Rapid analysis of organic and amino acids by capillary electrophoresis: application to glutamine and arginine contents in an ornamental shrub

Soluble nitrogen-containing compounds in plant extracts are often measured using chromatographic techniques that require not only previous derivatisation and a long analysis time, but are also costly. Two rapid methods were developed for analysing NO3−, organic, and amino acids by capillary electrophoresis (CE). A mixture of NO3−, organic, and amino acids was separated within 7 min, directly from a plant extract with good repeatability and linearity. An alternative method, requiring the previous purification of a plant extract on resin, improved the identification of amino acids in samples with numerous peaks and a low amino acid content. These two methods were used to evaluate the soluble nitrogen-containing compounds in an ornamental shrub (Ligustrum ovalifolium) subjected to three fertigation timetables. Arginine and glutamine were the main compounds observed in the plants during N redistribution. Their contents increased dramatically in autumn. In December, arginine followed an increasing gradient from the roots to the trunk and decreased from the lower to the upper parts of stems. The more fertilisation the plants received, the higher the arginine content. Glutamine content was lowest in the three treatments. In March, arginine and glutamine contents returned to their minimal values.