Boiling point analyzer

On-line composition is usually measured by gas chromatographs. Other analyzers include infrared and ultraviolet analyzers, mass spectrometers, boiling point analyzers, wet-chemical analyzers, flash point analyzers, and refractive index analyzers. 

As seen in Chapter 2, mixtures of hydrocarbons and petroleum fractions are analyzed in the laboratory using precise standards published by ASTM (American Society for Testing and Materials) and incorporated for the most part into international (ISO), European (EN) and national (NF) collections. We wiil recall below the methods utilizing a classification by boiling point ... 

The flame ionization detector is capable of measuring only gaseous hydrocarbons, in other words, hydrocarbons that have a low boiling point. Emission gases can, however, also contain hydrocarbons in liquid form at ambient temperature and pressure. Therefore, analyzers based on flame ionization detection are generally equipped with heating elements to keep rhe sampling line and the detector at about 200 °C. 

In HPLC, the mobile phase is a liquid in which the sample must be soluble, and detection is most often accomplished by ultraviolet (UV) absorption. It is generally a slower process than GC however, its advantage is that the compounds to be separated are not limited by their boiling point, although low-boiling compounds are almost never separated by HPLC. Solid mixtures, as long as they are soluble in the mobile phase, can be analyzed by HPLC, whereas the solids that are typically encountered in soil analysis are not usually volatile enough to analyze via GC. 

Characterization of LNAPL in pools underlying the site consisted of collecting and analyzing over 120 LNAPL samples. LNAPL product samples were distilled and analyzed to determine API gravity, lead, and sulfur content. Boiling point and percent recovery data were used to generate distillation curves. 

Another method (EPA 3611) that focuses on the to separation of groups or fractions with similar mobility in soils is based on the use of alumina and silica gel (EPA 3630) that are used to fractionate the hydrocarbon into ahphatic and aromatic fractions. A gas chromatograph equipped with a boiling-point column (nonpolar capillary column) is used to analyze whole soil samples as weU as the aliphatic and aromatic fractions to resolve and quantify the fate-and-transport fractions. The method is versatile and performance based and therefore can be modified to accommodate data quality objectives. 

The results of Na versus Pa are analyzed by an equation first derived by Brunauer, Emmet, and Teller, and the resultant isotherm is called the BET isotherm. Typically one measures the amount of N2 adsorbed for a particular pressure at 78 K (the boiling point of N2 at a pressure of 1 atm) as sketched in Figure 7-24. There are several regimes of an adsorption isotherm. At low densities the density increases linearly with pressure. When the density approaches one monolayer, the surface saturates. As the pressure approaches the saturation pressure of the gas, bulk condensation of liquid OCCUrs. This condensation can occur preferentially in pores of the solid due to capillary condensation, and the amount of gas and pressure where this occurs can be used to determine the pore volume of the catalyst. 

Elemental composition Sb 53.37%, Cl 46.63%. Tbe compound may be identified from its melting and boiling points. Antimony may be analyzed by AA or ICP spectroscopy. Tbe trichloride may be hydrolyzed with limited quantities of water, the thick white precipitate turns to colorless crystals of Sb405Cl2 which is separated and analyzed for elemental composition. 

Elemental composition Os 74.82%, 0 25.18%. The compound can be identified by its physical properties, such as, odor, color, density, melting-, and boiling points. Its acrid odor is perceptible at concentrations of 0.02 mg/hter in air. The oxide also produces an orange color when a small amount of the compound or its aqueous solution is mixed with an aqueous solution of ammonia in KOH (see Reactions). Aqueous solution of the tetroxide may be analyzed for osmium by AA or ICP spectrometry (see Osmium). Vapors of the tetroxide may be purged from an aqueous solution by helium, adsorbed over a trap, and desorbed thermally by helium onto a GC. Alternatively, a benzene or carbon tetrachloride solution may be injected onto the GC and the compound peak identified by mass spectrometry. The characteristic mass ions for its identification should be 190 and 254. 

Several studies have analyzed the challenging problem of the isolation of aromatic hydrocarbons from their mixtures with alkanes. Their boiling points are often close and the formation of azeofropes of various compositions is a common difficulty. 

In extraction, analyte is dissolved in a solvent that does not necessarily dissolve the entire sample and does not decompose the analyte. In a typical microwave-assisted extraction of pesticides from soil, a mixture of soil plus acetone and hexane is placed in a Teflon-lined bomb (Figures 28-8 and 28-13) and heated by microwaves to 150°C. This temperature is 50° to 100° higher than the boiling points of solvents at atmospheric pressure. Pesticides dissolve, but the soil remains behind. The liquid is then analyzed by chromatography. 

AO 356 g sample of a solid organic compound, when dissolved in 9 15 ml of carbon tetrachlonde (density = 1 595 g/ml), raises the boiling point of the carbon tetrachlonde by 0 560°C When analyzed, this compound is found to be 55 0% C, 2 75% H, 12 8% N, and 29 4% O What is the true formula of this compound9... 

For chemical substances to be analyzed by gas chromatography, they must be relatively nonpolar and volatile. Fatty acids are not readily vaporized at temperatures attainable in a gas chromatograph (up to 200°C). FAMEs have much lower boiling points than fatty acids. Polar fatty acids also have very long retention times unless extremely nonpolar column packings are used. 

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