Andrew C. Dennis

Rapid analysis of ecstasy and related phenethylamines in seized tablets by Raman spectroscopy

Raman spectroscopy with far-red excitation has been used to study seized, tableted samples of MDMA (N-methyl-3,4-methylenedioxyamphetamine) and related compounds (MDA, MDEA, MBDB, 2C-B and amphetamine sulfate), as well as pure standards of these drugs. We have found that by using far-red (785 nm) excitation the level of fluorescence background even in untreated seized samples is sufficiently low that there is little difficulty in obtaining good quality data with moderate 2 min data accumulation times. The spectra can be used to distinguish between even chemically-similar substances, such as the geometrical isomers MDEA and MBDB, and between different polymorphic/hydrated forms of the same drug. Moreover, these differences can be found even in directly recorded spectra of seized samples which have been bulked with other materials, giving a rapid and non-destructive method for drug identification. The spectra can be processed to give unambiguous identification of both drug and excipients (even when more than one compound has been used as the bulking agent) and the relative intensities of drug and excipient bands can be used for quantitative or at least semi-quantitative analysis. Finally, the simple nature of the measurements lends itself to automatic sample handling so that sample throughputs of 20 samples per hour can be achieved with no real difficulty.

Composition profiling of seized ecstasy tablets by Raman spectroscopy.

Raman spectroscopy with far-red excitation has been investigated as a simple and rapid technique for composition profiling of seized ecstasy (MDMA, N-methyl-3,4-methylenedioxyamphetamine) tablets. The spectra obtained are rich in vibrational bands and allow the active drug and excipient used to bulk the tablets to be identified. Relative band heights can be used to determine drug/excipient ratios and the degree of hydration of the drug while the fact that 50 tablets per hour can be analysed allows large numbers of spectra to be recorded. The ability of Raman spectroscopy to distinguish between ecstasy tablets on the basis of their chemical composition is illustrated here by a sample set of 400 tablets taken from a large seizure of > 50,000 tablets that were found in eight large bags. The tablets are all similar in appearance and carry the same logo. Conventional analysis by GC-MS showed they contained MDMA. Initial Raman studies of samples from each of the eight bags showed that despite some tablet-to-tablet variation within each bag the contents could be classified on the basis of the excipients used. The tablets in five of the bags were sorbitol-based, two were cellulose-based and one bag contained tablets with a glucose excipient. More extensive analysis of 50 tablets from each of a representative series of sample bags have distribution profiles that showed the contents of each bag were approximately normally distributed about a mean value, rather than being mixtures of several discrete types. Two of the sorbitol-containing sample sets were indistinguishable while a third was similar but not identical to these, in that it contained the same excipient and MDMA with the same degree of hydration but had a slightly different MDMA/sorbitol ratio. The cellulose-based samples were badly manufactured and showed considerable tablet-to-tablet variation in their drug/excipient ratio while the glucose-based tablets had a tight distribution in their drug/excipient ratios. The degree of hydration in the MDMA feedstocks used to manufacture the cellulose-, glucose- and sorbitol-based tablets were all different from each other. This study, because it centres on a single seizure of physically similar tablets with the same active drug, highlights the fact that simple physical descriptions coupled with active drug content do not in themselves fully characterize the nature of the seized materials. There is considerable variation in the composition of the tablets within this single seizure and the fact that this variation can be detected from Raman spectra demonstrates that the potential benefits of obtaining highly detailed spectra can indeed translate into information that is not readily available from other methods but would be useful for tracing of drug distribution networks.

Raman spectroscopy of the high- and low-spin states of the spin crossover complex Fe(phen)2(NCS)2: an initial approach to estimation of vibrational contributions to the associated entropy change

Abstract Raman spectra of the spin-crossover complex Fe(phen) 2 (NCS) 2 in the solid state have been recorded at 785 nm as a function of temperature to investigate the contribution of intramolecular vibrations to the entropy change, Δ S , associated with spin crossover. The modes of major interest for estimating the contribution lie in the range 100–500 cm −1 , where the largest qualitative changes with temperature in the Raman spectra were observed. Analysis of these data, with the working assumption of an average frequency in this range as representative of the 15 distortion modes of an idealised FeN 6 octahedron, leads to the conclusion that the intramolecular vibrations represent a primary contribution to the total Δ S .

Analysis of luminescent samples using subtracted shifted Raman spectroscopy

A novel method of obtaining high-quality Raman spectra of luminescent samples was tested using cyclohexane solutions which had been treated with a fluorescent dye. The method involves removing the fixed pattern irregularity found in the spectra taken with CCD detectors by subtracting spectra taken at several different, closely spaced spectrometer positions. It is conceptually similar to SERDS (shifted excitation Raman difference spectroscopy) but has the distinct experimental advantage that it does not require a tunable laser source. The subtracted spectra obtained as the raw data are converted into a more recognisable and conventional form by iterative fitting of appropriate double Lorentzian functions whose peak parameters are then used to ‘reconstruct’ a conventional representation of the spectrum. Importantly, it is shown that the degree of uncertainty in the resultant ‘reconstructed’ spectra can be gauged reliably by comparing reconstructed spectra obtained at two different spectrometer shifts (δ and 2δ). The method was illustrated and validated using a solvent (cyclohexane) the spectrum of which is well known and which contains both regions with complex overlapping bands and regions with isolated bands. Possible sources of error are discussed and it is shown that, provided the degree of uncertainty in the data is correctly characterised, it is completely valid to draw conclusions about the spectra of the sample on the basis of the reconstructed data. The acronym SSRS (subtracted shifted Raman spectroscopy; pronounced scissors) is proposed for this method, to distinguish it from the SERDS technique.

Vibrational spectrum of the spin crossover complex [Fe(phen)2(NCS)2] studied by IR and Raman spectroscopy, nuclear inelastic scattering and DFT calculations

The vibrational modes of the low-spin and high-spin isomers of the spin crossover complex [Fe(phen)(2)(NCS)(2)] (phen = 1,10-phenanthroline) have been measured by IR and Raman spectroscopy and by nuclear inelastic scattering. The vibrational frequencies and normal modes and the IR and Raman intensities have been calculated by density functional methods. The vibrational entropy difference between the two isomers, DeltaS(vib), which is--together with the electronic entropy difference DeltaS(el)--the driving force for the spin-transition, has been determined from the measured and from the calculated frequencies. The calculated difference (DeltaS(vib) = 57-70 J mol(-1) K(-1), depending on the method) is in qualitative agreement with experimental values (20-36 J mol(-1) K(-1)). Only the low energy vibrational modes (20% of the 147 modes of the free molecule) contribute to the entropy difference and about three quarters of the vibrational entropy difference are due to the 15 modes of the central FeN(6) octahedron.

Examination of the physical state of chlorhexidine within viscoelastic, bioadhesive semisolids using Raman spectroscopy

This study examined the effects of polymeric components on the physical state of chlorhexidine within bioadhesive, semisolid formulations using Raman spectroscopy. Semisolid formulations were prepared in which chlorhexidine base (CHX, 5%w/w, particle size <63 microm) was dispersed in aqueous (phosphate-buffered saline, pH 6.8) polymer matrices consisting of one or more polymeric components, namely HEC (3%w/w), PVP (3%), and PC (PC, 3%). Raman spectra were recorded using 785-nm excitation and were typically accumulated for 360 s. The Raman spectra were dominated by the presence of CHX. The spectra of CHX in HEC and in HEC/PVP gels were indistinguishable from that for solid CHX as a result of the insolubility of CHX in these formulations. However, in systems containing PC and CHX, there was a shift in the strongest band from 1564 cm(-1) to 1608 cm(-1), which may be accredited to protonation of the basic CHX by the numerous carboxylic acidic groups on PC. Identical shifts in the band positions were observed when this protonation was modeled using ethanoic acid, supporting the view that there was a simple acid base reaction between PC and CHX. However, there were notable differences in the relative intensities of the peaks from these samples, with the spectrum of CHX in the PC matrix displaying properties intermediate between those of CHX dissolved in ethanoic acid and solid CHX diacetate. This may be accredited to the limited solubility of the CHX-PC ion pair. In matrices containing HEC and PC, no peak was observed at 1564 cm(-1), whereas the intensity of the peak at 1608 cm(-1) was increased. Therefore, in these formulations CHX was completely converted to the di-cation as a result of the synergistic effects of PC (which protonated CHX) and HEC (which solubilized the di-cation). In the absence of either HEC or PC, complete protonation was not achieved. It is suggested that this enhancement of solubility of H(2)CHX(2+) may be due to hydrogen bonding, given the hydroxylated nature of HEC. In conclusion, this study has shown the applicability of Raman spectroscopy for both the analysis of opaque, semisolid formulations and, additionally, for the examination of the state of therapeutic agents within such matrices. In particular, using Raman spectroscopy, it was uniquely possible to identify the roles of various polymeric components on both the ionization and solubilization of CHX within aqueous semisolid systems.

Characterization of silicone elastomer vaginal rings containing HIV microbicide TMC120 by Raman spectroscopy.

Silicone elastomer vaginal rings are currently being pursued as a controlled‐release strategy for delivering microbicidal substances for the prevention of heterosexual transmission of HIV. Although it is well established that the distribution of drugs in delivery systems influences the release characteristics, in practice the distribution is often difficult to quantify in‐situ. Therefore, the aim of this work was to determine whether Raman spectroscopy might provide a rapid, non‐contact means of measuring the concentrations of the lead candidate HIV microbicide TMC120 in a silicone elastomer reservoir‐type vaginal ring. Vaginal rings loaded with TMC120 were manufactured and sectioned before either Raman mapping an entire ring cross‐section (100 μm resolution) or running line scans at appropriate time intervals up to 30 h after manufacture. The results demonstrated that detectable amounts of TMC120, above the silicone elastomer saturation concentration, could be detected up to 1 mm into the sheath, presumably as a consequence of permeation and subsequent reprecipitation. The extent of permeation was found to be similar in rings manufactured at 25 and 80°C.

Off-line reaction monitoring of the oxidation of alkenes in water using drop coating deposition Raman (DCDR) spectroscopy

The application of drop coating deposition Raman (DCDR) spectroscopy to the field of reaction progress monitoring is addressed in this contribution. Although, DCDR spectroscopy has seen recent application in the study of biological fluids, its application in other areas has not yet been explored. Here we apply the technique to the catalysed oxidation of alkenes to epoxides in aqueous solutions at concentrations <10 mM. The effect of surface characteristics, background interferences, homogeneity of distribution of analytes, drying time, as well as instrumental limits of detection and calibration are discussed. We demonstrate that reproducible spectra can be obtained routinely, with relatively little variance, with short acquisition times and samples volumes of 2-10 μl and as little as 1 μg of analyte. The utility of the technique compared with online reaction monitoring by (1)H NMR and Raman spectroscopy is demonstrated in the excellent correlation between data obtained off and on-line.

Resonance Raman spectroscopy of bioadhesive transdermal patches for percutaneous local anaesthesia

Raman spectroscopy is a technique of increasing interest due mainly to its non-invasive nature. It has been widely employed in the characterisation of drug penetration across the skin barrier (Anibogu et al 1995) and in determining the structural similarities between skin from different species (Williams et al 1994). In addition, water exhibits negligible Raman scattering, making the technique suitable for the analysis of pharmaceutical and biological systems. For example, as Raman spectroscopy is insensitive to skin hydration, it has been employed in monitoring drug release from aqueous systems into the stratum corneum (Williams et al 1993). The local anaesthetic amethocaine has been formulated successfully as a gel (McCafferty and Woolfson 1988) and more recently as a bioadhesive transdermal patch, offering enhanced drug stability and patient convenience (Woolfson et al 1998). In order to check whether drug release is retarded by interaction of amethocaine with the polymeric components of the patch system, resonance Raman spectroscopy has been employed as a non-invasive characterisation technique. In addition, several recent technical advances in this area, particularly concerning diode laser excitation sources and holographic notch filters, have been employed (Angel et al 1996). Bioadhesive films were formulated as described previously (Woolfson et al 1998). Raman spectra were recorded on an Andor RAMANSPEC dispersive instrument employing a diode laser source operating at 785nm (20mW), a wavelength at which background fluorescence from samples is significantly reduced (Wang and McCreery 1989). Figure 1 shows spectra of loaded and unloaded gels. The scattering due to the patch backing film and gel (Fig.l(b)) was sufficiently weak not to cause significant spectral interference. In conjunction with automatic background subtraction, this allowed the direct, non-destructive acquisition of spectra of amethocaine in the gels. Figure 1 indicates that the anaesthetic is apparently unaffected by, and exhibits no physicochemical interactions with, the gel into which it is loaded. This is significant in terms of drug release, showing that the drug is unbound within the polymer matrix. Thus, the materials chosen for the local anaesthetic patch are compatible with the system. This is consistent with previous thermal analysis and drug stability studies (Woolfson and McCafferty 1993).