Determination of tretinoin in creams by high-performance liquid chromatography.

A stability indicating reversed-phase high-performance liquid chromatographic method has been developed to quantify tretinoin (all-trans-retinoic acid) in cream formulations. Tretinoin cream samples were dissolved directly in tetrahydrofuran and diluted for injection. Separation was accomplished on a 15 cm Nova-Pak C18 column using a tetrahydrofuran-phosphate buffer solvent system (42:58, v/v) and 1.0 ml/min flow-rate. The method is able to separate tretinoin from its degradation products formed under stressing conditions. Excellent precision and accuracy were found for the assay of tretinoin in the cream formulations.

Liquid chromatographic separation of metals by on-column chelation with 4-(2-pyridylazo) resorcinol.

A method for the separation of trace levels of Zn(II), Fe(II), Ni(II) and Co(II) by on-column formation of their complexes with 4-(2-pyridylazo)resorcinol and subsequent separation of the complexes by reversed-phase liquid chromatography is described. Either acidic or buffered mobile phases can be used. For the separation using acidic mobile phases the role of the mobile-phase pH, concentration of PAR, and type of stationary phase is described. For buffered (slightly acidic) mobile phases it is shown that the complexing ability of the buffer can be used to influence the separation. Data on the use of this system for quantitative analysis are included.

Preconcentration of some transition and rare-earth elements by Donnan dialysis.

A method using Donnan dialysis for the preconcentration of some transition and rare-earth elements is described. Enrichment factors of about 20 are obtained in 1 hr. Calibration curves that are linear over 2 orders of magnitude are obtained with a relative precision of about 3% when Co(II) is used as an internal standard. The effect of aluminium in the receiver electrolyte on the interference caused by phosphate in the sample solution is discussed.

The use of brilliant green in ion-pair chromatography.

Brilliant Green is used as the stationary phase in the ion-pair chromatography of butanoic, pentanoic, octanoic and lauric acids, with hexane-dichloromethane as eluent.