Effect of Chloride Ions on the Reaction of Diphenylamine with Dna.

It is known that diphenylamine under conditions of the Dische test may react with certain sugars when present at high concentrations (1). Further, it has been long recognized that a high mineral acid content in the reagent enhances the reaction with hexoses (2, 3). This is the basis of a method for fructose and inulin determination (2, 4). However, for analytical determination of DNA, the reagent is usually applied to partially purified material (acid precipitated) from which interfering substances are removed. Currently less severe methods of purification are being employed to isolate DNA in polymeric native forms using CsCl density gradients, sucrose gradient centrifugation, or column chromatography with salt elution. The preparation is likely to be contaminated with high molecular weight polymeric sugars (5) as well as with these apparently innocuous suspending media. These, when present in the standard Dische test, might be expected to condition the reagent to act as a hexose reagent (2), thus reducing the sensitivity of the DNA determination while producing a falsely high positive reading. The following observations concern the quantitative and qualitative effects of halogen ions in the standard Dische reaction.