D. Blanco Gomis

Determination of sugars and alcohols in apple juice and cider by high performance liquid chromatography

The application of a high-performance liquid chromatographic produre to the separation and determination of major sugars, sorbitol, glycerol and ethanol in apples, apple juice and cider is described. The HPLC system consisted of a cation-exchange resin column in calcium form, a solvent system of an aqueous solution with calcium EDTA and a refractive index detector. The analysis was completed after 16 minutes. A recovery greater than 91% was observed for all compounds with most recoveries nearing 100%. The coefficients of variation ranged from 2% to 6%.SummaryThe application of a high-performance liquid chromatographic produre to the separation and determination of major sugars, sorbitol, glycerol and ethanol in apples, apple juice and cider is described. The HPLC system consisted of a cation-exchange resin column in calcium form, a solvent system of an aqueous solution with calcium EDTA and a refractive index detector. The analysis was completed after 16 minutes. A recovery greater than 91% was observed for all compounds with most recoveries nearing 100%. The coefficients of variation ranged from 2% to 6%.

High-performance liquid chromatographic determination of furfural and hydroxymethylfurfural in apple juices and concentrates

SummaryA rapid and sensitive method for determining 2-furaldehyde (FUR) and 5-hydroxymethyl-2-furaldehyde (HMF) in apple juices and juice concentrates has been developed. The method for FUR and HMF involves the solid-liquid extraction of the juice by using a C-18 cartridge prior to reversed-phase separation with detection at 280 nm. The mobile phase was acetonitrile-water (8/92, v/v) at a flow rate of 1.0 ml/min. Recoveries from apple juices and juice concentrates spiked at different levels ranged from 94.1 to 104.0 (FUR) and 94.5 to 100.5 (HMF). The quantification limit for both, FUR and HMF, was 5 ppb.

Application of HPLC to characterization and control of individual acids in apple extracts and ciders

SummaryThree HPLC methods have been tested in order to compare their separation of apple and cider organic acids. Optimum results for simultaneous determination of malic, citric, quinic, succinic, lactic and shikimic acids have been obtained using an RP-18 column with phosphate buffer as the mobile phase.This method was applied to organic acids monitoring during the ripening of apples and throughout the fermentation process. After filtration and degasification the organic acids in the sample were separated, and quantified by using a diode array detector.Recovery studies show good results for all solutes (88%–106%). The coefficients of variation show excellent precision (5%).

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.

Determination of amino acids in apple extracts by high performance liquid chromatography

SummaryA rapid and sensitive method for the simultaneous determination of primary amino acids in apple is described. After sample preparation, amino acids were derivatized with o-phthaldialdehyde/2-mercaptoethanol and separated on a reversed phase column with a gradient of phosphate buffer-tetrahydrofuran-methanol as the mobile phase. Detection was carried out with a fluorescence detector at excitation and emission wavelengths of 340 nm and 425 nm respectively. Recovery studies showed good results for all substances (91–109%) (with coefficients of variation ranging, from 0.1 to 9.0%). This method was applied to the monitoring of amino acids during the ripening of apples.

High-performance liquid chromatographic determination of major organic acids in apple juices and ciders

SummaryA reversed-phase high-pressure liquid chromatographic method is presented for the simultaneous separation and determination of malic, citric, lactic, succinic and ascorbic acids in apple juices and ciders. After filtration and/or degasification, the organic acids in the sample are separated on a LiChrosorb/C18 column and quantified by using a rapid diode array detector.The method is considered to be a suitable choice for the accurate and precise determination (C.V. 5%) of these compounds.

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.

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.

A comparative study of different extraction systems for the spectrophotometric determination of potassium with 18-crown-6

Abstract A comparative study on the extractive-spectrophotometric determination of potassium with 18-crown-6 employing different colored counterions and organic extraction solvents is described. Extraction systems using methyl orange/chloroform, bromcresol purple/chloroform and bromcresol green/benzene demonstrated good preliminar features for such purpose and are studied in detail. Analytical performance characteristics including: sensitivity, selectivity, precision, linearity, etc. are given for each method. The main disadvantage of this type of determinations is the lack of reproducibility. Some explanations to this fact are discussed. A new method for the determination of trace amounts of potassium based on its extraction into chloroform with 18-crown-6 and methyl orange is proposed. The linear working range goes from 0.5 to 7 ppm of potassium, the apparent molar absorptivity being 8.8 × 10 3 liters mol −1 · cm −1 , and the precision, expressed in terms of relative standard deviation, of ±4.6%.