The aqueous phase was decanted from the reactor contents and filtered
through a 0.22 μm filter. The dissolved product yield in the water phase was determined gravimetrically from a 2.5 ml aliquot,
dried at 60 °C for 12 h. The concentration of ammonium ions in the
water phase was determined spectrophotometrically using a Randox
Urea analysis test kit (Merck, Millipore). The sample was diluted with
deionised water to a concentration of 1 vol% prior to analysis. Subsequently
10 μl of sample was reacted for 5 min with 1000 μl of a urease
reactant, followed by the addition of 200 μl of sodium hypochlorite solution
to induce the colour change. After 10 min, sample absorbance
was measured at 600 nm and urea concentration calculated relative to
a standard solution. From this, ammonium ion concentration was calculated.
Total nitrogen content analysis was carried out using a MerckMillipore
Spectroquant Total Nitrogen Cell Test kit and photometer,
based on the Koroleff method of persulphate digestion to transform organic
and inorganic N compounds into nitrate. Each sample was diluted
to 0.1% prior to analysis. 10 ml of diluted sample was digested for 1 h at
120 °C, then allowed to cool to room temperature and reacted with a
benzoic acid derivative form a nitro compound.
Phosphate concentration in the aqueous phase was determined
using the Merck-Millipore Spectroquant test kit and photometer system.
Prior to analysis, each sample was diluted by a factor of 5–1000, depending
on estimated phosphate content, and reacted with the reagents
provided. Aqueous samples (6 ml), diluted in 11.6 ml deionised water
were acidified with 0.4 ml 67% v/v HNO3 prior to analysis using Perkin
Elmer Optima 2100 ICP-OES to determine the Fe, Zn and Mg content.