Basic Laboratory Equipment Use Flashcards

A technician needs to accurately transfer 185 µL of a buffer solution. The lab has P20, P200, and P1000 micropipettes available. Which micropipette should be used for the highest accuracy and precision?

Answer: P200

The P200 micropipette, with a typical range of 20-200 µL, is the most appropriate choice. Micropipettes are most accurate and precise when used in the middle to upper portion of their specified volume range. Using a P1000 for 185 µL would be at the low end of its range (100-1000 µL or 200-1000 µL), leading to greater potential inaccuracy. A P20 (2-20 µL) cannot handle this volume.

Before starting a microcentrifuge, a technician places two 1.5 mL tubes containing samples of unequal mass opposite each other in the rotor. What is the most likely consequence of this action?

Answer: The centrifuge will generate excessive noise and vibration, potentially damaging the unit.

Centrifuges must be properly balanced by mass to operate safely and effectively. Placing tubes with unequal masses opposite each other creates an imbalance. At high rotational speeds, this imbalance causes significant vibration, which can damage the motor and rotor, posing a serious safety risk.

A biotechnician is preparing to measure the pH of a critical buffer solution. Which of the following is the most important first step to ensure an accurate reading?

Answer: Calibrating the meter using at least two standard buffers of known pH.

Before use, a pH meter must be calibrated against standard solutions of known pH (e.g., pH 4.0, 7.0, 10.0). This process adjusts the meter's response to match the known pH values of the standards, ensuring that subsequent measurements of unknown samples are accurate. While other steps are part of good practice, calibration is the prerequisite for accuracy.

What are the three critical parameters that an autoclave utilizes to achieve sterilization of laboratory equipment and media?

Answer: High temperature, high pressure, and steam.

An autoclave, or steam sterilizer, sterilizes items by subjecting them to high-pressure saturated steam at a high temperature (typically 121°C or higher) for a specific amount of time. The combination of steam, pressure, and heat effectively kills all microorganisms, including resilient bacterial spores.

When using a spectrophotometer to measure the absorbance of a colored solution, what is the primary purpose of first inserting a 'blank' cuvette containing only the solvent?

Answer: To calibrate the instrument by setting the absorbance of the solvent to zero.

The purpose of a blank is to zero the spectrophotometer. The blank contains all components of the sample except for the analyte being measured. By setting the absorbance of the blank to zero, the instrument subtracts any absorbance caused by the solvent or the cuvette itself, ensuring that the final reading reflects only the absorbance of the analyte.

A protocol requires a 15-minute incubation of an enzymatic reaction at exactly 37°C. Which of the following is the most critical step when using a standard laboratory water bath for this procedure?

Answer: Ensuring the water level is high enough to cover the portion of the tube containing the reaction mixture.

For effective and uniform heat transfer, the reaction mixture inside the tube must be fully submerged below the water level in the bath. If the sample liquid is above the water level, it will not be heated to the target temperature, leading to inaccurate results. While using a lid and preheating the bath are good practices, ensuring the sample is submerged is most critical for the incubation itself.