A number of chemical or microbiological assay techniques have been used for many years.
HPLC methods using UV detection are available, although sensitivity and selectivity can be
a problem. The use of mass spectrometric (MS) detection following HPLC has been used in
more recent methods.
Niacin (nicotinic acid and nicotinamide) can be determined colorimetrically using the König
reaction with cyanogen bromide. The derivatives are coupled to aromatic amines to form
coloured compounds which, under controlled conditions, are proportional to the niacin
content.
Microbiological assay using Lactobacillus plantarum has been widely used for many years
for many of the water–soluble vitamins including niacin. It relies on the specific requirement
for niacin by Lactobacillus plantarum to enable their growth in a supporting medium. Under
appropriate conditions, the amount of growth is proportional to the amount of niacin in the
test extract. Such assays can be considered routine but require overnight incubation, can be
subject to contamination and require considerable laboratory set-up and maintenance time.