Hach Digesdahl 23130-20 - Page 35

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Solid Samples
1. Weigh 0.25 grams of a Primary Standard for Kjeldahl Nitrogen.
Digest the standard following the general digestion procedure.
2. Any of the three standards may be used. Ammonium p-toluenesulfonate
(185.5 mg/L TKN) is the least difficult to digest. Glycine
p-toluenesulfonate (141.63 mg/L TKN) is moderately difficult to digest,
and Nicotinic Acid p-toluenesulfonate (118.58 mg/L TKN) is the most
difficult to digest.
Liquid Samples
1. Weigh 10.000 grams of a Primary Standard for Kjeldahl Nitrogen.
2. Transfer to a 1-liter volumetric flask and dilute to the mark.
3. Using a volumetric pipet, add 15 mL of the prepared solution to the
digestion flask and digest the standard following the general
digestion procedure.
4. Any of the three standards may be used. Ammonium
p-toluenesulfonate (111.03 mg/L TKN) is the least difficult to digest.
Glycine p-toluenesulfonate (84.98 mg/L TKN) is moderately difficult
to digest, and Nicotinic Acid p-toluenesulfonate (71.15 mg/L TKN) is
the most difficult to digest.
A primary standard set, containing one bottle of each of the standards,
may be purchased from Hach Company. Table 2 lists some of the
properties of the three primary standards.
Table 2 Some Properties of Kjeldahl Nitrogen Standards (#22778-00)
Ammonia PTSA Glycine PTSA Nicotinic Acid PTSA
Formula C
7
H
11
O
3
SN C
9
H
13
O
5
SN C
13
H
13
O
5
SN
Structure
Molecular Weight 189.235 247.277 295.316
Melting Point, °C — 199 179
% Nitrogen 7.402 5.664 4.743
% Protein 46.261 35.403 29.643
Digestability Index 0 3 10
Moisture
Absorption
at 25 % RH
at 50% RH
at 90% RH
0.04%
0.07%
0.14%
0.03%
0.047%
0.15%
0.00%
0.01%
0.08%
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