Abstract: A flow injection system incorporating multiple incubation coils is used for the automated determination of olive oil 2-thiobarbituric acid reactive substances (TBARS). The use of a laboratory-made parallel flow injection (PA-FI) analyzer. allows the simultaneous incubation of 10 samples. Olive oil samples are injected in a 2.0 x 10^-2 M 2-thiobarbituric acid (TBA) stream in n-propanol and then acidified by merging with a 0.10 M trichloroacetic acid stream in n-propanol. The resulting reaction mixture is diverted to an incubation coil through a stream selection valve. All incubation coils, that are immersed in a water bath at 95±1°C, are loaded in 5 min and then the flow stops for 25 min. After sample incubation, the reaction mixture is cooled by passing through an ice bath and the reaction products are measured at 532 nm. The proposed PA-FI method achieves olive oil analysis without pretreatment and minimizes solvent consumption (1.9 mL of n-propanol, 2.7 mg of TEA and 16 mg of trichloroacetic acid per analysis). Precision was found to be better than 4.6% RSD (n=10). The linear range was (0.4-10) x 10^-4 M (calculated as malondialdehyde (MDA)) and was suitable for olive oil analysis. The proposed method compares well with a manual method (relative difference 0-6.2% for the analysis of 30 olive oil samples). The analysis rate is 20 samples hr-1, while individual samples are incubated for 30 min. The PA-FI analyzer. developed allows automation of methods that require long incubation times without loss of sampling rate, overcoming the one sample at a time disadvantage of Fl.

Abstract: Free malonaldehyde (I) and other thiobarbituric acid-reactive substances were determined in oxidized lipids (prep. described) by HPLC on a column (15 cm x 6 mm) of Inertsil ODS-2 (5 µm) with linear gradient elution (0.7 mL min-1) from aqueous 50 to 100% methanol over 30 min, and held at 100% methanol for 15 min. The eluate was mixed (0.7 mL min-1) with 0.5% 2-thiobarbituric acid in 0.05 M HCl in a reaction coil (20 m x 0.4 mm) at 55°C and the resulting red pigment was determined fluorimetrically at 553 nm (excitation at 515 nm). The calibration graph was rectilinear up to 4 nM-I and the detection limit was 0.5 nM. The procedure was applied in the analysis of thermally oxidized methyl linoleate, the degradation products of methyl linoleate hydroperoxides and the oxidation products of rat liver microsomes.

Abstract: Mercaptopyrimidines (e.g., thiouracils and thiobarbituric acid) were determined by their kinetic catalytic effect upon the cited reaction. At the µg level such compounds could be determined in 50 mL of sample at pH 6 containing 1 g of NaN3 and 10 mL of 0.01 M iodine; after a 2-min induction period, 0.01 M NAASO2 was used for back-titration with starch as indicator. The operating range was typically from ~2 to between 15 and 30 µg of analyte. Determination at the ng level could be achieved by automatic titration with dead-stop end-point detection in 15 mL of solution containing 0.2 g of NaN3 and 4 mL of 0.1 M HCl. Direct titration was with 2.5 mM iodine in 0.2 M KI added at 10 µL min-1. A flow injection technique could also be used with a stream (1.4 mL min-1) of 50 µM-iodine containing 2% of NaN3 and 0.15 M KI at pH 5.9.

Abstract: The on-line voltammetric behavior of several groups of biologically important molecules, (a) 1,4-benzodiazepines, (b) 2-thiobarbituric acids and (c) thioamides, is investigated. A flow through voltammetric cell based on the wall jet principle is described and the DC and pulse working modes are studied in on-line situations. Direct oxidation at the glassy carbon electrode, direct oxidation at a mercury coated glassy carbon electrode and cathodic stripping on this mercury coated glassy carbon electrode have been evaluated with respect to analytical optimization, i.e., in terms of linear range, limit of detection etc.