Cláudio C. Oliveira

Development of a green chromatographic method for determination of colorants in food samples.

A green chromatographic analytical method for determination of Tartrazine, Brilliant Blue and Sunset Yellow in food samples is proposed. The method is based on the modification of a C18 column with a 0.25% (v/v) Triton X-100 aqueous solution at pH 7 and in the usage of the same surfactant solution as mobile phase without the presence of any organic solvent modifier. After the separation process on the chromatographic column, the colorants are detected at 430, 630 and 480 nm, respectively. The chromatographic procedure yielded precise results and is able to run one sample in only 8 min, consuming 15.0mg of Triton X-100 and 38.8 mg of phosphate. When the flow rate of the mobile phase is 1 ml min(-1) the retention times are 2.1, 3.6 and 7.0 min for Tartrazine, Brilliant Blue and Sunset Yellow, respectively; and all peak resolutions are ca. 2. The analytical curves present the following linear equations: area=7.44 10(5)+2.71 10(5) [Tartrazine] (R=0.998, n=7); area=1.09 10(5)+3.75 10(5) [Brilliant] (R=0.9995, n=7) and area=-7.34 10(4)+2.33 10(5) [Sunset] (R=0.998), n=7) and, the limits of detection for Tartrazine, Brilliant Blue and Sunset Yellow were estimated as 0.125, 0.080 and 0.143 mg l(-1). When the proposed method is applied to food samples analysis, precise results are obtained (R.S.D.<5%, n=3) and in agreement with those obtained by using the classical spectrophotometric method. The traditional usage of organic solvent as mobile phase in HPLC is not used here, which permits to classify the present method as green.

Toxicity assessment from electro-coagulation treated-textile dye wastewaters by bioassays.

In this study the pollutant removal from a textile dyeing wastewater has been investigated by using the electro-coagulation technique with iron electrodes. In order to obtain optimal values of the system state variables, a 3(3) full factorial experimental design was applied. The electro-coagulation (EC) process response was evaluated on the basis of COD removal and decolourization values. The electrolysis time and density current were statistically significant for the COD removal and decolourization. Based on the lettuce seeds (Lactuca sativa) and brine shrimp (Artemia salina), the lowest toxicity level was achieved in 5 min of electrolysis time. Due to the remaining high toxicity level above 30 min of electrolysis time, the EC process is not adequate to be used in a single effluent treatment, suggesting that this electrochemical process of up to 5 min could be used as part of a complete effluent treatment system.

Development of a green chromatographic method for determination of fat-soluble vitamins in food and pharmaceutical supplement.

A green chromatographic analytical method for determination of fat-soluble vitamins (A, E, D3 and K1) in food and pharmaceutical supplement samples is proposed. The method is based on the modification of a C18 column with a 3.00% (w/v) sodium dodecyl sulphate (SDS) aqueous solution at pH 7 (0.02 mol L(-1) phosphate buffer solution) and in the usage of the same surfactant solution as mobile phase with the presence of 15.0% (v/v) butyl alcohol as an organic solvent modifier. After the separation process, the vitamins are detected at 230 nm (K1, D3 and E), 280 nm (A, E, D3 and K1) and 300 nm (K1, D3 and E). The chromatographic procedure yielded precise results (better than 5%) and is able to run one sample in 25 min, consuming 1.5 g of SDS, 90 mg of phosphate and 7.5 mL of butyl alcohol. When the flow rate of the mobile phase is 2 mL min(-1) the retention times are 4.0, 9.6, 13.0 and 22.7 min for D3, A, E and K1 vitamins, respectively; and all peak resolutions are higher than 2. The analytical curves present the following linear equations: area=6290+34852 (vitamin A), R2=0.9998; area=4092+36333 (vitamin E), R2=0.9997; area=-794+30382 (vitamin D3) R2=0.9998 and area=-7175+82621 (vitamin K1), R2=0.9996. The limits of detection and quantification for vitamins A, E, D(3) and K(1) were estimated for a test pharmaceutical vitamin supplement sample as 0.81, 1.12, 0.91 and 0.83 mg L(-1) and 2.43, 3.36, 2.73 and 2.49, respectively. When the proposed method was applied to food and pharmaceutical sample analysis, precise results were obtained (R.S.D.<5% and n=3) and in agreement with those obtained by using the classical chromatographic method that uses methanol and acetonitrile as mobile phase. Here, the traditional usage of toxic organic solvent as mobile phase is avoided, which permits to classify the present method as green.

Comparative analysis of eight esterification methods in the quantitative determination of vegetable oil fatty acid methyl esters (FAME)

The results of the quantitative determination of fatty acid methyl esters of vegetable oils, (soybean, flaxseed, and palm oils) by eight basic and acid catalysis esterification methods were compared. The selected methods were described by Metcalfe, 1966 (MET, ref. 17); Bannon, 1982 (BAN, ref. 18); Joseph and Ackman, 1992 (JAC, ref. 3); Hartman and Lago, 1973 (HLA, ref. 19); Jham, 1982 (JHA, ref. 20); ISO 5509, 1978 (ISO, ref. 21); Bannon, 1982 (BBA, ref. 15) and Schuchardt and Lopes, 1988 (SLO, ref. 22). Despite the large variation in the determination of unsaturated fatty acids, all the methods were efficient in the analysis of saturated fatty acids. The results obtained show that fatty acid analysis may be affected by oil composition and that JAC, ISO, and BBA methods are more efficient. ISO, and BBA are recommended for low acidity samples due to their low reagent toxicity and cost. The JAC method is recommended only for high acidity samples, as the ISO and BBA methods are carried out in basic medium and cannot analyze the free fatty acids.

Optimization of the selectivity of a cyanopropyl stationary phase for the gas chromatographic analysis of trans fatty acids

The quantification of monounsaturated and polyunsaturated trans fatty acids in partially hydrogenated fats by gas-liquid chromatography on a CP-Select CB-FAME capillary column was optimized using equivalent chain length values of fatty acids methyl esters that could coelute in the temperature range from 155 to 200 degrees C. The most appropriate temperature for the simultaneous determination of these trans isomers is around 197 degrees C. It is proposed a system to discriminate trans from cis octadecenoic fatty acid methyl esters based on the angular coefficient values of the equivalent chain length curves. The limits of detection and quantification were 0.28 and 0.93 mg g(-1). Quantification was performed in the range from 0.93 to 280 mg g(-1). Quantification accuracy was estimated by spike recovery of elaidic and trans-13-octadecenoic acids in hydrogenated fat samples. The obtained levels were from 97.60 to 103.28% for elaidic acid and from 98.12 to 99.27% for trans-13-octadecenoic acid. These results indicate that the accuracy of the methodology proposed for the quantification of monounsaturated and polyunsaturated trans fatty acids in hydrogenated fats is adequate.

Validation of the determination of fatty acids in milk by gas chromatography

Fatty acid methyl esters (FAMEs) in commercial milk samples were analyzed by gas chromatography coupled with flame ionization detection. The saturated fatty acids (SFA) were the most abundant. The major SFA were palmitic acid (16:0), estearic acid (18:0), and myristic acid (14:0). Significant differences (P 80%), indicating that the method can efficiently determine fatty acids in milk and dairy products.

Exploiting the bead injection concept for sequential determination of copper and mercury ions in river-water samples

A procedure involving bead-injection concept and sequential determination of copper and mercury ions in river-water samples is proposed. The method is based on the solid-phase extraction of both metal ions on the same beads surface (Chelex 100 resin) and in their subsequent reaction with the colorimetric reagents (APDC and Dithizone for copper and mercury ions, respectively). For this task, a resin mini-column is established in the optical path by the selection, introduction and trapping of a defined volume of the Chelex-100 resin beads suspension in the flow system. The passage of the sample solution through the resin mini-column promotes the sorption of Cu(II) ions and, making the APDC colorimetric reagent flows through the beads, the formation of the coloured complex on the solid phase surface occurs. The absorbance of the formed APDC-Cu complex is then monitored at 436nm and the spent beads are discarded. Packing another resin mini-column in the flow cell and repeating the concentration step it is possible to carried out the mercury determination by using Dithizone as reagent. The absorbance of the Dithizone-Hg complex is monitored at 500nm. After each measurement, the spent beads are wasted and a new portion of fresh one is trapped in the system, letting it ready for the next measurement. The bead injection system is versatile and can be used to concentrate different sample volumes, which permits the determination of a wide range of copper and mercury ions concentrations. When the sample-selected volumes are 100 and 1000mul the analytical ranges were 5.0 up to 500.0mugl(-1) and 2.5 up to 30.0mugl(-1) for Cu(II) and Hg(II) ions, respectively. Under these conditions, the detection limit was estimated as 0.63 and 0.25mugl(-1) for copper and mercury ions determination. The system consumes 2mg of Chelex 100 resin beads, 0.20mg of APDC or 1.25mg of Dithizone per determination and the traditional organic solvent extraction methodology, normally used in connection with APDC and Dithizone reagents, is not used here which permits to classify the present method as green.

Fatty acid contents of Brazilian soybean oils with emphasis on trans fatty acids

The fatty acid composition of the main soybean oil brands consumed by the Brazilian has been determined. The mean trans fatty acids (TFA) levels ranged between 0.8 and 2.6% of the total fatty acids and comprised 18:1, 18:2, and 18:3 isomers. 18:1 TFA levels were lower than 0.1% in all the studied brands. Among the polyunsaturated TFA, 18:3 predominated, with levels ranging from 0.5 to 1.4%. This group comprised mono and di-trans fatty acids and the main acid was 18:3 9c,12c,15t. The amounts of 18:2 TFA ranged from 0.3 to 1.1% with a predominance of acid 18:2 9c,12t . Alpha-linolenic acid contents ranged from 3.5 to 5.4%, with a mean value of 4.1%. The degree of isomerization of linoleic and alpha-linolenic acids ranged from 0.5 to 2.1% and from 9.1 to 27.2%, respectively. This study probably indicates that the thermal treatment applied to soybean oil during the deodorization step in the last years is too intense and that it results in a significant decrease in oil alpha-linolenic acid content and an increase in the n-6/n-3 ratio in the Brazilian diet.

Optimised photocatalytic degradation of a mixture of azo dyes using a TiO2/H2O2/UV process

The aim of the present study was to optimise the photocatalytic degradation of a mixture of six commercial azo dyes, by exposure to UV radiation in an aqueous solution containing TiO(2)-P25. Response surface methodology, based on a 3(2) full factorial experimental design with three replicates was employed for process optimisation with respect to two parameters: TiO(2) (0.1-0.9 g/L) and H(2)O(2) (1-100 mmol/L). The optimum conditions for photocatalytic degradation were achieved at concentrations of 0.5 g TiO(2)/L and 50 mmol H(2)O(2)/L, respectively. Dye mineralisation was confirmed by monitoring TOC, conductivity, sulfate and nitrate ions, with a sulfate ion yield of 96% under optimal reactor conditions. Complete decolorisation was attained after 240 min irradiation time for all tested azo-dyes, in a process which followed a pseudo-first kinetic order model, with a kinetic rate constant of approximately 0.018 min(-1). Based on these results, this photocatalytic process has promise as an alternative for the treatment of textile effluents.

Voltammetric determination of pyridoxine (vitamin B6) in drugs using a glassy carbon electrode modified with chromium(III) hexacyanoferrate(II)

A CrIII hexacyanoferrate(II) (CrHCF)-modified glassy carbon electrode was used to determine pyridoxine (vitamin B6) in three drugs by cyclic voltammetry. The influence of several parameters on the voltammetric electrode response was analyzed. The linear range found was of 1.33 × 10-6 mol L-1 to 1.32 × 10-5 mol L-1 of vitamin, with r = 0.9990 and relative standard deviation of 4.2%. The limits of detection and quantification were 3.46 × 10-7 mol L-1 and 1.05 × 10-6 mol L-1, respectively. The voltammetric proposed method for determination of vitamin B6 presented good accuracy and the experimental results demonstrated that the CrHCF-modified glassy carbon electrode has a large potential for the analysis of pyridoxine in real samples. Furthermore, it has the advantages of a fast response, a low detection limit, low cost, and simple development and application.