The choice of the PCR enzyme in combination with an appropriate buffer can profoundly affect PCR outcome. Template purity and quality are also critical to PCR success. Sequence and primer concentrations also determine overall assay quality. Nucleotides are vital components in amplification reactions and purity and concentration of these reagents significantly influences PCR results. Most thermostable DNA polymerases require divalent cations to function (in most cases Mg2+, and for fewer DNA polymerases Mn2+). Concentrations of Mg2+ or Mn2+ must typically be optimized. In some cases, additives can enhance PCR efficiency, specificity, and yield. The appropriate cycling parameters contribute to a successful PCR.