John W. Birks

The atmosphere after a nuclear war: Twilight at noon

The immediate effects of a global nuclear war are so severe that any additional longterm effects might at first thought be regarded as insignificant in comparison. However, our investigation into the state of the atmosphere following a nuclear exchange suggests that other severely damaging effects to human life and the delicate ecosystems to which we belong will occur during the following weeks and months. Many of these effects have not been evaluated before.

Detection of nitro-polycyclic aromatic hydrocarbons in liquid chromatography by zinc reduction and peroxyoxalate chemiluminescence

Detection limits in the range 0.25-8.5 pg have been obtained for nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) in high-performance liquid chromatography (HPLC). The nitro-PAHs are reduced on-line to the corresponding amino-PAHs and detected by peroxyoxalate chemiluminescence. Quantitative reduction is achieved on a short (3.5 X 0.32 cm) column packed with a 1:1 mixture of glass beads (ca. 40 micron) and zinc particles (40-80 micron). The mobile phase consists of 70-80% acetonitrile, the balance being a 50-mM tris(hydroxymethyl)aminomethane hydrochloride (pH 6.5) buffer, which is necessary both for the reduction and for catalysis of the chemiluminescent reaction. The amino-PAHs are excited by energy transfer from the decomposition products of the reaction between hydrogen peroxide and bis(2,4,6-trichlorophenyl)oxalate. These reagents are introduced by post-column mixing, and the emission is detected by means of a conventional fluorescence detector with its light source turned off. We reported the high sensitivity and selectivity of peroxyoxalate chemiluminescence toward amino-PAHs in earlier work. The method yields a linear response over at least three orders of magnitude, and in most cases the detection limits are better than those obtained by fluorescence detection with the same fluorometer. The reduction column may be placed either before or after the analytical column, so that the analytes are eluted either as the nitro-PAHs or the corresponding amino-PAHs. This feature provides a second characteristic retention time and is useful in identifying the detected compounds. The technique has been applied to the selective detection of nitro-PAHs in carbon black. The carbon black samples were Soxhlet extracted with toluene, evaporated to dryness, and the extracts redissolved in methylene chloride for direct injection into the HPLC column. The principal compounds found in the carbon black samples were poly-substituted nitro-PAHs and unsubstituted PAHs. This method provides a sensitive and selective method for the analysis of complex samples for these environmentally important mutagens.

Crocheted PTFE reactors for post-column photochemistry in HPLC

SummaryConstruction of crocheted photochemical reactors for use in high performance liquid chromatography is described. The design of these reactors is optimal for low intensity light sources because of their cylindrical configuration. Band broadening is minimized by the use of tightly crocheted narrow bore tubing and fittings modified to reduce dead volume. These reactors are suitable for most post-column photochemical reactions with the additional possibility of serving as mixing/delay coils, deoxygenation devices for electrochemical detectors, and as low dispersion detector cells for chemiluminesckent reactions.

Fluorine-induced chemiluminescence detection of biologically methylated tellurium, selenium, and sulfur compounds

SummaryThe sensitive detection of volatile, methylated selenium and tellurium compounds based on capillary gas chromatography coupled to fluorine-induced chemiluminescence detection is described. The method requires no sample derivatization, and the detection limits for selenides and tellurides (low pg range) are the lowest reported to date. This technique can resolve and speciate complex mixtures of methylated tellurium, selenium, and sulfur gases and is useful for analysis of selenium and tellurium gases in environmental samples that also contain usually interfering reduced sulfur gases. Applications of the technique for analysis of bacterial and fungal headspace samples are presented.

Photochemical reaction detection in HPLC

Abstract The versatility of post-column reaction detection in chromatography is greatly enhanced by exploiting the principles of organic photochemistry. Improvements in photochemical reactor design will result in further advantages.

Ozone and meteorological boundary-layer conditions at Summit, Greenland, during 3-21 June 2000

The temporal and spatial distributions of boundary-layer ozone were studied during June 2000 at Summit, Greenland, using surface-level measurements and vertical profiling from a tethered balloon platform. Three weeks of continuous ozone surface data, 133 meteorological vertical profile data and 82 ozone vertical profile data sets were collected from the surface to a maximum altitude of 1400 m above ground. The lower atmosphere at Summit was characterized by the prevalence of strong stable conditions with strong surface temperature inversions. These inversions reversed to neutral to slightly unstable conditions between B9.00 and 18.00 h local time with the formation of shallow mixing heights of B70–250 m above the surface. The surface ozone mixing ratio ranged from 39 to 68 ppbv and occasionally had rapid changes of up to 20 ppb in 12 h. The diurnal mean ozone mixing ratio showed diurnal trends indicating meteorological and photochemical controls of surface ozone. Vertical profiles were within the range of 37–76 ppb and showed strong stratification in the lower troposphere. A high correlation of high ozone/low water vapor air masses indicated the transport of high tropospheric/ low stratospheric air into the lower boundary layer. A B0.1–3 ppb decline of the ozone mixing ratio towards the surface was frequently observed within the neutrally stable mixed layer during midday hours. These data suggest that the boundary-layer ozone mixing ratio and ozone depletion and deposition to the snowpack are influenced by photochemical processes and/or transport phenomena that follow diurnal dependencies. With 37 ppb of ozone being the lowest mixing ratio measured in all data no evidence was seen for the occurrence of ozone depletion episodes similar to those that have been reported within the boundary layer at coastal Arctic sites during springtime. r 2002 Elsevier Science Ltd. All rights reserved.

Photooxygenation-chemiluminescence high-performance liquid chromatographic detector for the determination of aliphatic alcohols, aldehydes, ethers and saccharides

Abstract A novel chemiluminescene high-performance liquid chromatographic (HPLC) detector capable of quantitating many oxygen-containing compounds that cannot be determined by either absorption or fluorescence has been developed in our laboratory. The photooxygenation chemiluminescence (POCL) detector functions by first oxygenating the analytes —aliphatic alcohols, aldehydes, ethers, and saccharides— in a photochemical reaction to produce H 2 O 2 . The H 2 O 2 is then quantitated in the cobalt(II)–luminol chemiluminescence reaction. Since the photochemical reaction is sensitized by anthraquinonedisulfonate, the analytes themselves need not absorb light. The sensitivity of the detector varies for each analyte; however, the detection limits of most analytes are in the low microgram range. This paper demonstrates the use of this detector coupled to HPLC and presents optimization studies of the photochemistry and the chemiluminescence.

New gas chromatographic-electron-capture detection method for the determination of atmospheric aldehydes and ketones based on cartridge sampling and derivatization with 2,4,6-trichlorophenylhydrazine

Abstract The derivatizing reagent 2,4,6-trichlorophenylhydrazine (TCPH) was applied for the first time to the determination of atmospheric aldehydes and ketones using gas chromatography (GC) with electron-capture detection. TCPH is volatile enough to be used with GC without the problems of thermal decomposition or complex procedures associated with other derivatives such as 2,4-dinitrophenylhydrazine. Small cartridges packed with octadecyl silica impregnated with TCPH had collection efficiencies greater than 99% for all carbonyls tested, except for acetaldehyde and propionaldehyde which had collection efficiencies of 80 and 94%, respectively. TCPH requires only 6 min at 100°C for complete reaction with low-molecular-mass carbonyls in the absence of an acid catalyst. Detection limits were determined by the blank and were 0.1 ppb (v / v) for formaldehyde in a 10-1 sample and much lower (typically 0.02–0.03 ppb, v / v) for many other carbonyls. As with other cartridge methods, a negative interference from ozone at 300 ppb (v / v) was found for the reagent and positive interferences were found for several other carbonyls. These interferences were eliminated through the use of sodium thiosulfate as an ozone scavenger.

Minimization of water vapor interference in the analysis of non-methane volatile organic compounds by solid adsorbent sampling.

Water vapor can be a significant interference in the analysis of air for non-methane volatile organic compounds (NMVOCs) using solid-adsorbent sampling techniques. The adsorbent materials used in sampling cartridges have different hydrophobic characteristics, and it is therefore necessary to characterize solid-adsorbent cartridges over a wide range of humidity. Controlled humidity experiments were performed to assess the extent of water vapor interference when samples are collected onto AirToxics solid-adsorbent cartridges. It was found that elevating the temperature of the cartridge to 10 degrees C above the temperature of the air sample greatly reduced water vapor adsorption and interferences and resulted in > or = 90% recovery of NMVOCs, biogenic VOCs and chlorofluorocarbons. Similar collection efficiencies were obtained at ambient temperature by reducing the relative humidity to > or = 60% in the sample by dilution with dry, scrubbed ambient air. A procedure also was developed and optimized for dry-purging cartridges prior to analysis. However, under optimized conditions, significant losses of C3-C5 compounds still occurred under highly humid conditions. It was determined that these losses were due to reduced retention during sampling rather than loss during the dry purge procedure. The dry purge method was shown to be adequate at high humidities for sampling NMVOCs with retention indices greater than 500.

Determination of carbonyl compounds in air by HPLC using on-line analyzed microcartridges, fluorescence and chemiluminescence detection

SummarySensitive and selective detection of dansylhydrazones of atmospheric carbonyl compounds (aldehydes and ketones) can be achieved using high performance liquid chromatography (HPLC) with fluorescence or chemiluminescence detection. The carbonyl compounds are derivatized by drawing air through small glass cartridges packed with porous glass particles impregnated with dansylhydrazine. After sampling, the contents of the cartridges are analyzed on-line by using a small plug of water (200 μL) to transfer and focus the hydrazone derivatives at the head of a HPLC column. Greatly increased sensitivity over traditional methods derives from 1) analysis of the entire contents of the sampling cartridge, and 2) detection by fluoresence or peroxyoxalate chemilum-inescence. Results are compared for photo-initiated and H2O2-initiated peroxyoxalate chemiluminescence. This novel and practical system enables the detection of sub-ppbv concentrations of formaldehyde, acetaldehyde, acetone and higher carbonyls in air using relatively short sampling times.