When using a Vernier UV-Vis spectrophotometer in the laboratory, which of the following is an essential step to ensure accurate measurements?

• A. Calibrate the spectrophotometer with a blank solution before measuring samples.
• B. Always use tap water as the solvent for all samples.
• C. Handle cuvettes with bare hands to avoid contamination.
• D. Record absorbance values without setting the wavelength.

Answer: (A)

Verified step by step guidance

1. Understand that a Vernier UV-Vis spectrophotometer measures the absorbance of light by a sample at specific wavelengths to determine concentration or other properties.
2. Recognize that to obtain accurate absorbance readings, the instrument must be calibrated to zero absorbance using a blank solution, which contains all components except the analyte of interest.
3. Prepare the blank solution, typically the pure solvent or buffer used to dissolve the sample, and place it in the cuvette to calibrate the spectrophotometer before measuring any samples.
4. Avoid using tap water as a solvent unless it is the exact solvent for your sample, because impurities in tap water can affect absorbance readings and lead to inaccurate results.
5. Handle cuvettes carefully, preferably by the frosted sides or with gloves, to prevent fingerprints or contamination that can scatter light and distort measurements, and always set the correct wavelength before recording absorbance values.