Despite
this, we recommend fresh solutions. The postcolumn reaction solution
was composed of 240 mL of 25% ammonium (NH3(aq)), 77 mg of PAR,
and 57 mL of acetic acid diluted to 1 L, pH 10.2 ( 0.1. The pH of the
PAR solution determines which metals that can be detected. The PAR
postcolumn reagent solution was continuously degassed with helium,
because PAR is easily oxidized by oxygen. The PDCA eluent flow
was kept at 0.8 mL/min, and the PAR postcolumn flow was 0.4 mL/
min. This combination showed the optimal absorption. The standard
solutions were prepared to contain 0.05 M HCl and ascorbic acid 2
g/L.