Snow sampling methods

Acidity (pH) and redox-potential (Eh) of melted snow samples were measured by conventional methods using a Yokogawa pH 81 ionometer. The main cations and anions in the melted snow fraction were determined by titrimetric analysis. In group 1 (Institute of Mineralogy UB RAS), AAS (Fe, Mn, Cu, Zn, Ni, Co, Pb, Cd) and titrimetric analysis (Ca, Mg, S, Cl, C) were performed to determine elements in melted snow and solid residue upon filtrating 1 liter snow sample through a 0.5 micrometer pore size filter. 

Extending this investigation and applying the same analytical method, Kolb and Puttmann [26] measured MTBE levels in snow samples (up to... 

An unusual application is described by Fedoseeva, Nechaev, and Strel tsova, who measured the adsorption of thirty-five organic substances on snow surfaces. Toluene was used as solvent since it does not dissolve ice to any appreciable extent, and has a lower density than ice. Of the 34 substances studied only formic, monochloracetic, and trichloracetic acids, and methyl and ethyl alcohols were adsorbed. The type II isotherm for trichloracetic add seemed to exhibit a B-point , use of which led to a surface area of the snow sample of 2.8 0.3 m g, which is similar to the value obtained from the low-temperature N2 adsorption. Further work on the use of calorimetry for the determination of surface areas is described by Rahman, who compares flow and static measurements of the heats of adsorption of stearic add from n-heptane by Fc203 and FeS. It is reported that heats of adsorption determined by these two methods differ by a constant factor that depends to some extent on the operating conditions used in the flow calorimetry. Under standardized conditions and using an FcaOa sample as a reference material, it is considered that flow calorimetry using the adsorption of stearic acid from n-heptane is a reliable method of finding the surface area of oxides. 

In the case of carboxylic acids, analytical procedures are quite different due to their ionic character. Ion chromatography is the method of choice for more volatile carboxyhc acids and data are regularly included with inorganic analysis of major ions such as phosphate and sulphate [65,66]. Formic, acetic and propionic acids are most commonly reported. Recent studies have only been carried out in air. Concentrations in snow were most recently reported by Kippenberger and co-workers [67], who used a liquid chromatography method with time of flight mass spectrometric detection on snow samples from the Fee glacier in Switzerland (at altitudes from 3,056 to 3,580 m asl). The authors also provided older comparison data from remote and urban sites [68-70],... 

Gas chromatography, coupled with flame-ionisation, electron capture (for halogenated species) and mass spectrometric detectors, is the most popular tool for determination of SVOCs in melted snow samples [44]. A prerequisite is the efficient separation of the analytes from the aqueous matrix, which can be accomplished using filtration onto quartz fibre filters and sohd phase extraction [88]. Solid phase micro-extraction, which utilises equihbrium-based adsorption of analytes onto a polymer fibre bundle, has also been proposed and tested in laboratory studies [13, 89]. Both methods allow for an efficient transfer into the injection port of a gas chromatograph without water contamination. Directly coupled inlet sampler with GC-EID instrumentation has also been used [90]. The air sample was pre-concentrated using adsorbents (Carbotrap B, Carbosieve), followed by heating and collection on a cryofocuser (a fused silica capillary tube packed with... 

Although fog, mist, and snow samples require matrix-specific sample collection and sample preparation steps, the resulting aqueous solutions are very similar to rain and may therefore be analyzed using methods developed for rain samples. However, matrix-specific methods and applications are also available [7,73,76]. 

Snow, especially its water-soluble fraction, is one of the most sensitive and informative indicators of mass-transfer in the chain air - soil - drinking water. Therefore analytical data on snow-melt samples were selected for inter-laboratory quality control. Inter-laboratory verification of analytical results estimated in all the groups have shown that relative standard errors for the concentrations of all the determined elements do not exceed (5-15)% in the concentration range 0.01 - 10000 microg/1, which is consistent with the metrological characteristics of the methods employed. All analytical data collected by different groups of analysts were tested for reliability and... 

With analytical methods such as x-ray fluorescence (XRF), proton-induced x-ray emission (PIXE), and instrumental neutron activation analysis (INAA), many metals can be simultaneously analyzed without destroying the sample matrix. Of these, XRF and PEXE have good sensitivity and are frequently used to analyze nickel in environmental samples containing low levels of nickel such as rain, snow, and air (Hansson et al. 1988 Landsberger et al. 1983 Schroeder et al. 1987 Wiersema et al. 1984). The Texas Air Control Board, which uses XRF in its network of air monitors, reported a mean minimum detectable value of 6 ng nickel/m (Wiersema et al. 1984). A detection limit of 30 ng/L was obtained using PIXE with a nonselective preconcentration step (Hansson et al. 1988). In these techniques, the sample (e.g., air particulates collected on a filter) is irradiated with a source of x-ray photons or protons. The excited atoms emit their own characteristic energy spectrum, which is detected with an x-ray detector and multichannel analyzer. INAA and neutron activation analysis (NAA) with prior nickel separation and concentration have poor sensitivity and are rarely used (Schroeder et al. 1987 Stoeppler 1984). 

Hemmi et al. [ 11 ] has described a differential pulse polarographic procedure for the determination of nitrate in environmental samples such as silage, grass, plants, snow and water. This method utilizes the catalytic reaction between nitrate and uranyl ion in the presence of potassium sulfate. The differential pulse polarographic peak is proportional to the nitrate ion concentration from 1 to 50 pmol/1. The detection limit for nitrate in water is 8 x 10 7 mol/1. Using this procedure, between 1 and 70 mg/g nitrate was found in vegetation samples. 

There is no simple device which enables the measurement of dry deposition in a manner as convenient as for wet deposition. Instead, comparatively less direct methods must be used, none of which is fully proven as yet. For particle exchange, leaf-washing and through-fall techniques (1) can provide measurements of the accumulated deposit on natural surfaces. Likewise, accumulation on snow surfaces can be sampled, and subjected to subsequent chemical analysis. It is evident, however, that such methods only apply in certain circumstances. Budget techniques are sometimes advocated, such as in the case of calibrated watersheds, but these have rarely delivered unequivocal results. The difficulty that arises is that the dry deposition must necessarily be computed as the difference between poorly determined in-flow and out-flow measurements. These, and. a wide variety of other experimental methods, have been reviewed elsewhere (2). 

The ideal analytical technique to be used in the challenging task of reconstructing past changes and recent variations in the concentration of trace substances in polar snow and ice should present several important features. Of these, extremely low detection limits, multi-element capability, low sample consumption and the possibility to avoid, as far as possible, any preconcentration step which could be a source of contamination are the most appreciated. Nevertheless, there is currently no technique with all the special features listed above several instrumental methods have been used in the past for trace element determination in polar snow and ice (see Table 3.4). 

Chemical preconcentration of the samples (e.g., extraction into chloroform and dithizone) was used in the past by several authors in order to determine the very low concentration of Pb in ancient Antarctic ice (6, 45, 64). Although this method gave reliable results, it needed a huge amount of sample (500-1000 g) and a long period of sample treatment with organic solvents. Another method is based on the preconcentration onto W wire loops that can be placed directly in a graphite furnace of instrument AAS for the atomisation of adsorbed metals for the analysis (44, 65). To minimise the contamination problems from the air of the laboratory the whole preconcentration procedure was carried out inside a vertical laminar flow clean bench. Detection limits of 0.01, 0.47, 0.22 and 0.24 pg/g were obtained for Cd, Cu, Pb and Zn respectively (44). These extremely low detection limits have recently enabled the concentrations of heavy metals in Antarctic ancient ice and recent snow to be determined (28, 72). 

The low concentrations of Pb found in Greenland and Antarctic snow and ice makes reliable concentration and isotopic composition measurements difficult to determine. Contamination with anthropogenic Pb during sample collection or drilling must be minimised, then extreme precautions must be taken to access a contamination-free sample (12, 28). Sensitive analytical methods which can analyse pg quantities of Pb are also required. A number of different methods meet this requirement however, discussion in this chapter will be limited to Thermal Ionisation Mass Spectrometry (TIMS) because this is the only technique, to date, to be successfully used to measure isotope abundances in polar ice. IDMS is an integral part of the technique used to measure the isotopic composition of the samples. 

Table 12.4 shows the typology and number of specimens. In general, the biotic matrices (mosses, marine organisms) are stored in freezers at -80 or -150°C and the abiotic matrices (sediments, soils, ice, snow) are stored in freezers at -30°C and -80°C, depending on the analytical method used for analysing the samples. The... 

The density change of each layer was measured in the following method. First, we measured the weight of each wooden frame. Second, initial snow was sieved and initial mass of each layer was weighed. Third, after the experiment, we confirmed there were no voids between the layers and mass of each layer was weighed. The density of each layer was calculated from the volume and mass of the sample. 

The search for surface deposits that preserve anomalous oxygen isotope fractionations led fi om improbable sites such as the hyper-arid, super-hot Atacama Desert, Chile, to super-cold sampling pits dug in snow at the South Pole. The proxy dragnet focused on these remote sites because aridity and freezing are two viable methods for preserving water-soluble, direct products of atmospheric chemistry for detailed investigations. Anomalously fractionated... 

Photo-acoustic spectroscopy has been used for ultratrace levels of Hg in air and snow (de Mora etal. 1993). X-ray fluorescence is nondestructive, rapid, requires minimal sample preparation, and was, for example, used successfully to determine the maximal level of mercury in maternal hair to assess fetal exposure (Toribora et al. 1982). However, the procedure is less sensitive compared to AAS and INAA if no pre-concentration is used. Electrochemical methods have been replaced as detectors in chromatography by other instrumental techniques because of poorer detection limits. High-performance liquid chromatography (HPLC) with reductive amperometric electrochemical reduction, however, was shown to be capable of speciating Hg(II), methyl- ethyl- and phenylmercury, with detection limits <2pgL (Evans and McKee 1987). 

Stripping voltammetric methods have phenomenal detection limits (below 100 ppt) for metals Zn, Cd, Pb, Bi, Cu, Sn, Tl, As, Se. The precision in pure solutions is 5-10%. Time for complete (six to eight elements) determination is up to 40 min. The method is an absolute favourite in the analysis of marine and river waters, rain and snow (Golimovsky et al., 1985 Nuernberg, 1985 Van den Berg, 1986 Donat and Bruland, 1988). The determination is independent of salt content Therefore the technique is very useful in marine water analysis. For all other environmental samples where digestion is necessary (soil, plants, sediments, aerosols) the fantastic detection limits are reduced to the normal JLg/kg level (Adeluji et al., 1985 Ostapczuk et al., 1988). This is due to the necessity to obtain interference-free solutions and connected to the problem with reagent blanks. 

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