PASCO CI-6735 User Manual
Instruction Manual and
Experiment Guide for the
PASCO scientific
Model CI-6735
NITRATE ION SELECTIVE
ELECTRODE
012-06616A
9/97
© 1997 PASCO scientific $7.50
®
10101 Foothills Blvd. • P.O. Box 619011 • Roseville, CA 95678-9011 USA
Phone (916) 786-3800 • FAX (916) 786-8905 • web: www.pasco.com
better
ways to
teach science
Nitrate Ion Selective Electrode 012–06616A
Always use eye protection
and gloves when working
with chemicals.
012–06616A Nitrate Ion Selective Electrode
Table of Contents
Introduction......................................................................................................................................... 1
Theory .................................................................................................................................................. 1
Equipment ........................................................................................................................................... 3
Included: ....................................................................................................................................... 3
Additional Required: .................................................................................................................... 3
Required Solutions.............................................................................................................................. 3
General Preparation ........................................................................................................................... 4
Electrode Preparation.................................................................................................................... 4
Electrode Slope Check Using ScienceWorkshop .......................................................................... 4
Measurement....................................................................................................................................... 5
Measuring Hints............................................................................................................................ 5
Sample Requirements ................................................................................................................... 5
Units of Measurement................................................................................................................... 5
Measurement Procedure .................................................................................................................... 6
Direct Measurement...................................................................................................................... 6
Low Level Nitrate Determination .................................................................................................7
Electrode Characteristics ................................................................................................................... 9
Reproducibility ............................................................................................................................. 9
Interferences.................................................................................................................................. 9
Temperature Influences............................................................................................................... 10
Electrode Response ..................................................................................................................... 10
Limits of Detection ..................................................................................................................... 11
pH Effects ................................................................................................................................... 11
Electrode Life ............................................................................................................................. 11
Maintenance ...................................................................................................................................... 12
Electrode Storage ........................................................................................................................ 12
Specifications..................................................................................................................................... 12
Troubleshooting Guide ..................................................................................................................... 12
Glassware/Plastic-ware ............................................................................................................... 12
Electrode ..................................................................................................................................... 12
Standards & Reagents ................................................................................................................. 13
Sample ........................................................................................................................................ 13
Technique .................................................................................................................................... 13
Troubleshooting Hints ...................................................................................................................... 14
Technical Support ............................................................................................................................. 17
i
Copyright, Warranty , and Equipment Return
PleaseFeel free to duplicate this manual
subject to the copyright restrictions below.
Copyright Notice
The PASCO scientific 012-06616A manual is
copyrighted and all rights reserved. However,
permission is granted to non-profit educational
institutions for reproduction of any part of the Nitrate
Ion Selective Electrode manual providing the
reproductions are used only for their laboratories and
are not sold for profit. Reproduction under any other
circumstances, without the written consent of PASCO
scientific, is prohibited.
Limited Warranty
PASCO scientific warrants the product to be free from
defects in materials and workmanship for a period of
one year from the date of shipment to the customer.
PASCO will repair or replace at its option any part of
the product which is deemed to be defective in
material or workmanship. The warranty does not
cover damage to the product caused by abuse or
improper use. Determination of whether a product
failure is the result of a manufacturing defect or
improper use by the customer shall be made solely by
PASCO scientific. Responsibility for the return of
equipment for warranty repair belongs to the
customer. Equipment must be properly packed to
prevent damage and shipped postage or freight
prepaid. (Damage caused by improper packing of the
equipment for return shipment will not be covered by
the warranty.) Shipping costs for returning the
equipment after repair will be paid by PASCO
scientific.
Credits
Author: Peter Boyle
Editor: Steve Miller
Equipment Return
Should the product have to be returned to PASCO
scientific for any reason, notify PASCO scientific by
letter, phone, or fax BEFORE returning the product.
Upon notification, the return authorization and
shipping instructions will be promptly issued.
ä
NOTE: NO EQUIPMENT WILL BE
ACCEPTED FOR RETURN WITHOUT AN
AUTHORIZATION FROM PASCO.
When returning equipment for repair, the units must
be packed properly. Carriers will not accept
responsibility for damage caused by improper
packing. To be certain the unit will not be damaged in
shipment, observe the following rules:
➀ The packing carton must be strong enough for the
item shipped.
➁ Make certain there are at least two inches of packing
material between any point on the apparatus and the
inside walls of the carton.
➂ Make certain that the packing material cannot shift in
the box or become compressed, allowing the
instrument come in contact with the packing carton.
Address: PASCO scientific
10101 Foothills Blvd.
P.O. Box 619011
Roseville, CA 95678-9011
Phone: (916) 786-3800
FAX: (916) 786-3292
email: techsupp@pasco.com
web: www.pasco.com
ii
012–06616A Nitrate Ion Selective Electrode
E=E
X
E
X
C
f
C
t
C
X
γ
C
f
Introduction
The PASCO scientific Nitrate Ion Selective Electrode is used to quickly, simply, accurately, and economically
measure nitrate in aqueous solutions.
Theory
The Nitrate Ion Selective Electrode consists of an electrode body containing a liquid internal filling solution in
contact with a gelled organophilic membrane containing a nitrate ion exchanger. When the membrane is in contact
with a solution containing free nitrate ions, an electrode potential develops across the membrane. This electrode
potential is measured against a constant reference potential, using an ISE Amplifier and ScienceWorkshop Interface.
The level of nitrate ions, corresponding to the measured potential, is described by the Nernst equation:
–Slog
0
where:
= measuredelectrode potential
= referencepotential(a constant)
E
0
mV
S = electrodeslope( ≈ 55
decade
)
= level ofnitrateions in solution
The activity, X, represents the effective concentration of the ions in solution. The total nitrate ion concentration,
C
is the sum of free nitrate ion, Cƒ, and complexed or bound perchlorate ion, Cb. The electrode is able to respond
t
to only the free ions, whose concentration is
=
=
b
Since nitrate ions form very few stable complexes, the free ion concentration may be equated to the total ion
concentration.
The activity is related to the free ion concentration, C
, by the activity coefficient, γ, by:
ƒ
=
Activity coefficients vary, depending on total ions strength, I, defined as:
I =
1
2
ΣCXZ
2
X
1
Nitrate Ion Selective Electrode 012–06616A
C
X
where:
= concentrationofion
X
ZX= chargeof ion X
Σ = sum of all of the types of ionsin the solution
In the case of high and constant ionic strength relative to the sensed ion concentration, the activity coefficient, γ ,
is constant and the activity, X, is directly proportional to the concentration.
To adjust the background ionic strength to a high end constant value, ionic strength adjuster (ISA) is added to
samples and standards. The recommended ISA for nitrate is (NH
ionic strength adjusters as long as ions that they contain do not interfere with the electrode’s response to nitrate ions.
Strongly acidic (pH = 0 - 2) and strongly basic (pH = 12 - 14) solutions are particularly troublesome to measure.
The high mobility of hydrogen and hydroxide ions in samples make it impossible to mask their effect on the junction
potential with any concentration of equitransferent salt. One must either calibrate the electrode in the same pH range
as the sample or use a known incremental method for ion measurement.
. Solutions other than this may be used as
4) 2S04
2
012–06616A Nitrate Ion Selective Electrode
Equipment
• Nitrate Ion Selective Electrode
• Nitrate Ion Selective Electrode fill solution
• Pipette for fill solution
to ISE
Amplifier
filling pipette
Figure 1.
Included Equipment
Sodium Ion Selective
Electrode
R
O
E
O
L
1
P
0
1
M
3
A
S
R
n
e
f
e
tio
r
e
u
n
l
c
o
e
S
Fi
l
l
4
I
M
C
K
filling
solution
Additional Required:
Required Equipment
PASCO CI-6738 ISE (Ion Selective Electrode)
Amplifier
• ScienceWorkshop 2.2.5 or higher
• PASCO ScienceWorkshop Computer
Interface
• Semi-logarithmic 4-cycle graph paper
for preparing calibration curves.
• Magnetic stir plate
• Lab-ware made of plastic, not glass, for
all low level measurements
Required Solutions
The stock solutions listed in this section may be
created as described in the text or ordered directly
from PASCO. The solutions available for order,
and their respective prices are listed on the ‘ISE
Working Solution Price List’.
• Deionized or distilled water for solution and standard preparation
• Ionic Strength Adjuster (ISA) , 2 M (NH
4) 2SO4
To prepare this solution, half fill a 1,000 ml volumetric flask with distilled water and add 264 grams of
reagent-grade ammonium sulfate, (NH
. Swirl the flask gently to dissolve the solid. Fill the flask to
4) 2S04
the mark with distilled water, cap, and upend several times to mix the contents. ISA is added at the rate of
2 ml of ISA to each 100 ml of standard or sample to adjust the ionic strength to about 0.12 M.
• Reference Filling Solution, 0.l M (NH
• Nitrate Standard, 0.1 M NaNO
3
4) 2SO4
/0.0l M KCl
To prepare this solution, add 8.50 grams of reagent-grade sodium nitrate to a one liter volumetric flask about
half full of distilled water. Swirl the flask gently to dissolve the solid. Fill to the mark with distilled water,
cap, and upend several times to mix the solution.
• Nitrate Standard, 1,000 ppm NO
-1
3
To prepare this solution, add 1.37 grams of reagent-grade sodium nitrate to a one liter volumetric flask about
half full with distilled water. Swirl the flask gently to dissolve the solid. Fill to the mark with distilled water,
cap, and upend several times to mix the solution.
• Nitrate Standard, 100 ppm NO
-1
3
To prepare this solution, add 0.61 grams of reagent-grade sodium nitrate to a one liter volumetric flask about
half full with distilled water. Swirl the flask gently to dissolve the solid. Fill to the mark with distilled water,
cap, and upend several times to mix the solution.
3
Loading...