Hach NT3100sc User Manual page 26

Section A Instructions for laboratory measurements
Notes on NO and NO
3
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 and NO LCK / TNT measurement ranges
3 2
Nitrate:
• LCK339 / TNT835: 1.0 – 60.0 mg/L NO
• LCK340 / TNT836: 22 – 155 mg/L NO
• LCK540 / TNT838: 66 – 664 mg/L NO
Nitrite:
• LCK341 / TNT839: 0.05 – 2 mg/L NO
• LCK342 / TNT840: 2 – 20 mg/L NO
• LCK343 / TNT841: 7 – 295 mg/L NO
Nitrite removal
If the sample contains 2 mg/L or more of NO
before an LCK / TNT test for NO
To remove NO , add a small quantity (spatula tip) of amidosulfonic acid to approximately 20 mL of
2
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 concentration with one of the LCK / TNT tests.
3
Conversions
Conversion
mg/L NO –N to mg/L NO
3
mg/L NO –N to 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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measurements with LCK / TNT cuvette tests
2
| 0.23 – 13.5 mg/L NO
3
| 5 – 35 mg/L NO
3
| 15 – 150 mg/L NO
3
| 0.015 – 0.6 mg/L NO
2
| 0.6 – 6.0 mg/L NO
2
| 2 – 90 mg/L NO
2
is started.
3
Multiply by
4.43
3
3.28
2
3
–N
3
–N
3
–N
2
–N
2
–N
2
, the NO must be removed with amidosulfonic acid
2 2
Example
7 mg/L NO –N × 4.43 = 31 mg/L NO
3
0.55 mg/L NO –N × 3.28 = 1.8 mg/L NO
2
–N
3
2