What instrument and wavelength are commonly used to quantify DNA in the lab?

What instrument and wavelength are commonly used to quantify DNA in the lab?

• A. Spectrophotometer measuring absorbance at 260 nm
• B. Fluorometer measuring DNA concentration
• C. Gel electrophoresis device measuring DNA size
• D. pH meter measuring acidity

Answer: (A)

Quantifying DNA most commonly uses a spectrophotometer to measure absorbance at 260 nm. DNA absorbs UV light at this wavelength because of its nucleotide bases, and the absorbance is proportional to the amount of DNA present (Beer-Lambert law). Practically, an absorbance of 1.0 at 260 nm corresponds to about 50 µg/mL for double-stranded DNA when measured with a 1 cm path length. You blank the instrument with the buffer, then use the A260 value to estimate concentration and check purity with the A260/A280 ratio (roughly 1.8–2.0 suggests relatively pure DNA). The A260/A230 ratio can also indicate other contaminants. While fluorescence methods with DNA-binding dyes offer higher sensitivity in some cases, or gel electrophoresis can show size and relative abundance, the 260 nm absorbance method is the standard quick way to quantify DNA. A pH meter, on the other hand, measures acidity and does not quantify DNA.

Quantifying DNA most commonly uses a spectrophotometer to measure absorbance at 260 nm. DNA absorbs UV light at this wavelength because of its nucleotide bases, and the absorbance is proportional to the amount of DNA present (Beer-Lambert law). Practically, an absorbance of 1.0 at 260 nm corresponds to about 50 µg/mL for double-stranded DNA when measured with a 1 cm path length. You blank the instrument with the buffer, then use the A260 value to estimate concentration and check purity with the A260/A280 ratio (roughly 1.8–2.0 suggests relatively pure DNA). The A260/A230 ratio can also indicate other contaminants. While fluorescence methods with DNA-binding dyes offer higher sensitivity in some cases, or gel electrophoresis can show size and relative abundance, the 260 nm absorbance method is the standard quick way to quantify DNA. A pH meter, on the other hand, measures acidity and does not quantify DNA.