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Vapor Generation Methods

Several methods to generate controlled vapor concentrations that are currently in use are briefly described in this section. Each vapor generation technique serves a specific purpose. The most important difference among these techniques is the range of the vapor concentration generated. [Pg.71]

Vapor concentration depends on several factors such as the size of the dispersion bottle, the temperature of the liquid, and the carrier gas flow rate. It can be expected that the carrier gas at a higher flow rate may not be vapor saturated at the outlet since it is constantly passing through the liquid without sufficient residence time to reach liquid — vapor equilibrium. Increasing the volume above the liquid or decreasing the flow rate of the dilution gas prolongs residence time and increases the saturation level of the generated vapor at the outlet. If equilibrium can be established. [Pg.71]

Many practitioners also calculate average concentration based on the gravimetric method during a test. The gravimetric method measures the weight change after a test period. The evaporation rate (R va) of the chemical is calculated as follows  [Pg.72]

When the flow rate of the carrier gas is controlled as a constant during the test and temperature change is minimal, concentration can be calculated as [Pg.73]


E. Pena-Vazquez, J. Villanueva-Alonso and P. Bermejo-Barrera, Optimisation of a vapor generation method for metal determination using ICP-OES, J. Anal. At. Spectrom., 22(6), 2007, 642-649. [Pg.150]

AFS is based on the absorption of radiation of a certain frequency (the energy transition from the outermost electronic orbitals to a higher energy state) and the subsequent deactivation of the excited atoms with the release of radiation. The most useful type of fluorescence, resonance fluorescence, involves a fluorescence emission radiation of the same wavelength as that used for excitation. Because of the inherent sensitivity of the fluorescence emission process, AFS is one of the most sensitive atomic techniques. All the benefits of AFS are enhanced when this spectromet-ric technique is used in combination with vapor generation methods, especially for covalent-hydride-forming elements. [Pg.271]

The use of vapor-generation methods prior to IGP-MS or AAS detection improves the LOD of the method. This is because the sample introduction methods facilitated by liquid aspiration are very inefficient (1-5%), compared to methods for gaseous or vapor sample introduction (>90%). [Pg.617]

To fully understand the reasons behind vapor generation methods, reference to a few basic laws of physics is necessary. Physical, chemical, and gas laws dictate the behavior of a gas under different conditions. For purposes of simplicity, under normal circumstances, a gas generated in the laboratory is assumed to behave similarly to the ideal gas. We briefly review the Ideal Gas Law for its applicabiUty to various generation techniques, and provide a method for vapor concentration calculation. [Pg.66]

Several vapor generation methods use direct contact of the liquid with a carrier gas stream. These include sparging (the carrier gas bubbles through the liquid) syringe injection of the liquid material directly into a carrier gas-flow stream and head-space vapor saturation. Solid-state vapor generation exploits the use of vapors... [Pg.69]

Tevault, D.E., Ong, K.Y., Wasserman, M.B., Vapor generation methods for chemical warfare agents, U.S. Army Edgewood Chemical and Biological Center, Maryland, ECBC-TR-148, March 2001. [Pg.256]

Atomic absorption spectroscopy is more suited to samples where the number of metals is small, because it is essentially a single-element technique. The conventional air—acetylene flame is used for most metals however, elements that form refractory compounds, eg, Al, Si, V, etc, require the hotter nitrous oxide—acetylene flame. The use of a graphite furnace provides detection limits much lower than either of the flames. A cold-vapor-generation technique combined with atomic absorption is considered the most suitable method for mercury analysis (34). [Pg.232]

Dihydro-lH-l,5,2-azasilaboroles derive from the 2,5-dihydro-lH-l,2-aza-boroles ( 6.5.3.3) by substitution of the carbon neighboring N by a silicon atom. They may act as four-electron donors using electron density from the C=C double bond and the N atom. The B atom behaves as an acceptor center. Two pathways are known for complex synthesis reaction with a generated transition-metal complex fragment and reaction with metal atoms by the metal-vapor synthesis method. [Pg.78]

Ullrafine particles (UFPs) of metal and semiconductor nitrides have been synthesized by two major techniques one is the reactive gas condensation method, and the other is the chemical vapor condensation method. The former is modified from the so-called gas condensation method (or gas-evaporation method) (13), and a surrounding gas such as N2 or NII2 is used in the evaporation chamber instead of inert gases. Plasma generation has been widely adopted in order to enhance the nitridation in the particle formation process. The latter is based on the decomposition and the subsequent chemical reaction of metal chloride, carbonate, hydride, and organics used as raw materials in an appropriate reactive gas under an energetic environment formed mainly by thermal healing, radiofrequency (RF) plasma, and laser beam. Synthesis techniques are listed for every heal source for the reactive gas condensation method and for the chemical vapor condensation method in Tables 8.1.1 and 8.1.2, respectively. [Pg.406]

M. Colon, M. Iglesias and M. Hidalgo, Development of a new method for sulfide determination by vapor generator-inductively coupled plasma-mass spectrometry, Spectrochim. Acta, Part B, 62, 2007, 470 475. [Pg.158]

Total mercury, inorganic mercury, and methylmercury in water were determined using a simple and ultrasensitive method, based on cold vapor generation (CVG), coupled to atomic fluorescence... [Pg.228]

Acetylation of cellulose to the triacetate has been carried out without breaking down of the structure with acetic anhydride containing pyridine to help open up the cell wall structure and to act as a catalyst (71). This led Stamm and Tarkow (72) to test the liquid phase reaction on wood. High dimensional stabilization without break down of the structure was obtained, but excessive amounts of chemical were used. They hence devised a vapor phase method at atmospheric pressure that proved suitable for treating veneer up to thicknesses of 1/8 inch. Acetic anhydride pyridine vapors generated by heating an 80-20% mixture of the liquids were circulated around sheets of veneer suspended in a box lined with sheet stainless steel. Hardwood veneer,... [Pg.142]

The affinity that the solvent vapor has for the activated charcoal or the charcoal s adsorptivity is reflected in the "collection" efficiency. Early studies(i> 2) show that for many solvents, collection efficiencies are similar. No generalization is without exception and therefore test atmospheres should be generated where this information is important. The collection efficiency and desorption efficiency, together with the analytical precision and accuracy are incorporated into the total coefficient of variation for the method. Many solvent vapor sampling methods are not this thoroughly documented in the literature because of the difficulty of generating known test atmospheres. In this study both direct injection and flowing of vapor-air mixtures over the charcoal were used for efficiency determinations these values are reported in table 1 and required much time and effort to obtain. [Pg.216]

We have produced carbon tubules by quasi-free vapor condensation. This method is different from the previously reported generation method of carbon tubes (I, 2). Atomic resolution images obtained with a scanning tunneling microscope (STM) reveal that the detailed structures of the tube surfaces are networks of perfect honeycombs. In addition, we observe a superpattern on the tubes due to an incorporated inner tube with different helicity. The smallest tube imaged in our experiments has a diameter of —10 A, which is of the size of Cgo- We suggest that the tubule growth starts with the formation of a fullerene hemisphere. [Pg.227]

Methods have been developed for the determination of mercury in fish, shellfish, foods, food sources, and pharmaceuticals. AAS, usually with cold vapor generation (CVAAS), is one of the primary methods used to measure mercury in these complex matrices (Carrillo et al. 1986 Friese et al. 1990 Landi et al. 1990 ... [Pg.555]

Figure 28-5 Continuous sample introduction methods. Samples are frequently introduced into plasmas or flames by means of a nebulizer, which produces a mist or spray. Samples can be introduced directly to the nebulizer or by means of flow injection (FIA) or high-performance liquid chromatography (HPLC). In some cases, samples are separately converted to a vapor by a vapor generator, such as a hydride generator or an electrothermal vaporizer. Figure 28-5 Continuous sample introduction methods. Samples are frequently introduced into plasmas or flames by means of a nebulizer, which produces a mist or spray. Samples can be introduced directly to the nebulizer or by means of flow injection (FIA) or high-performance liquid chromatography (HPLC). In some cases, samples are separately converted to a vapor by a vapor generator, such as a hydride generator or an electrothermal vaporizer.
In the USA, the regulatory focus is on consumer and worker exposure to formaldehyde vapors released from the fabric, so the test method specified is AATCC Test Method 112-2003. In this method, 1 g of fabric is suspended over 50 ml of distilled water in a sealed quart jar. The jar is placed in an oven for either 4 h at 65 °C or 20 h at 49 °C. Any formaldehyde vapors generated are absorbed by the water. An aliquot of the formaldehyde-water solution is taken and analyzed colorimetrically using the Nash reagent.Typical levels of formaldehyde found in properly processed fabrics treated with modem cross-linking reagents are less than 100 ppm. The Nash method is based on the reaction of acetylacetone with formaldehyde and an ammonium salt to form a yellow complex with an absorbance maximum at 414 nm. The mild conditions of the reaction ( pH 7, 5 min at 58 °C) eliminate many potential interferences. [Pg.112]

Lehnman, W. "Formaldehyde Vapor Generation Using Syringe Pump Method" Weyerhaeuser, Tacoma, Washington, 1983. [Pg.186]


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