A novel spot test based on digital images for determination of methanol in biodiesel.

Methanol is used in transesterification reaction for biodiesel production, being an important quality parameter to evaluate the purity of the final product. Methanol concentrations higher than 0.20% (m/m) reduce the biofuel efficiency. The Brazilian, United States, and European standards recommend the reference method based on gas chromatography with flame ionization detection, which involves a time-consuming procedure and requires high-cost equipment. In this work, it is proposed a simple and low cost spot test based on digital images acquired with a smartphone camera for the determination of methanol in biodiesel. The procedure was based on the oxidation of methanol to formaldehyde and subsequent reaction with Schiff reagent, resulting in a violet product. Analytical signals were based on the reflected radiation measured on the G channel (RGB system), which refers to the complementary color of the reaction product. Linear responses were obtained within 20-500 mg kg-1 and 500-2000 mg kg-1 methanol for 600 and 150 µL of sample aqueous extracts, respectively. The coefficient of variation (n = 10) and the limit of detection (99.7% confidence level) were estimated as 4.8% and 10 mg kg-1 (600 µL of sample), respectively. The procedure requires only 75 µg of potassium permanganate, 6 mg of oxalic acid, and 1.5 mg of p-rosaniline and generates ca. 1.2 mL of residue per determination. The results agreed with those obtained by the reference procedure at the 95% confidence level, demonstrating that the proposed method is an alternative for routine analysis of the biofuel.

Development of non-enzymatic glucose sensor using recycled cobalt from cell phone Li-ion batteries.

This article aims to present an alternative to recycling of spent Li-ion batteries applied to electrochemical sensor manufacturing. The cobalt, from cathode of Li-ion batteries, was recovered by electrodeposition onto AISI 430 stainless steel substrate and applied as glucose sensor. The composition of cathode utilized was obtained by AAS measures and corresponds to LiNi0,40Co0,60O2. Despite this composition, in the cobalt electrodeposition onto AISI 430 stainless steel the Ni is less of 1.7% (w/w) due the anomalous electrodeposition. The sensitivity of cobalt electrode for glucose detection is 70.2 µA/mmol cm(2) and the linear range is 1-10 mmol/L. This result shows that the Co electrodeposited onto AISI 430 stainless steel is a promissory and low-cost non-enzymatic glucose sensor.

Determination of cadmium and lead in beverages after leaching from pewter cups using graphite furnace atomic absorption spectrometry.

Two simple methods have been developed to determine cadmium and lead in different kinds of beverages and vinegar leached from pewter cups produced in Brazil. Leaching experiments have been carried out with different solutions: beer, sugar cane spirit, red and white wine, vinegar and a 3% acetic acid solution. The solutions were kept in cups with and without solder for 24h. Lead and cadmium have been determined using graphite furnace atomic absorption spectrometry with deuterium background correction. The limits of detection were 0.05 and 1.4 µg L(-1), and the characteristic mass was 1.0 pg and 19 pg for Cd and Pb, respectively. With the developed methods it was possible to determine accurately cadmium and lead by direct analysis in these liquids and to evaluate the leaching of these metals from pewter cups. The results presented in this work show that pewter cups are not cadmium- and lead-free; this point goes against the manufacturers' declaration that their products are lead-free.

An automatic flow procedure for the determination of 3-hydroxybutyrate in animal serum and plasma.

An automatic flow procedure based on the multicommutation concept, comprising three-way solenoid valves, for the spectrophotometric determination of 3-hydroxybutyrate in animal serum and plasma is proposed. The 3-hydroxybutyrate was enzymatically converted to acetoacetate with the reduction of NAD+ to NADH monitored at 340 nm. It was possible to carry out up to 600 determinations without a significant decrease in the analytical signal, with 5 mg of 3-hydroxybutyrate dehydrogenase immobilized on porous silica beads and packed in a column. The system enabled 60 determinations/h of 3-hydroxybutyrate in the range of 10-150 mg L(-1), with a consumption of 0.9 mg of NAD+ and 200 microL of sample per determination. A detection limit of 2 mg L(-1) for both animal serum and plasma and coefficients of variation of 1.4% and 1.2% (n = 17), respectively, were determined. Animal serum and plasma samples were analyzed without previous treatment, the results of which agreed with those obtained using the conventional method (UV kit, Sigma).

Multicommuted flow system for the determination of glucose in animal blood serum exploiting enzymatic reaction and chemiluminescence detection.

An automatic flow procedure based on multicommutation dedicated for the determination of glucose in animal blood serum using glucose oxidase with chemiluminescence detection is described. The flow manifold consisted of a set of three-way solenoid valves assembled to implement multicommutation. A microcomputer furnished with an electronic interface and software written in Quick BASIC 4.5 controlled the manifold and performed data acquisition. Glucose oxidase was immobilized on porous silica beads (glass aminopropyl) and packed in a minicolumn (15 x 5 mm). The procedure was based on the enzymatic degradation of glucose, producing hydrogen peroxide, which oxidized luminol in the presence of hexacyanoferrate(III), causing the chemiluminescence. The system was tested by analysing a set of serum animal samples without previous treatment. Results were in agreement with those obtained with the conventional method (LABTEST Kit) at the 95% confidence level. The detection limit and variation coefficient were estimated as 12.0 mg l(-1) (99.7% confidence level) and 3.5% (n = 20), respectively. The sampling rate was about 60 determinations h(-1) with sample concentrations ranging from 50 to 600 mg l(-1) glucose. The consumptions of serum sample, hexacyanoferrate(III) and luminol were 46 microl, 10.0 mg and 0.2 mg/determination, respectively.