Talanta 68 (2006) 1720–1725 Flow-injection in-line complexation for ion-pair reversed phase high performance liquid chromatography of some metal-4-(2-pyridylazo) resorcinol chelates Supalax Srijaranai a,∗ , Saiphon Chanpaka a , Chutima Kukusamude a , Kate Grudpan b a Department of Chemistry, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand b Department of Chemistry, Faculty of Science, Chaing Mai University, Chaing Mai 50200, Thailand Received 22 December 2004; accepted 9 March 2005 Available online 21 September 2005 Abstract Flow injection (FI) was coupled to ion-pair reversed phase high performance liquid chromatography (IP-RPHPLC) for the simultaneous analysis of some metal-4-(2-pyridylazo) resorcinol (PAR) chelates. A simple reverse flow injection (rFI) set-up was used for in-line complexation of metal-PAR chelates prior to their separation by IP-RPHPLC. The rFI conditions were: injection volume of PAR 85 L, flow rate of metal stream 4.5 mL min -1 , concentration of PAR 1.8 × 10 -4 mol L -1 and the mixing coil length of 150 cm. IP-RPHPLC was carried out using a C 18 Bondapak column with the mobile phase containing 37% acetonitrile, 3.0 mmol L -1 acetate buffer pH 6.0 and 6.2 mmol L -1 tetrabutylammonium bromide (TBABr) at a flow rate of 1.0 mL min -1 and visible detection at 530 and 440 nm. The analysis cycle including in-line complexation and separation by IP-RPHPLC was 16 min, which able to separate Cr(VI) and the PAR chelates of Co(II), Ni(II) and Cu(II). © 2005 Elsevier B.V. All rights reserved. Keywords: Flow injection; In-line complexation; Ion pair reversed phase high performance liquid chromatography; Metal-PAR chelates 1. Introduction Liquid chromatography has been widely recognized as one of the methods for multi-element and sensitive analysis of metal ions. Various modes of liquid chromatography have been used, including normal phase [1–3], reversed phase and ion exchange chromatography (IEC) [4–10]. Since the introduction of ion- pair reversed phase high performance liquid chromatography (IP-RPHPLC) [11,12] for the separation of charged solutes, IP- RPHPLC has gained wide acceptance as an alternative method to IEC for charged analytes, including metal ions. IP-RPHPLC offers multi-element detection capacity, selectivity and sensitiv- ity of analysis. Moreover, the reversed-phase stationary phase has the benefit of lower cost compared to the IEC stationary phase. Most of the reports on IP-RPHPLC for metal analysis [13–16] are based on the separation as their chelates. Pre-complexation of metal ions with appropriate ligands has many advantages such ∗ Corresponding author. Tel.: +66 43 202222/41x2243; fax: +66 43 202373. E-mail address: supalax@kku.ac.th (S. Srijaranai). as increasing selectivity between metal ions, the ability to deter- mine speciation and increasing sensitivity for chelates with high absorptivity. Among the many ligands successfully used for IP- RPHPLC separation of metal ions, 4-(2-pyridylazo) resorcinol (PAR) is one of the most widely used ligands. PAR is an azo dye has been used for the spectrometric determination of over 40 different metals [17]. PAR forms ionic complexes with large absorptivity (∼10 4 L cm -1 mol -1 ) [18] at about 500 nm. It has been shown to be an effective reagent for the determination of metals using HPLC with either pre-column [19] or post column complexation techniques [20,21]. Typically, complexation of metal ions is performed by batch or external to the chromatographic system before injection. Ex- ternal complexation is time consuming and the large amounts of chemicals used mean more waste to discharge. It is prone to con- tamination, especially for trace level determinations. Nowadays, the main consideration includes automation of the method, low operating costs, less waste as well as high sample throughput. Flow injection (FI) has been known with features of a simple operational basis, using inexpensive hardware, straightforward thus leading to convenient operation, high sample throughput, cost effective performance and versatility. FI has been widely 0039-9140/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2005.03.043