chapter  1
14 Pages

Basic Laboratory Skills I

Balances.• Top-loading electronic balances are commonly used nowadays. An electronic balance can be categorized as either regular or analytical depending on its weighing resolution, or “readability.” A regular balance typically has a range of hundreds to thousands of grams and readability from milligrams to grams, while an analytical balance’s range is typically of tens to hundreds of grams and its readability is ≤0.1 mg. When weighing samples, choose the right balance based on the weight of the sample and the accuracy requirement. A special type of mechanical balance, the trip balance, is also used in lab. (See Section IV for more details.) Centrifuges.• There are a variety of centrifuges for different centrifugation needs, and one of the determining factors for centrifuge selection is the centrifugal force that is required for sedimentation of components in the sample. Typically, minicentrifuges and microcentrifuges are used for quick processing of small volumes of samples ( typically <2 ml each), whereas larger centrifuges, with either bench-top or floor models, accommodate larger volumes and offer more centrifugal power. Glassware.• Glass beakers, Erlenmeyer flasks, test tubes, and bottles of different volumes are examples of typical glassware used in lab. To clean glassware, first wash with detergent until clean-water will flow as a sheet rather than streaks on clean glass surface-then rinse with water, and finally rinse with de-ionized water. Gloves.• Disposable latex and nitrile gloves are the most commonly used in labs. Latex gloves are relatively inexpensive but have poor chemical resistance. Nitrile gloves have much better chemical resistance and should be worn when handling organic solvents or caustic reagents. Liquid transfer.• Liquid transfer is handled in many different ways depending on the liquid volume and the accuracy requirement. Micropipettes, electronic

pipette-aids, transfer pipettes, and graduated cylinders are some of the most commonly used liquid transfer tools. (See Section III for more details.)

pH meter.• This is used for measuring the pH of solutions. Operate your pH meter according to the user’s manual. It should be calibrated using pH standard buffers from time to time. Important: Do not allow the electrode to dry.