Chemical Instrumentation & Calibration Flashcards
7 cards from real CPC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Chemical Instrumentation & Calibration flashcards as text
In HPLC, what is the van Deemter equation used to describe?
Answer: The dependence of column plate height on mobile phase linear velocity
The van Deemter equation (H = A + B/u + Cu) describes how band broadening (plate height H) varies with mobile phase velocity, identifying optimal flow rate.
Which phenomenon causes baseline drift in a differential refractometer (RI) detector during gradient HPLC elution?
Answer: Changes in mobile phase composition alter the bulk refractive index
RI detectors respond to the overall refractive index of the column effluent; solvent composition changes during gradient elution cause continuous baseline drift.
In FTIR spectroscopy, what is the function of the Michelson interferometer?
Answer: To generate an interferogram by combining beams with varying path difference
The Michelson interferometer splits the IR beam, introduces a variable path difference with a moving mirror, and recombines the beams to create an interferogram that is Fourier-transformed into a spectrum.
What does the term 'linearity of calibration' mean in method validation?
Answer: The ability of the method to produce responses proportional to analyte concentration over a defined range
Linearity demonstrates that instrument response is directly proportional to analyte concentration across the working range, typically verified by the coefficient of determination (R²).
Which mass spectrometry ionization technique is most suitable for intact large biomolecules like proteins?
Answer: Electrospray ionization (ESI)
ESI is a soft ionization technique that produces multiply charged intact molecular ions from large polar biomolecules without fragmentation.
When calibrating a volumetric flask using gravimetric water delivery, the measured mass is corrected for buoyancy. What standard density value is typically used for air buoyancy correction?
Answer: 0.0012 g/mL
Air density is approximately 0.0012 g/mL (1.2 mg/mL) at standard conditions; this value is used to calculate the buoyancy correction for weighing water in air.
In a quadrupole mass filter, ions are selected by:
Answer: Their stable oscillating trajectories under specific DC and RF voltage ratios
A quadrupole mass filter passes only ions with a specific m/z that have stable trajectories under the combined DC and RF fields applied to four rod electrodes.