Laboratory Techniques and Procedures
Laboratory Techniques and Procedures tests practical bench competence: glassware and calibration, accurate liquid handling, sterilization and disinfection, separation techniques, instrumentation, biosafety and biomedical waste management. Answers should follow standard operating procedure, never improvisation.
Core rules
- Volumetric glassware (flask, pipette, burette) is calibrated to contain or to deliver at a stated temperature; beakers and measuring cylinders are approximate and must not be used for accurate volumes.
- Sterilization: autoclave at 121 °C and 15 psi for 15–20 minutes for media and glassware; dry heat at 160 °C for 2 hours; membrane filtration for heat-labile liquids; ethylene oxide for plastics.
- Centrifugation: balance tubes by weight opposite each other. RCF = 1.118 × 10⁻⁵ × r × RPM², so RPM alone never defines a protocol.
- Spectrophotometry: Beer–Lambert law A = εcl; zero the instrument with a blank and use a cuvette suited to the wavelength.
- Chromatography separates by differential partition or adsorption; electrophoresis separates by charge and size.
- Biomedical waste: yellow for anatomical and soiled waste, red for contaminated recyclable plastic, white for sharps, blue for glass and metallic implants.
Worked example
A serum sample is diluted 1 in 10 with saline, then that dilution is made 1 in 5. The total dilution factor is 10 × 5 = 50, so a measured concentration is multiplied by 50 to recover the original value. Serial dilutions multiply; they never add.
Traps
- Confusing RPM with RCF when reproducing a published protocol.
- Reading the top of the meniscus instead of the bottom for clear aqueous solutions.
- Skipping the blank or running an expired standard.
- Treating autoclave tape as proof of sterility; only a biological indicator confirms it.