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
A laboratory balance is found to have a repeatability of ±0.2 mg but a linearity error of ±1.0 mg across its range. For accurate weighing, which error component is more critical to correct?
Answer: Linearity error, because it introduces systematic bias across the weighing range
Linearity error is a systematic error that varies with load and cannot be reduced by averaging; it must be corrected through span and linearity calibration.
In flame atomic absorption spectroscopy, the acetylene-nitrous oxide flame is preferred over air-acetylene for which element?
Answer: Aluminum (Al)
Aluminum forms refractory oxides that require the higher temperature (~2800°C) of the N₂O-acetylene flame to achieve complete atomization.
What is the primary advantage of using an internal standard in GC-MS quantitation?
Answer: It compensates for variability in injection volume and instrument response
An internal standard, typically a stable isotope-labeled analog, is added at a fixed concentration to all standards and samples so that variations in injection volume and instrument sensitivity cancel out in the ratio.
Which technique measures the oscillation frequency of a piezoelectric crystal coated with a thin film to determine mass deposited on its surface?
Answer: Quartz crystal microbalance (QCM)
In a QCM, mass deposited on the quartz crystal surface decreases the resonant frequency according to the Sauerbrey equation, enabling nanogram-level mass detection.
What is the metrological purpose of performing a two-point span calibration on a gas analyzer?
Answer: To establish the zero offset and correct the sensitivity (slope) of the response
Two-point span calibration uses a zero gas and a certified span gas to correct both the zero offset and the sensitivity (gain) of the analyzer, ensuring accurate readings across the range.
In ion chromatography, which suppressor device reduces the background conductivity of the eluent while enhancing analyte ion conductivity?
Answer: Membrane suppressor
A membrane suppressor converts the eluent counterion (e.g., Na⁺ from NaOH) to water via ion exchange while converting analyte anions to their highly conductive acid forms.
When performing calibration of a pipette by gravimetric method, which correction factor accounts for the difference between water density at ambient temperature and 1.0000 g/mL?
Answer: The Z-factor (temperature correction)
The Z-factor (or Z-value) converts the mass of dispensed water to volume at the test temperature, correcting for the temperature-dependent density of water and air buoyancy.