Biomedical subjects

Marina Franco Maggi Tavares

Publications and source records attributed to Marina Franco Maggi Tavares.

4 recordsLinked to original sources

PubMed2006

Method development and validation for isoflavones in soy germ pharmaceutical capsules using micellar electrokinetic chromatography.

The separation of six soy isoflavones (Glycitein, Daidzein, Genistein, Daidzin, Glycitin and Genistin) was approached by a 3(2) factorial design studying MEKC electrolyte components at the following levels: methanol (MeOH; 0-10%) and sodium dodecylsulfate (SDS; 20-70 mmol L(-1)); sodium tetraborate buffer (STB) concentration was kept constant at 10 mmol L(-1). Nine experiments were performed and the apparent mobility of each isoflavone was computed as a function of the electrolyte composition. A novel response function (RF) was formulated based on the production of the mobility differences, mobility of the first and last eluting peaks and the electrolyte conductance. The inspection of the response surface indicated an optimum electrolyte composition as 10 mmol L(-1) STB (pH 9.3) containing 40 mmol L(-1) SDS and 1% MeOH promoting baseline separation of all isoflavones in less than 7.5 min. The proposed method was applied to the determination of total isoflavones in soy germ capsules from four different pharmaceutical laboratories. A 2h extraction procedure with 80% (v/v) MeOH under vortexing at room temperature was employed. Peak assignment of unknown isoflavones in certain samples was assisted by hydrolysis procedures, migration behavior and UV spectra comparison. Three malonyl isoflavone derivatives were tentatively assigned. A few figures of merit for the proposed method include: repeatability (n=6) better than 0.30% CV (migration time) and 1.7% CV (peak area); intermediate precision (n=18) better than 6.2% CV (concentration); recoveries at two concentration levels, 20 and 50 microg mL(-1), varied from 99.1 to 103.6%. Furthermore, the proposed method exhibited linearity in the concentration range of 1.6-50 microg mL(-1) (r(2)>0.9999) with LOQ varying from 0.67 to 1.2 microg mL(-1). The capsules purity varied from 93.3 to 97.6%.

Algorithms↗

PubMed2005

Determination of alpha-hydroxy acids in cosmetic products by capillary electrophoresis.

In this work, a simple and reliable method for the simultaneous analysis of alpha-hydroxy acids such as tartaric, glycolic and lactic acids in cosmetic products was developed using capillary electrophoresis with indirect UV detection at 254 nm. A buffer solution containing 10 mmoll(-1) potassium phthalate (pH 4.1) and 0.5 mmoll(-1) cetyltrimethylammonium bromide as electroosmotic flow modifier allowed baseline resolution of the analytes in approximately 3 min. A few validation parameters of the proposed method include: good linearity for all compounds in the range from 10 to 100 mgl(-1) with coefficients of correlation larger than 0.9999. The average recoveries of tartaric, glycolic and lactic acids in commercial samples were 99.12, 99.41 and 99.43%, respectively. The method presented acceptable precision with average relative standard deviation of 0.54% (assay of commercial samples), 0.44% (peak area) and 0.16% (migration time).

Cosmetics↗

PubMed2005

Optimizing the separation of food dyes by capillary electrophoresis.

In this work, the separation of eleven food dyes was evaluated by MEKC in electrolytes composed of tetraborate (TBS), Brij 35, and acetonitrile (ACN) using a factorial design at the following levels: TBS concentration (5 and 10 mmol L(-1)), pH (9.5 and 10.1), Brij concentration (5 and 20 mmol L(-1)), and ACN (5 and 15%). Several response functions were evaluated and indicated 10 mmol L(-1) TBS (pH 10.1), 15% ACN, and 20 mmol L(-1) Brij 35 as best values. However, baseline resolution was not achieved (R(cp) = 0.76) and the method lacked robustness. New conditions were sought by studying the dye mobility versus Brij concentration (5-20 mmol L(-1)). A set of well resolved and more uniformly spaced peaks was obtained with an electrolyte consisting of 7.5 mmol L(-1) TBS (pH 10.1), 10 mmol L(-1) Brij, and 15% ACN. Under these new conditions, complete resolution of the 11 dyes was achieved in less than 9 min. Migration time and peak area repeatabilities were better than 1.6% and 5% CV and the LODs were 0.47 to 2.3 microg mL(-1). The methodology was applied to fruit juice powders, lollipops, and other hard and soft chewable treats.

Coloring Agents↗

PubMed2003

Novel approach for the analysis of glycated hemoglobin using capillary isoelectric focusing with chemical mobilization.

In this work, a novel CIEF methodology for the analysis of the glycated hemoglobin, HbA(1c), in dimethylpolysiloxane coated fused-silica capillaries (DB-1, 50 microm I.D., 27 cm, 0.20 microm coating thickness), using a narrow pH ampholyte mixture (4% pH 6-8:pH 3-10, 10:1, v/v) in 0.30% methylcellulose, was developed. In the focusing procedure, a 0.100-mol l(-1) phosphoric acid solution was used as anolyte and a 0.040-mol l(-1) NaOH solution was used as catholyte. During method development, two types of mobilization of the focused hemoglobins were tested: pressure and chemical mobilization. Chemical mobilization performed better, allowing the complete baseline resolution of the hemoglobin of interest, HbA(1c), from its adjacent peak, HbA, in less than 8 min. In the chemical mobilization procedure, the catholyte was replaced by a 0.040-mol l(-1) NaOH solution containing 0.080 mol l(-1) NaCl. The proposed methodology was applied to the analysis of 31 hemolysate samples and validated with respect to the selectivity, inter-assay and intra-assay precision (both migration time and hemoglobin percentage concentration). In addition, HbA(1c) determinations were compared for the CIEF method and a chromatographic standardized procedure using cation-exchanger columns (Variant, Bio-Rad), adopted in a local clinical laboratory, showing excellent correlation (r(2)=0.872, n=31). The slope was found to be statistically equal to one but the intercept differed from zero. Also the Bland-Altman plot indicates bias, implying that the CIEF method yields HbA(1c) concentration higher than the reference method. The separation of the hemoglobins HbA, HbA(2), HbF and HbA(1c) and the variants HbS and HbC was also demonstrated (8 min run). The resolving power of the proposed CIEF method allowed baseline resolution of hemoglobins with a pI difference as small as ca. 0.03, as it is the case for the pairs HbC/HbA(2) and HbA/HbA(1c).

Calibration↗