Simultaneous Determination of Rhodium and Iridium Using Derivative Spectrophotometry after Preconcentration of Their 2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol Chelates onto Microcrystalline Naphthalene

Abstract

The economy and efficiency of the analytical procedure for the separation and determination of precious metals, such as rhodium and iridium in geological samples and related materials, are still a challenge to the analyst. Because of their low concentration levels in natural sources, a necessary first step in any analytical procedure needs to be the preconcentration of these elements. The most common and well-documented concentration-cum-separation technique is liquid-liquid extraction. However, this technique is tedious, time consuming (extraction involves several steps and equilibrium distribution between the two phases takes longer time in certain cases) and often requires a large volume of high purity toxic solvents. Column methods using various adsorbents are effective for the preconcentration of metal ions. But their main disadvantages are the lengthy method to prepare the column materials and other stringent conditions. The sorption and desorption of metal ions are carried out at low flow rates, which make these methods time consuming.1,2 To overcome these drawbacks, Satake and co-workers 3,4 developed a method called "Solid-liquid separation after the adsorption of metal-chelates onto microcrystalline naphthalene". This method is very simple, economic and less time-consuming.Only a few photometric reagents have been used for the trace determination of rhodium and iridium in solutions. The similarities in chemical properties of rhodium and iridium make it difficult to eliminate the interference between them in zero-order (normal) spectrophotometry. Tertipis and Beamish 5 separated and determined rhodium and iridium using tin(II) bromide. Stokely and Jocobs 6 proposed a simultaneous zeroorder spectrophotometric determination using 1-(2-pyridylazo)-2-naphthol. Zhenya 7 reported a simultaneous dual-wavelength spectrophotometric determination using tin(II) bromide and 2-mercaptobenzothiazole. Shkil 8 separated rhodium from iridium in acid medium using 2-mercaptobenzothiazole. Wilson and Jacobs 9 separated relatively a large amount of iridium from rhodium by extracting iridium into tributyl phosphate. All of these methods utilized time-consuming solvent extraction for separation. Moreover, they are not sufficiently sensitive and selective. Derivative spectrophotometry has the advantage of higher selectivity than zero-order spectrophotometry. This increased selectivity results because bands that are overlapped in zeroorder absorption spectra can be separated in the derivative mode. Theoretical and practical studies done by O'Haver and Green 10,11 and Fell and co-workers 12,13 showed that this technique can lead to a faster and more accurate determination of multi-component mixtures that previously would have required time-consuming separation techniques. Rhodium and iridium were preconcentrated from a fairly large volume of their aqueous solutions using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) and tetraphenylborate onto microcrystalline naphthalene in the pH ranges 5.0 -6.5 and 3.5 -5.5, re...

Ion pair-dispersive liquid-liquid microextraction of trace amount of rhodium ion in water and road dust samples prior to flame atomic absorption spectrometry determination

“…As can be seen the LOD of the proposed IP-DLLME-FAAS method, with a sample volume of only 10. 0 mL, is lower than some of the previously proposed methods 6,10,11,[16][17][18] and higher than some of the other methods. 3,19,20 While, the extraction time is very shorter than all of the mention methods because no need any Rh-ligand complex formation, which indicates the fact that IP-DLLME is a very sensitive and rapid technique that can be used for the pre-concentration and determination of Rh(III) from real samples.…”

“…In Table 3 are compared the main analytical characteristics (i.e., LR, ER and LOD) of the proposed IP-DLLME-FAAS method for the determination of Rh(III) with those of some of the best previously reported methods for this purpose including SPEspectrophotometry, 6,11 FIA-FAAS, where Rh (III) is adsorbed on a cross-linked polystyrene sorbent, 16 ETAAS after separation, using Dowex 1×8-200, 17 differential pulse polarography, after preconcentration onto microcrystalline naphthalene, 18 laser induced-thermal lens spectrometry after cloud point extraction, 19 FAAS determination after preconcentration onto carbon nanotube, 3 FAAS determination after cloud point extraction 20 and liquid-liquid extraction prior inductively coupled plasma optimal emission spectrometer determination (ICP-OES) 10 . As can be seen the LOD of the proposed IP-DLLME-FAAS method, with a sample volume of only 10.…”

“…1 Due to increasing in the applications of Rh, for example in automobile Pt-Rh catalysts, development of high sensitive analytical methods for this element has been a demand in environmental science. Most sensitive analytical techniques, such as graphite furnace atomic absorption spectrometry (GFAAS), 2 flame atomic absorption spectrometry (FAAS), 3 adsorptive stripping voltammetry (ASV), 4 inductively coupled plasma-atomic emission spectrometry (ICP-AES), 5 derivative spectrophotometry 6 and inductively coupled plasma-mass spectrometry (ICP-MS) 7 have been used for this purpose. However, all of these methods, except FAAS, are high cost methods with complex instrumentation.…”

Differential Pulse Polarographic Determination of Zinc and Manganese in Commercial Sodium Salts and Water Samples after Preconcentration of Their 2-(2-Pyridylazo)-5-diethylaminophenol Chelates Using Ammonium Tetraphenylborate-Naphthalene Adsorbent

“…Tetraphenylborate anion has been used as a counter ion in the extraction and adsorption of some cationic metal chelates into molten naphthalene 17 and microcrystalline naphthalene 9 techniques, respectively. It forms a weak ion pair with NH4 + ion in aqueous solution and coprecipitates along with microcrystalline naphthalene when the pH of the solution is above 8.5.…”

“…5 A number of solid-phase extraction (SPE) methods have been reported in the literature which utilizes various materials, such as ion-exchange resin, functionally modified polymers and C18-glass beads as adsorbents. [6][7][8][9] Although, these methods result in better recovery and an excellent preconcentration factor, the slow sorption and desorption process, and a tedious procedure for preparing the adsorbents make these methods troublesome and time-consuming. Therefore, from economy and simplicity point of view, a conventional determination method with an improved analytical procedure, which can match the modern analytical instruments in terms of its specificity and sensitivity, would find many applications in common laboratories.…”