AACC AACC Laboratory Instrumentation & Technology 1 — Questions and Answers
Question 1: Which detector is most commonly used in high-performance liquid chromatography (HPLC) for measuring UV-absorbing analytes in clinical chemistry?
- Flame ionization detector
- UV-Vis spectrophotometric detector (Correct answer)
- Thermal conductivity detector
- Electron capture detector
Correct answer: UV-Vis spectrophotometric detector
UV-Vis spectrophotometric detectors are the most widely used in HPLC for clinical analytes that absorb ultraviolet or visible light.
Question 2: What is the primary purpose of an internal standard in mass spectrometry-based clinical assays?
- To increase sample volume
- To correct for ion suppression and instrument variability (Correct answer)
- To serve as a positive control
- To calibrate the column temperature
Correct answer: To correct for ion suppression and instrument variability
Internal standards compensate for matrix effects such as ion suppression and variations in instrument response, improving quantitative accuracy.
Question 3: In a clinical chemistry analyzer, what does a reagent blank correct for?
- Patient sample turbidity
- Absorbance contributed by the reagent itself (Correct answer)
- Hemolysis interference
- Calibrator drift over time
Correct answer: Absorbance contributed by the reagent itself
A reagent blank measures the absorbance of reagents without sample, allowing the analyzer to subtract this background from patient readings.
Question 4: Which ionization technique is considered 'soft' and is commonly used for large biomolecules in clinical mass spectrometry?
- Electron ionization (EI)
- Chemical ionization (CI)
- Electrospray ionization (ESI) (Correct answer)
- Fast atom bombardment (FAB)
Correct answer: Electrospray ionization (ESI)
Electrospray ionization is a soft ionization method that produces intact molecular ions, making it ideal for proteins, peptides, and other large biomolecules.
Question 5: What is carryover in automated clinical analyzers?
- A QC failure mode due to reagent expiration
- Contamination of one sample by a preceding high-concentration sample (Correct answer)
- Evaporation of calibrator solutions
- Bubble formation in the reaction cuvette
Correct answer: Contamination of one sample by a preceding high-concentration sample
Carryover occurs when residual analyte from a high-concentration sample contaminates the subsequent sample, causing falsely elevated results.
Question 6: In flow cytometry used in clinical laboratories, what physical property is measured by the side scatter (SSC) signal?
- Cell size
- Cell granularity and internal complexity (Correct answer)
- Surface antigen expression
- DNA content
Correct answer: Cell granularity and internal complexity
Side scatter reflects light at approximately 90° and correlates with the internal complexity and granularity of a cell.
AACC AACC Laboratory Instrumentation & Technology 1
Which detector is most commonly used in high-performance liquid chromatography (HPLC) for measuring UV-absorbing analytes in clinical chemistry?