Liquid-column pressure measure, methods

Liquid-Column Methods Liquid-column pressure-measuring devices are those in which the pressure being measured is balanced against the pressure exerted by a column of liquid. If the density of the liquid is known, the height of the liquid column is a measure of the pressure. Most forms of liquid-column pressure-measuring devices are commonly called manometers. When the height of the liquid is... 

Hultman et al. [130] developed a LC/MS/MS method for the quantitative determination of esomeprazole and its two main metabolites 5-hydro-xyesomeprazole and omeprazole sulfone in 25 /il human, rat, or dog plasma. The analytes and their internal standards were extracted from plasma into methyl ferf-butyl ether-dichloromethane (3 2). After evaporation and reconstitution of the organic extract, the analytes were separated on a reversed-phase liquid chromatography column and measured by atmospheric-pressure positive ionization mass spectrometry. 

Very useful for the kinetic studies of dispersity changes in a foam is the method based on simultaneous measurement of local expansion ratio and border pressure at one and the same level in the foam column [5]. This method can be applied to polyhedral foams in which the liquid is mainly in the borders. A formula for the length of a dodecahedron edge is obtained when Eqs. (1.43), (1.45) and (4.10) are solved together... 

The earliest satisfactory, measurements on vapour pressure were made with water by Dalton, who passed the liquid into the vacuous part of a barometer tube surrounded by a water-jacket, and measured the depression of the mercury column. This simple method, also used by Gay-Lussac, Ure, Magnus, and Regnault, with improved apparatus, is subject to errors, e.g. for the change of shape of the mercury meniscus in contact with the liquid (with water, according to Regnault, this depresses the mercury column by 0T2 mm.) and the depression of the mercury column due to the weight of the liquid. It cannot, of course, be used with liquids (e.g. bromine) which attack mercury. 

The first is the pressure compensation method, originally developed by Bartell and Walton. The principle is that it is not the capillary pressure that is measured (as the weight of a liquid column) but the pressure required to compensate for it, that is the pressure to keep the height inside the capillary at the same level as outside. This principle has found application in the measurement of the wetting of powders, to which we shall return in secs. 5.4i. 

Barometry measures a broad variety of pressures using an equally broad variety of measurement techniques, including liquid column methods, elastic element methods, and electrical sensors. Electrical sensors include resistance strain gauges, capacitances, piezoresistive instruments, and piezoelectric devices. The technologies range from those developed by French mathematician Blaise Pascal, Greek mathematician Archimedes, and Torricelli to early twenty-first century MEMS sensors and those used to conduct nanoscale materials science. 

Melting points are given for solids. For liquids the boiling point and pressure of measurement are enclosed in parentheses and are listed in the melting point column. When the compound melts with decomposition, (dec) is placed after the melting point. When the compound decomposes without melting, dec is placed before the decomposition point. The numbers enclosed in parentheses in the final column refer to methods of synthesis in the text. 

There are a number of different methods used to express a pressure measurement. Some of them are natural units, i.e., based on a force per unit area, as with pound (force) per square inch (abbreviated Ibf/in or psi) or dyne per square centimeter (dyn/cm ). Others are based on a fluid height, such as inches of water (in H2O) or millimeters of mercury (mm Hg) units such as these are convenient when the pressure is indicated by a difference between two levels of a liquid as in a manometer or barometer. This measurement is based on the pressure at the base of a column (height) of fluid. Barometric pressure and atmospheric pressure are synonymous and measure the ambient air pressure. Standard barometric pressure is the average atmospheric pressure at sea level, 45° north latitude at 32°F. It is used to define another unit of pressure called the atmosphere (atm). Standard barometric pressure is 1 atm and is equivalent to 14.696 psi and 29.921 in Hg. As one might expect, barometric pressure varies with weather and altitude. 

Differential Pressure. The differential pressure method measures the pressure of a vertical column of the fluid as well as the height of the column to obtain the density. This method has the advantages of relatively simple equipment, small component size, and the possibility of application as a field-type instrument. But it also has several disadvantages. The method is dependent upon two separate measurements, pressure differential and fluid liquid level. Errors in the accuracy of either of these two separate measurements will affect the overall method accuracy. Because of the extreme low density of liquid hydrogen, for instance, the accuracy, sensitivity, and hysteresis of the differential pressure measurement can be adversely affected. 

In many applications in mass spectrometry (MS), the sample to be analyzed is present as a solution in a solvent, such as methanol or acetonitrile, or an aqueous one, as with body fluids. The solution may be an effluent from a liquid chromatography (LC) column. In any case, a solution flows into the front end of a mass spectrometer, but before it can provide a mass spectrum, the bulk of the solvent must be removed without losing the sample (solute). If the solvent is not removed, then its vaporization as it enters the ion source would produce a large increase in pressure and stop the spectrometer from working. At the same time that the solvent is removed, the dissolved sample must be retained so that its mass spectrum can be measured. There are several means of effecting this differentiation between carrier solvent and the solute of interest, and thermospray is just one of them. Plasmaspray is a variant of thermospray in which the basic method of solvent removal is the same, but the number of ions obtained is enhanced (see below). 

Specifically for triazines in water, multi-residue methods incorporating SPE and LC/MS/MS will soon be available that are capable of measuring numerous parent compounds and all their relevant degradates (including the hydroxytriazines) in one analysis. Continued increases in liquid chromatography/atmospheric pressure ionization tandem mass spectrometry (LC/API-MS/MS) sensitivity will lead to methods requiring no aqueous sample preparation at all, and portions of water samples will be injected directly into the LC column. The use of SPE and GC or LC coupled with MS and MS/MS systems will also be applied routinely to the analysis of more complex sample matrices such as soil and crop and animal tissues. However, the analyte(s) must first be removed from the sample matrix, and additional research is needed to develop more efficient extraction procedures. Increased selectivity during extraction also simplifies the sample purification requirements prior to injection. Certainly, miniaturization of all aspects of the analysis (sample extraction, purification, and instrumentation) will continue, and some of this may involve SEE, subcritical and microwave extraction, sonication, others or even combinations of these techniques for the initial isolation of the analyte(s) from the bulk of the sample matrix. 

---