GE Analytical Instruments ©2006 12-7 DLM 14291 Rev. A
Preparation of Dilute Standards
The best way to prepare dilute standards is by serial dilution. The containers for
the dilute standards must be free of nitrite contamination (rinse with nitrite-free
water before use). Microfuge tubes (1.5 mL) or similar disposable containers are
suitable containers. To prepare the 1 mL of the dilute standards:
• Arrange 7 or 8 tubes in a rack and add 900 µL of nitrite-free water to each
tube.
• Set one tube aside and label the tube Water Blank.
• Add 100 µL of the stock solution to the first tube, mix thoroughly and label the
tube 10 mM (Note: the actual concentration will depend on the concentration
of the stock solution and the tube should be labeled accordingly).
• Using a new pipette tip, transfer 100 µL of the 10 mM standard to the next
tube, mix thoroughly and label the tube 1 mM.
• Using a new pipette tip, transfer 100 µL of the 1 mM standard to the next tube,
mix thoroughly and label the tube 100 µM.
• Using a new pipette tip, transfer 100 µL of the 100 µM standard to the next
tube, mix thoroughly and label the tube 10 µM.
• Repeat these steps to prepare 1 µM and 100 nM standards or lower
concentration standards if necessary.
• Intermediate dilutions can be prepared from the dilute standards. For example,
50 µM, 5 µM and 0.5 µM standards can be prepared by 1:1 dilutions of the 100,
10 and 1 µM standards (100 µL of the standard plus 100 µL of nitrite-free water.
• Set aside or discard the two most concentrated standards (10 mM and 1 mM) as
these will not be used.
WARNING:
ALWAYS USE NEW PIPETTE TIPS FOR EACH DILUTION. SOME NITRITE REMAINS IN
THE TIP AND WILL CONTAMINATE SUBSEQUENT DILUTIONS.
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