Dissolved gases determination methods

Extraction or dissolution almost invariably will cause low-MW material in a polymer to be present to some extent in the solution to be chromatographed. Solvent peaks interfere especially in trace analysis solvent impurities also may interfere. For identification or determination of residual solvents in polymers it is mandatory to use solventless methods of analysis so as not to confuse solvents in which the sample is dissolved for analysis with residual solvents in the sample. Gas chromatographic methods for the analysis of some low-boiling substances in the manufacture of polyester polymers have been reviewed [129]. The contents of residual solvents (CH2C12, CgHsCI) and monomers (bisphenol A, dichlorodiphenyl sulfone) in commercial polycarbonates and polysulfones were determined. Also residual monomers in PVAc latices were analysed by GC methods [130]. GC was also... 

Szathmary and Luhmann [50] described a sensitive and automated gas chromatographic method for the determination of miconazole in plasma samples. Plasma was mixed with internal standard l-[2,4-dichloro-2-(2,3,4-trichlorobenzyloxy) phenethyl]imidazole and 0.1 M sodium hydroxide and extracted with heptane-isoamyl alcohol (197 3) and the drug was back-extracted with 0.05 M sulfuric acid. The aqueous phase was adjusted to pH 10 and extracted with an identical organic phase, which was evaporated to dryness. The residue was dissolved in isopropanol and subjected to gas chromatography on a column (12 m x 0.2 mm) of OV-1 (0.1 pm) at 265 °C, with nitrogen phosphorous detection. Recovery of miconazole was 85% and the calibration graph was rectilinear for 0.25 250 ng/mL. 

Experimental methods exist to determine a critical value for any one of these factors when the others are held constant. However, parameters such as pH, concentration of inhibiting ions (e.g., SO4"), dissolved gas, test area, flow rate, and surface finish influence the resistance to pitting. ... 

Unsteady-State Mass Balance Method One widely used technique for determining Kj a in bubbling gas-liquid contactors is the physical absorption of oxygen or COj into water or aqueous solutions, or the desorption of such a gas from a solution into a sparging inert gas such as air or nitrogen. The time-dependent concentration of dissolved gas is followed by using a sensor (e.g., for O2 or CO2) with a sufficiently fast response to changes in concentration. 

For the determination of sorption data, gravimetric methods are usually used the most difficult task is to take into account the buoyancy effect. This effect is negligible at low pressures, but becomes important at SCF densities. Accurate equations of state for pure fluids are used to calculate gas densities, and swelling data are needed to calculate the volume of the polymeric phase. Generally, the amount of dissolved gas increases with increasing pressure until a saturation value is reached. 

The solubility of the gas is needed so that CAI the concentration of the reactant A at the interface, can be calculated. The solubility is often expressed through the Henry Law constant M, this is defined by PAe = 3KCA, where PAe is the partial pressure of the gas A at equilibrium with liquid in which the concentration of the dissolved gas is CA. This immediately raises a problem for many systems how can the solubility, which requires gas and liquid to be at equilibrium, be determined when the gas reacts with the liquid The answer is by one of several methods. 

The calculation methods for the gas solubility are largely based on the Henry constant, which gives a relationship between the liquid-phase concentration of a physically dissolved gas and its partial pressure. The determination of such coefficients in presence of chemical reactions becomes complicated and, therefore, different estimations based on chemically inert systems are often applied. One of these methods uses the Henry coefficients of similar, but chemically inert, species in order to estimate the solubility of a reactive component An example is represented by the N2O analogy for the determination of CO2 solubility in amine solutions [47]. 

In these equations P is the headspace pressure in atmospheres, a is the gas-to-seawater ratio (Vg/V ), and is the total volume of the flask (here 1 L). By this procedure the initial concentration of a dissolved gas (C f) in seawater can be determined. Normally single extractions are done, but subsequent extractions can be used to check the amount of gas remaining in the seawater. The uncertainties associated with the headspace method can be evaluated by referring to Equation 2. In addition to the headspace gas concentration, Cg, the uncertainty in C f is dependent on the uncertainties in H and the ratio a. By using a propagation of error procedure on Equation 2, the uncertainties associated with the vacuum extraction flask can be estimated for different gases (2). The results show that for a gas that is not very soluble (H > 3), the total uncertainty is 5 %. For a more soluble gas H < 0.5) whose Henry s constant is not accurately known in seawater, the uncertainty is 30 %. 

In this section we consider the rate of absorption of gases into liquids that are agitated so that dissolved gas is transported from the interfacial surface to the interior by convective motion. The next section, based on this one, treats chemical methods for determining interfacial areas and mass-transfer coefficients in agitated gas-liquid reactors. 

De Vos and Jonkhoff described a gas chromatographic method to determine caffeine in several pharmaceutical preparations, e.g. tablets and suppositories. The tablet and suppository assay was carried out by dissolving or suspending the preparation in chloroform, to which the internal standard, lidocaine, had been added. The gas chromatographic separation was obtained on a 3 % OV-1 packed column at 160°C. Caffeine could be determined with a standard deviation of about 2 %. 

External mass transfer, such as diffusion to particles or to the outside of pipes or cylinders, requires different correlations from those for internal mass transfer, because there is boundary-layer flow over part of the surface, and boundary-layer separation is common. The mass-transfer coefficients can be determined by studying evaporation of liquid from porous wet solids. However, it is not easy to ensure that there is no effect of internal mass-transfer resistance. Complications from diffusion in the solid are eliminated if the solid is made from a slightly soluble substance that dissolves in the liquid or sublimes into a gas. This method also permits measurement of local mass-transfer coefficients for different points on the solid particle or cylinder. 

The loss of volatile hydrocarbons shown by analysis of the surface oil samples is by evaporation and solution. Water samples were collected under the oil slicks to determine the concentrations of dissolved constituents. A total of 68 water samples were collected with time, 5 and 10 ft under the oil slicks. Each was analyzed for C2-Ck> low-molecular-weight hydrocarbons using the gas equilibration method. 

The mechanism of displacement of superviscous crudes from reservoirs of different geological characteristics is not yet fully understood. The oil fields subject to this particular study all belong to strata of Miocene age. These reservoirs either do not have any aquifer drive or else their contact with formation water present outside of the oil trap is limited. Therefore, their water drive is weak and they produce essentially by dissolved gas drive. Application of new EOR methods called for detailed study of geological characteristics of the oil field and for the determination of permeabilities of its reservoir rocks. The dominance of the dissolved gas drive and the absence of the aquifer drive in most of the oil fields in question were also taken into account. 

Tribe, L.A., Briens, C.L., and Margaritis, A. (1995), Determination of the volumetric mass transfer coefficient (kLa) using the dynamic gas out-gas in method Analysis of errors caused by dissolved oxygen probes, Biotechnology and Bioengineering, 46(4) 388-392. 

The solubility of common gases in hydrocarbon liquids is determined to meet requirements of aerospace industry. This test method is based on the Clausius-Clapeyron equation, Henry s law, and the perfect gas law. The results are important in the lubrication of gas compressors where dissolved gas may cause erosion due to cavitation. In fuels, dissolved gases may cause interruption of fuel supply and foaming in tank. The liquid density is determined experimentally. Using this density, the Ostwald coefficient is taken from a chart and used for e calculation of the Bunsen coefficient (solubility of gas). The solubility of the gas or mixture of gases and Henry s law constant are also calculated. 

ExtAClct on methods wherein the dissolved gas in a previously saturated solution is removed under conditions in which the pressure, volume and temperature may be determined. 

Determination of the amount of dissolved gas has been carried out by various physical and chemical methods in different apparatuses ... 

Shapras and Claver [38] have described a gas chromatographic method for the determination of various volatiles in polystyrene, styrene-acrylonitrile copolymers, styrene-butadiene, styrene-acrylonitrile-butadiene terpolymers and other co-polymers. In this procedure, the polymer is dissolved in dimethyl formamide containing a known amount of toluene as internal standard. A portion of this solution is injected into two columns in series comprising 20% Tween 81 on Chromosorb W, followed by 10% Resoflex-446 on Chromosorb W. Using a hydrogen flame ionisation detector, less than 10 ppm of various monomers and other volatile impurities can be determined in the polymer by this procedure. Shapras and Claver state that the polymer present in the solution injected into the gas chromatographic column deposits on the injection block and is removed by reaming after every 50 sample injections. 

The approach to be followed in the determination of rates or detailed kinetics of the reaction in a liquid phase between a component of dissolved gas and a component of the liquid is, in principle, the same as that outlined in Chapter 2 for gas-phase reactions on a solid catalyst. In general, the experiments are carried out in flow reactors of the integral type. The data may be analyzed by the integral or the differential method of kinetic analysis. However, for a single reaction, two continuity equations, in general, are required one for the absorbing component A in the gas phase and one for A in the liquid phase. In addition, a material balance is required, linking the consumption of B, the reactant of the liquid phase, to that of A. The continuity equations for A, which contain the rate equations derived in... 

It is possible to remove small particles using dispersed or dissolved gas flotation devices. These units are primarily used for removing suspended hydrocarbons from water. Gas is normally dispersed into the water or released from a solution in the water, forming bubbles approximately 30-120 pm in diameter. The bubbles form on the surfaces of the suspended particles, creating particles whose average density is less than that of water. These rise to the surface and are mechanically skimmed. In the feed stream, chemicals called "float aids" are normally added to the flotation unit to aid in coagulation of solids and attachment of gas bubbles to the solids. The optimum concentration and chemical formulation of float aids are normally determined from batch tests in small-scale plastic flotation models on-site. Because of the difficulty of predicting particle removal efficiency with this method, it is not normally used to remove solids from water in production facilities. 

From Eqs. (5) and (6), both the total amount of dissolved gas mixture in polymer ( i+ 2) and the actual amount of each individud gas dissolved in polymer ( ,) can be theoretically determined. Since this study used a vapor (gas mixture) resovroir with a known and fixed composition (w,), we can solve these two coupled equations for the two unknowns i and 2- The X,i,(ory—i e., (ni+ 2)/[l- i+ 2)]—will be determined hereafter. In order to solve Eqs. (5) and (6), a thamodynamic model must be set up to calculate and the chemical potentials for gas component in the vapor phase (gas mixture) and polymer phase (ternary mixture), respectively. As usual, is determined with an EOS [25, 28, 31, 36], which is applied to the binary mixture system for the vapor phase. We have used classical thermodynamics [35] to derive the in the ternary mixture system the proposed methods of calculating fit are shown below ... 

To summarize, a general method of setting up a thermodynamic model for the study of phase equihbrium in a polymer/gas mixture system was successfully estabUshed using an EOS. This study used the SS-EOS as an example. Using the proposed methodology, the total amount of dissolved gas mixture in polymer, the actual amount of each individual gas dissolved in the polymer, and the swollen volume can be determined theor cally. 

Ammonia may be estimated by dissolving the gas in a known volume of standard acid and then back-titrating the excess acid. In a method widely used for the determination of basic nitrogen in organic substances (the Kjeldahl method), the nitrogenous material is converted into ammonium sulphate by heating with concentrated sulphuric acid. The ammonia is then driven off by the action of alkali and absorbed in standard acid. 

Analytical and Test Methods. o-Nitrotoluene can be analyzed for purity and isomer content by infrared spectroscopy with an accuracy of about 1%. -Nitrotoluene content can be estimated by the decomposition of the isomeric toluene diazonium chlorides because the ortho and meta isomers decompose more readily than the para isomer. A colorimetric method for determining the content of the various isomers is based on the color which forms when the mononitrotoluenes are dissolved in sulfuric acid (45). From the absorption of the sulfuric acid solution at 436 and 305 nm, the ortho and para isomer content can be deterrnined, and the meta isomer can be obtained by difference. However, this and other colorimetric methods are subject to possible interferences from other aromatic nitro compounds. A titrimetric method, based on the reduction of the nitro group with titanium(III) sulfate or chloride, can be used to determine mononitrotoluenes (32). Chromatographic methods, eg, gas chromatography or high pressure Hquid chromatography, are well suited for the deterrnination of mononitrotoluenes as well as its individual isomers. Freezing points are used commonly as indicators of purity of the various isomers. 

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