WPI APOLLO 4000, Instruction Manual

Page: 32 / 74

APOLLO 4000
NITRIC OXIDE DETECTION
WORLD PRECISION INSTRUMENTS C-8
428). However, in the presence of oxygen
Cu (I) is readily oxidized to Cu (II). This will
happen naturally if the compound is
exposed to air and/or there is inadequate
storage of CuCl. The oxidation product Cu
(II) is much less efficient at catalyzing the
conversion of SNAP to NO, and this would
appear during calibration as an apparent
low sensitivity of the electrode to NO.
Since Cu (I) is readily oxidized to Cu (II)
special precautions must be taken to keep
it in its reduced state prior to any
calibration. It is recommended that CuCl be
stored under inert conditions and if used in solution then the solution must be
degassed with inert gas and absent of all oxygen.
NOTE : If your laboratory is not adequately equipped to satisfy the conditions for
storage and use of CuCl please refer to the following section in the manual which
describes a similar calibration procedure based on the use of copper (II) sulfate
(CuSO
4
) or cupric (II) chloride CuCl
2,
in which Cu [II] is the active catalyst for the
conversion of SNAP to NO.
Getting Started
Prepare the following solutions:
#1—Saturated solution of cuprous chloride: This should be prepared by
adding 150 mg CuCl to 500 mL distilled deoxygenated water. The distilled water
can be deoxygenated by purging with pure nitrogen or argon gas for 15 min. The
saturated CuCl solution will have a concentration of approximately 2.4 mM at room
temperature and should be kept in the dark prior to use.
#2—Standard SNAP solution: Dissolve 5 mg EDTA in 250 mL of HPLC pure
water (HPLC grade, Sigma). Deoxygenate the solution using the method described
above. Add 5.6 mg SNAP to the solution. The Molarity of the SNAP solution ( SNAP
f.w.= 220.3) can then be easily calculated. Since the SNAP solution is very
sensitive to light and temperature it should be stored in the dark and in a
refrigerator until required. ( Note: The decomposition of SNAP at low temperature,
Figure C4 —
Responses of an
NO electrode to the
successive
additions of
100 nM SNAP into
CuCl saturated
solution (pH=5.5).
Also shown (inset)
is the resulting
calibration plot.