Esters, determination

The experimental details already given for the detection and characterisation of aliphatic esters (determination of saponification equivalents h3 diolysis Section 111,106) apply equally to aromatic esters. A sfight modification in the procediu-e for isolating the products of hydrolysis is necessary for i)henolic (or phenyl) esters since the alkaline solution will contain hoth the alkali phenate and the alkali salt of the organic acid upon acidification, both the phenol and the acid will be hberated. Two methods may be used for separating the phenol and the acid ... 

The Detection of Artificial Esters in Essential Oils.—The custom of valuing certain essential oils, such as lavender, bergamot, geranium, petit-grain, etc., by the determination of their ester-content, has led to the use of scientific adulterants in the form of artificial esters which have been deliberately employed for the purpose of misleading the analyst. Of course, the ester determination is not a true criterion of value, as most of this class of oUs owe their perfume value to various other bodies as well. The first compounds of this nature employed for adulteration were ethyl succinate and ethyl oxalate. For the detection of these in lavender oil the foUowing test was proposed by Guildemeister and Hoffman —... 

The determination of alcohols in essential oils depends on the conversion of these compoimds into their acetic esters, and then carrying out an ester determination as described above. 

Selected entries from Methods in Enzymology [vol, page(s)] Application in fluorescence, 240, 734, 736, 757 convolution, 240, 490-491 in NMR [discrete transform, 239, 319-322 inverse transform, 239, 208, 259 multinuclear multidimensional NMR, 239, 71-73 shift theorem, 239, 210 time-domain shape functions, 239, 208-209] FT infrared spectroscopy [iron-coordinated CO, in difference spectrum of photolyzed carbonmonoxymyo-globin, 232, 186-187 for fatty acyl ester determination in small cell samples, 233, 311-313 myoglobin conformational substrates, 232, 186-187]. 

Applications in infrared spectroscopy A and B bands, iron-coordinated CO, 232, 186-187 application to allosteric mechanisms, 249, 566 bacteriorhodopsin, 246, 9, 380-381 caged compounds, 246, 6, 520-521 DNA [base pair formation, 246, 506 conformation, 246, 506-507 denaturation thermodynamics, 246, 506 ligand interactions, 246, 6, 507 sample requirements, 246, 506] fatty acyl ester determination in small cell samples, 233,... 

Saponification see Hydrolysis Saponification equivalent of an ester, determination of. 392, 1065 Saturated aliphatic hydrocarbons, 233 reactions and characterisation of 234, 1058 table of, 235 ... 

An electron-withdrawing group, such as nitro, at 4 - position of the benzyl ester determined a significant enhancement of both affinity and selectivity (compound MRS 1334). Any other modifications, including heterocycles at the 4-position, aminoalkyl or thioalkyl groups at the 3- and 5-positions, appeared detrimental in term of both affinity and selectivity. 

The methyl esters can be also determined by GC-FID. Using a 30 m x 0.32 mm ID x 0.25 pm (film thickness) capillary column, such as DB-1701 or equivalent, the compounds can be adequately separated and detected by FID. The recommended carrier gas (helium) flow rate is 35 cm/s, while that of the makeup gas (nitrogen) is 30 cm/min. All of the listed herbicides may be analyzed within 25 min. The oven temperature is programmed between 50 and 260°C, while the detector and injector temperatures should be 300 and 250°C, respectively. The herbicides may alternatively converted into their trimethylsilyl esters and analyzed by GC-FID under the same conditions. FID, however, gives a lower response as compared with ECD. The detection level ranges from 50 to 100 ng. For quantitation, either the external standard or the internal standard method may be applied. Any chlorinated compound stable under the above analytical conditions, which produces a sharp peak in the same RT range without coeluting with any analyte, may be used as an internal standard for GC-ECD analysis. U.S. EPA Method 8151 refers the use of 4,4,-dibromooctafluorobiphenyl and 1,4-dichlorobenzene as internal standards. The quantitation results are expressed as acid equivalent of esters. If pure chlorophenoxy acid neat compounds are esterified and used for calibration, the results would determine the actual concentrations of herbicides in the sample. Alternatively, if required, the herbicide acids can be stoichiometrically calculated as follows from the concentration of their methyl esters determined in the analysis ... 

A 100-mL sample aliquot adjusted to pH 11.5 sample extracted with methyl tert-butyl ether (MTBE) chloroacetic acid partitions into aqueous phase basic and neutral compounds in MTBE phase discarded the aqueous phase now adjusted to pH 0.5 and extracted again with MTBE the MTBE extract dried and concentrated chloroacetic acid in the MTBE extract esterified with diazomethane the methyl ester determined by capillary GC on an ECD (U.S. EPA Method 552, 1990). 

Knothe, G., Matheaus, A. C., and Ryan, T. W. III. 2003. Cetane Numbers of Branched and Straight-Chain Fatty Esters Determined in an Ignition Quality Tester. Fuel, 82, 971-975. 

Angular Rotation Determine as directed under Optical (Specific) Rotation, Appendix IIB, using a 100-mm tube. Ester Value Determine as directed under Ester Determination, Appendix VI, using about 5 g of sample, accurately weighed. 

Assay Determine as directed in Ester Determination under Esters, Appendix VI, using a 2-g sample, accurately weighed, but heat the mixture for 30 min on the steam bath. Use 98.15 as the equivalence factor (e) in the calculation. 

Ester Determination Weigh accurately the quantity of the sample specified in the monograph, and transfer it into a 125-mL Erlenmeyer flask containing a few boiling stones. Add to this flask and, simultaneously, to a similar flask for a residual blank titration (see General Provisions) 25.0 mL of 0.5 N alcoholic potassium hydroxide. Connect each flask to a reflux condenser, and reflux the mixtures on a steam bath for exactly 1 h, unless otherwise directed in the monograph. Allow the mixtures to cool, add 10 drops of phenolphthalein TS to each flask, and titrate the excess alkali in each flask with 0.5 N hydrochloric acid. Calculate the percentage of esters ( ) in the sample by the equation... 

Saponification Value Proceed as directed for Ester Determination or Ester Determination (High-Boiling Solvent), as specified in the monograph. Calculate the saponification value (SV) by the equation... 

Transfer a 10-mL sample, previously dried with sodium sulfate, into a 125-mL glass-stoppered Erlenmeyer flask previously cooled in an ice bath. Add to the cooled oil 20 mL of dimethyl aniline (monomethyl-free), and mix thoroughly. To the mixture add 8 mL of acetyl chloride and 5 mL of acetic anhydride, cool for several min, permit to stand at room temperature for another 30 min, then immerse the flask in a water bath maintained at 40° 1° for 16 h. Wash the ace-tylated oil with three 75-mL portions of ice water, followed by successive washes with 25-mL portions of 5% sulfuric acid, until the separated acid layer no longer becomes cloudy or emits an odor of dimethyl aniline when made alkaline. After removal of the dimethyl aniline, wash the acetylated oil first with 10 mL of sodium carbonate TS and then with successive portions of water until the washings are neutral to litmus. Finally, dry the acetylated oil with anhydrous sodium sulfate, and proceed as directed for Ester Determination under Esters, this Appendix. Calculate the percentage of linalool (CioHigO) by the equation... 

Note When this method is applied to essential oils containing appreciable amounts of esters, perform an Ester Determination, this appendix, on a sample of the original oil and calculate the percentage of total linalool by the equation... 

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