**3. Flow injection spectrophotometric determination of iron (III) using diphenylamine-4-sulfonic acid sodium salt (Reproduced with permission from the paper of Asan Adem et al., 2008. Copyright of Institute of Chemistry, Slovak Academy of Sciences)**

In recent years, low cost automatic and userfriendly analytical methods have become attractive for the determination of trace levels of iron in many kinds of samples (Chen et al., 2006; Pons et al., 2005a; Lunvongsa et al., 2006b). Among these, flow-injection analysis (FIA) is a well accepted technique owing to its high sample throughput, cost effective performance, versatility, flexibility, and ease of operation. Also, FIA is compatible with a wide range of detection systems (Guo & Baasner, 1993; Ensafi et al., 2004). Up to date, FIA for the determination of iron(III) has been generally combined with optical detectors (Pulido-Tofino et al., 2000; Saitoh et al., 1998). The spectrophotometric detector based on measuring the absorbance of colored complexes formed with various chromogenic reagents is one of the most frequently used detectors for the determination of iron in many kinds of samples (Yegorov et al., 1993; Yamamura and Sikes, 1966; Ampan et al., 2002; Bruno et al., 2002; Tesfaldet et al., 2004; Van Staden and Kluever, 1998; Mulaudzi et al., 2002; Reguera et al., 1997; Pojanagaron et al., 2002; Araujo et al., 1997; Asan et al., 2003; Udnan et al., 2004; Alonso et al., 1989; M¨uller et al., 1990; Themelis et al., 2001; Kass and Ivaska, 2002; Weeks and Bruland, 2002). A large number of flow-injection spectrophotometric methods have been developed for the determination of iron using desferal (Yegorov et al., 1993), 1,10 phenantroline (Yamamura and Sikes, 1966; Ampan et al., 2002; Bruno et al., 2002; Tesfaldet et al., 2004), tiron (Van Staden and Kluever, 1998; Mulaudzi et al., 2002), ferrozine (Reguera et al., 1997), norfloxaxin (Pojanagaron et al., 2002), thiocyanate (Araujo et al., 1997), DMF (Asan et al., 2003), and salicylate (Udnan et al., 2004) as chromogenic reagents. However, many of the proposed methods have a high limit of detection (Alonso et al., 1989; M¨uller et al., 1990), suffer from many interfering metal ions, such as Zn and Co (Guo and Baasner, 1993), have a short linear dynamic range (Themelis et al., 2001; Kass and Ivaska, 2002), tedious procedures (Pons et al., 2005b), or low sampling rates (Teixeira and Rocha, 2007; Lunvongsa et al., 2006a).

Fig. 4. Structure of the diphenylamine-4-sulfonic acid sodiumSalt

In this study, a highly sensitive and very simple spectrophotometric flow-injection analysis (FIA) method for the determination of iron (III) at low concentration levels is presented. The method is based on the measurement of absorbance intensity of the red complex at 410 nm formed by iron (III) and diphenylamine-4-sulfonic acid sodium salt (DPA-4-SA). It is a simple, highly sensitive, fast and low cost alternative method using the color developing reagent DPA-4-SA in acetate buffer at pH 5.50 and the flow-rate of 1 mL min*−*1 with the sample throughput of 60 h*−*1. The accuracy of the method was evaluated using the standard addition method and checked by the analysis of the certified material Std Zn/Al/Cu 43 XZ3F.
