F. Capitan

Determination of colorant matters mixtures in foods by solid-phase spectrophotometry

Abstract A new, simple, sensitive and inexpensive method for simultaneous determination of Sunset Yellow FCF (SY), Quinoline Yellow and their respective unsulphonated products (Sudan I (SUD) and Quinoline Yellow Spirit Soluble (QYSS)) in mixtures is proposed. Sunset Yellow and Quinoline Yellow were selectively fixed in Sephadex DEAE A-25 gel (pH 5.0) and SUD and QYSS were selectively fixed in C 18 silica gel (pH 5.0) and the absorbances of both systems were measured directly in solid-phase. The applicable concentration ranges were from 3.0 to 500.0 ng ml −1 for Quinoline Yellow Water Soluble (QYWS), from 3.0 to 200.0 ng ml −1 for QYSS, from 15.0 to 500.0 ng ml −1 for SY and from 20.0 to 200.0 ng ml −1 for SUD. The method was applied to the determination of these compounds in soft drinks, fruit liqueurs and ice creams.

Simultaneous determination of aluminium and beryllium by first-derivative synchronous solid-phase spectrofluorimetry.

A method for the simultaneous determination of aluminium and beryllium in mixtures by first-deravative synchronous solid-phase spectrofluorimetry has been developed. Aluminium and beryllium reacted with morin to give fluorescent complexes, which were fixed on a dextran-type resin. The fluoresnce of the resin, packed in a 1-mm silica cell, was measured directly with a solid-surface attachment. The constant wavelength difference chosen to optimize the determination was Deltalambda = lambda(em) = 75 nm. Aluminium was measured at lambda(em)lambda = 445/520 nm and beryllium at lambda(em)lambda(em) = 430/505 nm. The range of application is between 0.5 and 5.0 ng/ml for both aluminium and beryllium. The accuracy and precision of the method are reported. The method has been successfully applied to the determination of aluminium and beryllium in synthetic mixtures and natural waters.

Simultaneous determination of molybdenum and tungsten by first-derivative synchronous solid-phase spectrofluorimetry

Abstract A method for the simultaneous determination of trace amounts of molybdenum and tungsten in mixtures by first-derivative synchronous solid-phase spectrofluorimetry is described. Molybdenum and tungsten reacted with carminic acid to give red fluorescent complexes, which were fixed on a dextran-type anion-exchange resin. The fluorescence of the resin, packed in a 1-mm silica cell, was measured directly with a solid-surface attachment. The constant wavelength difference chosen to optimize the determination was Δλ=λ(em)-λ(ex)=70 nm. Molybdenum was measured at λ(ex) and λ(em)=506 and 576 nm, and tungsten at λ(ex) and λ(em)=520 and 590 nm. The range of application is between 2.0 and 20.0 μg 1 −1 for molybdenum and between 2.0 and 20.0 μg 1 −1 for tungsten. The accuracy and precision of the method are reported. The method was applied to the determination of molybdenum and tungsten in synthetic mixtures and natural waters.

Determination of beryllium in water by ion-exchange spectrofluorimetry

A method for the determination of trace amounts of beryllium has been developed, based on ion-exchange spectrofluorimetry. Beryllium reacts with morin to give a highly fluorescent complex, which was fixed on a dextran-type anion-exchange resin. The fluorescence of the resin, packed in a 1-mm quartz cell, was measured directly using a solid-surface attachment. The concentration range of the method is 0.10–0.70 µg l–1, the relative standard deviation 1.4% and the detection limit 0.02 µg l–1. The method was applied to the determination of beryllium in natural waters. The aluminium and calcium levels can be determined first in order to reduce their interfering effect. The proposed method is more sensitive and selective than that using morin alone.

Determination of submicrogram amounts of gallium by ion-exchanger fluorimetry. Determination of gallium in natural waters.

A method for microdetermination of gallium at ng/ml level has been developed, based on ion-exchanger fluorimetry. The gallium reacts with salicylidene-o-aminophenol to give a highly fluorescent complex, which is fixed on a dextran-type cationic resin. The fluorescence of the resin, packed in a 1-mm silica cell, is measured directly with a solid-surface attachment. The range of concentration of the method is 2.0-10.0 ng/ml, the RSD 1.3% and the detection limit 0.3 ng/ml. The method has been applied to the determination of gallium in natural waters. The gallium content found in tap water was higher than that in raw water. This is related to the use of commercial aluminium salts in the water-treatment plant.

Determination of trace amounts of tungsten with carminic acid by ion-exchange spectrofluorimetry.

A spectrofluorimetric method for the determination of trace amounts of tungsten was developed, based on ion-exchange spectrofluorimetry. Tungsten reacts with carminic acid to give a red fluorescent complex, which was fixed on a dextran-type anion-exchange resin. The fluorescence of the resin, packed in a 1-mm quartz cell, was measured directly using a solid-surface attachment. The applicable concentration range was 1.0–20.0 µg l–1, with a relative standard deviation of 1.5% and a detection limit of 0.3 µg l–1. The method was applied to the determination of tungsten in natural waters. The method is more sensitive and selective than that using carminic acid alone.

Determination of nitrite in sea-water by ion-exchanger colorimetry

SummaryA microdetermination method (at theμg/l level for nitrite) has been developed, based on ion-exchanger colorimetry. The nitrite is reacted with sulphanilamide andN-(1-naphthyl)ethylenediamine to form an azo dye which is then sorbed on Dowex 50W-X2. The resin phase absorbance at 550 and 800 nm is measured directly. The relative detection limit is 0.27μg/l and the distribution ratio is 2.6×104. The method has been applied to determination of nitrite in 500-ml sea-water samples and compared with a conventional technique.ZusammenfassungEine Mikromethode zur Bestimmung von Mikrogramm Nitrit/Liter mit Hilfe der lonenaustausch-Kolorimetrie wurde ausgearbeitet. Zu diesem Zweck wird Nitrit mit Sulfanilamid und N-(1-Naphthyl)ethylendiamin zu einem Azofarbstoff umgesetzt, der an Dowex 50W-X2 adsorbiert wird. Die Absorbanz der Harzphase wird unmittelbar bei 550 und 800 nm gemessen. Die relative Nachweisgrenze beträgt 0,27μg/l, das Verteilungsverhältnis 2,6×104. Das Verfahren wurde zur Bestimmung von Nitrit in 500-ml-Proben Meerwasser verwendet und mit konventionellen Methoden verglichen.

Microdetermination of vanadium by ion-exchanger colorimetry

Abstract A microdetermination method for vanadium by ion-exchanger colorimetry has been developed. Vanadium is sorbed on the anion-exchanger Dowex 1-X8 as vanadium-benzohydroxamic acid complex in 3 M HCl medium. The resin-phase absorbance at 516 and 800 nm is measured directly. The detection limit is 0.28 μg/liter and the distribution ratio is 340. It is possible to enhance the sensitivity by increasing the sample volume.

Spectrophotometric determination of trace amounts of iron(III) in salicylates by extraction of the mixed-ligand iron-salicylate-purpurin complex

A sensitive method is described for the determination of microgram amounts of iron(III) by means of its reaction at pH 9.0 with salicylate and purpurin (1,2,4-trihydroxyanthraquinone) and extraction into 4-methylpentan-2-one. The molar absorptivity of the 1:1:2 iron(III)-salicylate-purpurin complex is 4.7 × 104 l mol–1 cm–1 at 590 nm. Beers law is obeyed up to a concentration of 10 µg of iron in 40 ml of aqueous phase. Iron contents in salicylate, acetylsalicylate and pharmaceutical products containing these compounds can be determined at levels of the order of 10–5%.

Determination of boron with chromotropic acid by first-derivative synchronous spectrofluorimetry

SummaryA method for the determination of traces of boron by first-derivative synchronous spectrofluorimetry is proposed. It is based on the formation of a fluorescent complex with chromotropic acid at pH 6.7. The constant wavelength difference chosen to optimize the determination is Δλ=λem−λex=24 nm. The range of application is between 2.0 and 20.0 μ/l of boron, the detection limit 0.4 μg/l and the relative standard deviation 3.2%. A study was made of the influence of several ions as potential interferents. The method has been satisfactorily applied to the determination of boron in plants, fertilizers and natural waters.