Simultaneous determination of fat-soluble vitamins and provitamins in milk by microcolumn liquid chromatography.

The fat-soluble vitamins A, D2, D3, E and K1, retinyl acetate, retinyl palmitate, tocopherol acetate, ergosterol and 7-dehydrocholesterol in milk were separated on a packed reversed-phase fused-silica microcolumn, and determined with UV detection. Conventional liquid chromatographic equipment was adapted for such purposes, providing a highly efficient and sensitive analytical system. The vitamins could be separated in gradient mode with detection limits comprised between 0.02 ng/ml for retinol and 2 ng/ml for vitamin E. All vitamins were separated in less than 17 min. Recovery studies showed good results for all solutes (89-107%) and the intra-day coefficients of variations ranged from 2 to 8%. Application of the proposed method to the quantification of fat-soluble vitamins in milk is reported.

Determination of acaricides in honey by liquid chromatography with ordinary, narrow-bore, and microbore columns.

Narrow-bore and microbore columns packed with octadecylsilane were used to compare their sensitivity and efficiency in the separation of coumaphos, fluvalinate, bromopropylate, and 4,4'-dibromobenzophenone from honey with those of ordinary columns. The best sensitivity for acaricides was accomplished by using a 150 mm × 0.32 mm i.d., 5 µm Spherisorb ODS-2 capillary column, methanol-water (90:10 v/v) as the mobile phase, and 5 µL/min as the flow rate. Detection limits for individual acaricides using a UV detection range from 0.40 to 0.74 µg/kg of honey were comparable to those obtained by gas chromatography using an electron capture detector. All acaricides were separated in <12 min. The coefficients of variations on real samples were <6.2%.

Simultaneous determination of vitamins D3, E and K1 and retinyl palmitate in cattle plasma by liquid chromatography with a narrow-bore column.

A reversed-phase high performance liquid chromatographic method is described for the simultaneous determination of vitamins D3, E and K1 and retinyl palmitate in plasma. Narrow-bore columns are recommended because this alternative provides a good separation efficiency, plus greater economy and sensitivity. Detection limits for individual vitamins range from 0.42 to 2.8 ng. All vitamins were separated in less than 9 min. Recovery studies showed good results for all solutes (88.8-100.3%) and the intra-day coefficients of variations ranged from 1.0 to 4.5%. This method permits the simple determination of fat-soluble vitamins using 1 ml of cattle heparinized plasma.

Sequential extraction--spectrofluorometric determination of lead and cadmium using cryptands.

A spectrofluorimetric method for the determination of ultratrace amounts of lead and cadmium is described based on the sequential extraction of the ternary ion-association complexes formed between the cation, a cryptand as the ligand and eosin as a counter ion. A linear working range from the detection limit (0.5 ng ml(-1) to 250 ng ml(-1) of lead and to 1 50 ng ml(-1) of cadmium was obtained. The relative standard deviation was 2-4%. The proposed method has been applied successfully to the determination of lead and cadmium in zinc metals and soft drinks.

Ion-pair extraction and fluorimetric determination of cadmium with cryptand 2.2.1 and eosin.

A method is described for the direct spectrofluorimetric determination of ultratraces of cadmium by extraction into 1,2-dichloroethane of the ion-pair formed between the eosinate anion and the cationic complex of Cd(2+) with cryptand 2.2.1. The detection limit for cadmium is 0.5 ng/ml, and the linear working range is from the detection limit to 150 ng/ml. The relative standard deviation is 1.5% at the 100 ng/ml level. The equilibrium constant has been estimated and refined by the Letagrop-DISTR program. The proposed method has been tested in the determination of cadmium in high-purity zinc. The results show good agreement with those found by the more common ICP emission photometry and anodic stripping voltammetry methods.

Fluorimetric determination of ultratraces of lead by ion-pair extraction with cryptand 2.2.1 and eosin.

A spectrofluorimetric study of the extraction of lead into 1,2-dichloroethane, as an ion-pair formed between the cryptand 2.2.1-lead complex and the eosinate counter-ion is described. Optimum conditions for the extraction have been established and a new spectrofluorimetric determination of ultratraces of lead is proposed (detection limit 0.8 ng/ml; relative standard deviation 2.4% at the 60 ng/ml level). The metal:ligand:counter-ion molecular ratio in the extracted mononuclear ion-pair is 1:1:1. The equilibrium constants involved in the extraction have been estimated and refined by the Letagrop-DISTR program.

Extractive fluorimetric determination of ultratraces of lead with cryptand 2.2.2 and eosin.

A new speetrofluorimetric method for determination of ultratraces of lead is based on solvent extraction into chloroform of the ion-pair formed between the positively-charged cryptate of lead with cryptand 2.2.2 and the eosinate anion. The detection limit for lead is 1 ng ml , and the linear working range is from the detection limit to 250 ng ml . The relative standard deviation is 3.7% at the 100 ng ml level. The method is highly selective for the extraction and determination of lead in the presence of other cations, and has been tested for direct determination of lead contamination in soft drinks. Aggregation of the extracted ion-pair in the organic phase has been demonstrated in fundamental extraction studies.

Extractive fluorimetric determination of ultratraces of lead with 18-crown-6 and eosin.

A highly sensitive and selective spectrofluorimetric procedure for the determination of lead in the range 0.003-0.5 ppm, based on solvent extraction of the ion-pair formed between the eosinate anion and the cationic complex of Pb(2+) with 18-crown-6, has been developed. The relative standard deviation is 3.7% at the 0.1 ppm level. The metal :ligand: counter-ion molecular ratio in the ion-pair extracted is 1:1:1, but aggregation of the complex may occur in the organic phase. The system proposed is exceptionally selective for extraction of lead in the presence of other cations frequently associated with it. The proposed method has been tested in the determination of lead in tap water. The results show good agreement with those found by the more common extractive atomic-absorption method using ammonium tetramethylenedithiocarbamate.

Extraction-spectrophotometric determination of niobium with dibenzo-18-crown-6 and thiocyanate.

A method is described for the direct spectrophotometric determination of micro-amounts of niobium by extraction into a benzene solution of dibenzo-18-crown-6 (L) from 3M hydrochloric acid containing potassium thiocyanate. The molar absorptivity of the extracted complex is 3.85 +/- 0.03 x 10(4) 1.mole(-1).cm(-1) (relative standard deviation 0.8%). Co-ordinatively unsaturated complexes of the type [NbO(SCN)(3)](2)L and NbO(SCN)(3)L are extracted, along with ion-pairs, especially when small amounts of L are used for extraction. The ion-pair complex [NbOCl(2)(SCN)(3)][(LK)(2)] seems to be the main species formed in the organic phase.

Ion-pair extraction and fluorimetric determination of potassium with 18-crown-6 and eosin.

A highly sensitive and selective fluorimetric determination of potassium is proposed, based on solvent extraction of the ion-pair formed between a large anion and the cationic complex of K(+) with a crown ether. Sensitivity is achieved by selection of a highly fluorescent counter-ion of the fluorescein group (eosin). A linear working range from 0.01 to 1 ppm of potassium is obtained, which gives a higher sensitivity than any similar method for potassium determination. The relative standard deviation is 4-5%. Selectivity is achieved by matching the radius of the cavity of the 18-crown-6 to the ionic radius of potassium. The system used is exceptionally selective for extraction of potassium in the presence of alkali or alkaline-earth metal cations. The proposed method has been successfully applied to the determination of potassium in blood serum.