Section A Instructions for laboratory measurements
Notes on NO
3
and NO
2
measurements with LCK / TNT cuvette tests
Select the measurement range of the LCK / TNT test to keep the measured concentration between
the middle and the maximum limit of the range, because the lower range frequently has more scatter.
Use the mean value from three cuvettes for each measurement.
NO
3
and NO
2
LCK / TNT measurement ranges
Nitrate:
• LCK339 / TNT835: 1.0 – 60.0 mg/L NO
3
| 0.23 – 13.5 mg/L NO
3
–N
• LCK340 / TNT836: 22 – 155 mg/L NO
3
| 5 – 35 mg/L NO
3
–N
• LCK540 / TNT838: 66 – 664 mg/L NO
3
| 15 – 150 mg/L NO
3
–N
Nitrite:
• LCK341 / TNT839: 0.05 – 2 mg/L NO
2
| 0.015 – 0.6 mg/L NO
2
–N
• LCK342 / TNT840: 2 – 20 mg/L NO
2
| 0.6 – 6.0 mg/L NO
2
–N
• LCK343 / TNT841: 7 – 295 mg/L NO
2
| 2 – 90 mg/L NO
2
–N
Nitrite removal
If the sample contains 2 mg/L or more of NO
2
, the NO
2
must be removed with amidosulfonic acid
before an LCK / TNT test for NO
3
is started.
To remove NO
2
, add a small quantity (spatula tip) of amidosulfonic acid to approximately 20 mL of
sample and mix. The reaction causes nitrogen gas bubbles to form. When no more bubbles are seen
(or after 20 minutes maximum), the nitrite removal is complete. Use the reacted sample to measure
the NO
3
concentration with one of the LCK / TNT tests.
Conversions
Conversion Multiply by Example
mg/L NO
3
–N to mg/L NO
3
4.43 7 mg/L NO
3
–N × 4.43 = 31 mg/L NO
3
mg/L NO
2
–N to mg/L NO
2
3.28 0.55 mg/L NO
2
–N × 3.28 = 1.8 mg/L NO
2
Sampling
Collect the sample as near as possible to the probe immediately when the instructions are given
during the matrix calibration procedure. Use filtration to remove solids from the sample before the
test is started. Use the two filters that follow:
• Pleated filter for removal of suspended material
• 0.45 µm syringe filter for removal of biologically active bacteria
For the step-by-step test procedure, refer to the instructions for the applicable LCK / TNT tests.
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