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 X-ray fluorescence (XRF) spectrometry, what is the matrix effect known as 'absorption enhancement'?
Answer: A matrix element's fluorescence radiation excites additional analyte X-rays, increasing the signal
Enhancement occurs when secondary fluorescence from a matrix element has sufficient energy to excite the analyte, producing more analyte X-rays than would be generated by the primary beam alone.
Which electrochemical technique applies a linearly varying potential and measures the resulting current to identify and quantify redox-active species?
Answer: Linear sweep voltammetry
Linear sweep voltammetry scans the electrode potential at a constant rate and records current versus potential, producing peaks at characteristic potentials for each redox species.
What does the 'signal-to-noise ratio' (S/N) of 3:1 conventionally represent in analytical instrument performance?
Answer: The limit of detection (LOD)
By ICH and EPA convention, an S/N of 3:1 defines the limit of detection, the lowest concentration at which the analyte can be reliably distinguished from background noise.
In NMR spectroscopy, what is the effect of increasing the external magnetic field strength (B₀) on chemical shift dispersion?
Answer: Chemical shifts in ppm remain constant, but absolute frequency differences increase
Chemical shifts expressed in ppm are field-independent, but the absolute frequency separation (in Hz) between peaks increases linearly with B₀, improving resolution of closely spaced signals.
A laboratory uses a thermocouple thermometer whose calibration certificate shows a correction of +0.8°C at 100°C. Which action is correct?
Answer: Add 0.8°C to every reading taken near 100°C
A calibration correction is added algebraically to the instrument reading; a correction of +0.8°C means the true value is 0.8°C higher than what the thermometer displays.
In dynamic light scattering (DLS), what physical property of nanoparticles is directly measured?
Answer: Hydrodynamic diameter via translational diffusion coefficient
DLS measures fluctuations in scattered light intensity caused by Brownian motion; the autocorrelation function yields the translational diffusion coefficient, from which hydrodynamic diameter is calculated via the Stokes–Einstein equation.
Which systematic error in analytical balances causes readings to change with temperature even when no load change occurs?
Answer: Thermal drift of the load cell or electromagnetic force compensation system
Thermal drift occurs because the electronic components and mechanical structure of the balance respond to temperature changes, altering the apparent zero and span; periodic re-zeroing and internal calibration mitigate this.