Sergio Dilli

Reversed-phase high-performance liquid chromatography of diethyldithiocarbamate complexes using radial compression columns

The diethyldithiocarbamate complexes of Co(III), Cr(III), Cu(II), Hg(II), Ni(II), Pb(II), Se(IV) and Te(IV) are separable on a Waters Assoc. Radial Pak C18 column using a mobile phase of methanol-acetonitrile-water (40:35:25), provided the column has been conditioned by prior injection of a concentrated mixture of the complexes. Alternatively, the column can be conditioned by flushing with 0.005 M disodium ethylenediamine tetraacetate (EDTA), with subsequent addition of 1.2510-5 M EDTA to the mobile phase. Diethyldithiocarbamate complexes of Pb(II), Cd(II) and Fe(III) gave poor peak shape due to substitution reactions with nickel from stainless steel components of the chromatographic system. The analysis of a synthetic electroplating solution containing salicylsulphonic acid, sulphanilamide and six inorganic ions is illustrated.

Determination of nitrate and nitrite in cured meats using high-performance liquid chromatography

Several existing chromatographic techniques for the determination of nitrate and nitrite were evaluated and found to be unsuitable for the analysis of cured meats because of interferences present in these samples. An alternative procedure was developed, based on the use of a low capacity anion-exchange column with chloromethanesulphonate as eluent, and using ultraviolet absorbance at 210–214 nm as the detection method. This analytical method was shown to be rapid, sensitive and precise, and satisfactory recovery was observed when nitrate and nitrite were added to several food samples. A comparison of this method with a conventional spectrophotometric method showed poor agreement between the two techniques and is attributed to deficiencies in the spectrophotometric method. The proposed chromatographic procedure is shown to be applicable to the analysis of vegetables and cheese as well as cured meats.

Analysis of selenium at the ultra-trace level by gas chromatography

Summary Methodology available for the quantification of selenium by gas chromatography is examined. In particular, evolution of the sensitive analytical procedure, whereby selenium may be determined as a substituted piaselenol with the electron capture detector, is reviewed at length. Reaction conditions are highly selective and contribute to a method suitable for selenium at the ultra-trace level. Factors considered include reagents and reaction conditions, chromatographic requirements, detection limits, sample processing and sources of interference.

Investigation of two fluorinated reagents for ther analysis of selenium by gas chromatography

As potential reagents for the determination of traces of selenium by gas chromatography, the compounds 4-fluoro-o-phenylenediamine and 4-trifluoromethyl-o-phenylenediamine have been examined and compared with seven o-diamines previously reported for analytical purposes. Retention times of the fluoro-piaselenols are shorter than all other compounds but, with the electron-capture detector, their responses differ widely. However, the detection limit of the trifluoromethylpiaselenol compares favourably with the commonly used derivative, 5-nitropiaselenol. The analytical requirements of 4-trifluoro-o-phenylenediamine as a reagent, and the results of its application to the determination of selenium in various biological matrices, are presented.

Liquid chromatography of metal chelates. Chromatographic studies of homologous dialkyldithiocarbamates

Abstract The chromatographic behaviour of a selected group of metal dithiocarbamates was investigated by reversed-phase, liquid chromatography. Ligands with the general formula R 2 NCSSNa, where R is CH 3 CH 2 –, CH 3 CH 2 CH 2 –, (CH 3 ) 2 CH–, CH 3 CH 2 CH 2 CH 2 – or CH 3 CH 2 CH 2 CH 2 CH 2 – were synthesised and used to prepare the corresponding complexes of zinc(II), arsenic(III), iron(III), cadmium(II), lead(II), nickel(II), copper(II), mercury(II), cobalt(III) and chromium(III). The chromatographic behaviour of the metal complexes on a C 18 column was examined with the mobile phases comprising methanol–water, acetonitrile–water and methanol–acetonitrile–water. With the exception of one ligand [where R=(CH 3 ) 2 CH–], the majority of the chelates were resolved satisfactorily. Although the Cd(II) and Pb(II) complexes were not resolved by the binary solvent systems, those derived from the straight-chain, higher homologues (C 3 –C 5 ) were successfully separated with ternary solvent mixtures. Chelates of Zn(II), Fe(III) and the diethyldithiocarbamate of As(III) were not observed using any of these mobile phases.

Further studies of diethyldithiocarbamate complexes by high-performance liquid chromatography

Abstract Normal- and reversed-phase high-performance liquid chromatography have been used to study the behaviour of the diethyldithiocarbamate complexes of Cu(II), Co(III), Cr(III), Ni(II), Hg(II), Pb(II), Se(IV), Zn(II), Fe(III), As(III) and Cd(II). A variety of commercially available columns was employed in an effort to identify significant differences in column performance. An analytical procedure suitable for the determination, in biological materials, of the more stable chelates (Cu, Co, Cr, Ni and Hg) by reversed-phase high-performance liquid chromatography is presented, following clarification of the optimal reaction conditions for formation of the Cr(III) complex.

Determination of pyrethroid residues on paddy rice by reversed-phase high-performance liquid chromatography.

Several synthetic pyrethroids and the synergist piperonyl butoxide have been determined as aged residues on paddy rice by reversed-phase high-performance liquid chromatography with detection at 225 nm. These compounds are commonly used as protectants for stored grains. Studies on the comparative rates of extraction of both the pesticides and interfering material from the grain were conducted with acetone, methanol, and hexane as extracting solvents. Acetone was the best of these solvents because it provided quantitative extraction of the pesticides over a 48-h period, and did not give high levels of ballast material. Pyrethroids present in the extract at levels in excess of 0.5 microgram/ml could be determined by direct injection, but at lower concentrations, clean-up and preconcentration were required. Clean-up of acetone extracts was accomplished with either Florisil or alumina pre-columns, and up to a tenfold preconcentration was achieved by adsorption of the pesticide on a C18 pre-column, or by concentrating the extract through evaporation of the solvent. These approaches gave good recoveries and linear calibration plots. Detection limits were of the order of 0.05 microgram/ml.

Analysis of trace amounts of barbiturates in saliva

A simple gas chromatographic method is presented for the determination of trace quantities (0.1-1.0 microgram/ml) of amobarbital, pentobarbital and phenobarbital in saliva. The barbiturate is extracted with chloroform, alkylated with bis(2-chloroethyl) sulphate, and quantified using a non-polar (SE-30) column and electron-capture detection. The procedure has been applied to the determination of the salivary half-lives of amobarbital and, for the first time, pentobarbital following administration of the drugs to human volunteers. The scale and sensitivity of detection are suitable for use in forensic or other medico-legal work.

Retention of fluorinated transition-metal β-diketonates in gas chromatographic columns

Abstract Retention of the Al(III), V(III), Cr(III), Fe(III), Mn(III), Co(III) and Cu(II) derivatives of the β-diketones, 1,1,1-trifluoropentane-2,4-dione, 1,1,1,5,5,5-hexafluoropentane-2,4-dione, 1,1,1-trifluoro-5-methylhexane-2,4-dione, 1,1,1-trifluoro-5,5-dimethylhexane-2,4-dione, 1,1,1,3,3-pentafluoro-6,6-dimethylheptane-3,5-dione and 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dione in chromatographic columns with various supports has been studied. Chemical effects due to the nature of the support, ligand and the metal ion probably contribute to the observed magnitude of the retention. Irreversability of the phenomenon is interpreted as arising from dissociation in the stationary phase and retention therein or to reaction at active sites on the support. Several mechanisms for these reactions are proposed.

Gas chromatography of some oxovanadium(IV) tetradentate β-ketoamine chelates

Abstract The gas chromatographic elution behaviour is reported, for the first time, for the oxovanadium(IV) chelates of seven tetradentate β-ketoamines on a non-polar column. Interaction with Chromosorb W as support is shown to be appreciably greater than with Chromosorb 750. Detection limits using the Chromosorb 750 support and flame ionization detection are less than nanogram amounts of elemental vanadium. The separation of copper and nickel from vanadium complexes is demonstrated.