Sulphur gases sampling

In contrast, their experiments showed that decomposing sulphides evolved only CS2 and COS, in order of decreasing abundance. In addition, measurements of the Eh and pH of the final solutions from moist and saturated sulphide mineral experiments showed that CSi and COS were formed under metastable oxidising conditions (Fig. 8-5). Pyrite produced the largest amounts of sulphur gases, more than chalcopyrite, sphalerite and galena (Fig. 8-6). Moist (not saturated) and non-sterile (as compared to sterile) conditions enhanced sulphur-gas evolution from pyrite samples. Sulphur gas evolution from saturated pyrite samples is shown in Fig. 8-7. 

Surface microlayer samples have shown sulphur-gas anomaly patterns that are more closely related to known mineralisation than sulphur-gas patterns from deeper soil samples (Lovell, 1979). At Johnson Camp, Arizona, mineralisation is best expressed by sulphur compounds from the surface microlayer, while sulphur compounds from 0-5 cm reflect the same mineralisation to a lesser extent, and sulphur compounds from 30-40 cm show the least expression of the mineralisation. A comparison of concentrations of COS, CS2, and SO2 degassed from soils collected at depths of 0.5-2 cm and 30-40 cm at the same sites near Casa Grande, Arizona, showed almost identical patterns of sulphur-gas concentrations over a 150 km (58 square miles) area. Average concentrations of COS, CS2 and SO2 were slightly higher in the shallow samples than in the deeper samples (Hinkle, unpublished data, 1981). These data indicate that, at least in arid areas, surficial soil and microlayer samples are superior to deeper augered samples. 

Total (non-speciated) sulphur analysis may yield all the information needed or desired for some sampling programmes. When only a total sulphur measurement is required, the gas sample is passed through an empty Teflon column, by-passing the chromatographic column, and is sent directly into the detector (Tracor, 1973 Lovell, 1979). Total sulphur analyses can be very rapid, requiring less than 2 min. per analysis. 

A soil-gas sample collected by hollow probe needs no further preparation for injection into a GC system. However, the results obtained from sulphur analysis of a soil gas may be inaccurate representatives of their original state in the field. The time elapsed between collection of the sample in the field and analysis in the laboratory permits many changes in the sample. Some sulphur components may adsorb on the walls of the glass, plastic, or stainless-steel syringes or sample carriers used for sample transportation. Non-adsorbed components may interact with each other. The most reliable soil-gas analyses are those made almost immediately after collection. Even these analyses may not be completely accurate. 

Soil-gas samples collected on adsorbents should be stored in the same manner as soil samples to prevent drying out and loss of sulphur compounds. Samples collected in solutions or on filters are generally analysed immediately or shortly after collection. 

A different approach was used by Lovell (1979) and Lovell et al. (1980) who used the soils themselves as sulphur-gas adsorbents. The field programme consisted of three soil sampling traverses with a total of 185 sites (Fig. 8-17). The sample interval was generally 30 m, but where traverses A-A and C-C overlay Zone I, the interval was narrowed to 10 m... 

Whilst the general pattern of anomalous sulphur-gas concentrations in a study area remains fairly constant from season-to-season, the concentrations themselves may vary. Therefore, analytical results should be interpreted on samples that were collected during the same time period. Interpolation of results obtained from different field seasons will probably lead to confusion. 

As with other procedures for the production of a gas sample for isotopic analysis, caution is required to ensure complete conversion at each stage of the preparation to obviate kinetic fractionation. Sulphides may be oxidized directly to SO2 for isotopic analysis [113] and recently methods have been developed for the thermal decomposition of sulphates [114,115]. An alternative approach is the initial conversion of either sulphate or sulphide to hydrogen sulphide [116, 117] from which the sulphur is precipitated as silver sulphide. This latter sulphide is easily oxidised in a reproducible manner to provide pure SO2 for isotopic analysis. 

Solid-phase microextraction (SPME) was used for headspace sampling. The FFA were extracted from the headspace with PA, Car/PDMS, and CW/DVB fibers. It was examined whether addition of salt (NaCl) and decreasing the pH by addition of sulphuric acid (H SO ) increased the sensitivity. FFA were analyzed using gas chromatography coupled to mass spectrometry in selected ion monitoring. 

An important application of gas chromatography is its use for determination of the elements carbon, hydrogen, nitrogen, oxygen and sulphur in organic and organometallic samples. A brief account of the procedure used is given here,... 

To determine the quinine content of tonic water it is first necessary to de-gas the sample either by leaving the bottle open to the atmosphere for a prolonged period or by stirring it vigorously in a beaker for several minutes. Take 12.5 mL of the de-gassed tonic water and make up to 25 mL in a graduated flask with 0.1M sulphuric acid. From this solution prepare other dilutions with 0.05M... 

Aircraft turbines in jet engines are usually fabricated from nickel-based alloys, and these are subject to combustion products containing compounds of sulphur, such as S02, and oxides of vanadium. Early studies of the corrosion of pure nickel by a 1 1 mixture of S02 and 02 showed that the rate of attack increased substantially between 922 K and 961 K. The nickel-sulphur phase diagram shows that a eutectic is formed at 910 K, and hence a liquid phase could play a significant role in the process. Microscopic observation of corroded samples showed islands of a separate phase in the nickel oxide formed by oxidation, which were concentrated near the nickel/oxide interface. The islands were shown by electron microprobe analysis to contain between 30 and 40 atom per cent of sulphur, hence suggesting the composition Ni3S2 when the composition of the corroding gas was varied between S02 02 equal to 12 1 to 1 9. The rate of corrosion decreased at temperatures above 922 K. 

Tan [71] devised a rapid simple sample preparation technique for analysing polyaromatic hydrocarbons in sediments. Polyaromatic hydrocarbons are removed from the sediment by ultrasonic extraction and isolated by solvent partition and silica gel column chromatography. The sulphur removal step is combined into the ultrasonic extraction procedure. Identification of polyaromatic hydrocarbon is carried by gas chromatography alone and in conjunction with mass spectrometry. Quantitative determination is achieved by addition of known amounts of standard compounds using flame ionization and multiple ion detectors. 

Goerlitz and Law [59] determined chlorinated insecticides in sediment and bottom material samples, which also contained polychlorobiphenyls by extracting the sample with acetone and hexane. The combined extracts were passed down an alumina column. The first fraction (containing most of the insecticides and some polychlorinated biphenyls and polychlorinated naphthalenes) was eluted with hexane and treated with mercury to precipitate sulphur. If the polychlorinated hydrocarbons interfered with the subsequent gas chromatographic analysis, further purification on a silica gel column was necessary. 

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