George Davidson

Exposure to airborne dust contaminated with pesticide in the Aral Sea region.

The Aral Sea region is one of the worlds foremost ecological disaster zones and there is increasing local concern for the health of millions of people living in this region. We have found that dust deposition rates across eastern Turkmenistan are among the highest in the world and that the dust is contaminated with pesticide.

Identification and analysis of polymer additives using packed-column supercritical fluid chromatography with APCI mass spectrometric detection

Packed-column supercritical fluid chromatography (pSFC) with detection using atmospheric pressure chemical ionisation (APCI) mass spectrometry (MS) provides a versatile method for the detection and quantification of 20 polymer additives, including common antioxidants, light stabilisers and slip agents. Using MS with APCI in both positive and negative ion modes both molecular mass data and informative fragmentation patterns were obtained. The pSFC-MS technique was shown to be linear over a wide concentration range (0.05–25 µg ml–1) and picogram limits of detection with positive ion APCI (single ion monitoring) were determined for Tinuvin 327 (68 pg) and Irganox 1010 (390 pg). The corresponding figures for negative ion APCI were 150 and 470 pg, respectively. Standard mixtures of additives could be separated in less than 15 min with a high degree of resolution. Experiments on additives extracted from polyethylene confirmed these observations, and it was possible not only to identify a number of the additives, but also, in the case of the antioxidant Irgafos 168, an oxidation product.

Vibrational spectra of some “pure” π-allyl complexes

Abstract IR and Raman spectra are described for (π-C3H5)2M (M = Ni, Pd), (π-2-methylallyl)2Ni and (π-C3H5)3M′ (M′ = Rh, Ir). In each case, the internal allyl vibrations can be assigned assuming effectively non-interacting ligands of Cs symmetry. The skeletal vibrations are consistent with C2h symmetry for the bis-, and C3v symmetry for the tris-complexes.

The vibrational spectrum of (butadiene) iron tricarbonyl

Abstract The vibrational spectrum of C 4 H 6 Fe(CO) 3 has been studied. An assignment of the frequencies on the basis of the local symmetry of the Fe(CO) 3 fragment (C 3v ) explains most of the observations, but the FeC and CO stretching modes of E symmetry are both split. Therefore the effective symmetry must be C s The C 4 H 6 vibrations are assigned on the basis of C s symmetry throughout.

The analysis of β-agonists by packed-columnsupercritical fluid chromatography with ultra-violet and atmospheric pressure chemical ionisation mass spectrometric detection

Packed-column supercritical fluid chromatography (pSFC) using ultra-violet (UV) and atmospheric pressure chemical ionisation (APCI) mass spectrometry (MS) provides a versatile method for the identification and quantification of β-agonists. We have achieved good separation of clenbuterol, salbutamol, terbutaline and fenoterol with good resolution and reasonable retention times using a high concentration of methanol modifier in the supercritical CO2, together with small amounts of both acidic (trifluoroacetic acid, TFAA) and basic (triethylamine, TEA, or diethylamine, DEA) additives. APCI-MS gave unambiguous identification of the 4 analytes, and increasing cone voltage provided informative fragmentation patterns. The pSFC-MS technique was shown to be linear (R2 ≥ 0.996) over the concentration range 1–50 µg ml–1. Single ion monitoring (SIM) gave detection limits (on-column) of 2.5 ng (clenbuterol), 0.83 ng (terbutaline), 7.6 ng (salbutamol) and 2.7 ng (fenoterol). The pSFC-MS system was shown to be reproducible within a day, between days, and between restrictors. Analysis of milk samples ‘spiked’ with β-agonists showed that the matrix caused no interference, with detection limits of approximately 500 µg l–1 of β-agonists. More dilute solutions could be analysed by pre-concentration before the SFC stage.

Analysis of artemisinin by a packed-column supercritical fluid chromatography-atmospheric pressure chemical ionisation mass spectrometry technique

A packed-column supercritical fluid chromatography-atmospheric pressure chemical ionisation mass spectrometry method was studied for the determination of artemisinin from Artemisia annua L. extracts. The technique does not require any kind of derivatisation prior to the analysis. All samples were simply dissolved in methanol and injected into the mobile phase. Detection was achieved by using mass spectrometry with atmospheric pressure chemical ionisation. The ionisation technique is relatively soft and provides protonated molecular ion and informative structural fragmentation for the compound. Benzophenone was used as a chromatographic standard for the determination of the analytical reproducibility. The supercritical carbon dioxide mobile phase used in the system was modified by 10% methanol. The average absolute retention time was 3.54 min with a standard deviation of 0.017 min and a relative standard deviation of 0.4% with respect to benzophenone for the procedure. The correlation coefficient was 0.998 and detection limit 370 pg on column.

A study of the vibrational spectrum of ethyleneiron tetracarbonyl

Abstract An almost complete assignment of the vibrational modes of the comples (C 2 H 4 )Fe(CO) 4 has been made. The (strongly coupled) CH 2 in-plane symmetric deformation and C=C stretching frequencies are 1510 and 1193 cm −1 , with the Fe-(C 2 H 4 ) stretch and tilts at 361,305 and 401 cm −1 .

The vibrational spectra of mesitylenechromium tricarbonyl and mesitylenemolybdenum tricarbonyl

The infrared (15062-4000 cm(−1) and Raman spectra (50–3200 cm−1) of [1,3,5C6H3(CH3)3]M(CO)3 were obtained, for M = Cr and Mo. The method of “local symmetry” was used to obtain a vibrational assignment. The results were largely in agreement with previous, incomplete, infrared studies of these and similar molecules.

A preliminary study of the analysis of explosives using packed-column supercritical fluid chromatography with atmospheric pressure chemical ionisation mass spectrometric detection

Abstract A packed-column supercritical fluid chromatographic (SFC) separation of explosive compounds hyphenated to atmospheric pressure chemical ionisation (APCI) mass spectrometric (MS) detection has been developed. Nitroaromatics, nitramines and nitrate esters can be resolved and identified, with theoretical limits of detection of approximately 100 ng on column. This represents a development over previously described gas chromatography–thermal energy analysis (GC–TEA), gas chromatography– electron capture detection (GC–ECD) and SFC methods for the analysis of explosives due to the molecular identification afforded by the mass spectrometry. Explosives in the combinations expected in commercially available mixtures can be separated and identified. A successful application to a laboratory trial simulating casework is described.

A study of vibrational force constants in some transition metal-ethylene π-complexes

Abstract Approximate force-fields have been calculated for the complex-fragments (C 2 H 4 )Fe and (C 2 H 4 )Pt. The metalligand bonding is much stronger in the later case, as shown by the larger value of f (MC) and the smaller value of f (CC). Many of the normal modes were shown to be derived from more than one type of internal coordinate, and hence the vibrational wavenumbers themselves are of limited value in discussions of bonding in such molecules.