C_+Experiment+00+_v+F10 - 0INTRODUCTION TO THE LABORATORY...

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0- INTRODUCTION TO THE LABORATORY Each student is to perform the exercises individually in any order. 1. Reproducible pipeting Pipetman™ single sample pipettes 2. Spectrophotometry: Theory and Operation Schimadzu Spectrophotometer (Photometric and Spectrum functions) Nanodrop Spectrophotometer (Basic Operations) Plate reader Spectrophotometry 3. Calibrating the pH meter. EXERCISE 1: Reproducible Pipeting - gravimetric analysis A. Pipetman TM Micropipettes: Specifications Accuracy: Accuracy means the closeness with which the dispensed volume approximates the volume set on the pipette. Accuracy is specified as "mean error", the maximum amount by which the mean value of a large number of replicate measurements of the same volume will deviate from the set volume. Precision: Precision means the "scatter" of individual measurements around the mean of a large number of replicate measurements of the same volume; how close the values are to one another. Specifications for precision are generally tighter than for accuracy. In most experiments, where sample measurements are compared to standards, the precision specification will determine the accuracy of results as long as both samples and standards are measured with the same Pipetman . B. Operation: Practice pipeting with a Pipetman TM 1. Adjust the P-1000 pipeting device to 0.9 ml (= 900μl). Always dial down to the desired volume. 2. Attach a disposable tip to the end of the pipette shaft and press on firmly to ensure an airtight seal. 3. Depress the plunger to the FIRST POSITIVE STOP and hold in place. 4. Holding the pipette vertical, immerse the end of the disposable tip into a beaker of water. With the tip immersed in water, gently release the plunger and allow the pipette tip to fill with liquid. Never let it snap up by just letting go of the plunger/pushbutton. Wait a few seconds to make sure that the PIPETMAN™ SPECIFICATIONS Volume Increment Accuracy Precision Model μl μl (mean error) (repeatability) Relative % Absolute μ1 Relative % Absolute μl 2 5 0.1 2 0.04 P-20 10 0.02 1 0.1 0.5 0.05 20 1 0.2 0.3 0.06 50 1 0.5 0.4 0.2 P-200 100 0.2 0.8 0.8 0.25 0.25 200 0.8 1.6 0.15 0.3 100 3 3 0.6 0.6 P-1000 500 2 0.8 4 0.2 1 1000 0.8 8 0.13 1.3 1
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0- full volume of liquid is drawn up into the pipette. Note: be sure air bubbles are not drawn up into the pipette. 5. To dispense the sample, place the tip against the wall of a 1.5 ml plastic microcentrifuge tube in a tube rack, then depress the plunger slowly to the FIRST POSITIVE STOP and continue depressing the plunger through to the SECOND FULL STOP position to fully eject the liquid in the pipette tip. Note: placing the pipette tip in contact with the plastic surface of the microcentrifuge tube is critical to reproducible pipeting. The contact tends to leave about the same amount of liquid on the pipette tip at each stage so that the volume transferred is reproducible. 6. With the plunger still fully depressed, withdraw the pipette from the microcentrifuge tube.
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This note was uploaded on 11/21/2010 for the course MCB 120L 69059 taught by Professor Fairclough during the Fall '10 term at UC Davis.

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C_+Experiment+00+_v+F10 - 0INTRODUCTION TO THE LABORATORY...

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