Alcohol determination

Typical normal-phase operations involved combinations of alcohols and hexane or heptane. In many cases, the addition of small amounts (< 0.1 %) of acid and/or base is necessary to improve peak efficiency and selectivity. Usually, the concentration of polar solvents such as alcohol determines the retention and selectivity (Fig. 2-18). Since flow rate has no impact on selectivity (see Fig. 2-11), the most productive flow rate was determined to be 2 mL miiT. Ethanol normally gives the best efficiency and resolution with reasonable back-pressures. It has been reported that halogenated solvents have also been used successfully on these stationary phases as well as acetonitrile, dioxane and methyl tert-butyl ether, or combinations of the these. The optimization parameters under three different mobile phase modes on glycopeptide CSPs are summarized in Table 2-7. 

Approximately 5%-10% of ethanol is excreted unchanged in the breath and urine. The blood-to-breath ratio of ethanol is 2,000 to 1, an important relationship that permits blood alcohol determination from expired air, providing the basis for the use of breath alcohol measurement for clinical, research, and forensic applications. 

Molecular diffusion ( ) has been used in various ways in micro analysis. In Figure 27, is seen the Conway diffusion dish, in which the substance to be tested is placed on the outside, and the reagent is placed in the central cup. The cup is covered, and after a time, the substance being analyzed diffuses into the central cup where it produces an effect which can then be interpreted in various ways. In the Figure, carbon monoxide is being determined. This same method is very useful for alcohol determination, where dichromate oxidizes the alcohol after it diffuses into the dichromate from the blood. 

F. Vanhouteghem, W. Pyckhout, C. Van Alsenoy, L. Van den Enden, and H. J. Geise, The molecular structure of gaseous allyl alcohol determined from electron diffraction, microwave, infrared and geometry relaxed ab initio data. J. Mol. Struct. 140, 33 48 (1986). 

Tab. 1.4 Dielectric relaxation parameters of water and lower alcohols determined by femtosecond terahertz pulse spectroscopy at 25 C1 ...

Rowe, E. S., F. Zhang, T. W. Leung, J. S. Parr, and P. T. Guy, Thermodynamics of membrane partitioning for a series of n-alcohols determined by titration calorimetry Role of hydrophobic effects , Biochemistry, 37,2430-2440 (1998). 

In theory the fermentation could be followed equally satisfactorily by measuring the alcohol content of the solution. In fact, however, alcohol determinations are much slower and more complicated than density determinations, so they are seldom, if ever, used. It is possible for the fermentation to stop—successive density determinations showing the same value—while there is some sugar left in the solution, although this is not normal behavior for fermentations. It is good practice to analyze for low levels of sugars in all wines when they have apparently completed their fermentations. 

With the same type of column used by Pecina et al. (26) (v. C1-C5 alcohols), determinations of DEG in wines were carried out (27). The eluent used is a 0.002 N solution of H2S04 at a flow of... 

Methyl alcohol. Methyl alcohol may be detected by the reactions indicated on p. 254. If the aqueous solution contains only methyl alcohol, or this with small quantities of acetone (for detection of acetone, see below, paragraph 3), the amount of this alcohol in 100 grams of the varnish may be deduced from the density of the distillate (see table, Vol. I, p. 40). If ethyl alcohol (detected as in paragraph 2) also is present, the methyl alcohol is determined either colorimetrically or by combustion (see p. 258). The amount thus found is deducted from the total alcohol determined from the density of the distillate by means of the ordinary tables for ethyl alcohol, the remainder being the amount of the latter alcohol.1... 

Table 1 Results of the alcohol determination in the IHRM and CRM LGC5404...

Under base-catalyzed conditions, two molecules of acetone can condense to form diacetone alcohol. At room temperature (25 °C), about 5% of the acetone is converted to diacetone alcohol. Determine the value of AG° for this reaction. 

Solubility in Alcohol Determine as directed under Solubility in Alcohol, Appendix VI. One milliliter of sample dissolves to form a clear solution in 2 mL of 70% alcohol. 

Solubility in Alcohol Determine as directed under Solubility in Alcohol, Appendix VI. One milliliter of sample dissolves in 1 mL of 90% alcohol, often with turbidity, and remains in solution on further addition of alcohol to a total of 10 mL. Specific Gravity Determine by any reliable method (see General Provisions). 

Ester Value Determine as directed under Ester Value, Appendix VI, using about 5 g of sample, accurately weighed. Ester Value after Acetylation Determine as directed under Ester Value, Appendix VI, except acetylate a 10-mL sample as directed under Total Alcohols, Appendix VI, and use about 1.5 g of the dried, acetylated oil, accurately weighed. Solubility in Alcohol Determine as directed under Solubility in Alcohol, Appendix VI. The oil does not usually dissolve clearly in 95% alcohol. 

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