Richard Gill

Novel techniques for peak recognition and deconvolution by computer-aided photodiode array detection in high-performance liquid chromatography

Abstract Digital algorithms for manipulating spectrochromatographic data, obtained by means of linear photodiode array detectors, have been examined as tests for peak purity in high-performance liquid chromatography and for their quantitative performance. Two model systems, noscapine and papaverine, and the red pigments R112 and R3, served as examples of closely overlapping and slightly overlapping systems, respectively. The absorbance ratio plot as a function of time performed less well in recognising peak overlap than the second derivative of the elution profile (d2A/dt2). A novel approach has been developed for optimising the spectral suppression technique, where a difference absorbance function deconvolutes a component of known spectral properties to permit detection of 1% noscapine in papaverine, for which the spectra differ substantially. Spectral suppression was less successful in deconvoluting trace amounts of R112 and R3, the spectra of which are closely similar. Spectral deconvolution with a “dummy” linear absorbance standard, and a non-absorbing reference wavelength, permitted the elution profiles of both model systems to be completely resolved. This method revealed the elution profile of an unknown, closely overlapping peak in a forensic sample containing papaverine and noscapine.

Determination of morphine by flow injection analysis with chemiluminescence detection

Chemiluminescence detection has been used in combination with flow injection analysis to determine 1 fmol of morphine by its reaction with permanganate in an acidic tetraphosphate solution. Structurally similar narcotics can also be determined by the same procedure. A mechanism for the chemiluminescent reaction is suggested.

Determination of morphine in body fluids by high-performance liquid chromatography with chemiluminescence detection

HPLC has been used in combination with chemiluminescence detection for the determination of morphine in biological fluids. Solid-liquid extraction procedures for the isolation of morphine from whole blood and urine are described, as is the synthesis of the internal standard, N-ethylnormorphine. Improved selectivity and sensitivity over UV detection is apparent. The procedure has a detection limit of 5 ng of morphine on-column after extraction from blood or urine. The utility of the procedure has been tested on forensic case samples.

High-performance liquid chromatography retention data for 84 basic drugs of forensic interest on a silica column using an aqueous methanol eluent

High-performance liquid chromatography retention characteristics have been measured for 84 basic drugs of forensic interest using a silica column with a methanol-aqueous ammonium nitrate eluent. The drugs are from two classes of major interest, namely, the narcotic analgesics (including antagonists, metabolites and analogues) and drugs structurally and pharmacologically related to amphetamine.

High-performance liquid chromatography systems for the separation of benzodiazepines and their metabolites

The high-performance liquid chromatographic (HPLC) retention characteristics of 21 benzodiazepine drugs and some of their metabolites have been examined on both silica and ODS-silica packing materials. Four HPLC systems have been considered and retention data are presented for the drugs on these systems. The correlation of retention data on the systems is considered with reference to the problem of identifying unknown benzodiazepines.

High-performance liquid chromatography systems for the separation of local anaesthetic drugs with applicability to the analysis of illicit cocaine samples

Two high-performance liquid chromatography (HPLC) systems are presented which are suitable for the separation of local anaesthetic drugs. An octadecyl-silica column is used with aqueous methanolic eluents (15 and 50% respectively) containing n-hexylamine-orthophosphoric acid buffers and data for 36 compounds are given. The HPLC systems have application for the identification of unknown drugs in this class while the first eluent (15% methanol, pH 2.5) is particularly useful for the examination of illicit cocaine samples because it gives good separation of common adulterants and impurities.

The application of retention indices using the alkylarylketone scale to the separation of the barbiturates by HPLC. I. The effect of the eluent

SummaryIn order to determine the applicability of retention indices, based on the alkylarylketone scale, as the basis of a reproducible method of reporting retentions, the separation of ten barbiturates and a set of column test compounds were examined on an octadecylsilyl bonded silica (ODS-Hypersil) column with methanol-buffer pH 8.5 as eluent. The effects on the capacity factors and retention indices, on changing the eluent composition, pH, ionic strength and temperature, showed that the retention indices of the barbiturates were much less susceptible to minor changes in the eluent than the capacity factors. For non-ionised compounds the retention indices were virtually independent of the experimental conditions.

The application of retention indices using the alkylarylketone scale to the separation of the barbiturates by HPLC. II The effect of the stationary phase

SummaryThe capacity factors and retention indices, based on the alkylarylketone scale, of ten barbiturates and a set of five column test compounds have been compared on a series of different octadecylsilyl bonded (ODS) silica columns under identical elution conditions of 40:60 methanol-buffer pH 8.5 at 30 °C. The retentions were highly reproducible on columns prepared from the same batch or different batches of ODS-Hypersil, but large differences in the capacity factors were found when column packings from different manufacturers were compared. Retention indices were more reproducible than capacity factors but they could not compensate for differences between the different packing materials.

Retention reproducibility of thiazide diuretics and related drugs in reversed-phase high-performance liquid chromatography

A method has been developed for the separation of thiazide diuretics and a number of related drugs by high-performance liquid chromatography on an ODS-Hypersil column with acetonitrile-1% aqueous acetic acid as the eluent. The effects caused by changes in the separation conditions on the reproducibility and robustness of alternative methods for recording retentions (including capacity factors, retention indices based on the alkyl aryl ketone scale, and relative capacity factors compared to a thiazide standard) have been examined. The results confirm that good interlaboratory reproducibility will only be achieved when operators control the temperature of the column and use the same brand of column packing material. The retentions should be recorded using a relative method, as these were found to be virtually independent of minor variations in the eluent composition.

High-performance liquid chromatography systems for the analysis of analgesic and non-steroidal anti-inflammatory drugs in forensic toxicology

High-performance liquid chromatography retention data are presented for over 40 analgesic drugs on an ODS-silica packing material to assist in the identification of these compounds. Three isocratic eluents prepared from isopropanol, formic acid and an aqueous phosphate buffer have been used. One eluent has been used for the analysis of paracetamol in whole blood.