Laboratory Instrumentation, Glassware and Reagents
What this domain tests
This domain covers spectrophotometry, centrifugation, pipetting, glassware and reagent handling - the practical basis of accurate measurement.
Core rules
- A spectrophotometer follows Beer-Lambert law: absorbance is proportional to concentration and path length. Zero the instrument with a reagent blank before reading standards and samples.
- Use clean, scratch-free cuvettes; wipe the outside; avoid bubbles and fingerprints. Match cuvettes and use the correct wavelength.
- Balance the centrifuge by placing tubes of equal weight opposite each other. Do not open the lid until the rotor stops.
- Calibrate micropipettes and balances regularly; use the correct tip and never pipette by mouth.
- Class A volumetric glassware is calibrated for accuracy. Clean glassware with detergent, rinse with distilled water and dry; do not use soda-lime glass for strong alkali.
- Store reagents at the recommended temperature, label opening dates, and never use expired or contaminated reagents.
Worked example
A glucose sample has absorbance 0.30; a 100 mg/dL standard has absorbance 0.60. Reasoning: concentration is proportional to absorbance, so sample concentration = (0.30/0.60) × 100 = 50 mg/dL. The blank must be subtracted from both readings first.
Traps
- Reading without a blank or with a dirty cuvette.
- Using an unmatched cuvette or the wrong wavelength.
- Centrifuging unbalanced tubes.
- Assuming a pipette is accurate without calibration.