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Amplified DNA Product Separation for Forensic Analysts

Quality Control

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The capillary and reagents used in electrophoresis have an effect on the quality of data produced. Laboratories can determine the quality of formamide by measuring its conductivity and/or resolution.02, 03

Conductivity is the measure of the ability of a material to conduct an electrical charge and is the reciprocal of resistance. Conductivity is measured in units of microSiemens (µS/cm) or microMhos (µMhos/cm). The lower the conductivity value, the higher the quality of the formamide. The conductivity can be measured with a conductivity meter and generally 80 µS or less is acceptable.03

The decomposition resulting in high-conductivity formamide occurs through the following steps:

  • Hydrolysized with water, it will react with the water in the air to produce ammonium formate.
  • Further reaction with the water in the air ionizes the ammonium formate to produce ammonium hydroxide (may have an ammonia odor) and formic acid.

Impurities such as formic acid (smaller negatively charged ions), ammonia, and other unknown impurities could:

  • Compete with the DNA fragments to reduce the amount of DNA injected
  • Produce lower signal-to-noise ratio (lower signal, more noise)
  • Degrade and decompose DNA fragments, especially if in small concentration and for long-standing periods of time on the capillary electrophoresis instrument, resulting in multiple interference peaks around peaks of interest, reducing resolution and selectivity.

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