Atmospheric pressure sampling

Reaction products leave the reactor and are cooled in two countercurrent heat exchangers with water. Effluent is then depressurized to atmospheric pressure. Samples are collected for the analysis. 

Only one intrusion occurs, meaning that water did not expel from the porosity even after a storage of several weeks at atmospheric pressure sample SI. 

The determination of the carbon residue of petroleum or a petroleum product is applicable to relatively nonvolatile samples that decompose on distillation at atmospheric pressure. Samples that contain ash-forming constituents will have an erroneously high carbon residue, depending on the amount of ash formed. All three methods are apphcable to relatively nonvolatile petroleum products that partially decompose on distillation at atmospheric pressure. Crude oils having a low carbon residue may be distilled to a specified residue with the carbon residue test of choice then applied to that residue. 

The gas phase alkylation of toluene with methanol was carried out in a fixed-bed tubular reactor at atmospheric pressure. Samples were sieved to retain particles with 0.35-0.40 mm in diameter for catafytic measurements. A mixture of toluene/methanol of 1 1 molar ratio was vaporized in a preheating section and delivered to the reactor. The reaction was carried out at 400 °C, employing a space velocity (WHSV) of 2 h. Toluene conversion (Xtoi) was calculated as Xtoi (%) = [EYj / (ZYj + Ytoi.)]100, where ZYj is the molar fiactions of the aromatic reaction products, including benzene, and Ytoi is the outlet molar fiaction of toluene. The selectivity to product j was determined as Sj (%) = [Y/EYj.lOO. The Sei-bz selectivity includes the sum of ethylbenzene and styrene, which are the side-chain alkylation products. In-situ poisoning experiments were carried out by doping the toluene/methanol mixture with either acetic acid or 3,5-dimethyl pyridine in a concentration range between 0-15000 ppm... 

There is also a trade-off between maximum allowable power input and sample pressure. In the example given above, a sample at a ten-fold higher pressure 130 Pa would not show power saturation effects until the power input reached lOmW. For atmospheric pressure samples power saturation ceases to be significant. 

The hydrogenation of EPA was performed in a semi-batch reactor, at atmospheric pressure. Sample weight corresponding to 0,09 g of Ni... 

Chamber B is filled with partially degassed sample material at 0°C. Chamber A is filled with air at 37.8°C and at atmospheric pressure. 

Chemical ionization and atmospheric-pressure ionization are covered in Chapters 1 and 9, respectively.) The corona discharge is relatively gentle in that, at atmospheric pressure, it leads to more sample molecules being ionized without causing much fragmentation. 

The advent of atmospheric-pressure ionization (API) provided a method of ionizing labile and nonvolatile substances so that they could be examined by mass spectrometry. API has become strongly linked to HPLC as a basis for ionizing the eluant on its way into the mass spectrometer, although it is also used as a stand-alone inlet for introduction of samples. API is important in thermospray, plasmaspray, and electrospray ionization (see Chapters 8 and 11). 

The end or front of the plasma flame impinges onto a metal plate (the cone or sampler or sampling cone), which has a small hole in its center (Figure 14.2). The region on the other side of the cone from the flame is under vacuum, so the ions and neutrals passing from the atmospheric-pressure hot flame into a vacuum space are accelerated to supersonic speeds and cooled as rapid expansion occurs. A supersonic jet of gas passes toward a second metal plate (the skimmer) containing a hole smaller than the one in the sampler, where ions pass into the mass analyzer. The sampler and skimmer form an interface between the plasma flame and the mass analyzer. A light... 

For liquid chromatography, a sample of the mixture solution is injected through a loop injector which allows a quantity of the solution to be placed in a small tubular loop at atmospheric pressure. By manipulating a valve, the high-pressure flow of solvent to the column is diverted through the loop, carrying the sample with it (Figure 35.5). 

A typical loop injector showing the sampling position with pressurized solvent flowing through one loop onto the column and the sample solution placed in the other loop at atmospheric pressure. Rotation of the loop carrier through 180° puts the sample into the liquid flow at high pressure with only momentary change in pressure in the system. 

To achieve sufficient vapor pressure for El and Cl, a nonvolatile liquid will have to be heated strongly, but this heating may lead to its thermal degradation. If thermal instability is a problem, then inlet/ionization systems need to be considered, since these do not require prevolatilization of the sample before mass spectrometric analysis. This problem has led to the development of inlet/ionization systems that can operate at atmospheric pressure and ambient temperatures. Successive developments have led to the introduction of techniques such as fast-atom bombardment (FAB), fast-ion bombardment (FIB), dynamic FAB, thermospray, plasmaspray, electrospray, and APCI. Only the last two techniques are in common use. Further aspects of liquids in their role as solvents for samples are considered below. 

Thus, either the emitted light or the ions formed can be used to examine samples. For example, the mass spectrometric ionization technique of atmospheric-pressure chemical ionization (APCI) utilizes a corona discharge to enhance the number of ions formed. Carbon arc discharges have been used to generate ions of otherwise analytically intractable inorganic substances, with the ions being examined by mass spectrometry. 

Samples containing mixtures of peptides can be analyzed directly by electrospray. Alternatively, the peptides can be separated and analyzed by LC/MS coupling techniques such as electrospray or atmospheric pressure chemical ionization (APCI). 

The existence of tridymite as a distinct phase of pure crystalline siUca has been questioned (42,58—63). According to this view, the only tme crystalline phases of pure siUca at atmospheric pressure are quart2 and a highly ordered three-layer cristobaUte having a transition temperature variously estimated from 806 250°C to about 1050°C (50,60). Tridymites are considered to be defect stmctures in which two-layer sequences predominate. The stabihty of tridymite as found in natural samples and in fired siUca bricks has been attributed to the presence of foreign ions. This view is, however, disputed by those who cite evidence of the formation of tridymite from very pure siUcon and water and of the conversion of tridymite M, but not tridymite S, to cristobahte below 1470°C (47). It has been suggested that the phase relations of siUca are deterrnined by the purity of the system (42), and that tridymite is not a tme form of pure siUca but rather a soHd solution of minerali2er and siUca (63). However, the assumption of the existence of tridymite phases is well estabUshed in the technical Hterature pertinent to practical work. 

A liquid chromatography-mass spectrometry (LC-MS) method that can quantitatively analyze urinar y normal and modified nucleosides in less than 30 min with a good resolution and sufficient sensitivity has been developed. Nineteen kinds of normal and modified nucleosides were determined in urine samples from 10 healthy persons and 18 breast cancer patients. Compounds were separ ated on a reverse phase Kromasil C18 column (2.1 mm I.D.) by isocratic elution mode using 20 mg/1 ammonium acetate - acetonitrile (97 3 % v/v) at 200 p.l/min. A higher sensitivity was obtained in positive atmospheric pressure chemical ionization mode APCI(-i-). 

The evaluation of the various XRF measurements will be discussed for different effects in EDXRS the spectra evaluation is perfonned by different programs with varying assumptions, partially different mass attenuation coefficients are used, the calibration procedures are principally different (e.g., thin foils with given thickness, or, infinitely thick samples), measurement under atmospheric pressure or in vacuum, secondary excitation (enhancement) mainly of Al by Si radiation. 

The tetrahydrofurfuryl alcohol available from the Quaker Oats Company, or the Practical grade from the Eastman Kodak Company, has been used. If the material a ailable does not hydrogenate satisfactorily, it may be purified by hydrogenation over Raney nickel at 150 /100-200 atmospheres pressure. A sample of good quality boils at 177-178°/740 mm. and does not become dark-colored when a few milliliters are shaken with 1 drop of concentrated sulfuric acid at room temperature. 

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