Generally speaking, high throughput can be achieved by a short sequence of multiple samples or by a high degree of parallelization.
Dumas runs in a rapid sequential mode whereas Kjeldahl is slower, but digests 20 samples at once. This results in a comparable throughput over a working day as digestion and distillation of subsequent batches are carried out simultaneously.
With an NIR instrument, results are obtained in 30 – 60 seconds. Manual sample changing is the limiting factor for an increased throughput.
None of the methods measures protein directly. While Kjeldahl determines the digestible nitrogen content, Dumas covers all nitrogen sources and requires like NIR a calibration (secondary methods). It is therefore essential to declare the procedure/regulation which has been followed.
Both, Kjeldahl and Dumas measure the nitrogen content and use protein factors to calculate the protein content. Where Kjeldahl does this directly (titration), Dumas’ detector signals needs to be correlated to a calibration curve.
NIR measures the electromagnetic radiation reflected, transmitted or absorbed by the samples. The generated spectra are compared to a set of spectra with known protein content. The better the reference values (typically generated by Kjeldahl), the better the NIR result.
Cheap, nitrogen-rich chemicals like melamine are used to adulterate sample in order to increase the nitrogen content and eventually the protein content of food/feedstuff.
Both, Kjeldahl and Dumas are in principal “blind” for the source of nitrogen which makes them vulnerable for adulterations. However, it is possible to separate non-protein nitrogen (NPN) from protein nitrogen prior to analysis if a sample appears suspect. A suspicious sample is best detected using NIR.
Properly calibrated, NIR is an ideal method to detect adulterants. Further inspection and quantification of the suspect sample can then be done by any established method.
The Kjeldahl digestion and distillation instruments of BUCHI can be used for much more than the determination of nitrogen containing compounds such as: COD, heavy metals, hydroxyproline, SO2, formaldehyde, CN, diacetyl, alcohol, TVBN, volatile acids, phenols and others.
Classical Dumas instruments are limited to nitrogen determination, although there are optional accessories that enable the determination of sulfur.
With NIR, there is virtually no limitation in the determination of any kind of chemical or physical properties as long as it is abundant enough: protein, moisture, ADF, NDF, amino acids, macro chemical composition, nutraceuticals, antioxidants and much more.