Search

A study of the on-line phase-transfer catalysed dansylation of phenolic compounds is presented. The extraction-dansylation is performed in the extraction coil of a home-made flow-injection extraction unit. After phase separation, the organic phase is fed to a normal-phase liquid chromatographic system with fluorescence detection. Ethynyloestradiol, oestradiol and paracetamol are used as test compounds. The influence of temperature on the reaction is examined. Calibration graphs showed good linearity (r greater than 0.996) and limits of detection are satisfactory (8 x 10(-7) M for ethynyloestradiol, 2 x 10(-6) M for oestradiol and 5 x 10(-7) M for paracetamol). The method is not applicable for the assay of oxychinoline, phenylephrine and morphine.

Benzalkonium chloride was assayed by on-line extraction of the benzalkonium ion with picrate to chloroform. The absorbance of picrate was measured. The extractions were performed with a home-made flow injection extraction unit. Calibration curves (1.5-180 x 10(-4)% w/v) were straight lines (r = 0.9993) and the relative standard deviation of a series of injections was less than or equal to 2%. Pharmaceutical benzalkonium preparations, containing xylometazoline, timolol, phenylephrine or carbachol could also be assayed. The method was compared with a modified HPLC assay.

Three electrochemical detection systems for the liquid chromatography of N-acetylcysteine in plasma have been compared: a dropping-mercury electrode detector, an amalgamated-gold electrode detector and a system in which iodine is generated electrochemically in the column effluent. The last detector approaches the reproducibility of the first (R.S.D. = 2%) and is as sensitive as the second, with a detection limit of 0.1 micrograms/ml plasma.