Determination of Total Nitrogen, Total Kjeldahl Nitrogen and Total Phosphorus According to ASTM D8001

Kjeldahl nitrogen is a typical titration application, following digestion and ammonia. The ASTM D8001 standard now provides an alternative approach involving persulfate digestion and subsequent IC determination without the need for distillation.

Moreover, total phosphorus and total nitrogen can be determined using this method. This article shows the results of control samples consisting of organic substances. Since these organic substances are dissolvable in ultrapure water, it is possible to determine the nitrogen concentration corresponding to Kjeldahl Nitrogen and Total Nitrogen.

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Nitrogen and phosphorous containing compounds in ultrapure water.

Sample preparation

Alkaline persulfate digestion as outlined in the ASTM D8001 standard before Metrohm inline ultrafiltration and IC analysis.


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Metrosep A Supp 16 - 250/4.0 6.1031.430
Metrosep A Supp 16 Guard/4.0 6.1031.500


Eluent 5.5 mmol/L sodium carbonate
2.5 mmol/L sodium hydrogen carbonate
Suppressor regenerant 500 mmol/L sulfuric acid
Rinsing solution STREAM


Conductivity detection following the sequential suppression


930 Compact IC Flex Oven/SeS/PP/Deg 2.930.2560
IC Conductivity Detector 2.850.9010
858 Professional Sample Processor 2.858.0020
800 Dosino (suppression) 2.800.0010
IC equipment: Inline Ultrafiltration 6.5330.110
MSM Rotor A 6.2832.000
Adapter sleeve for Suppressor Vario 6.2842.020


Flow rate 0.8 mL/minutes
Injection volume 20 μL
Pmax 15 MPa
Recording time 42 minutes
Column temperature 45 °C

Method detection limit (MDL)

Calculated from the standard deviation of 7 injections

Nitrate-N [μg/L] Phosphate-P [μg/L]
MDL-1 14.9 17.2
MDL-2 13.5 14.6
MDL-3 15.6 14.6
MDL-4 14.4 16.9
MDL-5 14.5 18.0
MDL-6 13.2 15.6
MDL-7 15.8 16.2
Mean 14.6 16.4
Std. dev. 0.98 1.11
MDL (3.14 x SD) 3.1 3.5

Nitrate-N: nitrate as nitrogen

Phosphate: phosphate as phosphorus


Sample Nitrate as nitrogen Phosphate as phosphorus
expected [mg/L] actual [mg/L] recovery [%] expected [mg/L] actual [mg/L] recovery [%]
NH4Cl 1.0 1.06 106 - - -
Glycine 2.5 2.63 105 - - -
Tripolyphosphate - - - 10.0 9.10 91
Phytic acid - - - 5.0 4.22 84*

* Phytic acid recovery is improved when using slightly higher persulfate concentration

This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.

For more information on this source, please visit Metrohm AG.

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