Electrifying alkaloids: Poppy principal isolated by electromembrane extraction for HPLC

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  • Published: Nov 14, 2011
  • Author: Steve Down
  • Channels: Sample Preparation
thumbnail image: Electrifying alkaloids: Poppy principal isolated by electromembrane extraction for HPLC

Poppy alkaloids

A relatively new extraction process, electromembrane extraction, has been applied by Iranian scientists to the removal of thebaine, a major poppy alkaloid, from a series of different matrices for analysis by HPLC. Thebaine occurs naturally in poppy seeds and is regarded as a marker compound to distinguish between legal and illegal use of opiates.

The opium alkaloids codeine, morphine and thebaine can be administered for pain relief and poppy seeds containing the alkaloids are often consumed alone or in other foods. So, the alkaloids can enter the body and be excreted in urine in an acceptable and permissible manner.

On the other hand, heroin is manufactured illegally from morphine and both drugs have illicit uses. Heroin and morphine will be detected in the urine of drug users, but thebaine will not, so its presence is an indication of other forms of usage.

Yadollah Yamini and colleagues from Tarbiat Modares University and the Research Center for Organic Chemical Synthesis, Terhan, decided to investigate novel methods of extracting thebaine from human urine, poppy seed capsules, illicit drugs and environmental water to provide a speedier, simpler procedure.

Electromembrane extraction was first reported in 2006 and the applications published to date suggested that it offered the desired characteristics. Essentially, the process is similar to hollow fibre liquid-phase microextraction, but with the application of an electric field across the membrane to improve the efficiency.

Electromembrane extraction of thebaine

A commercial porous polypropylene hollow fibre was selected by the researchers and a platinum wire acting as cathode was positioned within the fibre cavity which was filled with the acceptor solution. This assembly was placed in the sample solution, along with a second platinum wire as anode.

When the predetermined voltage was switched on, the analytes crossed the membrane and were transferred from the sample to the acceptor solution. Portions of this were removed for the direct analysis of thebaine by HPLC with UV-vis detection at 285 nm.

The performances of several acceptor solutions were compared based on the HPLC peak areas and the best was an aqueous solution of 2-nitrophenyl octyl ether. It outperformed the corresponding 2-nitrophenyl pentyl and phenyl ethers, nitrobenzene and silicone oil.

An earlier report had indicated that alkylated phosphate agents such as bis- and tris(2-ethylhexyl) phosphate improved transfer across the membrane but, in this case, the recoveries were markedly reduced, so they were excluded.

The optimum extraction voltage and time were assessed using response surface methodology. The recoveries increased rapidly up to 300 V and 15 minutes, at which the steady state was reached. At greater values, the peak areas fell, probably due to saturation of the analyte in the acceptor phase and back extraction to the sample solution. The recoveries were also improved by acidification of both liquid phases but the addition of salt had a negative effect.

Under test conditions with spiked water samples and spiked urine from a healthy volunteer, the recoveries were 45-55% and the enrichment factors were 95-110. The HPLC detection limits were lower than 0.015 µg/L. The method compared favourably with a range of published procedures with a good linear response range and low intra-day relative standard deviations.

Tracking thebaine

The optimised method was applied to a number of real samples. Iranian tap water, river water and well water were spiked with thebaine and gave relative recoveries higher than 96%, indicating the lack of a matrix effect on the extraction procedure.

Urine from seven opium addicts also gave good relative recoveries of 94.9-99.6% and thebaine was detected in some of the samples.

Poppy seed capsules from plants of the Papaver bracteatum Lindl species were air dried and subjected to an initial ultrasonic extraction with aqueous methanol followed by electromembrane extraction of the extract. Codeine tablets and street heroin were analysed by dissolution in dilute hydrochloric acid before electromembrane extraction.

In all cases, the relative recoveries were greater than 95.9%. No thebaine was found in the codeine tablet, as expected, but the poppy capsule and street heroin were found to contain 0.055 and 0.0034% by weight, respectively.

The key advantages of electromembrane extraction are the reduction in extraction time to a few minutes, the good enrichment factors and high selectivity. The risk of carryover from one extraction to the next is removed by discarding the hollow fibre after single use, which is possible due to its minimal cost.

In this case, the extract within the fibre could be removed and thebaine was analysed directly by HPLC with no further treatment, providing an opportunity to distinguish between legal and illegal use of opiates.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

The poppy alkaloid thebaine has been extracted from various matrices by electromembrane extraction in a rapid process with high enrichment factors for subsequent HPLC analysis

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