Response surface methodology toward the optimization of high-energy carotenoid extraction from Aristeus antennatus shrimp

High-energy assisted extraction techniques, like ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE), are widely applied over the last years for the recovery of bioactive compounds such as carotenoids, antioxidants and phenols from foods, animals and herbal natural sources. Especially for the case of xanthophylls, the main carotenoid group of crustaceans, they can be extracted in a rapid and quantitative way with the use of UAE and MAE.     

Catalytic-kinetic potentiometric determination of thyroxine

A kinetic method is described for the determination of thyroxine (0.4–4 μg ml^?1), based on its catalytic effect on the reduction of cerium(IV) by arsenic(III). The reaction is monitored potentiometrically; the time required for a 20-mV change in potential is inversely proportional to the thyroxine concentration. The method is applicable to tablets.     

Chemiluminometric determination of vanillin in commercial vanillin products

Vanillin, ethylvanillin and 4-hydroxy-3-methoxy-benzylalcohol have been found to chemiluminesce by the action of potassium permanganate in sulphuric or polyphosphoric acid media. Both acid media have been compared and sulphuric acid allows the sensitive determination of 0.15-10.0, 0.010-1.0 and 0.0030-0.30 μg mL⁻¹ of vanillin, ethylvanillin and 4-hydroxy-3-methoxy-benzylalcohol with limits of detection equal to 0.045, 0.0030 and 0.00090 μg mL⁻¹, respectively. Recoveries of vanillin from commercial vanillin products are within the range of 95-109%. Comparison with results from the official method shows differences within the range of 0.5-3.0%. The chemiluminogenic reaction mechanism is also discussed.     

Continuous-flow molecular emission cavity analysis for organic sulphur compounds by alkaline hydrolysis

Alkaline hydrolysis of various organic sulphur compounds (thioacetamide, thiosemicarbazide, thiodiacetic acid and dithiooxamide) in a continuous-flow analyzer produces sulphide which can be removed from the solution after acidification. Hydrogen sulphide evolved is measured by molecular emission cavity analysis. Samples can be analyzed at a rate of 30 h^?1 with a relative error of 1–2%.