commercial catalogs and occasionally the research literature troduce different notations. Some consider"NTP"a general term for deoxynucleotides, but the absence of the letter"d"indicates a ribonucleotide to others Commercial literature also describes ribonucleotides as“"RTP's” If the letter“d” Is present, the name describes a deoxynucleotide. If"d"is absent, check the literature piece closely to avoid a common purchasing error. Dideoxynu cleotides are generically referred to as"ddNTPs. What Makes a Nucleotide pure? Using dATP as an example, what categories of impurities could be present? One potential contaminant is a nucleotide other than dATP, such as dCTP. A second class of impurity could be the mono-, di-, or tetraphosphate form of the deoxyadenosine nucleotide. Since most if not all commercial nucleotides are chem. ically synthesized from highly analyzed precursors, contamination with a nucleotide not based on deoxyadenosine is very unlikely a third class of impurities is the non-UV-absorbing organic and inorganic salts accumulated during the synthesis and purification p ocedures While essentially all commercial nucleotides are chemically synthesized, the final products are not necessarily identical Manufacturing processes vary; raw materials and intermediates of the nucleotide synthesis reactions are subjected to different purification strategies and processes. It is these intermediate eps, and the scrutiny of the products' final specifications, that allow manufacturers to legitimately claim that nucleotides are extremely pure A formal definition of extremely pure does not exist, but com- mercial preparations of such products typically contain greater than 99% of the desired nucleotide in the triphosphate form Contaminating nucleotides are rarely detected in commercial preparations, even using exceedingly stringent high-performance chromatography procedures, but some contaminants escape HPLC detection. Freedom from non-UV-absorbing materials is typically judged by comparison of a measured molar extinction (Am) coefficient to published extinction coefficients (E)values Nuclear magnetic resonance(NMR) may also be used to monitor for contaminants such as pyrophosphate Are Solution Nucleotides always More Pure Than Lyophilized Nucleotides? Nucleotides were first made commercially available as solvent precipitated powders. The lyophilized and extremely pure solution Nucleotides, Oligonucleotides, and Polynucleotides 269commercial catalogs and occasionally the research literature in￾troduce different notations. Some consider “NTP” a general term for deoxynucleotides, but the absence of the letter “d” indicates a ribonucleotide to others. Commercial literature also describes ribonucleotides as “RTP’s.” If the letter “d” is present, the name describes a deoxynucleotide. If “d” is absent, check the literature piece closely to avoid a common purchasing error. Dideoxynu￾cleotides are generically referred to as “ddNTP’s.” What Makes a Nucleotide Pure? Using dATP as an example, what categories of impurities could be present? One potential contaminant is a nucleotide other than dATP, such as dCTP. A second class of impurity could be the mono-, di-, or tetraphosphate form of the deoxyadenosine nucleotide. Since most if not all commercial nucleotides are chem￾ically synthesized from highly analyzed precursors, contamination with a nucleotide not based on deoxyadenosine is very unlikely. A third class of impurities is the non-UV-absorbing organic and inorganic salts accumulated during the synthesis and purification procedures. While essentially all commercial nucleotides are chemically synthesized, the final products are not necessarily identical. Manufacturing processes vary; raw materials and intermediates of the nucleotide synthesis reactions are subjected to different purification strategies and processes. It is these intermediate steps, and the scrutiny of the products’ final specifications, that allow manufacturers to legitimately claim that nucleotides are extremely pure. A formal definition of extremely pure does not exist, but com￾mercial preparations of such products typically contain greater than 99% of the desired nucleotide in the triphosphate form. Contaminating nucleotides are rarely detected in commercial preparations, even using exceedingly stringent high-performance chromatography procedures, but some contaminants escape HPLC detection. Freedom from non-UV-absorbing materials is typically judged by comparison of a measured molar extinction (Am) coefficient to published extinction coefficients (e)values. Nuclear magnetic resonance (NMR) may also be used to monitor for contaminants such as pyrophosphate. Are Solution Nucleotides Always More Pure Than Lyophilized Nucleotides? Nucleotides were first made commercially available as solvent￾precipitated powders.The lyophilized and extremely pure solution Nucleotides, Oligonucleotides, and Polynucleotides 269