DSC purity

Since procaine hydrochloride melts without decomposition, the DSC method can be used to establish the absolute purity of the material. The DSC purity of the tested sample was found to be 100.14 mole%, and the enthalpy of fusion for this sample was determined to be 31.5 kJ/mole (7.52 Kcal/mole). 

PHOSPHOLIPID SYNTHESIS. Phospholipids were synthesized (H.Schuster, S.S. Hall, and R.Mendelsohn, in preparation) according to the procedures of Tulloch (26), modified with more modern and efficient coupling steps, and scaled up to produce 2-3 grams of specifically deuterated material. Derivatives were fully characterized with NMR, MS, FT-IR, and Differential Scanning Calorimetry (DSC). Purity is estimated from NMR data at > 98X. The extent of deuteration, as estimated from the residual intensity of the CHD rocking modes at... 

The DSC impurity analysis is described in USP. With modern equipment including robotic systems and data aquisition, the DSC purity analysis is a state-of-the-art technique for pharmaceutical development. 

Fig. 15 Stability screening. Example of DSC purity results obtained for a drug substance sensitive to moisture. From the top to the bottom Initial sample (purity 99.9%), sample stored under humid conditions at 50°C (purity 99.7%), sample stored under humid conditions at 80°C (purity 99.1%).

Giron, D. Goldbronn, C. Place of DSC purity analysis in pharmaceutical development. J. Thermal. Anal. 1995, 44, 217-251. 

Table 10.5. Comparison of GC Assay and DSC purity Values for Some Zone-refined...

Compound GC Assay J. T. Baker ULTREX Lot No. (area-%) DSC Purity (mole-%)... 

The DSC method for calculating purity is not universally applicable to all compounds. The material being studied should not undergo decomposition during melting. The DSC curves in Figure 1020 represent cases in which the DSC purity method should not be applied (70). 

Figure 10.20. DSC curves of compounds that should not be studied bv the DSC purity method (2t).

Other programs which can be used to calculate reaction kinetics from DSC data were formulated by Kauffman and Beech (41) and Rogers and Smith (42). Heuvel and Lind (43) used a computer to correct DSC data for effects due to thermal lag and heat capacity changes, while Sondack (44) developed a simple equation for linearization of data in DSC purity determinations. 

A DSC purity measurement is not performed under equilibrium conditions and is therefore only approximate. The estimate should be verified by comparison with values from other techniques such as high-performance liquid chromatography (HPLC). For purity measurements the energy and temperature calibration of the DSC system should be as precise as possible. Allowance must be made for the difference between the instrument and sample baselines when estimating and Tg (Figure 5.22). 

The important parameters during a DSC purity determination are the following ... 

Quantification of amorphous content using DSC Purity determination using DSC... 

Figure 8.25 The van t Hoff plot showing a DSC purity calculation. The curved line shows the original data before use of the x-correction algorithm.

Gustin GM. Broad range purity analysis by melting point depression using a singular feature common to aU DSC purity scans. Thermochim Acta 1980 39(2) 81-93. 

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