Laboratory Instrumentation and Analytical Principles Flashcards

According to Beer's law, what happens to absorbance if the concentration of an analyte doubles while path length and molar absorptivity stay constant?

Answer: Absorbance doubles

Beer's law (A = abc) states absorbance is directly proportional to concentration.

A sample reads 10% transmittance on a spectrophotometer. What is its absorbance?

Answer: 1.0

A = 2 − log %T = 2 − log 10 = 1.0.

Which material is commonly used to verify wavelength accuracy of a spectrophotometer?

Answer: Holmium oxide glass filter

Holmium oxide has sharp, known absorbance peaks used to check wavelength calibration.

Stray light in a spectrophotometer most significantly causes which problem?

Answer: Negative deviation from linearity at high absorbance

Stray light reaching the detector limits measurable absorbance, flattening the curve at high concentrations.

What is the main advantage of a double-beam spectrophotometer over a single-beam design?

Answer: It compensates for light source fluctuations

Splitting the beam between sample and reference corrects for changes in source intensity and detector response.

Which light source is used for measurements in the ultraviolet range?

Answer: Deuterium lamp

Deuterium lamps provide continuous emission in the UV region (about 165–375 nm).

Which detector offers the highest sensitivity for low light levels in spectrophotometry?

Answer: Photomultiplier tube

Photomultiplier tubes amplify the signal through a series of dynodes, giving very high sensitivity.