Notes from Basic Lab Methods for Biotech by Seidman

Weighing MaterialsProper use of balances

Notes from Basic Lab Methods for Biotech by Seidman

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

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

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

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

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

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

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

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