Chinese J. Adv. in Biochem. & Biophys. (Shengwu Huaxue Yu Shengwu Wuli Jinzhan) 20, 134-136 (1993). TLC of oligonucleotides on silica with isopropanol - water - conc. NH3 6:3:1. Quantification by densitometry (absorbance) at 260 nm. Comparison of results with those obtained by UV spectrophotometry.

J. Planar Chromatogr. 12, 63-65 (1999). Determination and quantification of impurities and synthetic by-products in theophylline by videodensitometry and classical TLC scanning densitometry, in each case using equipment from two different manufacturers. No significant differences of the performance of the two scanners were found in terms of detection limit (approx. 24 ng for Scanner I and 23 ng for Scanner II) and precision (variation coefficients 3.2 and 4.1% resp.) Detection by videodensitometry is possible for concentrations larger than 25 ng/spot; quantification requires approx. 100 ng/spot. The limits of impurities in pharmaceutical drugs set by Ph Eur - usually 0.1% - could not be quantified by videodensitometry at its current stage of development. - Regression curves show average variation coefficients of approx. 17.4 for videodensitometer I and 5.9% for videodensitometer II. The use of videodensitometry for impurity testing is nevertheless useful in special cases where higher deviations are considered acceptable for assays, and when higher concentrations are available for quantitation of the main component.

J. Chromatogr. 645, 189-192 (1993). HPTLC of DNA 5-methylcytosine on alkyl amino modified silica with isobutyric acid - water - NH3 177:8:3. Detection under UV 254 nm. Quantification by scintillation counting. Comparison with traditional two-dimensional procedure on polyethyleneimine cellulose and HPLC method.