Glaucia Maria Ferreira Pinto

Use of solid-phase extraction and high-performance liquid chromatography for the determination of triazine residues in water: validation of the method.

A method for determination of some triazine residues in water has been developed. The method involves concentration with C18 solid-phase extraction cartridges followed by high-performance liquid chromatographic analysis using a C18 column with UV detection at 230 nm, a mobile phase of methanol-water (60:40, v/v) at pH 4.6 (phosphoric acid) and a flow-rate of 0.8 ml/min. After optimization of the extraction and separation conditions, the method was validated. The method can be used for determination of atrazine, simazine, cyanazine and ametryn in water, within the international limits of 0.1 microg/l.

Monoglycerides and Diglycerides Synthesis in a Solvent-Free System by Lipase-Catalyzed Glycerolysis

Five lipases were screened (Thermomyces lanuginosus free and immobilized forms, Candida antarctica B, Candida rugosa, Aspergillus niger, and Rhizomucor miehei) to study their ability to produce monoglycerides (MG) and diglycerides (DG) through enzymatic glycerolysis of soybean oil. Lipase from C. antarctica was further studied to verify the enzyme load (wt% of oil mass), the molar ratio glycerol/oil, and the water content (wt% of glycerol) on the glycerolysis reaction. The best DG and MG productions were in the range 45–48% and 28–30% (w/w, based on the total oil), respectively. Using immobilized lipases, the amount of free fatty acids (FFA) produced was about 5%. However, the amount of FFA produced when using free lipases, with 3.5% extra water in the system, is equivalent to the MG yield, about 23%. The extra water content provides a competition between hydrolysis and glycerolysis reactions, increasing the FFA production.

Determination of bentazon residues in water by high-performance liquid chromatography : Validation of the method

A method for determination of bentazon residues in water has been developed. The method involves solid-phase extraction with C18 extraction tubes and high-performance liquid chromatographic analysis. A C18 column and guard column were used with UV detection at 230 nm, a mobile phase of methanol-water (60:40, v/v) at pH 4.6 (phosphoric acid) and a flow-rate of 0.8 ml/min. After optimization of the extraction and separation conditions, the method was validated. The method developed can be used for determination of bentazon in water, within the international limits of 0.1 microgram/l, with a 500-fold pre-concentration.

USE OF SOLID PHASE EXTRACTION AND HPLC FOR DETERMINATION OF HERBICIDE MULTIRESIDUE RECOVERIES IN WATER

A method for simultaneous determination of some herbicide residues in water has been developed. The method involves concentration with C18 solid phase extraction (SPE) cartridges followed by high performance liquid chromatographic (HPLC) analysis using a C18 column with diode array detection, a mobile phase of 50 : 50 (v/v) methanol:water at pH=3.75 (phosphoric acid), and a flow rate of 0.8 mL/min. Method recovery was studied for four different levels of fortification: 0.2, 0.4, 2, and 4 μg/L. A plot of recovery mass x added mass verified the influence of fortification levels in recovery. The recoveries obtained were 58 to 118%, with RSD=1–15% (3–7 replicates) for the herbicides bentazon, cyanazine, 2,4-D, atrazine, simazine, diuron, and linuron in water.

C-18 STATIONARY PHASES SORBED ON ZIRCONIZED SILICA FOR USE IN HPLC

Silica, with 10 μm diameter particles and 8.7 nm pore size, was zirconized (to 16.2% ZrO2) by reaction with zirconium butoxide, then functionalized by sorption of PMODS (poly(methyloctadecylsiloxane)) using an evaporation procedure with hexane as solvent. Infrared spectroscopy was used to examine the surface concentration of silanol groups. The thermal stability of the material was verified by thermogravimetric analysis. The C-18 stationary phase was used to pack 150 × 3.9 mm i.d. columns, which exhibited satisfactory efficiencies (25000–30000 plates/m). The values of asymmetry factor, α, k and Rs were within acceptable limits.