Retention reproducibility of basic drugs in high-performance liquid chromatography on a silica column with a methanol-ammonium nitrate eluent. The effect of the mobile phase and the operating conditions

Fluorine-18 and carbon-11 labeled amphetamine analogs--synthesis, distribution, binding characteristics in mice and rats and a PET study in monkey

No-carrier-added (NCA) (+-)-p-[18F]fluoroamphetamine (2a) and (+-)-6-[18F]fluoro-3,4-methylene-dioxy-amphetamine (2b) were synthesized through a multistep synthesis by nucleophilic substitution of the appropriate precursors (p-nitrobenzaldehyde, 1a and 6-nitropiperonal 1b, respectively) with [18F]fluoride followed by condensation with nitroethane and reduction with LAH in 20-30% yield (EOB) in a synthesis time of 90-109 min from EOB. NCA (-)-[11C]methamphetamine (4a) and (+-)-3,4-methylene-dioxy-N-[11C]methamphetamine (4b) were synthesized by methylation of the appropriate desmethyl precursors 3a and 3b with [11C]H3I in 40-60% yield (EOB) in a synthesis time of 30 min from EOB. Animal studies in mouse and rat revealed that the relative tissue uptake of these radiotracers was kidneys > lungs > liver > spleen > brain > heart > blood. The uptakes of these radiotracers in mouse brain were high and similar at 5 min post-injection (approx. 5%/g) but radioactivity then declined rapidly (approx. 1%/g at 60 min post-injection). For compounds 2a and 2b, the activity in the femur did not increase with time indicating in vivo defluorination may not be the major route of metabolism. Monoamine uptake inhibitors (nomifensine, fluoxetine and nisoxetine) did not inhibit but enhance the uptake of (-)-[11C]methamphetamine (4a) in the rat brain by greater than 50%. A PET study in a Rhesus monkey revealed that the uptakes of (-)-[11C]methamphetamine in different brain regions were similar and the retention of the radioactivity in these regions remained constant throughout the study. Analysis of arterial plasma by HPLC showed that 50% of radioactivity remained as 4a at 60 min post-injection.

Retention reproducibility of basic drugs in high-performance liquid chromatography on a silica column with a methanol-high-pH buffer eluent. Changes in selectivity with the age of the stationary phase

The long-term reproducibility of the separation of basic drugs by high-performance liquid chromatography using a silica column with a methanol-high-pH eluent was examined. The relative capacity factors of specific tertiary amines changed systematically compared with the other drugs on storage of the columns for 1 year. The changes were enhanced on storing the column in mobile phase and were accelerated by prolonged washing with water. A comparison of freshly packed columns suggested that similar changes also occurred with the dry silica on storage. These effects may be a contributor to previously observed batch-to-batch differences in the silica.

Separation of basic drugs by high-performance liquid chromatography on a silica column using a methanol-ethylenediamine buffer

The application of methanol-aqueous ethylenediamine-ammonium nitrate eluents has been investigated for the high-performance liquid chromatographic separation of basic drugs on silica stationary phases. These eluents were shown to be more reproducible than previously studied systems based on methanol-aqueous ammonia-ammonium nitrate eluents. The effects of different eluent pH and buffer concentrations have been examined.

International collaborative study of the retention reproducibility of basic drugs in high-performance liquid chromatography on a silica column with a methanol-ammonium nitrate eluent

An international collaborative study between 10 laboratories has been carried out to study the reproducibility of the separation of basic drugs on silica columns. The laboratories used common solutions of drugs on both a common batch of packing material and different batches of the same brand of packing material. These were also compared with separations on other brands of packing material. Variations within-batch, within-brand and between brands have been compared. The retentions of the drugs were compared using retention times, capacity factors and relative capacity factors compared with an internal standard. The last method was found to give the most reproducible results. Considerable variations were found between the different brands of silica with a smaller variation between the batches of a single silica brand. However, unlike earlier studies, significant variations were found for separations on a single batch of silica which were partly attributed to differences in eluent preparation and column temperature.

Retention reproducibility of basic drugs in high-performance liquid chromatography on a silica column with a methanol-ammonium nitrate eluent. Batch-to-batch reproducibility of the stationary phase

The effect of changing the brand and batches of the silica stationary phase used with a methanol-aqueous ammonium nitrate eluent for the high-performance liquid chromatographic separation of basic drugs has been studied. Considerable care had to be taken to obtain a reproducible eluent and the effect of small changes in the concentration of the ammonia solution were examined closely. Large differences in both the capacity factor and relative capacity factors were found for separations on columns packed with four different brands of silica. Significant differences were also observed with columns containing eighteen different batches of Spherisorb S5W, which had been manufactured over a period of several years.