Determination of oxalic acid in biological matrices by liquid chromatography with amperometric detection.

Oxalic acid was separated from interfering compounds with a solvent-generated ion-exchange chromatographic system, and detected with a copper electrode amperometric detector. The lower limit of detection in standard solutions was 5 ng. Complex samples, such as vegetable extracts and urine, could be analysed with a minimum of sample preparation.

Rod outer segment membranes: good acceptors for retinoids?

The exchange of all-trans retinoids (retinal, retinol, retinylpalmitate) between PC-vesicles, PC-vesicles and liver microsomes or PC-vesicles and rod outer segment membranes is investigated using 11,12(3)H labeled compounds. In the first two systems, retinal and retinol exchange rapidly, retinyl acetate slowly and retinyl palmitate not at all. Rod outer segment membranes however take up relatively small amounts of retinoids (retinylpalmitate less than retinol less than retinal) and rapidly lose 60-90% of their label in the presence of PC-vesicles.

Dark isomerization of retinals in the presence of phosphatidylethanolamine.

1. Dark incubation of retinoids (retinyl ester, retinol, retinal, retinaloxime) in suspensions of rod outer segment membranes leads to substantial isomerization (and partial degradation) in the case of retinals only. 2.

Quantitative determination of retinals with complete retention of their geometric configuration.

A method is described for the quantitative extraction of retinal in its original isomeric configuration from retinal-containing pigments. Using excess of hydroxylamine under denaturing conditions, the chromophore of retinal bearing natural products is converted into the corresponding retinaloxime with complete retention of geometric configuration. The retinaloximes can be quantitatively extracted with dichloromethane and analyzed by high-performance liquid chromatography.