FRED%BLEKUL13.BITNET@CUNYVM.CUNY.EDU (fred van leuven) (07/01/88)
Does anyone want to comment on the quantitation of DNA, either genomic or plasmid, by optical density measurement at 260 and 280 nm. We experience erroneous results relative to estimations of amounts from EtBr stained agarose gels. No obvious contaminants are to blame since the most spect acular difference was noted with a maxiprep of a 1 liter culture divided in 4 and processed in parallel 250 ml batches. The ratio of DNA recovered differed by a factor of 3 when measured spectrofotometrically but was comparable by EtBr staining on gel. The 4 batches were kept in line so that always the same order of additions and manipulations was respected. The "first" batch was quantitatively concordant what the two methods were concerned but a progressively decreasing amount of DNA was measured in the spectro from batch 2 to 4, so that batch 4 appeared to contain only a third of the amount of plasmid DNA relative to batch 1. Explain who can -all suggestions and tips welcome. Thanks and sincerely yours. Fred van Leuven. Acknowledge-To: <FRED@BLEKUL13>