Gaseous sample analysis

Fundamentally, introduction of a gaseous sample is the easiest option for ICP/MS because all of the sample can be passed efficiently along the inlet tube and into the center of the flame. Unfortunately, gases are mainly confined to low-molecular-mass compounds, and many of the samples that need to be examined cannot be vaporized easily. Nevertheless, there are some key analyses that are carried out in this fashion the major one i.s the generation of volatile hydrides. Other methods for volatiles are discussed below. An important method of analysis uses lasers to vaporize nonvolatile samples such as bone or ceramics. With a laser, ablated (vaporized) sample material is swept into the plasma flame before it can condense out again. Similarly, electrically heated filaments or ovens are also used to volatilize solids, the vapor of which is then swept by argon makeup gas into the plasma torch. However, for convenience, the methods of introducing solid samples are discussed fully in Part C (Chapter 17). 

Photometric Moisture Analysis TTis analyzer reqiiires a light source, a filter wheel rotated by a synchronous motor, a sample cell, a detector to measure the light transmitted, and associated electronics. Water has two absorption bands in the near infrared region at 1400 and 1900 nm. This analyzer can measure moisture in liquid or gaseous samples at levels from 5 ppm up to 100 percent, depending on other chemical species in the sample. Response time is less than 1 s, and samples can be run up to 300°C and 400 psig. 

CF-IRMS provides reliable data on micromoles or even nanomoles of sample without the need for cryogenic concentration because more of the sample enters the ion source than in DI-IRMS. CF-IRMS instruments accept solid, liquid, or gaseous samples such as leaves, soil, algae, or soil gas, and process 100-125 samples per day. Automated sample preparation and analysis takes 3-10 min per sample. The performance of CF-IRMS systems is largely determined by the sample preparation technology. A variety of inlet and preparation systems is available, including GC combustion (GC/C), elemental analyzer, trace gas pre-concentrator and other. The novel... 

A gaseous sample is pulled into an empty container such as a metal canister. In the laboratory, the sample is often chilled to isolate the volatile compounds. The container may then simply be rinsed with a solvent to capture these compounds. The solvent can then be directly injected into a suitable instrument for analysis, such as a gas chromatograph (GC). 

This completely automated spectrum analysis procedure represents the final element in our effort to reduce to routine practice the quantitative analysis of similarly constituted gaseous samples by FTIR. It has seen wide and successful application within our laboratory, having been the principle analytic method for two extensive hydrocarbon species-specific auto exhaust catalyst efficiency studies, a comprehensive study of the gases emitted by passive-restraint air bag inflators, several controlled furnace atmosphere analyses, several stationary source stack emission checks and several health-related ambient atmosphere checks. 

ASTM International (2007) ASTM D6866-08 Standard test methods for determining the biobased content of solid, liquid, and gaseous samples using radiocarbon analysis. ASTM International, West Conshohocken... 

Industrial analysis of hydrocarbon gases 25 years ago was limited almost to Orsat-type absorptions and combustion, resulting in crude approximations and inadequate qualitative information. The more precise method of Shepherd (56) was available but too tedious for frequent use. A great aid to the commercial development of hydrocarbon gas processes of separation and synthesis was the development and commercialization of high efficiency analytical gas distillation units by Podbielniak (50). In these the gaseous sample is liquefied by refrigeration, distilled through an efficient vertical packed column, the distillation fractions collected as gas and determined manometrically at constant volume. The operation was performed initially in manually operated units, more recently in substantially automatic assemblies. 

Gas chromatography is a very unique and versatile technique. In its initial stages of development, it was applied to the analysis of gases and of vapors from very volatile components. The work of Martin and Synge (36) and then James and Martin (54) in gas-liquid chromatography (GLC) opened the door for an analytical technique which has revolutionized chemical separations and analyses. As an analytical tool GC can be used for the direct separation and analysis of gaseous samples, liquid solutions, and volatile solids. 

Thus, a poly isobutylene coating on silver halide optical fiber was used for environmental analysis of chlorinated hydrocarbons in water in an instrument designed for operation in seawater 500 m under the surface (Fig. 9.27). The enrichment membrane concept can be used for FTIR-ATR analysis of liquid and gaseous samples alike. 

Figure 10.2 is a schematic diagram of a helium MIP-MS system, with gaseous sample introduction, developed by the Caruso group. This is the most popular method of sample introduction to date for MIP-MS analysis as the MIP at low pressures is not tolerant to liquid samples. A commercial ICP-MS system may be modified by mounting an MIP discharge source in place of the ICP source. A Beenakker cavity is commonly used as the microwave source and serves to focus the microwave energy. Cavity construction and dimensions have been described in detail by Evans et al. [18]. 

The sampling loops were replaced by two stainless steel U-tubes of 1.5- and 20-cc. capacity. The expansion bomb is a 1.7-liter stainless steel cylinder. The trap between the helium supply and the Beckman valve is 1/4-inch stainless steel tubing. A null detector is used to measure pressures in the inlet system. Samples are obtained in 10-ml. stainless steel cylinders fitted with a Vg-inch stainless steel Hoke valve with a V-stem and Teflon packing. When the sample is liquid, it is entirely vaporized into the 1.7-liter expansion bomb, and a gaseous sample is taken for infrared, near infrared, and gas chromatographic analysis. 

Using internal standards in quantitative analysis is advantageous, for instance, in cases where the sample thickness cannot be determined exactly, or in gaseous samples whose total pressure is unknown. The compound which serves as an internal standard should have a simple spectrum which does not interfere with the bands of the analyte. It should be a stable substance, readily available, and non-toxic. The following substances have been recommended as internal standards by Colthup et al. (1975)... 

Thermogravimetric analysis (TGA) is a successful and widely employed technique of measuring the change of weight of a sample as a function of the temperature whereas IR spectroscopy has been successfully employed to identify gaseous samples. Recent publications (Wieboldt et al. (1988) Belz (1989) demonstrate that a combination of these two techniques allows complete characterization of materials in terms of thermal stability and decomposition mechanisms. 

Applications of NTDs are mainly focused on the analysis of gaseous samples and biomedical analyses [64—68]. An important development direction is derivati-zation in the needle to enhance sensitivity [69]. NTD combines the advantages of SPME with the sensitivity of traditional sorbent traps. However, the main drawback is low reproducibility of the needle packing. 

GD-AES has also been used for GC detection in mercury speciation analyses [283]. Also, an atmospheric pressure GD atomic emission source was designed for direct sampling in liquid media however, the preliminary limits of detection for elements such as Na, Fe and Pb were in the range 11-14 ppm (ca. 60 ng) for 5 pi sample volumes [284]. Specific applications to liquid and gaseous samples, and couplings to chromatographs for wet speciation analysis can be found in recent reviews such as that by Baude et al. [285]. 

Laser-induced breakdown spectrometry was used for the analysis of gaseous samples containing elements such as F, Cl, S, P, As and Hg in air, and hydrides of column 111 and V elements (e.g. B,H, PH,) [184-189]. The aim was to measure trace amounts of analytes in hostile environments and gas impurities for hydride work. Mercury was detected at the parts-per-billion level in air using a photodiode array detector that recorded single-shot spectra over a range of 20 nm [186]. Cremers el al. [189] reported limits of detection of 8 and 38 pg/ml for chlorine and fluorine, respectively, the source of both... 

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