Head-space

All of this careful addition is to keep the reaction from starting before the bomb is sealed. It is also important to note that the chemist must scale up or scale down the amount of reactants so that the total amount of all the ingredients consumes no less than 90 of the volume space of her particular pipe bomb. Too much head space with its atmospheric air will lower the yield. The bomb is heated in an oil bath or oven at 105-115°C for 18-24 hours and the contents are then distilled with the 1,3 benzodioxole coming over at about 170-175°C with no vacuum, Alternatively, the chemist can only distill off the methanol, wash with dilute NaOH solution and extract with ether, etc. 

Ioffe, B. V. Vitenberg, A. G. Head-Space Analysis and Related Methods in Gas Chromatography. Wiley-Interscience New York, 1982. 

Residual monomers in SAN have been a growing environmental concern and can be determined by a variety of methods. Monomer analysis can be achieved by polymer solution or directly from SAN emulsions (27) followed by "head space" gas chromatography (gc) (28,29). Liquid chromatography (Ic) is also effective (30). 

The objective in packaging cool sterilized products is to maintain the product under aseptic conditions, to sterilize the container and its Hd, and to place the product into the container and seal it without contamination. Contamination of the head space between the product and closure is avoided by the use of superheated steam, maintaining a high internal pressure, spraying the container surface with a bactericide such as chlorine, irradiation with a bactericidal lamp, or filling the space with an inert sterile gas such as nitrogen. 

In an important next step, it has been found that flowers and other plant parts can be analyzed by using head space techniques without removing them from the living plant (3). It was immediately observed that there are remarkable differences in the volatile compositions observed from Hve and picked flowers. This is exemplified for jasmine flowers in Table 3. Reconstitutions produced from this information have provided perfumers with novel and fresh notes for use in their creations. This technique continues to be appHed to many kinds and varieties of flowers, leaves (herbs, spices), and fmits. The reasons for the remarkable differences observed are not known. 

Table 3. Head Space Constituents of Jasmine Flowers...

Solids addition entrains air into inerted head space, creates flammable... 

Some stabilizers or inhibitors require a certain oxygen concentration in the tank head space atmosphere in order to function. Where inerting is required, careful control is necessary to maintain this minimum oxygen concentration in inerting gas while still staying below the minimum oxygen concentration required for combustion. 

Stinton (1983) and Lees (1980) describe this accident. On July 11, 1978, at 12 05 P.M., the loading of a tank truck with propylene was completed. According to weight records obtained at the refinery exit after loading, it had been grossly overloaded head space was later calculated to be inadequate. The truck scale recorded a weight for the load of 23,470 kg (52,000 lb)—well over the maximum allowable weight of 19,099 kg (42,000 lb). The tank truck was not equipped with a pressure relief valve. 

This section addresses the effects of BLEVE blasts and pressure vessel bursts. Actually, the blast effect of a BLEVE results not only from rapid evaporation (flashing) of liquid, but also from the expansion of vapor in the vessel s vapor (head) space. In many accidents, head-space vapor expansion probably produces most of the blast effects. Rapid expansion of vapor produces a blast identical to that of other pressure vessel ruptures, and so does flashing liquid. Therefore, it is necessary to calculate blast from pressure vessel mpture in order to calculate a BLEVE blast effect. 

Although notable improvements have been made in methods used by the control laboratories serving the canning industry, a great deal of room remains for further improvement. A survey of some of the functions of control laboratories demonstrates the need for better methods of determining spray residues, traces of metals, vitamins, moisture, and head-space gases. As is the case in other industries, improved instrumentation offers a solution to some of the existing problems. 

Prediction of Copolymerization Conversion from Reactor Head-Space Vapor Composition... 

The estimation of the two parameters requires not only conversion and head space composition data but also physical properties of the monomers, e.g. reactivity ratios, vapor pressure equation, liquid phase activity coefficients and vapor phase fugacity coefficients. 

Using copolymerization theory and well known phase equilibrium laws a mathematical model is reported for predicting conversions in an emulsion polymerization reactor. The model is demonstrated to accurately predict conversions from the head space vapor compositions during copolymerization reactions for two commercial products. However, it appears that for products with compositions lower than the azeotropic compositions the model becomes semi-empirical. 

Pretreatment of hair samples also includes an extraction, usually with an alkaline sodium hydroxide solution, followed by cleaning up with LLE with n-hexane/ethyl acetate. Instead of LLE, the employment of SPE is also possible. Furthermore, the solid phase microextraction (SPME) in combination with head-space analysis is usable [104-106]. In the case of using hair samples, possible external contamination (e.g., by passive smoking of Cannabis) has to be considered as false positive result. False positive results can be avoided by washing of the hair samples previous to extraction [107]. Storage of collected samples is another important fact that can cause false results in their content of A9-THC and metabolites [108-110]. 

Weigh 50 g of sample into the headspace flask with a magnetic stirrer bar. Add immediately 50 mL of 1.5% stannous chloride solution in hydrochloric acid, and close the vessel with the silicone-rubber septum and the screw-cap. Transfer the head-space flasks into the electric oven (or water-bath) heated at 80 °C for 1 h. After 15 min, take the flasks out of the oven and mix the contents with the magnetic stirrer, heated at 50 °C, for 1 min. Return the flasks to the electric oven and repeat the mixing of the samples every 15 min. After 1 h, take the flasks out of the oven, mix the contents of each flask for 1 min, and inject an aliquot of headspace (100-1000 xL) on to the GC column with a gas-tight syringe. 

The so-called splash zone , the head space in a mixing vessel above the bulk phase of product, may be irrigated with condensation water, washing less persistent biocides away and allowing microbial growth to occur in this area. 

With a common intermediate from the Medicinal Chemistry synthesis now in hand in enantiomerically upgraded form, optimization of the conversion to the amine was addressed, with particular emphasis on safety evaluation of the azide displacement step (Scheme 9.7). Hence, alcohol 6 was reacted with methanesul-fonyl chloride in the presence of triethylamine to afford a 95% yield of the desired mesylate as an oil. Displacement of the mesylate using sodium azide in DMF afforded azide 7 in around 85% assay yield. However, a major by-product of the reaction was found to be alkene 17, formed from an elimination pathway with concomitant formation of the hazardous hydrazoic acid. To evaluate this potential safety hazard for process scale-up, online FTIR was used to monitor the presence of hydrazoic acid in the head-space, confirming that this was indeed formed during the reaction [7]. It was also observed that the amount of hydrazoic acid in the headspace could be completely suppressed by the addition of an organic base such as diisopropylethylamine to the reaction, with the use of inorganic bases such as... 

Both solvent-extracted and expelled coffee oils can be sprayed directly onto soluble coffee solids. The oil is adsorbed without degradation, provided moisture and oxygen are absent. However, the most volatile compounds do tend to leave the coffee powder and fill the head space of the container. 

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