Hach DR2400 - Page 505

Nitrogen, Total
Nitrogen, Total
NitrogenTot_TNT_Other_PSD_Eng_Ody.fm Page 5 of 8
Sample Collection, Storage and Preservation
Collect samples in clean plastic or glass bottles. Best results are obtained with
immediate analysis.
Preserve the sample by reducing the pH to 2 or less with at least 2 mL of
Concentrated Sulfuric Acid (Cat. No. 979-49). Store at 4 °C (39 °F) or less.
Preserved samples may be stored up to 28 days. Warm samples to room
temperature and neutralize with 5 N Sodium Hydroxide (Cat. No. 2450-32)
before analysis. Correct the test result for volume additions. See Section 3.1.3
Correcting for Volume Additions on page 29.
Accuracy Check
This method generally yields 95–100% recovery on organic nitrogen standards.
For proof of accuracy Hach offers a set of three Primary Standards for Kjeldahl
Nitrogen (Cat. No.22778-00). Use the deionized water included in the kit or
water that is free of all organic and nitrogen-containing species.
1. Prepare one or more of the following three solutions. Each preparation is for
an equivalent 25 mg/L N standard.
a. Weigh 0.3379 g of Ammonium p-Toluenesulfonate (PTSA). Dissolve in a
1000-mL volumetric flask with deionized water. Add deionized water to
the 1000-mL mark.
b. Weigh 0.4416 g of Glycine p-Toluenesulfonate (PTSA). Dissolve in a
1000-mL volumetric flask with deionized water. Add deionized water to
the 1000-mL mark.
c. Weigh 0.5274 g of Nicotinic p-Toluenesulfonate (PTSA). Dissolve in a
1000-mL volumetric flask with deionized water. Add deionized water to
the 1000-mL mark.
2. Analyze each of these solutions using the test procedure above. Calculate the
percent recovery for each using this formula:
The percent recovery values are shown in Table 3 :
Hach analysts have found Ammonia-PTSA to be the most difficult to digest.
Other compounds may yield different percent recoveries.
% recovery
measured concentration
25
----------------------------------------------------------------
100×=
Table 3
Compound Lowest Expected % Recovery
Ammonia-PTSA 95%
Glycine-PTSA 95%
Nicotinic-PTSA 95%