High‐performance liquid chromatography with sequential injection for online precolumn derivatization of some heavy metals

Abstract

HPLC was coupled with sequential injection (SI) for simultaneous analyses of some heavy metals, including Co(II), Ni(II), Cu(II), and Fe(II). 2-(5-Nitro-2-pyridylazo)-5-[N-propyl-N-(3-sulfopropyl)amino]phenol (nitro-PAPS) was employed as a derivatizing reagent for sensitive spectrophotometric detection by online precolumn derivatization. The SI system offers an automated handling of sample and reagent, online precolumn derivatization, and propulsion of derivatives to the HPLC injection loop. The metal-nitro-PAPS complexes were separated on a C(18)-muBondapak column (3.9x300 mm(2)). Using the proposed SI-HPLC system, determination of four metal ions by means of nitro-PAPS complexes was achieved within 13 min in which the parallel of derivatization and separation were processed at the same time. Linear calibration graphs were obtained in the ranges of 0.005-0.250 mg/L for Cu(II), 0.007-1.000 mg/L for Co(II), 0.005-0.075 mg/L for Ni(II), and 0.005-0.100 mg/L for Fe(II). The system provides means for automation with good precision and minimizing error in solution handling with the RSD of less than 6%. The detection limits obtained were 2 microg/L for Cu(II) and Co(II), and 1 microg/L for Ni(II) and Fe(II). The method was successfully applied for the determination of metal ions in various samples, including milk powder for infant, mineral supplements, local wines, and drinking water.

A review on sequential injection methods for water analysis

“…This means that by using the same manifold but placing different reagents on the selection valve ports, and changing the operational parameters, more than one analyte can be determined. From the listed papers, over 40% involved the determination of more than one analyte [34-36,39,40,45,49-53,55,59-61,72,74,78,83-85, 94,96,101-104,106,107,114,116,117,119,120,132,135,138,140,141,145, 148,149,153,155], with close to 18% describing the determination of more than two analytes [34][35][36]40,45,[49][50][51]53,74,83,78,102,101,116,140]. Some more detailed examples of bi-parametric determinations will be detailed in Section 3.4.2, as they usually involve quantifying two oxidation states.…”

“…There were also at least two references to coupling SIA with HPLC [49,54] showing how effective SIA can be in preparing the sample prior to injection. In the work described by Burakham et al [49], SIA is responsible not only for the preconcentration step but also for the selection of reagents in the different metals determination. In the work described by Sabarudin et al [58], a solid phase extraction was carried out in a SIA method prior to injection, which enabled the application to waste waters.…”

“…Among these, iron is the most determined metal in waters, if the two possible ionic forms are considered [49,59,71,74,83,103,127,[135][136][137]143,144,152]. This fact can be explained as iron determination can be fairly easy to obtain with spectrophotometric detection, due to well-known reactions.…”

“…[48][49][50][51]59,74,92,101,102,113], cadmium [40,47,50,51,83,90,99-101,126] and lead [40,41,50,51,58,81-83, 101,102,129] were mainly determined with ICP…”

Automated pre‐column derivatization of thiolic fruit‐antibrowning agents by sequential injection coupled to high‐performance liquid chromatography using a monolithic stationary phase and an in‐loop stopped‐flow approach

“…To achieve this task, we coupled sequential injection analysis (SI) to HPLC. The ''marriage'' of the two techniques in the past has been proven quite advantageous in terms of automated sample pre-treatment prior to separation including solid-phase extraction [16], derivatization [17][18][19] and online dilution [20]. After reaction the derivatives were separated efficiently using a monolithic stationary phase.…”