Scheme 1.The general reaction of luminol to produce light for determination of aqueous Fe(II). Fe2+(aq) ��catalyzes�� the second step in this reaction scheme. The light emitted after the third step proportional to [Fe2+(aq)] within a certain concentration …An FIA-CL instrument has been developed (FeLume �C Waterville Analytical, Waterville, ME) that may be configured to determine several analytes (Co2+, Cu2+, Fe2+, Cr2+, NO3-, PO43- and H2O2). The FeLume has been used specifically to determine sub-nanomolar concentrations of ferrous iron in both marine and freshwaters [30,42,43].When an iron-containing sample is free of organic matter, the relationship between chemiluminescence and [Fe(aq)2+] is approximately linear between 1 �C 1,000 nM Fe(aq)2+.
In the presence of fulvic acid, the linear dynamic range (LDR) is reduced to 1 �C 32 nM . It has been suggested that FIA-CL analysis of freshwater samples will not work well due to interferences by dissolved organic carbon (DOC) , while in coastal seawater, O’Sullivan et al.  found that DOM reduced the sensitivity of FIA-CL analysis of Fe(II). Similar results were obtained by Ussher et al.  in their evaluation of the effect of model ligands on Fe(II) analysis in seawater. Recently, researchers demonstrated other potential interferences that may occur with redox-active metals that produce CL of luminol  or species that interfere with the peroxy-luminol reaction leading to CL (step 2 in Scheme 1) .Coordination of Fe2+ by organic chelators and low pH both contribute to stabilizing iron against oxidation by O2 [47-49].
Carfilzomib Such stabilization may either depress or enhance the CL and resultant signal returned by the FeLume. Tight coordination of Fe2+ by organic species that persist in the mixing chamber of the FeLume results in lowering of the signal due to slower formation of the ROS required for CL of luminol. Low pH may produce a higher signal by slowing pre-injection oxidation of Fe2+(aq), yielding more H2O2 in the mixing chamber. Species that have strong affinity for ROS like ascorbate also act to suppress the CL of luminol by scavenging radicals necessary for step 2 in the mechanism shown in Scheme 1.Typical injection peaks (Figure 1) from this work demonstrate that certain organic compounds reduce the sensitivity of ferrous iron quantitation. The ��doublet�� peak shown in Figure 1 (typical at nanomolar [Fe2+]) is due to the acid in the samples overcoming the buffer capacity of the luminol solution. Lower pH decreases the signal by reducing luminol dehydrogenation (step 1 in the mechanism in Scheme 1) at nanomolar [Fe2+], but otherwise does not alter the relationship between signal and [Fe2+].