Leticia López-Martínez

Simultaneous Determination of Synthetic Dyes Tartrazine, Allura Red and Sunset Yellow by Differential Pulse Polarography and Partial Least Squares. A Multivariate Calibration Method

Synthetic azo dyes, such as tartrazine, sunset yellow and allura red have sensitive polarographic waves in solution (pH 9.2). However, the dyes polarographic waves are seriously overlapped making their simultaneous determination difficult without previous sample preparation. The aim of this work was to apply partial least squares (PLS) multivariate calibration to such commonplace electrochemical technique as differential pulse polarography (DPP) for the simultaneous determination of the dyes three component mixture at trace levels (0.05–1.00 μmol/L). The method has been applied in the determination of these synthetic dyes in commercial food products.

Simultaneous determination of methylxanthines in coffees and teas by UV-Vis spectrophotometry and partial least squares

This work describes a method to simultaneously determine caffeine (CF) and theobromine (TB) in coffee and tea samples using partial least squares (PLS-1). Sample preparation was required to eliminate strong interfering components. High-performance liquid chromatography (HPLC)-found concentrations of caffeine and theobromine (theophylline was not found in any analyzed sample) were used to construct universal calibration matrixes for coffee and tea. Due to the low levels of theobromine when compared to caffeine (up to 1000:1), theobromine addition standard was required to dramatically improve method performance. The method developed did not show statistically significant differences with an HPLC standard technique.

Simultaneous determination of binary mixtures of trimethoprim and sulfamethoxazole or sulphamethoxypyridazine by the bivariate calibration spectrophotometric method

The bivariate calibration algorithm was applied to the spectrophotometric simultaneous determination of trimethoprim (TMP), sulfamethoxazole (SMX) or sulphamethoxypyridazine (SMP) binary mixtures in pharmaceutical and veterinary products. The results obtained were compared with those from derivative spectrophotometry. The statistical evaluation of the method bias showed that the proposed procedure is comparable with commonly used first-derivative spectrophotometry. However, the advantage of bivariate calibration is its simplicity, due to the minimal spectra manipulation when compared with derivative techniques.

Determination of miconazole in pharmaceutical creams using internal standard and second derivative spectrophotometry.

A simple method is proposed for miconazole determination in pharmaceutical creams, based on extraction and second derivative spectrophotometry. In the presence of sodium lauryl sulfate (0.5%) and sulphuric acid (0.4 mol l(-1)), the miconazole and internal standard (IS) (methylene blue) were extracted to 100 microl of methylene chloride. The organic phase was evaporated in the nitrogen stream and the dry residue was dissolved in methanol (1.5 ml). The analytical signal was obtained as the ratio between second derivative absorbances measured at 236.9 nm (miconazole) and at 663.2 nm (IS). The use of IS in such multi-stage procedure enabled quite good analytical performance in calibration range 50.0 400 mg l(-1): linear correlation coefficient 0.9995, precision (measured as CV for ten replicates) at 50.0 mg l(-1) and at 400 mg l(-1) of miconazole was 1.5 and 0.5% respectively. Four commercial pharmaceutical creams were analyzed and the results obtained were in good agreement with the results obtained by reversed-phase high performance liquid chromatography (HPLC).

Application of the bivariate spectrophotometric method for the determination of metronidazole, furazolidone and di-iodohydroxyquinoline in pharmaceutical formulations

The bivariate calibration algorithm was applied to the spectrophotometric determination of metronidazole, furazolidone and di-iodohydroxyquinoline in pharmaceutical dosage forms. The results obtained were compared with the results of derivative spectrophotometry. The statistical evaluation of method bias was carried out, and it was shown that the proposed procedure may be competitive with commonly used first-derivative spectrophotometry. The advantage of the bivariate calibration is its simplicity, and the fact that there is no need to use the derivatization procedures.

Spectrophotometric determination of Allura Red (R40) in soft drink powders using the universal calibration matrix for partial least squares multivariate method

Abstract The Kool-Aid powders (Kraft General Foods) contain one or two of the following dyes: Allura Red (FD and C Red-40, R40), Sunset Yellow (FD and C Yellow-6, Y6) Tartrazine (FD and C Yellow-5, Y5), Erythrosine B (FD and C Red-3, R3), Amaranth (FD and C Red-2, R2) and Brilliant Blue FCF (FD and C Blue 1, B1), depending on the taste of the drink. In this work the “universal” calibration matrix is proposed for the determination of R40 in soft drink powders by partial least squares method using Spectrophotometric data. The training set of samples consists of 23 solutions: three of them contain only R40 at different concentrations and the rest of them are the binary mixtures of R40 with one of the following dyes: R3, R2, Y5 or Y6; all at the concentrations varying in the range 2–22 mg l−1 (exception: R3 2–12 mg l−1). The good analytical performance of R40 calibration was obtained (R2 = 0.9993, RMSD = 0.2125, REP = 2.20%) and this calibration matrix was applied to the analysis of the real samples containing only one dye (R40) and to the samples containing also other dyes, commonly used as the color additives in drink powders. The results obtained were compared with the results of the official spectrophotometric method and with the results of PLS algorithm for different binary dye calibration matrices. A good statistical agreement was obtained in each case, which confirms that some interferences occurring in Spectrophotometric determinations can be eliminated using PLS algorithm and including some possibly interfering compounds in calibration samples.

Simultaneous determination and classification of riboflavin, thiamine, nicotinamide and pyridoxine in pharmaceutical formulations, by UV-visible spectrophotometry and multivariate analysis

Soft Independent Modeling of Class Analogy and Partial Least Squares Regression were used in this work for the identification and quantification of thiamine, riboflavin, nicotinamide and pyridoxine by UV-Vis spectrophotometry, without separation or preconcentration steps in the analytical procedure. For quantitative purposes, the working range established was 1-14 mg L-1 for riboflavin, 2-26 mg L-1 for thiamine, 2-30 mg L-1 for nicotinamide, and 2-22 mg L-1 for pyridoxine. Recovery results higher than 95% were obtained in all cases during the analysis of synthetic and commercial samples. In the screening of each target vitamin, a classification model was built with two classes: (i) with the vitamin of interest, and (ii) without it. The discriminate capability of each classification model was evaluated for learning, independent testing and commercial samples, resulting in satisfactory findings with exception of riboflavin. Thus, a simple and reliable method is proposed for the simultaneous estimation of these compounds.

Enhanced spectrophotometric determination of chromium (VI) with diphenylcarbazide using internal standard and derivative spectrophotometry

In the present work, erioglaucine A was applied as internal standard to enhanced spectrophotometric determination of chromium (VI) with diphenylcarbazide. The following procedure was used: (1) addition of internal standard and formation of ion pairs of Cr (VI) with benzyltributylammonium bromide (BTAB) (sample volume 100 ml), (2) extraction to 10 ml of methylene chloride, (3) evaporation in nitrogen stream, and (4) redissolution in a micro-volume with addition of diphenylcarbazide for color development (final volume 200 mul). The preconcentration factor achieved was about 400 and it was shown that, using internal standard, the analytical errors due to sample treatment were reduced. The analytical signals for chromium and internal standard were obtained at 591.30 and 653.50 nm from first derivative spectra, normalized against (1)D(653.50nm). The analytical characteristics evaluated were: detection limit = 0.06 mug l(-1), quantification limit = 0.19 mug l(-1), precision for 1 mug l(-1) 14.2%, and for 10 mug l(-1) 3.2%, correlation coefficient of linear regression was 0.9985. The proposed procedure was applied to determination of chromium (VI) in tap water. Total chromium was determined by electrothermal atomic absorption spectrometry, the recovery of hexavalent chromium added was then evaluated and compared with the results of the proposed procedure. In this experiment, good agreement was obtained between results obtained by the two methods.

The Resolution of Dye Binary Mixtures by Bivariate Calibration Using Spectrophotometric Data

Abstract A new, simple spectrophotometric method for resolution of dye binary mixtures is proposed in this work. A simple mathematical algorithm was designed, in which the data are used from four linear regression calibration equations: two calibrations for each component at two selected wavelengths. The method of Kaiser was applied for the selection of the optimum two-wavelength sets for all mixtures under study. The recovery experiments were carried out in ten mixtures of the following dyes: Tartrazine, Amaranth, Erythrosin B, Sunset Yellow and Allura Red. The obtained results were compared with the results of a commonly used derivative spectrophotometric procedure (zero-crossing technique). The statistical evaluation of the method bias was performed and it was concluded that the proposed methodology may be competitive with the derivative procedure for the resolution of such dye binary mixtures.

Application of internal standard for derivative-spectrophotometric determination of azinphos-methyl in commercial formulations

The use of an internal standard is proposed in this work for first derivative spectrophotometric determination of azinphos in formulations. Generally, the spectrophotometric procedure is simpler and less expensive than chromatographic techniques recommended for the analysis of pesticides. However, while determining the pesticide in commercial formulations the, many-fold dilution required for such sensitive detection is a serious source of analytical error. It is known that an internal standard (IS), if properly chosen, can help eliminate this type of problem. A mixture of acetophenone (used as an IS in the high performance liquid chromatography (HPLC) procedure) and the blue dye Erioglaucine (A) was applied for the determination of azinphos-methyl in commercial formulations. To ensure the best conditions for the zero-crossing technique, the composition of the mixture was optimized to obtain the zero value of the first derivative absorbance of the IS at a minimum of the azinphos-methyl first derivative absorbance. Also, at the maximum of the first derivative spectrum of the IS, the differential absorption signal of the analyte was negligible. Analytical characteristics for the first derivative spectrophotometric procedure proposed were evaluated (r(2) = 0.9998, detection limit = 0.043 mg, quantification limit = 0.143 mg) and the analytical results obtained (35.02 +/- 0.20% of azinphos-methyl in the formulation) were in good agreement with the results obtained using the official HPLC method (35.44 +/- 0.32%).