Analysis Vacuum Distillates

Mass spectrometry allows analysis by hydrocarbon family for a variety of petroleum cuts as deep as vacuum distillates since we have seen that the molecules must be vaporized. The study of vacuum residues can be conducted by a method of direct introduction which we will address only briefly because the quantitative aspects are ek r metiy difficult to master. Table 3.6 gives some examples the matrices used differ according to the distillation cut and the chemical content such as the presence or absence of olefins or sulfur. 

SARA (Saturates, Aromatics, Resins, Asphaltenes) analysis is widely practiced on heavy fractions such as vacuum and atmospheric residues and vacuum distillates for two purposes ... 

The history of the discovery of amino acids is closely related to advances ia analytical methods. Initially, quantitative and qualitative analysis depended exclusively upon crystallization from proteia hydrolysates. The quantitative precipitation of several basic amino acids including phosphotungstates, the separation of amino acid esters by vacuum distillation, and precipitation by sulfonic acid derivatives were developed successively duriag the last century. 

One of the most frequent techniques for analyzing 1,4-dioxane is gas chromatography. Birkel et al. [319] proposed in 1979 a gas chromatographic method based on partial vacuum distillation of the sample, analyzing polysorbate 60 and 80 with sensitivity to the 0.5 ppm. Stafford et al. [320] proposed a direct injection GC method which meant an improvement to the Birkel s technique. Robinson and Ciurczak [321] described a direct GC method for the analysis of... 

The reaction of Na with Hg to form an amalgam that can then be separated from the NajO for oxygen analysis has been compared with the vacuum distillation technique . Ion-exchange techniques in which the sample is dissolved in a suitable solvent and the resulting separation of elements is achieved by an ion-exchange resin is less common. This technique is particularly suited to separating the volatile impurities such as K, Rb and Co. ... 

Major emphasis in studies of N-nitroso compounds in foods has been placed upon volatile nitrosamines, in part because these compounds are relatively easy to isolate from complex matrices by virtue of their volatility. Procedures utilizing atmospheric pressure or vacuum distillation have been used by most investigators, with variations of the method of Fine e al. (2) being among the most popular. This procedure employs vacuum distillation of a mineral oil suspension of the sample with optional addition of water to improve nitrosamine recovery from low moisture content samples (6) The usual approach to prevention of nitrosamine formation during analysis involves adding sulfamic acid or ascorbate to destroy residual nitrite at an early stage of sample preparation. 

Dibenzyl Ether [Brpnsted Acid Promoted Reduction of an Aldehyde to a Symmetrical Ether].311 To a stirred solution of benzaldehyde (5.4 g, 0.05 mol) and TFA (11.4 g, 0.1 mol) under argon was added dropwise, with cooling, Et3SiH (8.1 g, 0.07 mol) at a rate such that the temperature of the reaction mixture did not exceed 40°. The solution turned a crimson color that gradually disappeared. Analysis by GLC showed the complete absence of the aldehyde immediately after addition of all of the silane. The products were separated by vacuum distillation at 20 Torr, collecting the fractions up to 125°. Dibenzyl ether was obtained from the residue by freezing out 4 g (0.02 mol, 80%) mp 3-6° nD25 1.5608. 

Kozloski RP. 1985. Simple method for concentrating volatiles in water for gas chromatographic analysis by vacuum distilation. J Chromotgr 346 408-412. 

The rearrangement is considerably faster when the reaction solution is more concentrated. If 480 mL of dichloromethane is used, the rearrangement is complete within 20 min at -20°C. However, the checkers found that the crude product is contaminated with 3-10% of the Tischenko product (Note 14), which is difficult to remove by chromatography. This by-product can be removed by vacuum distillation (bp 136-144°C, 2 mm). Using this combined purification procedure, the checkers obtained 9.6 g (81%) of diphenylacetaldehyde of >99% purity by capillary GLC analysis (Note 13). 

The analysis involves gas chromatographic methods such as purge and trap, vacuum distillation, and headspace (Askari et al., 1996). On the other hand, samples for the determination of semi- and nonvolatile hydrocarbons need not be collected in such a rigorous manner. On arrival at the laboratory, they require extraction by techniques such as solvent or supercritical fiuid. Some cleanup of... 

Pait of the hydrocracked liquid was vacuum distilled into the fractions defined previously. Initially, a distillation was carried out for each of the 19 experiments, but later a sample was taken tom the product combined tom each of the duplicate experiments making up the contact The various fractions were stored in screw cap vials in a refrigerator. For the GC analysis, a sample of each of the fractions was used as an approximately 1% solution (v/v) in cyclohexane. 

Simulated distillation analysis was carried out on the extract and filtrate produced after precipitation, focusing on the fractions which boiled below 350°C. A Perkin Elmer model 8500 GC fitted with a wide-bore, OV-1 capillary colunm, 25 m long and 0.53 pm in diameter, was used. The oven temperature was held at 40 C for 1 minute and then increased at a rate of 4 C per minute to 250 C, where the temperature was held. There was no split on the injection and a FID detector was used. Initial fractionation of the samples was carried out by vacuum distillation. 

However, examination of the filtrate showed that it was much more fluid than the original extract and it appeared that some toluene remained in it. To investigate this, analysis of the extract and ffltrate were carried out by an initial vacuum distillation followed by GC analysis of the distillate. The results are shown in Table 10. 

C. S-Dodeoen-2-one. The 3-carboxy-5-dodecen-2-one (9.0 g, 0.040 mol) is stirred in 150 mL of carbon tetrachloride (Note 16) in a 500-mL, three-necked, round-bottomed flask which is fitted with a reflux condenser, thermometer. Teflon-covered magnetic stirrer, and a ground-glass stopper. After the orange-yellow solution is heated at reflux for 1 hr, TLC analysis shows the reaction to be complete (Note 17). The reaction mixture is concentrated under reduced pressure with warming to afford 7.1 g (0.039 mol, 98%) of a red-orange oil. The product is sufficiently pure for most purposes. It may be purified by vacuum distillation at 105-107°C/2.7 mm (5.2 g, 0.03 mol, 71%) which yields a pale yellow oil (Note 18). 

It is very common to combine methods in obtaining aroma isolates. The simultaneous distillation/extraction method previously described is an example. Another popular combination method initially involves the solvent extraction of volatiles from a food and then high-vacuum distillation of the solvent/aroma extract to provide a fat-free aroma isolate. This technique is broadly used today to provide high-quality aroma extracts for numerous purposes. The apparatus used in solvent removal has been improved upon to reduce analysis time and efficiency the modified method is termed solvent-assisted flavour extraction (SAFE) [16]. 

Evaporation and redissolving. The solvent of the combined upper layer is evaporated under nitrogen flow or low-temperature vacuum distillation. An oily material appears after it is dried. A precisely measured aliquot of mobile phase is normally used to redissolve theextract. These procedures are intended to not only increase the concentration of tocopherols and tocotrienols to the measurable level of the detector, but also to avoid uncertain volume change of organic layer during extraction, which results in inaccurate results. The redissolved sample is transferred to a vial for HPLC analysis. 

The precursor used to create the 3-APTHS solutions was 3-aminopropyl-triethoxysilane (3-APTES). Commercial 3-APTES obtained from Huls Petrarch Systems Inc. was twice vacuum-distilled. Individual ampules were filled with the distilled precursor and sealed for later use. Triply-distilled HPLC grade water was used to prepare the 3-APTHS solutions used for sample treatment. For isotopically labelled 3-APTHS studies, we used 99 atom % 15N labelled 3-APTES, and 97.8 atom % l80 labelled water. Both compounds were obtained from MSD Isotopes [12]. The substrates used were polished Si wafers 1.5 cm in diameter. The Cr was sputter-deposited to a thickness of 1000 A onto one half of the Si wafer so that both the Si and Cr surfaces had identical preparation histories up to and including the analysis for every sample prepared. 

Gas chromatographic analysis (0.53-mm id x 10 m poly (dimethyl silicone) fused silica column, temperature programmed from 140°C to 220°C) indicates that this product is 98% pure, with <1% 3-methyl-1-phenyl-1,3-butadiene and 1-2% of a less volatile, unidentified component. The checkers could obtain a very pure product by normal vacuum distillation. They found the impurities to be higher boiling compounds. 

A typical analysis of the monophenol cut from the vacuum distillation is listed below. This is from 200 parts net organic in the lignin. 

The pyridinium chlorochromate-on-alumina reagent (7.5 g, 6.1 mmol, Section 4.2.18, p. 426) is added to a flask containing a solution of carveol (0.60 g, 3.8 mmol) in hexane (10 ml). After stirring for 2 hours, the solution is filtered, and washed with three 10-ml portions of ether. The combined filtrates are evaporated and vacuum distilled to afford carvone yield 0.54 g (93%), b.p. 104°C/11 mmHg. Gas-liquid chromatography analysis is on a column of 10 per cent Carbowax 20M supported on 60-80 mesh Chromo-sorb W. 

Headspace analysis has been employed in the extraction of dithiocarbamate insecticide in vegetables [227]. Other techniques occasionally used are vacuum distillation followed by gas chromatography-mass spectrometry in the determination of volatile organic compounds in leaves, steam distillation in the determination of organochlorine insecticides in fruit and vegetables [229], and water distillation followed by high-performance liquid chromatography in the determination of 2-aminobutane in potatoes [102,230]. 

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