Notes from Basic Lab Methods for Biotech by Seidman Weighing Materials Proper 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 g  mL Sample weighs mg  1.43 mL Sample weighs g  L