User manual

Merck KGaA, 64271 Darmstadt, Germany,
Tel. [phone], Fax [phone]
[e-mail] http://fea.merck.de
1. Method
Nitrate ions are reduced to nitrite ions by a reducing
agent. In the presence of an acidic buffer, these nitrite
ions react with an aromatic amine to form a diazonium
salt, which in turn reacts with N-(1-naphthyl)-ethylene-
diamine to form a red-violet azo dye. The nitrate con-
centration is measured semiquantitatively by visual
comparison of the reaction zone of the test strip with
the fields of a colour scale.
Each strip also features a second reaction zone (alert
zone), the colour of which changes in the presence of
nitrite ions.
2. Measuring range and number of
determinations
Measuring range / colour- Number of
scale graduation
1)
determinations
10 - 25 - 50 - 100 - 250 - 500 mg/l NO
3
-
25 (Cat. No. 1.10020.0002)
or
2.3 - 5.6 - 11 - 23 - 56 - 113 mg/l NO
3
-N 100 (Cat. No. 1.10020.0001)
1)
for conversion factors see section 8
3. Applications
The determination can be performed not only in liquid
samples, but also on moist surfaces of e. g. freshly cut
fruit and vegetables (see section 7).
Sample material:
Groundwater, wellwater, and drinking water
Spring water and mineral water
Industrial water, wastewater, percolating water
Aquarium water
Pressed plant and fruit juices
Food and animal fodder after appropriate sample pre-
treatment
Soils and fertilizers after appropriate sample pretreat-
ment
This test is only conditionally suited for seawater
(false-low readings).
4. Influence of foreign substances
This was checked in solutions with 50 and 0 mg/l NO
3
-
.
The concentrations of foreign substances given in the
table lie below the limit at which the determination is
interfered with.
Concentrations of foreign substances in mg/l
Ag
+
50 Fe
3+
250 NO
2
-
0.5
Al
3+
1000 [Fe(CN)
6
]
4-
100 Pb
2+
1000
Ba
2+
1000 [Fe(CN)
6
]
3-
100 PO
4
3-
1000
Ca
2+
1000 Hg
+
50 S
2-
25
Cl
-
1000 Hg
2+
100 SCN
-
100
CN
-
1000 K
+
1000 SO
3
2-
500
Co
2+
1000 Mg
2+
1000 SO
4
2-
1000
CrO
4
2-
20 Mn
2+
1000 S
2
O
3
2-
250
Cu
2+
1000 MnO
4
-
10 Zn
2+
1000
Fe
2+
500 Ni
2+
1000
5. Reagents and auxiliaries
The test strips are stable up to the date stated on
the pack when stored closed at +2 to +8 °C.
Package contents:
Tube containing 25 test strips (Cat. No. 1.10020.0002)
or
containing 100 test strips (Cat. No. 1.10020.0001)
Other reagents:
Universal indicator strips pH 0 - 14, Cat. No. 109535
Sodium acetate anhydrous GR for analysis,
Cat. No. 106268
L(+)-Tartaric acid GR for analysis, Cat. No. 100804
Amidosulfuric acid GR for analysis, Cat. No. 100103
Nitrate standard solution CertiPUR
®
,1000 mg/l NO
3
-
,
Cat. No. 119811
6. Preparation
•
Extract solid sample materials by an appropriate
method.
•
Samples containing more than 500 mg/l NO
3
-
must
be diluted with distilled water.
•
The pH must be within the range 1 - 12.
If the pH is lower than 1, buffer the sample with so-
dium acetate; if it is greater than 12, adjust to approx.
3 - 5 with tartaric acid.
7. Procedure
Immerse both reaction zones of the test strip in the pre-
treated sample (15 - 25 °C) for 1 sec.
Shake off excess liquid from the strip and after 1 min
determine with which colour field on the label the colour
of the NO
3
-
reaction zone coincides most exactly.
If the NO
2
-
alert zone changes colour see “Notes on
the measurement”.
Read off the corresponding result in mg/l NO
3
-
or, if nec-
essary, estimate an intermediate value.
Determination on vegetable surfaces:
Cut plant material (e. g. fruit, vegetables, potatoes)
with a knife, lightly press the reaction zone of the test
strip on the moist surface for 1 - 10 sec, and after
1 min compare with the colour scale.
Notes on the measurement:
•
The colour of the reaction zone may continue to
change after the specified reaction time has
elapsed. This must not be considered in the
measurement.
•
If necessary (discolouration of the alert zone), elimi-
nate interfering nitrite ions:
To 5 ml of sample (pH < 10) add 5 drops of a 10 %
aqueous amidosulfuric acid solution and shake
several times.
Subsequently repeat the nitrate measurement.
•
If the colour of the reaction zone is equal to or more
intense than the darkest colour on the scale, repeat
the measurement using fresh, diluted samples until
a value of less than 500 mg/l NO
3
-
is obtained.
Concerning the result of the analysis, the dilution
(see also section 6) must be taken into account:
Result of analysis = measurement value x dilution factor
•
It is recommended to treat the measurement re-
sults obtained on moist surfaces only as guide-
line values.
8. Conversions
Units required = units given x
conversion
factor
mg/l NO
3
-N mg/l NO
3
-
0.226
mg/l NO
3
-
mg/l NO
3
-N 4.43
9. Method control
To check test strips and handling:
Dilute the nitrate standard solution with distilled water
to 250 mg/l NO
3
-
and analyze as described in section 7.
10. Note
Reclose the tube containing the test strips imme-
diately after use.
November 2009
1.10020.0001
1.10020.0002
NO
3
-
Nitrate Test