Water Determination Toluene Distillation Method

Moisture. Moisture was determined by the toluene distillation method. A 40 g sample of powder was added to 250 mL toluene in a 500 mL flask. The flask was fitted with a Bidwell-Sterling trap and the sample brought to a boil on a hot plate. The distillation was carried out for 2i hr. The distillate was allowed to cool to room temperature before the volume of water was read directly from the trap. 

Moisture Determination. Sample moisture was determined by using a modified A.O.A.C. toluene distillation method (7) for both the powders stored at 37 C (a adjusted over Mg(NO3)2T and the powders stored at 4 C (a unadjusted). Toluene (175mL) was added to 40g of unadjusted powder or 20g of adjusted powder in a 500 mL flat bottomed flask fitted with a Bidwell-Sterling trap and water cooled condenser. Samples distilled for 3 hours and then the volume of water collected was recorded. 

The water of crystallization can be moved from a-hydrate by refluxing it in a high-boiling organic solvent that is immiscible with water. For example, the moisture in lactose hydrate has been determined by the toluene distillation method that is often used to determine moisture in milk powder with lactose, prolonged distillation (5 hr) is necessary to remove the hydrate moisture. The powder remaining after distillation in a stable anhydrous form (Nickerson 1974). 

Under industrial conditions the moisture present in material must be determined by faster methods, such as by electrical methods of which three main varieties have become widespread moisture determination based on the change of the ohmic dc resistance, a measurement of the electrostatic capacitance (dielectric constant of the material), and a measurement of the loss in an ac field. Other quick methods are the chemical methods developed mainly for the most frequently occurring case, when the moisture is water, such as the Karl-Fischer analysis based on the chemical reaction of iodine in the presence of water [3], the distillation method, in which moisture is determined by distillation with toluene, and the extraction method, which is carried out with absolute ethanol. 

It is difficult to estimate the magnitude of the error due to insufficiently low humidity when distillation methods are used with organic liquids such as toluene (6, 28), xylene (6, 28), or chloroform (12). With organic liquids essentially immiscible with water and of high boiling point the error is probably very small. When methanol is used as an extraction solvent, as in the Fischer reagent method, the amount of unextracted water is undoubtedly some function of the concentration of water in the alcohol, but the error might be small because of substitution of adsorbed water by adsorbed alcohol (23, 34). This seems to be borne out by experiments of Schroeder and Nair (31), who deliberately added water to the alcohol to form a 0.5% water solution and found that the results of their moisture determinations were essentially the same as with anhydrous methanol, which contained about 0.05% water. 

Moisture. The water content of lecithin products is usually less than 1.0%. As a consequence of lecithin s essentially moisture-free state, lecithin products have very low water activity and do not adversely contribute to the microbiological profile of most food systems. Most lecithin products are preserved well in storage. Higher moisture levels usually indicate a greater potential for spoilage or chemical degradation. Moisture is determined by AOCS Official Method Ja 2b-87 (77). A less accurate moisture level can also be determined by azeotropic toluene distillation (AOCS Official Method Ja 2-46) (77). One cannot determine lecithin moisture by vacuum oven methods. These methods are known to degrade lecithin products and yield false moisture levels. 

Polymerization Method. To a solution of 5.18 mmole of HFB or PFB and 5.18 mmole of the appropriate bisphenol or bisthiophenol in 20 ml of solvent was added 22.4 mmole anhydrous of K2CO3 and 1.43 mmole of 18-crown-6 ether. The magnetically stirred, heterogenous mixture was heated in an oil bath and maintained under N2. Upon cooling to room temperature, the mixture was slowly poured into ca. 150 ml of methanol and was vigorously stirred. The filtered solids were washed three times in a blender with 300-ml portions of distilled water. The solids were air dried and subsequently placed in a vacuum oven (80 ) for 24 hr. Where soluble, the polymers obtained were characterized by IR and PMR analysis. Elemental analyses for all polymers were satisfactory. Polymer solubility was determined in THF, DMF, dioxane, toluene, m-cresol, chloroform, and sulfuric acid. The percent insoluble polymer was determined gravimetrically. Inherent viscosities of soluble polymers were determined in ca. 0.5% wt. solutions in either chloroform or THF. 

Principle This method determines water by distillation of a sample with an immiscible solvent, usually toluene. 

Some IPCs can be very simple, e.g., determining whether a condensate contains two phases. For example, a homogeneous distillate may indicate that the azeotropic removal of water from a toluene extract is complete. At this point it may be appropriate to test the contents of the distillation vessel to confirm that all water has been removed. Other IPCs will require relatively rigorous quantitation and sophisticated, expensive instrumentation. Often an IPC is chosen for convenience and dual use. For instance, the method used to follow a reaction may also... 

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