Gravimetric assaying

Theory The gravimetric assay of histamine acid phosphate is based upon the formation of insoluble histamine-nitranilic acid complex as depicted in the following equation ... 

Theory In general, quaternary nitrogen containing compounds like—choline chloride, acetylpyridinium chloride, benzethonium chloride, and bethanechol chloride readily form insoluble salts quantitatively with tetraphenyl boron and this puts forward the basis for the gravimetric assay of the above cited pharmaceutical substances. 

A gravimetric assay method based on the precipitation of chlorpromazine hydrochloride in hulk and in various dosage forms has been reported [179]. The method uses a KBrO-KBr mixture in the presence of 15%... 

Toei > recommended a procedure for the gravimetric assay of K+, using l,3,7,9-tetranitrophenothiazine-5-oxide or -5,5-dioxide in LiOH or Li2COg solution as a precipitating reagent. 

Finally, although it is not rigorously part of supercritical fluid extraction, a last step generally afforded hy analytical-scale supercritical fluid extractors is reconstitution of the extracted components in a solution that is appropriate for the subsequent analytical instrument. In the case of gravimetric assays, the net loss of sample weight or the net weight of extract components can be measured and reconstitution of extracted components is not necessarily employed. 

In the following examples, HP7680 SFE instruments (Hewlett-Packard) were used. With these instruments, samples are input to the instrument via containers referred to as extraction thimbles. Extracted components are collected and concentrated on soUd traps. The temperature of the solid trap can be independently set for extraction and reconstitution steps in a method. The chemical functionahty (none to quite polar) of the trap is selected by the choice of the packing material. A reconstitution solvent is used to move extracted components from the solid trap to automatic liquid sampler vials (or to waste). Depending upon the appUcation, the vials are presented to a subsequent analytical instrument or possibly manipulated for a gravimetric assay. With this instrument implementation, samples are input and fractions of extracted components in hquid solvents in 2-mL vials are output with no manual intervention between input and output steps. 

I. Gravimetric Assay. In vitro methods are more sensitive than in vivo methods, but the dose response curves are not as steep, and thus they are less precise. Baake et al. (B2) measured the weight of beef thyroid slices incubated for 24 hours in Krebs-Ringer phosphate buffer. 

The sample preparation method must not only deliver a measurable amount of sample but the compounds accompanying the analyte must not interfere with the analysis. As an illustration, consider a gravimetric assay in which the detection step has no discriminating power and the sample preparation provides all of the specificity. In contrast, an enzyme assay can be performed on a very complex sample without any sample preparation or isolation of the analyte, because the changes in substrate concentration can be linked directly to the activity of the enzyme. 

Both gravimetric and uv methods showed overestimation when compared to the nonaqueous procedure. Again, titration of the residues from the gravimetric assay gave values which agreed closely with those of nonaqueous titration (Table X). 

Gravimetric Assays Involving a Prior Solvent Extraction... 

According to the technique of gravimetric assays involving a prior solvent extraction, the compound to be determined is extracted with an appropriate solvent. The removal of the solvent yields a residue whose weight is determined. In some cases, the extraction can be carried out after a preliminary chemical treatment of the initial sample. Hence, we can distinguish the following two procedures ... 

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