Ramiro Avidad

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 the colorants tartrazine, ponceau 4R and sunset yellow FCF in foodstuffs by solid phase spectrophotometry using partial least squares multivariate calibration.

A method is proposed for the simultaneous determination of the colorants tartrazine (TT), sunset yellow FCF (SY) and ponceau 4R (PR) in foods. The colorants were fixed in Sephadex DEAE A-25 gel at pH 2.0 and then packed in a 1-mm silica cell. The spectra of the analytes fixed in the solid support were recorded between 400 and 800 nm against a blank and the partial least squares (PLS) multivariate calibration was used to obtain the results. The linear dynamic ranges of the calibration graphs were from 50.0 to 650.0 ng ml(-1) for the three colorants and these ranges were taking in account the optimisation of the calibration matrix using the PLS-1 algorithm. The experimental results showed that the optimum number of factors for the calibration matrix was four in all instances and the residual means standard deviation was 5.5267 for SY, 6.3878 for TT and 6.9816 for PR. The square of the correlation coefficients were 0.9977, 0.9978 and 0.9954 for SY, TT and PR respectively. The method was applied to the determination of the colorants in foods and results were compared with those obtained by means of HPLC as reference method. The results obtained can be considered as acceptable in most cases (eight of nine commercial samples). The relative standard deviations ranging between 0.5 and 10.8 for the commercial samples analysed.

Simultaneous determination of the colorants Sunset Yellow FCF and Quinoline Yellow by solid-phase spectrophotometry using partial least squares multivariate calibration

A method for the simultaneous determination of the colorants Sunset Yellow FCF and Quinoline Yellow using solid-phase spectrophotometry is proposed. The colorants were isolated in Sephadex DEAE A-25 gel at pH 5.0, the gel-colorants system was packed in a 1 mm silica cell and spectra were recorded between 400 and 600 nm against a blank. Statistical results were obtained by partial least squares (PLS) multivariate calibration. The optimized matrix by using the PLS-2 method enables the determination of the colorants in artificial mixtures and commercial soft drinks.

Determination of trace amounts of aluminium in natural waters by solid-phase spectrofluorimetry

A spectrofluorimetric method for the determination of trace amounts of aluminium was developed, based on solid-phase spectrofluorimetry. Aluminium reacted with salicylidene-o-aminophenol to form a fluorescent complex that was adsorbed on a dextran-type cation-exchange gel. The fluorescence of the gel, packed in a 1 mm silica cell, was measured directly with use of a solid-surface attachment. The applicable concentration range was from 0.20 to 14.00 µg l–1, with a relative standard deviation of 1.0% and a detection limit of 0.02 µg l–1. The method was applied to the determination of aluminium in natural waters. The method is more sensitive and selective than that based on salicylidene-o-aminophenol alone.

Determination of polycyclic aromatic hydrocarbon residues in water by synchronous solid-phase spectrofluorimetry

The polycyclic aromatic hydrocarbons (PAHs) benzo[a]pyrene (BaP), benzo[a]anthracene (BaA) and pyrene (Pyr), which exhibit native fluorescence in solution, were determined in water at trace levels by solid-phase spectrofluorimetry. The relative fluorescence intensity of BaP, BaA and Pyr fixed on Sephadex G-25 gel was measured after packing the gel beads in a 1 mm silica cell. By using the synchronous spectra at different values of Δλ, BaA, BaP and Pyr can be simultaneously determined in the presence of other PAHs. Spectral characteristics of the PAH–gel system are described. The concentration ranges over which the method was applicable were 0.3–2.5 ng ml–1 of BaP, 0.4–3.5 ng ml–1 of BaA and 0.5–4.5 ng ml–1 of Pyr with relative standard deviations of 1.4, 1.3 and 1.5% for BaP, BaA and Pyr, respectively. The detection limits were 0.03 ng ml–1 of BaP, 0.05 ng ml–1 of BaA and 0.08 ng ml–1 of Pyr. The method was applied to the analysis of waters from different sources.

Determination of Trace Amounts of Carbaryl in Water by Solid Phase Spectrofluorimetry

Abstract A simple and sensitive spectrofluorimetric method for the determination of carbaryl residues in water is presented. Carbaryl is hydrolized in alkaline medium to 1-naphthol. This hydrolysis product is fixed on QAE Sephadex A-25 gel at pH 11.20. The fluorescence of the gel, packed in a 1 mm silica cell, was measured directly using a solid-surface attachment. Spectral characteristics of 1-naphthol-gel system are described in detail. The applicable concentration range was 0.5–60.0 ng.ml−1, with a relative standard deviation of 0.9% and a detection limit of 0.1 ng.ml−1. The method was applied to the determination of carbaryl in natural waters.

Determination of morestan residues in waters by solid-phase spectrofluorimetry

Abstract Morestan in solution in a neutral medium shows native fluorescence. A method for the determination of trace amounts of morestan in waters by solid-phase spectrofluorimetry is described. Morestan is fixed on C-18 silica-gel, packed in 1-mm silica cell and measured directly with a solid-surface attachment giving fluorescence at λ em = 392 nm for wavelength of excitation λ ex = 370 nm. The applicable concentration range is 1.0–7.0 ng ml −1 with a relative standard deviation of 1.9% and a detection limit of 0.15 ng ml −1 . The influence of the presence of other pesticides and chemical species has also been studied. The method is found to be more sensitive and selective than other methods proposed in the literature. It was applied to the determination of morestan in natural waters. Recoveries were from 95% to 105%.

Close overlapping discrimination of polycyclic aromatic hydrocarbons by synchronous scanning at variable-angle solid-phase spectrofluorimetry

Abstract The polycyclic aromatic hydrocarbons (PAHs) fluorene, acenaphthene and phenanthrene have been determined in water at trace levels by solid-phase variable-angle synchronous scanning spectrofluorimetry. These PAHs were previously fixed on Sephadex G-15 gel, and then packed in a quartz cell with a 1-mm pathlength. The fluorescence of the PAHs-gel system was measured directly using a solid-surface attachment. The applicable concentration ranges were 0.70–7.00 ng ml −1 for fluorene, 4.0–60.0 ng ml −1 for acenaphthene and 0.50–5.00 ng ml −1 for phenanthrene. The detection limits were 0.07 ng ml −1 , for fluorene, 0.4 ng ml −1 for acenaphthene and 0.05 ng ml −1 for phenanthrene, the relative standard deviations being 0.94%, 0.95% and 0.74%, respectively. The method was applied to the determination of the cited PAHs in waters of diverse provenance. The recoveries obtained were 93.0–105.0%.

Determination of (1,1'-biphenyl)-2-ol residues in waters by solid phase spectrofluorimetry

SummaryA simple and sensitive spectrofluorimetric method for the determination of (1,1′-biphenyl)-2-ol residues in water is described. (1,1′-Biphenyl)-2-ol shows native fluorescence at a pH=10.20, it was fixed on QAE Sephadex A-25. The fluorescence of the gel packed in a 1 mm silica cell was measured directly using a solid-surface attachment. The applicable concentration range was 1.5–50.0 ng/ml with a relative standard deviation of 0.8% and a detection limit of 0.08 ng/ml. The method was applied to the determination of (1,1′-biphenyl)-2-ol in natural water. This method is more sensitive than other methods described in the literature.

Determination of iron at ng/ml level by solid phase spectrophotometry after preconcentration on cation exchange filters.

A cationic exchanger paper is used to retain analytes in solution and, after drying, to analyze directly by measuring the UV-Vis absorbance of the paper. The method was applied to determination of iron using its known 1,10-phenanthroline complex. Using 100 ml of sample the applicable concentration range was between 1.0 and 10.0 ng/ml with a detection limit of 0.2 ng/ml and a RSD around 2%. The method was applied to determination of iron total in snow, human serum and wine.