Technical Skills & Application Flashcards
7 cards from real STP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Technical Skills & Application flashcards as text
Which term describes the ability of an analytical method to measure only the intended analyte without interference from other substances?
Answer: Analytical specificity (selectivity)
Analytical specificity (or selectivity) is the ability of an assay to measure the target analyte alone, even in the presence of other potentially interfering compounds.
A laboratory scientist uses a haemocytometer to count cells. Under ×10 objective with a 10× eyepiece, the scientist counts 60 cells in a 1 mm² area at a depth of 0.1 mm. What is the cell concentration per mL?
Answer: 6 × 10⁵ cells/mL
Volume counted = 1 mm² × 0.1 mm = 0.1 mm³ = 1×10⁻⁴ mL; concentration = 60 / 1×10⁻⁴ = 6×10⁵ cells/mL.
In gel electrophoresis, what is the purpose of loading a DNA ladder alongside experimental samples?
Answer: To serve as a molecular weight reference for estimating fragment sizes
The ladder contains DNA fragments of known sizes that migrate predictably, allowing the sizes of experimental bands to be estimated by comparison.
Which biosafety level (BSL) is required for work with Mycobacterium tuberculosis?
Answer: BSL-3
M. tuberculosis is a BSL-3 pathogen because it can cause serious or potentially lethal disease and is transmissible via aerosol, requiring respiratory protection and negative-pressure rooms.
When using reverse transcription PCR (RT-PCR) to detect an RNA virus, what is the first enzymatic step?
Answer: Reverse transcriptase converts viral RNA into complementary DNA (cDNA)
Reverse transcriptase uses the viral RNA as a template to synthesise cDNA, which then serves as the template for conventional PCR amplification.
A method validation study shows a coefficient of variation (CV) of 2.1% for intra-assay precision and 8.4% for inter-assay precision. What is the most likely explanation for the difference?
Answer: Between-run variation from factors such as different reagent lots, operators, and calibrations contributes to higher inter-assay CV
Inter-assay (between-run) precision captures additional sources of variation — including operator, reagent lot, calibration, and environmental differences — that do not affect a single run.
Which component of a HPLC system is responsible for maintaining a constant flow rate of mobile phase through the column?
Answer: The pump
The high-pressure pump delivers mobile phase at a precise, constant flow rate, which is essential for reproducible retention times and quantitative results.