Organic compounds determination after dilution

In each class the problem may be resolved into two essential parts (i) the breakdown of the organic compound under appropriate conditions to give a quantitative yield of fluoride ions in aqueous solution, and (ii) the determination of the concentration of these fluoride ions. Methods of breaking down the organic compounds were examined and the procedure adopted for the phosphorofluoridate was different from that used for the fluoroacetate series. From both, however, sodium fluoride was obtained as the breakdown product containing all the fluorine present. After numerous preliminary experiments we came to the conclusion that on the macro-scale a very convenient method of determining the quantity of fluoride ions in the products was by precipitation as lead chlorofluoride,2 PbCIF, which was then dissolved in dilute nitric acid and the chloride was determined by the Volhard method and calculated to the equivalent amount of fluorine. We determined carefully the conditions for the quantitative precipitation of lead chlorofluoride. 

Iron carbonyls may be identified by electron diffraction and x-ray analysis. Also, its solutions in appropriate organic solvents, such as ether, methanol, or acetone may be analyzed by GC/MS. The characteristic mass spectra should indicate the molecular ions corresponding to the carbonyl as well as the mass spectra of CO and Fe(CO)n, where n is the number of CO units in the fragmented mass ions. Flame- or furnace-AA or ICP/AES analysis may be apphed on the nitric acid extract of the compound(s) after appropriate dilution to determine the concentration of iron (See Iron). 

The importance of the determination of sulphuric acid and sulphates lies very largely in the fact that sulphur in various forms of combination, and also free sulphur, is frequently determined quantitatively by primary conversion into sulphuric acid or sulphate, followed by actual estimation in the latter form. For example, a convenient volumetric process applicable to the Carius method for determining sulphur in organic compounds is to neutralise the solution of sulphuric acid after removal of the excess of nitric acid by evaporation, and then add silver nitrate, by which the sulphate is converted into silver sulphate. This is separated from the excess of silver nitrate by means of its insolubility in alcohol, and is then estimated by dissolving in dilute nitric acid and titrating the silver with standard thiocyanate solution.3... 

Since 1995, 21 compounds from five herbicide families have been quantified in soils by SPME. Researchers originally used soiEwater suspension samples, either by Dl- or HS- SPME.158,160, 168. Koc for six triazines in soils and sediments have been determined by SPME. Recoveries were satisfactory in the organic carbon range 0.2 to 2.4%, with detection limits included between 50 and 500 ng/g. Recent works suggest that the most reliable method consists of performing a Dl-SPME of a diluted organic extract obtained after conventional solid-hquid extraction. 

Dissolve 0.5 g. of hydroxylaniine hydrochloride in 2-3 cc. of water, add 2 cc. of 10 jier cent XaOH solution, 0.2 g. of the unknown, and exactly sufficient alcohol to dissolve the organic compound. The oxime is generally sparingly soluble and may crystallize from the dilute alcohol as it is formed. Often it is best to warm the reaction-mixture on the steam-bath for 10 minutes, using a condenser to avoid loss of solvent. If no sign of reaction is noted after one hour, the mixture is diluted with 2 volumes of water and the precipitated product tested to determine whether it is the oxime or the original unknown. The oximes are usually. soluble in dilute alkali and may be reprecipitated by exact neutralization of the alkaline solution. Why is an excess of acid to be avoided ... 

---