As shown inFig. 1, pump 1 (P1) was connected to the central
port of the four-port selection valve (V1) which managed a carrier
solution (CS, 0.01 mol L
–1
nitric acid) and standards/samples as
follows; port 1 and port 3 were used for the carrier solution aspiration, the vanadium standard/sample was aspirated through
port 2, and the iron standard/sample was aspirated through port 4.
Pump 2 (P2) connected to a switching valve (V3) was used to
switch the mixed reagent solutions (RS1and RS3) and the oxidants
(RS2and RS4);i.e. a couple of solutions in reservoirs, RS1and RS2,
for vanadium determination and another couple of solutions in
reservoirs, RS3and RS4, for iron determination were delivered alternately. Meanwhile, another switching valve (V2) with a heated
loop was used to perform the stopped-in-loop step