| With the rapid development of industry, more and more metallic elements enter our living environment through various channels. To study the influence of the metallic elements to the human body and the environment, some of the chemical analysis workers are working on some new analysis methods for metallic elements. Among them, from the perspective of the synthesis of a new chromogenic agent, this research can be said to be one of the hot spots in recent years in how can the selectivity and sensitivity of the method be improved, and how can the detection limit be reduced. Based on this, synthesis of two Pyridylazo reagent which has never been reported, namely 5-(5-cyano-2-pyridylazo)-2,4-diaminotoluene and 5-(5-sulfonic acid-2-pyridylazo)-2,4-diaminotoluene, and characterized, while a detailed discussion is made in the application of the 5-(5-cyano-2-pyridylazo)-2,4- diaminotoluene in the spectrophotometry and the 2-(5-bromo-2-pyridylazo)-5-dimethylaminoaniline is applied to the laser thermal lens. Details are as follows:(1) Synthesis of 5-CN-PADAT, and it’s characterized by elemental analysis, infrared spectroscopy and nuclear magnetic resonance spectroscopy.(2) Synthesis of 5-SO3H-PADAT, and it’s characterized by high-resolution mass spectrometry, infrared spectroscopy and nuclear magnetic resonance spectroscopy.(3) The study of 5-CN-PADAT color reaction with palladium(Ⅱ). In 1.2 mol/L HCl O4 medium, palladium(Ⅱ) could react with 5-CN-PADAT at room temperature for 5 min to form a 1:1 violet-red stable complex with the maximum absorption wavelength at 586 nm. Beer’s low was obeyed in the range of 0 ~ 1.2 μg/m L for palladium(Ⅱ). The linear regression equation was A=1.110 ρ(μg/m L) + 0.0086, with correlation coefficient of 0.9999 and apparent molar absorptivity of 1.20 × 105 L · mol-1 · cm-1. In strong acidic medium, the common metal ions did not interfere, so did the precious metal ions, such as Au(Ⅲ) in 1250 times, Os(Ⅳ) in 500 times, Ag+ and Rh(Ⅲ) in 250 times, Ir(Ⅳ) and Pt(Ⅳ) in 125 times, Ru(Ⅲ) in 75 times of palladium(Ⅱ). The proposed method has been applied for the determination of palladium(Ⅱ) in molecular sieve and palladium-carbon catalyst. The results were consistent with the reference values. The relative standard deviation(RSD, n=6) was 2.3 % and 3.7 %.(4) The study of 5-CN-PADAT color reaction with Rhodium. Test results showed that: At p H 4.0 ~ 5.6, Rh(III) color reaction with 5-CN-PADAT to form a 1:2 stable Rh(III)- 5-CN-PADAT. In range of 0.9 ~ 6.0 mol/L HCl O4, 1.2 ~ 7.2 mol/L H2SO4, 1.32 ~ 4.2 mol/L HCl or 3.0 ~ 9.0 mol/L H3PO4, the complex can be protons into another complex. In 2.4 mol/L H2SO4 medium, another complex maximum absorption wavelength at 580 nm,Beer’s low was obeyed in the range of 0 ~ 1.0 μg / m L for Rh(III). The linear regression equation was A= 2.110 ρ(μg/m L) + 0.0270, the correlation coefficient was 0.9995, ε = 2.28 × 105 L · mol-1 · cm-1. Compared with other similar reagents,this method is simple and high sensitive. The proposed method has been successfully applied for the determination of Rh(III) in rhodium-charcoal catalyst.(5) The study of 5-CN-PADAT color reaction with cobalt. At the p H range of 4.2 ~ 10, cobalt(II) color reaction with 5-CN-PADAT to form a stable Co(II)-5-CN-PADAT, the maximum absorption wavelength at 509 nm. In 2.4 mol/L H2SO4 medium, the complex can be protons into another complex. It’s color was shifted to red, showing maximum absorption wavelength at 579 nm. The linear regression equation was A= 2.319 ρ(μg/m L)- 0.0024,r = 0.9999. Beer’s low was obeyed in the range of 0 ~ 0.8 μg/m L for cobalt(II), apparent molar absorptivity of 1.36 × 105 L · mol-1 · cm-1. This method is high sensitive and applied to the determination of cobalt(II) in ores, the results are consistent with flame atomic absorption spectrometry.(6) The study of 5-CN-PADAT color reaction with Ru(II). At the p H range of 4.0 ~ 5.5, added to the hydroxylamine hydrochloride and heating, Ru(II) can be color reaction with 5-CN-PADAT to form the stable Ru(II)-5-CN-PADAT, the maximum absorption wavelength at 520 nm. In strong acidic medium, the complex’ color was shifted to red, showing maximum absorption wavelength at 538 nm. The optimal concentration of 0.03 ~ 0.78 mol/L HCl,0.03 ~ 0.6 mol/L H2SO4,0.03 ~ 1.2 mol/L H3PO4 or 0.03 ~ 0.2 mol/L HCl O4 is found to be respectively. In 0.3 mol/L HCl, Beer’s low was obeyed in the range of 0 ~ 0.9 μg/m L, apparent molar absorptivity of 4.90 ×104 L · mol-1 · cm-1. Compared with similar reagents, the method has good selectivity and shorter heating time, and successfully applied for the determination of Ru(II) in ruthenium-carbon catalyst and Ru-molecular sieve.(7) A new method for the determination of trace palladium based on the highly selective color reaction between 5-Br-PADMA and palladium(II) by laser thermal lens spectrometry has been established. The experimental results show that Pd(II) react with 5-Br-PADMA in strong acidic media at room temperature for 10 min to form a stable complex showing maximum absorption wavelength at 611 nm which is matched well with the wavelength of the He-Ne laser(632.8 nm). The linear range of this method is 5 ~ 150 ng/m L of palladium and the detection limit is 1.6 ng/m L. The sensitivity was enhanced by 115 times compared to conventional spectrophotometric method. The method has excellent selectivity. The common metal ions do not interfere, so do not the precious metal ions, such as Pt(IV), Rh(III), Ir(III), Ru(III), Os(IV) and Au(III), in 10 times of Pd. This method has been applied to the ditermination of Pd in alloy, ore and molecular sieve with satisfactory results. |
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