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Keep solutions in closed flasks of appropriate size. Always label flask with:
- Content, including buffer and other components
- Concentration
- pH, if it contains buffer
- Date
- Your initials
Solution can be measured using cylinders, automatic pipettes and syringes depending on the volume.
Cylinders
Fort accurate measurements use graduated glass cylinders. Note, to maintain accuracy, graduated cylinders should not be dried in an oven as heat my change geometry and, hence, volume. Read volume by lower edge of meniscus on flat surface at eye level.
Pipettes
For sample volumes below 5-10 ml use automatic pipettes with disposable tips. This is a reliable and reproducible tool with minimal practice. To get the feel of pipette operation, try dispensing distilled water in to a small flask standing on an analytical scale. Since density of pure water is 1, dispensed volume in ml should equal its weight in grams. Practice using pipette until you can get reproducible results to within 5% error. For good pipetting results:
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Use pipette of the right capacity, their accuracy is best at full capacity. Do not use 1mL pipette to measure 20 mL and vice versa.
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Do not dial pipettes beyond their capacity – this can upset calibration or damage the pipette.
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Distinguish stops of pipette knob – fist is for measuring, second for blowing remaining solution from the tip.
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Draw and dispense solutions slowly. Too fast drawing will contaminate or damage pipette mechanism, too fast dispensing may spray solution or leave excess in the tip – either will make measurement inaccurate.
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Dispense solutions completely – use the second stop of the knob to blow out the last drop of solution that typically remains in the tip and confirm visually that entire volume has been dispensed. When dispensed property, tip should be dry and empty.
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Replace tips between different reagents. Clean as it may be, you are likely to contaminate stock solutions if you use the same tip. You may, however, reuse the tip for the same solution.
Syringes
Research syringes, a.k.a Hamilton syringes or Hamiltons, are used for precise measurements and handling of liquid samples, especially at 2-200ml level. A big advantage of Hamilton syringes is that they allow to work with sample that are sealed under septae without opening the flask. When property handled, these syringes may be used in the lab for many years.
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To protect yourself and the syringe, keep on the rack all syringes that are not in immediate use.
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Keep syringes clean – wash between and immediately after use; in most cases 15-20 cycles in distilled water are enough.
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Needles are sharp – some Hamilton needles are dull on purpose, others are as sharp as disposable.
Keep needles sharp – sharp needles make clean cuts in septae that will be vacuum-tight after needle is withdrawn. Bent and dull needles will tear larger holes septa the will not seal well. Always pay attention and avoid making any contact of needle tip with solid surface – inside vial, on the bench, or on the rack. If needle is bent and you need to use it with the septum, replace the needle.
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Keep needles straight – it is much easier to work with, especially when one needs to penetrate rubber septum. Paying close attention and applying a small amount of vacuum silicone grease helps.
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Keep plungers straight – plungers of small volume syringes are thin and can be bent, which makes them practically unusable. If you notice increased resistance to plunger motion, pull it out and clean. Before re-inserting wet plunger and barrel in water to protect Teflon tip from damage.
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