New concepts in densitometry : Control analysis of pharmaceutical formulations

✍ Scribed by H. Bethke; R.W. Frei

• Publisher: Elsevier Science
• Year: 1974
• Tongue: English
• Weight: 571 KB
• Volume: 91
• Category: Article
• ISSN: 1873-3778
• DOI: 10.1016/s0021-9673(01)97922-1

✦ Synopsis

A study of a number of different pharmaceutical compounds has shown that with the calibration function AZ = m'c + n' (A = peak area, c = concentration) linear calibration curves can be obtained with concentrations between 1 and 10 pg per spot. For concentrations in the range of 0.3 to l.O,ug the function lt = m"c + n" (h = peak height) is preferred at higher amplification.

This actually means that with the densitometric evaluation of directly spotted liquid samples concentrations in the range 0.03-5 mg/ml can be analysed.

The time saved by direct sample spotting has been demonstrated with a typical example where nine analyses of a product with a 0.2,ug/ml concentration of active principle (2 Ccl/spot) can be carried out in one day, with a reproducibility of -4: 1.4 % relative S.D. For the same samples, using classical elution procedures, 3-4 days are required and extraction of samples prior to spotting (with danger of decomposition) is necessary.

The analysis of thyroacetic acid, which appears as an enzymatic breakdown product of thyronine and has a il,,,, value of 235 nm, has been carried out by UV reflectance at concentrations of 50 ng/spot using a standard addition approach. This is a good example of the applicability of this method to very low concentrations and at relatively short il,,,.. Instrumental modifications which facilitate the measuring process and data handling are discussed.