Salt-induced phase separation for the determination of metals as their diethyldithiocarbamate complexes by high-performance liquid chromatography

Abstract

R e vMgh-perfonnance liquid Chromatography wlth ultraviolet detection can be used to determine trace levels of Pt(II), Pd(II), Rh(III), Co(III), Ru(III), and I r in aqueous solution following complexation with dlethyidithlocarbamate. The metal Complexes are extracted into acetonitrile from aqueous solution by the addition of a saturated salt solution. Quantitative metal recovery from aqueous solution is achievable for most metals for a wide solution pH range. Detection limits for the metals are <3 ng of metaMmL of original aqueous sample. Analyses of real samples are highly reprodudbile and sensitive. I r can interfere in the determination of Pt(1I) and Rh( I I I). A general protocol for chromatographic separation and determination of Pt( I I), Pd( I I ) , Rh( I I I), Ru( I I I), and I r in aqueous solution Is presented.The use of dithiocarbamates for the determination of trace-level amounts of metals by chromatographic techniques has become popular in recent years. The ability to separate metal-dithiocarbamate complexes by high-performance liquid chromatography (HPLC) has been well documented (1-3). The actual application of dithiocarbamates for real sample analysis by chromatographic methods has also been addressedThe formation of metal-dithiocarbamate complexes for chromatographic separation has been carried out in three different ways. Solvent extraction for the preconcentration of trace metals from aqueous solution using dithiocarbamates has been used extensively in metal determinations by atomic absorption spectroscopy (14). 4-Methyl-2-pentanone has generally been used as the extracting solvent and is nebulized directly into a flame (15,16) or injected into a graphite furnace (17). A similar application of these solvent extraction techniques has been used to determine trace metals by liquid chromatography (4,9,10,18), generally extracting the complex into chloroform. The ultraviolet absorption spectrum of chloroform interferes with the UV detection of the complexes by HPLC and chloroform also presents solubility problems in certain reversed-phase applications; thus chloroform is usually removed by a slow vacuum evaporation and the sample is reconstituted into an appropriate solvent which can be injected into the chromatographic system.A number of workers (6, 7,18-22) add the dithiocarbamate ligand to their chromatographic mobile phase, allowing the metal-dithiocarbamate complexes to form in situ, which speeds up the analyses by avoiding solvent extraction. In situ methods have no capacity for preconcentrating the metal and are only applicable to metal species which rapidly form stable complexes in the mobile phase. The method also requires large amounts of complexing agent and the devotion of the (4-1 3).'Present address: E. I. Present address:HPLC system to metal determinations. Dithiocarbamates absorb in the ultraviolet region; thus visible detection wavelengths (which have smaller absorptivity coefficients than ultraviolet wavelengths) are required or electrochemical detection is needed.A third approach ...

Analysis of Metal Ions by High Performance Liquid Chromatography

“…Thc method of choice has been to form a highly absorbing stable metal complex and then to monitor the optical absorption of the complex. UVNIS detection of metal complexes has been used for many applications and showed excellent agreement with results obtained by AAS analyses (154)(155)(156)(157)(158)(159)(160)(161)(162)(163)(164)(165)(166)(167)(168)(169)(170)(171). Ligands used for complexation in the analysis of metal ions will be reviewed later in this paper.…”

“…The preconcentration methods include liquid-liquid extraction and solid phase extraction. Since most metal complexes are neutral, chloroform(154)(155)(156)(158)(159)(160) or acetonitrile(157) are used as the solvent for liquidliquid extraction. Solid phase extraction can be achieved by using Sep-Pak C18 cartridges(174,187).…”

The Decomposition of Phenylmercuric Nitrate in Sulphacetamide Drops During Heat Sterilization

“…Further, the ionic sulphacetamide sodium remains substantially in the lower phase whereas the hydrophobic dithiocarbamate complexes and diphenylmercury concentrate in the upper layer (partition coefficients upperjlower for the compounds were found to be 0.1 IS for sulphacetamide determined by dilution and interfering sulphacetamide while concentrating the organomercury compounds and provides a solution in acetonitrile suitable for direct injection onto the HPLC column. This approach has been used previously for pre-concentration of organometallic complexes before HPLC analysis (Mueller & Lovett 1987;Parkin et al 1992a).…”

Salting-out solvent extraction for the off-line preconcentration of benzalkonium chloride in capillary electrophoresis

“…The use of salting-out effect with water-miscible organic solvents, such as acetonitrile and acetone, for extraction is known for many years [7], especially its usage for the extraction of metal chelates into organic solvents prior to atomic absorption [8] and high performance liquid chromatography (HPLC) [9,10]; however, its exploitation as a preconcentration method for the trace analysis of neutrals as well as charged organic solutes have been very limited [11,12]. And, to the best of our knowledge, although polar organic solvents such as acetonitrile have been shown to be useful for sample pretreatment in CE (e.g., protein precipitation in biological samples) [3], the addition of salting-out agent to the sample solution to effect sample preconcentration in CE has not been reported.…”