Carrier Gas Flow Rate

Importantly, the operating efficiency of a chromatograph is directly dependent on the maintenance of a highly constant carrier gas-flow-rate. Carrier gas passes from the tank through a toggle value, a flow meter, a few feet of metal capillary restrictors, and a 0-4 m pressure gauze. The flow rate could be adjusted by means of a needle value mounted on the base of the flow meter and is controlled by the capillary restrictors. On the downstream side of the pressure regulator, a tee (T) may split the flow and direct it to the sample and the reference side of the detector. 

Thickness controllability (Table 9.1, no. 6) and reproducibility in OVPD is achieved by accurate adjustment of the flow of carrier gas by means of mass-flow controllers whereas in VTE quartz crystal monitors are used to control the rate of deposition by adjustment of the evaporation temperature. In VTE small deviations of the evaporation temperature are known to affect the stability of the deposition rate and consequently the layer thickness, which may also affect the roughness and morphology of the VTE-deposited layer. 

In contrast to LC detectors, GC detectors often require a specific gas, either as a reactant gas or as fuel (such as hydrogen gas as fuel for flame ionization). Most GC detectors work best when the total gas flow rate through the detector is 20-40 mL/min. Because packed columns deliver 20-40 mL/min of carrier gas, this requirement is easily met. Capillary columns deliver 0.5-10 mL/min thus, the total flow rate of gas is too low for optimum detector performance. In order to overcome the problem when using capillary columns, an appropriate makeup gas should be supplied at the detector. Some detectors use the reactant gas as the makeup gas, thus eliminating the need for two gases. The type and flow rate of the detector gases are dependent on the detector and can be different even for the same type of detector from different manufacturers. It is often necessary to refer the specific instrument manuals for details to obtain the information on the proper selection of gases and flow rates. All detectors are heated, primarily to keep the... 

The noise levels of detectors that are particularly susceptible to variations in column pressure or flow rate (e.g., the katharometer) are sometimes measured under static conditions (i.e., no flow of carrier gas). Such specifications are not really useful, as the analyst can never use the detector without a column flow. It could be argued that the manufacturer of the detector should not be held respon-... 

The selection of the proper intrinsic (plasma power, argon gas flow rate, auxiliary gas flow rate, powder carrier gas flow rate, etc.) and extrinsic (spray distance, powder feed rate, powder grain size, particle morphology, surface roughness, etc.) plasma parameters is crucial for sufficient powder particle heating, flow and surface wetting on impact and hence development of the desired coating porosity and... 

Short capillary column Carrier gas flow-rate Make-up gas flow-rate Fuel gas flow-rate Temperature programme Injection volume... 

In a promising development of oxygen determination, Kirsten [106] carried out the pyrolytic determination of oxygen in organic compounds at 1020°C with the use of amorphous carbon containing 20% of nickel. An important feature of the method is the addition of chlorohydrocarbon vapour to the flow of carrier gas. Kirsten [106] found that the reactor, i.e., the quartz tube, is rapidly rendered inoperative if the temperature is increased above 1020°C. To obtain quantitative results, it is sufficient to evaporate 1-chloropentane at a rate of 18ql/h. At present the Kirsten method is applied to Carlo Erba instrumentation. 

Carrier gas flow rate Auxiliary gas flow rate Plasma gas flow rate Dwell times... 

Fig. 10. (a) Photoreactor developed for the study of selective photo-odixations in conditions of continuous illumination with a continuous flow of (carrier gas + hydrocarbon + oxygen) through a thin layer of finely powdered photocatalyst. Reproduced with permission and minor adaptation from ref. 158. (b) Results obtained with photoreactor showing pressure dependence of the photoassisted steady-state rate of acetone formation under continuous UV-illumination of a dynamic (isobutane + 02 + He)/ Ti02) interface, (c) Comparison of flow diagrams and positions of sampling valve for utilisation of photoreactor in pulsed-reactant versus continuous reactant flow conditions. 

Generally a very narrow droplet spectrum is obtained and the relative uniformity of the coating is improved accordingly. A further advantage of this method is that the gas flow rate is independent of the aerosol flow rate, which is not the case with pneumatic spraying. A modern spray deposition process can be described by relatively few parameters such as flow of carrier gas Q, concentration of the solution C, solution flow q, droplet radius r, distance between nozzle and substrate d, temperature of the gaseous environment Te, temperature of the substrates Ts and their speed... 

For large volume splitless injection the sample is introduced at a temperature below or close to the pressure corrected solvent boiling point with the split vent closed. Solvent vapors are discharged through the separation column. Compared with the split injection configuration, volatile compounds are trapped in the solvent swollen stationary phase at the column inlet rather than lost through the split vent. Since the flow rate of gas through the vaporization chamber is the same as the carrier gas flow rate, solvent elimination is slow and this method is not widely used. The maximum volume of sample that can be introduced is about 20 - 30 p.1. 

General models of the electron-capture process are based on the kinetic model of Wentworth and co-workers [254,293,295,298,313-315]. The ionization chamber is treated as a homogeneous reactor into which electrons are continuously introduced at a constant rate and electron-capturing solutes are added at a variable rate in a constant flow of carrier gas. The major consumption of electrons is via electron capture and recombination with positive ions. The model can be expanded to allow for the presence of electron-capturing contaminants and the formation of excited state negative ions. The kinetic model provides a reasonable explanation of the influence of pulse sampling conditions and temperature on the detector response, but exactly calculated solutions are rare. Again, this is because the necessary rate constants are usually unavailable, and the identity and relative concentration of all species present in the detector are uncertain. The principal reactions can be summarized as follows ... 

The performance of the two-layer blend FET sensor upon exposure to dilute DMMP vapor was further studied in a test chamber connected to a constant flow rate of gas, which was switched between N2 and DMMP vapors. A bubbler containing DMMP liquid was used as the source of analyte vapor. Nitrogen gas was passed above the liquid surface and carried the analyte vapor to the test chamber. The mass of a bubbler was measured before and after testing to determine the total mass of analyte delivered by a specific volume of carrier gas, thereby allowing calculation of the average concentration of analyte vapor in the test chamber. 

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