Halocarbons analysis

The availability of tropospheric air samples from 55°N to 53°S latitudes obtained for halocarbon analysis [Makide and Rowland, 1981] has permitted an extension of our measurements of the world-wide distribution of trace atmospheric species to methane [Mayer et al., 1982]. Only about a doxen air samples were available for our initial latitudinal sequence in early 1978, but subsequent collections have provided much larger numbers of samples, as shown in Figures 5 and 6 for two collection periods during 1982 and 1983. From 1978-1981 most of our southern hemisphere sample collections were made at coastal sites in Brazil and Chile. However, comparisons were made of the relative latitudinal behavior of CHiCCh and CH4, based on the assumption that both are chiefly removed... 

The two chromatograms shown in Figs. 23-3 and 23-4 demonstrate two modes of halocarbon analysis. They differ only in the timing of P Tevents and the temperature programme of the GCoven, parameters that are all software controlled. 

Rasmussen, R.A. (ed.) 19 Rep. Workshop on Halocarbon Analysis and Measurement, NASA-NBS-NSF Boulder Colorado, March 1976... 

Analytical Procedures. Standard methods for analysis of food-grade adipic acid are described ia the Food Chemicals Codex (see Refs, ia Table 8). Classical methods are used for assay (titration), trace metals (As, heavy metals as Pb), and total ash. Water is determined by Kad-Fisher titration of a methanol solution of the acid. Determination of color ia methanol solution (APHA, Hazen equivalent, max. 10), as well as iron and other metals, are also described elsewhere (175). Other analyses frequendy are required for resia-grade acid. For example, hydrolyzable nitrogen (NH, amides, nitriles, etc) is determined by distillation of ammonia from an alkaline solution. Reducible nitrogen (nitrates and nitroorganics) may then be determined by adding DeVarda s alloy and continuing the distillation. Hydrocarbon oil contaminants may be determined by ir analysis of halocarbon extracts of alkaline solutions of the acid. 

Entz RC, Hollifield HC. 1982. Headspace gas chromatographic analysis of foods for volatile halocarbons. 

Analysis of the halohydrocarbons, halocarbons, and sulfur hexafluoride is usually achieved by gas chromatography that is equipped with an electron capture detector. Complex metal anions, such as cobalt hexacyanide, are used as nonradioactive tracers in reservoir studies. The cobalt in the tracer compound must be in the complex anion portion of the molecule, because cationic cobalt tends to react with materials in the reservoir, leading to inaccurate analytic information [1226]. 

Corwen [58] used this method for the analysis of ketones and aldehydes in seawater. Halocarbons were similarly separated from environmental samples by Kaiser and Oliver [59]. There have been many other applications of the technique [60-69]. The major advantage of the headspace method is simplicity in handling the materials. At most, only one chemical, the salt used in the salting-out procedure, needs to be added and in most cases the headspace gas can be injected directly into a gas chromatograph or carbon analyser. On the other hand the concentration of organic materials present is limited by the volume of seawater in the sample bottle. This is very much a batch process. 

Kaiser and Oliver [218] applied dynamic purge and trap analysis to determine halocarbons in seawater. 

Other reactants that have been used to generate chemiluminescent reactions useful for chemical analysis include atomic sodium to detect halocarbons and chlorine dioxide to detect H2S and CH3SH. 

Pellizzari ED, Sheldon LS, Bursey JT. 1985a. Method 25. GC/MS determination of volatile halocarbons in blood and tissue. In Environmental Carcinogens selected methods of analysis. Fishbein L, O Neill IK, eds. Lyon, France. International Agency for Research on Cancer, 7 435-444. 

EPA. 1982a. Methods for organic chemical analysis of municipal and industrial wastewater Purgeable halocarbons-method 601. Cincinnati, OH U.S. Environmental Protection Agency, Office of Research and Development. EPA- 600/4-82-057. 

Simmonds PG. 1984. Analysis of trace halocarbons in natural waters by simplified purge and cytotrap method. J Chromatogr289 117-127. 

Atlas, E and S. Schauffler, Analysis of Alkyl Nitrates and Selected Halocarbons in the Ambient Atmosphere Using a Charcoal Preconcentration Technique, Environ. Sci. Technol., 25, 61-67 (1991). 

This presentation focuses on the vertical distribution of halocarbons obtained by analysis of cryogenically collected whole-air samples. The balloon-borne cryogenic samplers developed and flown by the Max-Planck-Institut fur Aeronomie (MPAE) and the Kem-forschungsanlage Jiilich (KFA) are described by Fabian [17] and Schmidt [18]. Between 1977 and 1993, a total of 33 balloon ascents have been carried out by both institutions, 28 at northern midlatitudes (southern France, 44°N), 3 at high latitudes(Kiruna, 69°N) and 2 in the tropics (Hyderabad, 17,5°N). These stratospheric data are limited to balloon altitudes, i.e. up to about 35 km. Tropospheric data were obtained from balloon samples, samples collected aboard aircraft and at ground level. 

Tmdinger CM, Etheridge DM, Sturrock GA, Fraser PJ, Krummel PB, McCulloch A (2004) Atmospheric Histories of Halocarbons from Analysis of Antarctic Fim Air Methyl Bromide, Methyl Chloride, Chloroform, and Dichloromethane. J Geophys Res 109 D22310... 

Purge-and-trap collection is well suited to biological samples that are soluble in water and is readily adapted to biological samples from techniques that have been developed for the analysis of halocarbons such as chlorobenzene in water and wastewater. For water-insoluble materials, the purge-and-trap approach is complicated by the uncertainty of partitioning the analyte between sample slurry particles and water. 

If residual chlorine is present, add sodium thiosulfate (-100 mg/L) for its removal. Ascorbic acid may also be added to reduce residual chlorine. The latter is preferred if the analysis includes gaseous halocarbons. 

We are not yet sure what causes the positive effect of the carbon coating on the performance of AP-MgO in the reactions with halocarbons. The carbon coating may adsorb some of the reaction products or impurities in the feed, that allows for a faster reaction of the halocarbons with the oxide core. Further studies including mass-spectrometric analysis of the gas phase composition are required. 

There is growing evidence that the composition of the troposphere is changing. For example, analysis of historical ozone records has indicated that tropospheric ozone levels in both hemispheres have increased by a factor of 3-A over the last century. Methane concentrations have effectively doubled over the past 150 years and N2O levels have risen by 15% since pre-industrial times.Measurements of halocarbons have shown that this group of chemically and radiatively important gases to be increasing in concentration until relatively recently. 

---