• Reduction of shadow band synthesis during PCR amplification of repetitive sequences from modern and ancient DNA

      Schmerer, WM; Paleo DNA Laboratory, Department of Anthropology, Lakehead University, Thunderbay, Ontario, Canada. (Humana Press, 2003-01-01)
      Repetitive sequences like short tandem repeat (STR) loci are generally referred to as slippery DNA (1). They owe this nickname to a characteristic leading to slippage within the primer-template complex during PCR elongation of the new strand (2,3), resulting in the synthesis of byproducts shortened by one repeat unit compared with the original sequence. The generation of these so-called shadow bands (4) is a well-known problem connected with the amplification of repetitive DNA, complicating the genotype analysis of modern (e.g., ref. 5), forensic (6), and ancient (7,8) specimens. In some applications, the occurrence of this artifact makes it necessary to develop guidelines for allele designation (6,9).
    • Simultaneous qualitative and quantitative analyses of the major constituents in the rhizome of Ligusticum Chuanxiong using HPLC-DAD-MS.

      Yi, Tao; Leung, Kelvin Sze-Yin; Lu, Guang-Hua; Chan, Kelvin C.; Zhang, Hao (Tokyo: The Pharmaceutical Society of Japan, 2006)
      An HPLC-DAD-MS method was developed for the qualitative and quantitative analysis of the major constituents in Chuanxiong (the dried rhizome of Ligusticum chuanxiong Hort). Twenty compounds including phenolic constituents, alkylphthalides and phthalide dimers were identified using online ESI-MS and comparisons with literature data and standard compounds, and six of them were quantified by HPLC-DAD simultaneously. A comprehensive validation of the method including sensitivity, linearity, repeatability and recovery was conducted. The linear regressions were acquired with R(2) > 0.99 and limit of detection (LOD, S/N = 3) values were between 1.5 and 2.5 ng. The repeatability was evaluated by intra- and inter-day assays, and relative standard deviation (RSD) values were reported within 1.87%. The recovery studies for the quantified compounds were observed in the range of 96.36-102.37% with RSD values less than 2.63%. These phenolic constituents and alkylphthalides, the major constituents in Chuanxiong, are generally regarded as the index for the quality assessment of this herb. The overall procedure is accurate and reproducible, which is considered suitable for the qualitative and quantitative analyses of a large number of Chuanxiong samples.