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Weighing Materials

Weighing Materials. Proper use of balances. Terminology for weighing. Range : the span from lightest to heaviest weight that a balance is able to measure Capacity : the heaviest sample that a balance can weigh Sensitivity :

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Weighing Materials

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  1. Weighing Materials Proper use of balances Notes from Basic Lab Methods for Biotech by Seidman

  2. Terminology for weighing • Range: • the span from lightest to heaviest weight that a balance is able to measure • Capacity: • the heaviest sample that a balance can weigh • Sensitivity: • the smallest value of weight that will cause a change in the response of the balance. Notes from Basic Lab Methods for Biotech by Seidman

  3. Proper weighing procedure • Make sure the balance is level • Adjust the balance to zero • Tare the weighing container or weigh the empty container • Place the sample in a the weighing container and read the weight • Remove the sample • Clean the balance and surrounding area Notes from Basic Lab Methods for Biotech by Seidman

  4. Proper weighing techniques • Always use a calibrated weight to verify the scale is in proper working order (daily) • Always use a weigh boat or weigh paper; do not place materials directly on the pan • Do not touch the chemicals or material being weighed • Do not return unused chemicals to their storage bottle (unless you use a sterile spatula or spoon) Notes from Basic Lab Methods for Biotech by Seidman

  5. Factors affecting weight measurement • Not level • Drafts • Static • Not placing the load in the center of the pan • Placing an amount on the balance which is higher than its capacity • Temperature: explain this to me! Notes from Basic Lab Methods for Biotech by Seidman

  6. Calibration of Balances • First step is to zero the balance. It should read zero every time you press the zero button • Second calibration point is taken at the upper end of the capacity of the balance • Place a certified weight on the balance and verify it reads the correct weight • Some scales will prompt you to enter the weight • A third reading can be made using a lighter calibrated weight and verifying it reads the proper weight Notes from Basic Lab Methods for Biotech by Seidman

  7. Equipment Log Books • Notebooks or binders used to maintain operating procedures, calibration records, verification checks • Example: the equipment log book in the back of the room • Incubator temp charts • Refrigerator temp charts • Pipet calibration records • Balance calibration and verification charts Notes from Basic Lab Methods for Biotech by Seidman

  8. Critical Thinking Question • Suppose you need to prepare a solution that is 15 mg / mL. The material you are weighing is extremely difficult to get exactly 15 mgs. Suggest a strategy to get the correct concentration even if you cannot weigh 15 mgs. • Weigh out close to 15 mgs and then determine the proper amount of solution to add so that your solution is still at 15 mgs/mL Notes from Basic Lab Methods for Biotech by Seidman

  9. Critical Thinking Questions • How much volume of soln. at a conc. of 35ug/mL can be made in each of the following: • Sample weighs 0.003560 g • 101.7 mL • Sample weighs 0.050 mg • 1.43 mL • Sample weighs 1.0897 g • 31.134 L Notes from Basic Lab Methods for Biotech by Seidman

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