Laboratory Instrumentation and Analytical Principles Flashcards

According to Beer's law, absorbance is directly proportional to which of the following?

Answer: Concentration and light path length

Beer's law (A = abc) says absorbance equals molar absorptivity × path length × concentration, so absorbance rises in direct proportion to concentration and path length.

Which analytical principle do ion-selective electrodes use to measure sodium and potassium?

Answer: Potentiometry

Ion-selective electrodes are potentiometric. They measure the voltage difference between the indicator electrode and a reference electrode at essentially zero current, and that voltage relates to ion activity.

In flow cytometry, forward scatter (FSC) mainly reflects which cell characteristic?

Answer: Cell size

Forward-scattered light correlates with cell size. Side scatter reflects internal complexity or granularity, and fluorescence detects labeled antigens or DNA.

The Coulter (electrical impedance) principle counts and sizes cells by detecting which of the following?

Answer: Changes in electrical resistance as cells pass through an aperture

Cells are poor conductors. As each cell passes through a small aperture in a conductive diluent, it briefly increases resistance and produces a voltage pulse. The number of pulses gives the count, and pulse height is proportional to cell volume.

Nephelometry measures which of the following?

Answer: Light scattered at an angle by particles in solution

Nephelometry detects light scattered by particles, such as antigen-antibody complexes, usually at an angle to the incident beam. Turbidimetry measures the drop in transmitted light.

Which of these is used to check the wavelength accuracy of a spectrophotometer?

Answer: Didymium or holmium oxide filter

Didymium and holmium oxide glass filters have sharp absorbance peaks at known wavelengths, so they are used to verify wavelength calibration. Neutral density filters check photometric (absorbance) accuracy instead.