BackgroundCannabis has an adverse effect on the ability to drive safely, therefore a rapid disposable test for Δ9-tetrahydrocannabinol (Δ9-THC), the psychoactive component of cannabis, is highly desirable for roadside testing.ResultsA screen printed carbon electrode is used for the N-(4-amino-3-methoxyphenyl)-methanesulfonamide mediated detection of Δ9-THC in saliva. Mediator placed in an overlayer was galvanostatically oxidized and reacted with Δ9-THC to give an electrochemically active adduct which could be detected by chronoamperometric reduction. Detection of 25-50 ng/mL Δ9-THC spiked into undiluted saliva was achieved with a response time of 30 s. A trial of the sensors with four cannabis smokers showed sensitivity of 28 %, specificity of 99 % and accuracy of 52 %.ConclusionsRapid electrochemical detection of Δ9-THC in undiluted saliva has been demonstrated using a disposable sensor, however the sensitivity is lower than acceptable. Further optimization of the assay and sensor format is required to improve the sensitivity of response to Δ9-THC.

Methyl iodide photolysis at 193 nm has been studied through probing the I((2)P(1/2)-(2)P(3/2)) transition in the atomic iodine photofragment using diode laser spectroscopy. The I((2)P(1/2)) quantum yield has been determined through two different diode laser techniques and then compared. Frequency-modulated diode laser based absorption spectroscopy was used to extract nascent Doppler lineshapes from which an I((2)P(1/2)) quantum yield of unity is inferred. However when diode laser gain/absorption measurements were made, an I((2)P(1/2)) quantum yield of 0.68 ± 0.04 was found. The reason for this discrepancy is shown to lie in the diode laser gain/absorption method. Molecular iodine is found to be formed during the experiment via atomic iodine recombination and then in turn dissociates to produce both I((2)P(1/2)) and I((2)P(3/2)), thus distorting the returned quantum yield. This conclusion is supported both by the reduction of the I((2)P(1/2)) quantum yield with number of photolysis laser shots when measured using this technique and by the presence of fluoresence which is shown to have excited-state lifetimes and quenching rates that are consistent with those previously measured for the D and D' states of molecular iodine.

Absolute peak absorption cross sections and pressure broadening coefficients have been recorded with sub-Doppler limited instrumental resolution for selected rotational lines in the 2(0)(2)4(0)(1) vibronic band of the formaldehyde A(1)A2-X(1)A1 electronic transition. The measured absorption cross sections range between (0.18 +/- 0.01) and (10.1 +/- 0.08) x 10(-19) cm2 molecule(-1) and are considerably larger than values from the literature recorded using apparatus where instrumental broadening was significant. However, comparisons with spectral simulations with equivalent resolution from Smith et al. (J. Phys. Chem. A 2006, 110, 11645-11653) are in excellent agreement. Pressure broadening was studied for the collision partners CH2O, CO2, N2, O2, Ne, Kr, Ar, and He, and the resulting broadening coefficients were found to be reduced in comparison to equivalent values measured in infrared regions, consistent with the reduced dipole moment of the upper state probed in this work. Cavity-enhanced absorption spectroscopy (CEAS) measurements were undertaken using calibrated low concentration (2.9-4.6 ppmv) samples from a permeation source and demonstrate a noise equivalent absorption of 1.2 x 10(-6) cm(-1) Hz(-1/2). This implies a minimum detectable formaldehyde concentration with the current system in atmospheric air of 172 ppbv Hz(-1/2).

Frequency modulated diode laser based absorption at 1.315 microm has been used to measure the Doppler lineshapes of the I((2)P(1/2)-(2)P(3/2)) transition in atomic iodine produced from the 266 nm photolysis of both CF(3)I and C(2)F(5)I. Wavelength resolved laser gain is seen following photolysis as excited iodine atoms ((2)P(1/2)) are produced with a quantum yield close to unity from photolysis of both parent molecules. Time resolved measurements were made and the nascent speed distribution and translational anisotropy parameter, beta were determined. Mean atomic speeds of 800 and 850 ms(-1), which correspond to 83 and 68% of the maximum possible kinetic energy release into the iodine photofragment, were determined for photolysis of CF(3)I and C(2)F(5)I, respectively. The nascent translational anisotropy parameter was found to be beta = 1.77 +/- 0.05 for CF(3)I and beta = 1.69 +/- 0.05 for C(2)F(5)I. These values are explicable in terms of parent rotational motion and non-adiabatic processes in the exit channel.

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