Sulfuric acid Quinidine

The choice of the mobile phase is very important, as fluorescence is sensitive to fluorescence quenchers. Highly polar solvents, buffers, and halide ions quench fluorescence. The pH of the mobile phase is also important to fluorescence efficiency for example, quinine and quinidine only display fluorescence in strongly acidic conditions, whereas oxybarbiturates are only fluorescent in a strongly alkaline solution [67,68]. Due to the stability of the chromatographic sorbents, the use of very acidic or basic mobile phase may not be possible. One alternative is to alter the effluent pH postcolumn. Postcolumn addition of sulfuric acid has been used for the assay of ethynodiol diacetate and mestranol in tablets [69]. Another example is the determination of tetracycline antibiotics in capsules and syrup where EDTA and calcium chloride were added to enhance fluorescence [70]. 

Column yBondapak C18 (300x3.9 mm ID), mobile phase acetonitrile - methanol - 1% aqueous ammonium carbonate (65 31 4), flow rate 3.5 ml/min, detection with a fluorimeter after postcolumn addition of sulfuric acid (excitation 350 nm, emission 450 nm). Peaks 1, 3-hydroxy-quinidine 3, quinidine 6, dihydroquinidine 2,4 and 5 unidentified metabolites. Limit of sensivity 50 ng/ml plasma. (Reproduced with permission from ref. 34, by courtesy of the American Chemical Society). 

Quinine is separated from quinidine in normal phase TLC in mobile phases composed of chloroform, acetone, and ethyl acetate to which alcohols such as methanol, propanol, or butanol are added as polarity adjusters and ammonia or diethylamine to reduce spot tailing [43], Common solvent systems used for the separation of cinchona alkaloids include chloroform/diethylamine (90 10, v/v) or toluene/ethyl acetate/diethylamine (70 20 10, v/v/v). After spraying the chromatogram with sulfuric acid, these alkaloids show a blue fluorescence in UV-365 nm. Treatment afterwards with iodoplatinate reagent gives a violet coloration in the visible [53]. 

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