Sample weight percent purity

Under some conditions, it is difficult to incorporate an internal standard into a method. If the chromatogram is very complex, an internal standard may interfere with quantitation of a peak of interest. The development of highly precise sample transfer techniques, including modem autoinjectors, reduces the dependence of the experimentalist on the use of an internal standard to correct for effects of dilution and transfer losses. In many cases, external standardization can be used effectively. The weight percent purity is determined by comparing the area of each peak in a chromatogram with those generated by separately injected pure standards of known concentration. 

Calculate the weight percent purity of the sample as follows ... 

To determine the weight percent of each compound in the reaction sample, a standard and sample of known weight concentration were prepared and analyzed. The weight percent of each component purity was determined as described in the External Standard Method. 

Shomate and Kelley (8, 52.6-296.3 K) measured the low temperature heat capacities for VN. The purity of the mononitride sample based on an analysis for vanadium by permanganate titration was found to be 99.76 weight percent. Their C data corrected... 

The experimentally determined purity (purityexp) or activity is the amount of the API present in the material being tested. For chiral drug substances, the achiral purityexp is the amount of both enantiomers in the sample, while the chiral purityexp is the weight percent of the desired enantiomer. The purityexp is used to calculate the assay value of the batch and is used for DP manufacture and for the calculation of dosages used for toxicological testing. 

While the purity of ionic liquids has already been discussed from the synthetic perspective in Section 2.2, the following section aims to highlight this aspect from the viewpoint of an industrial company aiming to apply ionic liquids in its processes and products. What exactly is purity. Most people would define purity by the actual content of the desired compound expressed in weight percent. Already, this is not an easy thing to do with ionic liquids. As salts they intrinsically consist of two compounds, a cation and an anion. For example a sample of [EMIMJCl might contain 5 wt.% of [EMIM][HS04] as impurity. This means the ionic liquid is 100 wt.% pure in terms of the cation [EMIM]+ and 95 wt.% pure in terms of the anion chloride. 

A known amount of internal standard is added to a sample of AMS. The prepared sample is mixed and analyzed by a gas chromatograph (GC) equipped with a flame ionization detector (FID). The peak area of each impurity and the internal standard is measured and the amount of each impurity is calculated from the ratio of the peak area of the internal standard versus the peak area of the impurity. Purity by GC (the AMS content) is calculated by subtracting the sum of the impurities from 100.00. Results arc reported in weight percent. 

When molecules are synthesized by multi-step sequences or when new compounds are extracted from natural sources, their structure and purity must be elucidated. For this, a quantitative elemental analysis must be performed. This particular type of analysis allows us to find the percent elemental composition, in the pure state, of the molecule under study. The measurement of a single element, indeed two (C and H are the most frequent) will verify the accuracy of the molecular formula proposed for a molecule not as yet fully defined but for which a structure has been deduced from spectral studies. Elsewhere, purify of a compound for which the composition and the molecular weight are known, can be determined by comparison of the experimental results obtained from a sample with the theoretical ones (Figure 18.1). 

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