tested. None of them increases the absorbance markedly.
3.5. Effect of temperature and time At room temperature, the chromogenic reaction was slow. When the temperature was over 85°C, the reaction was fast and the absorbance of the complex was maximum and constant. Therefore, the 90°C water bath for 3 min was selected (Fig. 2 and Fig. 3). The complex was stable for at least 12 h.
Fig. 3. Effect of different times at 90°C water bath.
3.3. Effect of MMPT dosage When the dosage of MMPT was over 2.5 ml, the absorbance of complex was maximum and constant; 3.0 ml was chosen for use.
3.4. Effect of surfactants Surfactants Tween-20, Tween-80, emulsifier OP,
3.6. Molar ratio of complex The composition of the complex Pt-MMPT was established by continuous variation and the molar-ratio method, and found to be 1:3 (Pt: MMPT).
Table 2 Tolerated limits of foreign ions Foreign ions
Amount tolerated Foreign ions (mg)
Amount tolerated (mg)
2+ K+, Na+, NH+ , NO− 4 , Ca 3 , − Cl 2− 2− 3− SO2− 4 , SO3 , CO3 , PO4 2− SiO3 Mg2+, Ba2+, Sr2+, Cd2+, Ga3+, F−, Br− 3− U6+, W6+, AsO3− 4 , AsO3 ,
20
In3+, C2O2− 4
2
10 6 5
Zn2+, Al3+, Tl3+, Be2+ Sb3+, Sb5+, Co2+, Mo6+, Au3+, Pd2+, Cu2+, SCN− Cr3+, Mn2+, Pb2+, Ni2+, Zr4+
1.0 0.8 0.5
3
2+ Ti4+, La3+, NO− ,V6+, Sn2+, Ce4+, Bi3+, 2 , Hg 3+ + Fe , Ag
0.2
D. Ma et al. / Talanta 53 (2001) 937–941
941
Table 3 The results of determining of samples Sample
Standard content (mg/g)
Found (mg/g)
Average (mg/g)
RSD
Platinum ore Catalyst
3.52 1735
3.46, 3.29, 3.29, 3.41 1710, 1687, 1681, 1716, 1693, 1704
3.36 1699
2.50 0.8
Table 4 Recovery results of platinum(IV) Sample
Standard value (mg)
Added (mg)
Found (mg)
Average (mg)
Recovery (%)
Platinum ore Catalyst
3.52 8.68
4.00 9.00
7.43, 7.32, 7.21, 7.21 17.44, 17.38, 17.44, 17.27, 17.33, 17.21
7.29 17.35
97.0 98.1
3.7. Interference of coexistent ions
lysts, and recovery determined. The determined results are shown in Table 3 and Table 4.
When the tolerance limit was not more than 5% error with the 20 mg/25ml Pt(IV), over 50 coexistent ions tested did not interfere in the determination. The tolerated limits of these ions are listed in Table 2.
3.8. Detection limit and the apparent stability constant The detection limit of the method is 5.03× 10 − 5·g l − 1. By the continuous-variation method the apparent stability constant was estimated to be 5.26×1011.
4. Conclusion MMPT is a high-selectivity organic reagent for determining Pt(IV). The presence of precious ions, such as Au(III) and Pd(II), do not interfere with the determination. The method has given agreeable results for determining Pt(IV) in the catalysts and ores. Acknowledgements
.
3.9. Working cur6e The calibration graph was linear in the range of 0 32.0 mg/25 mL of platinum(IV). The linear regression equation was A=0.0176C +0.00207 (A-Absorbance, C-mg Pt(IV)/25mL). Its molar absorptivity is 8.58×104 l·mol − 1 cm − 1, and the correlation coefficient is r = 0.9995 (Fig. 4). Sandal’s Sensitivity is 0.0023 mg·cm − 2.
This study was partially financed by science funds in Henan province. References [1] [2] [3] [4] [5]
3.10. Analysis of samples
[6] [7]
The spectrophotometric method was applied to determination of platinum(IV) in ores and cata-
[8]
L.Y. Zhu, R.L. Wu, Henliang Fenxi 7 (1991) 61. S. Moily, A.M.A. Khader, Asian J. Chem. 5 (1993) 1140. J.W. Zhao, Q.H. Xu, Talanta 38 (1991) 909. Thimmegowda Ankapura, Sankegowda Halukuru, Anal. Chem. 56 (1984) 358. G.F. Wang, Y.M. Zhou, G.Q. Liu, Fenxi Huaxue 25 (1997) 617. Y.F. Li, Fenxi Huaxue 17 (1989) 1004. S.W. Zhang, F.L. Tang, F.X. Yang, F. Liu, Huaxue Shiji 4 (1982) 335. E. Joe Hodgking, W. Preston Reeves, J. Org. Chem. 29 (1964) 3098.
A high-selectivity spectrophotometric reagent for determining platinum(IV) Donglan Ma a,*, Ying Li a, Kuangbiao Ma a, Jianping Li a, Jianguo Chen b, Jiawei Yan b, Yulu Wang a a
Department of Chemistry, Henan Normal Uni6ersity, Major Open Laboratory in En6ironmental Engineering of Henan Pro6ince, Xinxiang, Henan 453002, P.R. China b Nanyang Higher Teacher’s College, Nanyang, Henan, 473000, P.R. China Received 16 July 1999; received in revised form 23 August 2000; accepted 28 August 2000
Abstract The new reagent N-(m-Methylphenyl)-N%-(sodium p-aminobenzenesulfonate)-thiourea (MMPT) was synthesized and its structure was confirmed by elemental analysis, IR, UV and 1HNMR spectra. The apparent molar absorptivities of usual ions were determined and the chromogenic reaction with microamounts of platinum(IV) was studied in detail. In the medium of an HAc-NaAc buffer solution, MMPT can react with platinum(IV) to form a green soluble complex. The maximum absorbance of the complex is at 754.4 nm (o754.4 = 8.58×104 L·mol − 1·cm − 1) and 332.8 nm (o332.8 =1.14×105 L·mol − 1·cm − 1). Beer’s law was obeyed for platinum concentrations in the range of 0 1.28 mg·L − 1; the correlation coefficient was r= 0.9995. At 754.4 nm, over 50 ions did not interfere with the reaction. It is one of the simplest and most selective methods available. It was convenient and rapid and has been applied to the direct determination of Pt(IV) in ores and catalysts with satisfactory results. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Spectrophotometric; N-(m-Methylphenyl)-N%-(sodium p-amino-benzenesulfonate)-thiourea (MMPT); Platinum(IV)
1. Introduction Platinum has important roles in environmental and biological fields. A platinum-based catalyst can remove 90% of the carbon monoxide, unburned hydrocarbons and nitrogen oxides in exhaust gases from vehicles, and platinum is the major component of the catalyst. Moreover, plat* Corresponding author. Fax: +86-373-3383145. E-mail address: [email protected] (D. Ma).
inum-containing compounds have found important application in treatment of cancerous tumors and rheumatoid arthritis. Numerous spectrophotometric determinations of platinum(IV) have been reported with chromogenic reagents [1–3], but high-selectivity reagents have been rarely reported. The determination of Pt(IV) is easily interfered with by other precious metals [4]. The reagent 2-(5bromo-2-pyridylazo)-5-dimethylaminoaniline (5Br-PADMA) can form a violet-red complex with
0039-9140/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 3 9 - 9 1 4 0 ( 0 0 ) 0 0 5 8 3 - X
938
D. Ma et al. / Talanta 53 (2001) 937–941
platinum(IV), whose apparent molar absorptivity is 8.3 ×104 l·mol − 1·cm − 1, but the determination of platinum(IV) is seriously interfered with by Co(II) and Pd(II), which must be separated in advance [5]. In the Pt-reagent binary coloring systems, an ultra high sensitivity reagent has appeared [6], with an apparent molar absorptivity of 1.75×105 l·mol − 1 cm − 1. However, its application is time-consuming and exhibits low selectivity. The reagent MMPT we synthesized can form complexes with most metal ions with maximum absorbance about 300 nm. For determining Pt(IV), 754.4 nm was selected as the working wavelength; over 50 ions did not interfere with the measurement. The method has been successfully used for the determination of microamounts of platinum(IV) in catalysts and ores.
bath. When the temperature rose over 85°C, excess m-methylphenyl-isothiocyanate [8] alcohol solution was added, and the solution immediately became two layers. When the oil layer disappeared, the solution was allowed to stand for 1 h. Then it was cooled to room temperature. The unreacted m-methylphenyl-isothiocyanate was extracted by ether. The water-layer was concentrated and a precipitate was obtained, then filtered, and recrystallized from alcohol. A light yellow powder was obtained in 84% yield.
2.4. Structure formula of MMPT
2.5. Property of MMPT 2. Experimental
2.1. Instruments SP3-300 IR spectrophotometer (PYE-Unicam Company, UK); JEOX-FX 90Q HNMR spectrophotometer (P.E. Company, USA); PERKINELMER LAMBDA 17 UV/VIS spectrophotometer (P.E. Company); 240C elemental analyzer (P.E. Company); pHS-2 meter (Shanghai Second Instrument Factory, China)
IR(KBr, cm − 1): 3440, 3280, 3160(NH); 2920(CH3); 1600(C6H5); 1210(C= S); 1040 (NHCSNH); 1180, 1125(Ar-SO3). HNMR: d 1H(ppm), 2.44(3H, s, CH3); 7.05– 7.88(8H, m, Ar–H); 4.8(3H, br, NH, NH–NH). UV: lmax = 246.0 nm, o246.0 = 6.0× 104 -1 −1 l·mol ·cm . Elemental Analysis (%): Calculated(Found), C 44.56(44.34), H 4.24(4.53), N 11.11 (10.81).
2.6. Apparent molar absorpti6ity of MMPT-M n + complexes
2.2. Reagent All reagents were of analytical grade. Distilled water was used throughout. Stock standard platinum solution (1.0 mg·ml − 1) was prepared by dissolving 0.2654 g H2PtCl6·5H2O in distilled water and standardized in a 100 ml calibrated flask. More dilute standard solutions were prepared from this stock solution. MMPT solution: 0.05% water solution. HAc-NaAc buffer solution: pH=4.0.
2.3. Synthesis of MMPT A 4.8 g portion of p-hydrazino-phenylsulfoacid [7] was placed in a three-necked flask and the pH value was adjusted to neutral with NaOH solution. Then this solution was heated slowly in a water
In weak acidic, neutral and weak alkaline media, 37 cation complexes with MMPT were studied. The apparent molar absorptivities (o) are listed in Table 1 (oB 103 not listed).
2.7. Procedure for determining microamounts of platinum(IV) Take a known volume of Pt(IV) solution in a 25 ml standard flask, add 2.0 ml HAc-NaAc buffer solution (pH 4.0) and 3.0 ml MMPT solution, dilute to about 20 ml with distilled water, shake, heat in 90°C water bath for 3 min, remove, cool to room temperature in flowing water, dilute to mark with distilled water and mix thoroughly. Measure the absorbance at 754.4 nm against a
D. Ma et al. / Talanta 53 (2001) 937–941
939
Table 1 The apparent absorptivity of different ions Mn+
Au Hg Ce Cu Pt Fe Mg Mn W Ag Pd Co Bi Sn Be V Zn Ca La Cd Nb
pH4.0
pH7.0
pH10.0
lmax/nm
o×10−4
lmax/nm
o×10−4
lmax/nm
o×10−4
332.8 294.0 332.8 366.0 709.2 368.8 755.0 332.8 305.6 306.4 313.2 336.0 365.6 283.2 294.2
0.83 1.01 0.12 0.23 0.45 1.36 2.65 2.83 0.26 0.11 0.22 0.23 0.11 2.15 0.47
295.2
1.14
345.0
0.49
316.8 311.2 675.6 320.0 756.0 294.0 305.0
0.36 0.47 0.31 1.81 2.54 2.07 0.28
338.4 333.6 290.0
0.24 0.32 0.13
333.0 338.4 297.2
0.38 0.19 0.27
334.8 286.4 294.4 244.8 258.8 298.8 277.6
0.13 2.53 0.21 0.43 0.37 0.45 0.12
332.8 313.2 314.2 342.4 244.8 324.8 338.4 238.4 246.8 248.4 332.8 343.4
0.53 0.79 0.59 0.12 0.32 0.10 0.14 0.14 0.26 0.64 0.79 0.19
reagent blank platinum.
prepared
similarly
without
There is less interference and higher sensitivity in NaAc-HAc buffer solution than in others. So, the NaAc-HAc (pH4.0) buffer solution was considered; its dosage was 2.0 ml.
3. Results and discussion
3.1. Spectra of absorbance The maximum absorbance of MMPT solution is at 246.0 nm. The complex Pt-MMPT’ s has maxima at 332.8 nm (o332.8 =1.14× 105 l·mol − 1·cm − 1) and 754.4 nm (o754.4 =8.58× 104 l·mol − 1·cm − 1). Considering its selectivity, the determining wavelength is selected at 754.4 nm (Fig. 1).
3.2. Effect of media Several buffer solutions (HAc-NaAc, KH2PO4 – Na2HPO4 and KH2PO4 – NaOH) were tested.
Fig. 1. Absorption spectra: (1) MMPT against water; (2) Pt(IV)-MMPT against MMPT.
D. Ma et al. / Talanta 53 (2001) 937–941
940
Fig. 2. Effect of different temperatures for 5 min.
Fig. 4. Working curve Pt(IV) mg/25 ml.
PVA, SLS, AG, Triton X-100, CTMAB, CPB were tested. None of them increases the absorbance markedly.
3.5. Effect of temperature and time At room temperature, the chromogenic reaction was slow. When the temperature was over 85°C, the reaction was fast and the absorbance of the complex was maximum and constant. Therefore, the 90°C water bath for 3 min was selected (Fig. 2 and Fig. 3). The complex was stable for at least 12 h.
Fig. 3. Effect of different times at 90°C water bath.
3.3. Effect of MMPT dosage When the dosage of MMPT was over 2.5 ml, the absorbance of complex was maximum and constant; 3.0 ml was chosen for use.
3.4. Effect of surfactants Surfactants Tween-20, Tween-80, emulsifier OP,
3.6. Molar ratio of complex The composition of the complex Pt-MMPT was established by continuous variation and the molar-ratio method, and found to be 1:3 (Pt: MMPT).
Table 2 Tolerated limits of foreign ions Foreign ions
Amount tolerated Foreign ions (mg)
Amount tolerated (mg)
2+ K+, Na+, NH+ , NO− 4 , Ca 3 , − Cl 2− 2− 3− SO2− 4 , SO3 , CO3 , PO4 2− SiO3 Mg2+, Ba2+, Sr2+, Cd2+, Ga3+, F−, Br− 3− U6+, W6+, AsO3− 4 , AsO3 ,
20
In3+, C2O2− 4
2
10 6 5
Zn2+, Al3+, Tl3+, Be2+ Sb3+, Sb5+, Co2+, Mo6+, Au3+, Pd2+, Cu2+, SCN− Cr3+, Mn2+, Pb2+, Ni2+, Zr4+
1.0 0.8 0.5
3
2+ Ti4+, La3+, NO− ,V6+, Sn2+, Ce4+, Bi3+, 2 , Hg 3+ + Fe , Ag
0.2
D. Ma et al. / Talanta 53 (2001) 937–941
941
Table 3 The results of determining of samples Sample
Standard content (mg/g)
Found (mg/g)
Average (mg/g)
RSD
Platinum ore Catalyst
3.52 1735
3.46, 3.29, 3.29, 3.41 1710, 1687, 1681, 1716, 1693, 1704
3.36 1699
2.50 0.8
Table 4 Recovery results of platinum(IV) Sample
Standard value (mg)
Added (mg)
Found (mg)
Average (mg)
Recovery (%)
Platinum ore Catalyst
3.52 8.68
4.00 9.00
7.43, 7.32, 7.21, 7.21 17.44, 17.38, 17.44, 17.27, 17.33, 17.21
7.29 17.35
97.0 98.1
3.7. Interference of coexistent ions
lysts, and recovery determined. The determined results are shown in Table 3 and Table 4.
When the tolerance limit was not more than 5% error with the 20 mg/25ml Pt(IV), over 50 coexistent ions tested did not interfere in the determination. The tolerated limits of these ions are listed in Table 2.
3.8. Detection limit and the apparent stability constant The detection limit of the method is 5.03× 10 − 5·g l − 1. By the continuous-variation method the apparent stability constant was estimated to be 5.26×1011.
4. Conclusion MMPT is a high-selectivity organic reagent for determining Pt(IV). The presence of precious ions, such as Au(III) and Pd(II), do not interfere with the determination. The method has given agreeable results for determining Pt(IV) in the catalysts and ores. Acknowledgements
.
3.9. Working cur6e The calibration graph was linear in the range of 0 32.0 mg/25 mL of platinum(IV). The linear regression equation was A=0.0176C +0.00207 (A-Absorbance, C-mg Pt(IV)/25mL). Its molar absorptivity is 8.58×104 l·mol − 1 cm − 1, and the correlation coefficient is r = 0.9995 (Fig. 4). Sandal’s Sensitivity is 0.0023 mg·cm − 2.
This study was partially financed by science funds in Henan province. References [1] [2] [3] [4] [5]
3.10. Analysis of samples
[6] [7]
The spectrophotometric method was applied to determination of platinum(IV) in ores and cata-
[8]
L.Y. Zhu, R.L. Wu, Henliang Fenxi 7 (1991) 61. S. Moily, A.M.A. Khader, Asian J. Chem. 5 (1993) 1140. J.W. Zhao, Q.H. Xu, Talanta 38 (1991) 909. Thimmegowda Ankapura, Sankegowda Halukuru, Anal. Chem. 56 (1984) 358. G.F. Wang, Y.M. Zhou, G.Q. Liu, Fenxi Huaxue 25 (1997) 617. Y.F. Li, Fenxi Huaxue 17 (1989) 1004. S.W. Zhang, F.L. Tang, F.X. Yang, F. Liu, Huaxue Shiji 4 (1982) 335. E. Joe Hodgking, W. Preston Reeves, J. Org. Chem. 29 (1964) 3098.