CHAPTER 1 INTRODUCTION
2.4 SPECTROPHOTOMETRIC TECHNIQUES
others. The UV-Vis detector detects absorption of chromophoric analytes based on molecular structure. It is more sensitive than refractive index but less sensitive than mass spectrometry. The different components in the mixture pass through the column at different rates due to differences in their partitioning behaviour between the mobile liquid phase and the stationary phase. The selectivity is not based only on the different types of the stationary phase but also to the mobile phase (Gunzeler and Williams 2001).
HPLC is normally used in the investigation of degradation products that are nonvolatile compounds or in the analysis of high PBDE, PBB and PCB congeners (Vonderheide 2009, references). For instance, Vilaplana et al. (2009) developed an analytical method based on HPLC–UV for the determination of BFRs in styrenic polymers. They were able to determine the highest PBDE congener (deca-BDE). HPLC technique is not limited to higher congeners only.
HPLC-MS can be used for detection of PBDEs (from lower to higher congeners). Bacaloni et al.
(2009) determined PBDEs using liquid chromatography–negative ion atmospheric pressure photoionization tandem mass spectrometry (LC/NI-APPI/MS/MS) from environmental water and industrial effluents. Five different PBDE congeners were detected; these include BDE-47, BDE-99, BDE-100, BDE-153 and BDE-154. HPLC analysis of PBBs and PCBs has been reported by (Von der Recke and Vetter. 2007).
In general chromatographic methods are robust and well established, but they are expensive and require specialized personnel and instrumentation. For instance, they require extensive clean-up and/ or a preconcentration step, which can be accomplished by the use of solid-phase extraction (SPE) and liquid-liquid extraction (LLE) techniques. The sample preparation step is time consuming and tiresome. Electrochemical techniques offer some advantages over chromatographic techniques, for example they are fast, low-cost instrumentation, minimum sample pretreatment and high sample throughput (Rodriguez-Mozaz et al. 2007).
2.4.1 Atomic Absorption Spectrophotometry
This technique is based on absorption of resonant radiation by the ground state atoms of the analyte. The absorption is proportional to the concentration of the analyte. In this technique, the analyte is vapourized by the use of either a flame or furnace. When a flame is used the technique is known as flame atomic absorption spectroscopy (FAAS). On the other hand when a furnace is used (commonly graphite furnace) the technique is known as graphite furnace atomic absorption spectroscopy (GFAAS). Atomic absorption spectroscopy is commonly used for the determination of metals in liquid form (Gunzeler and Williams 2001).
Determination of heavy metals in different environmental (water, sedments and soils), food plant and human samples using FAAS and GAAS has been reported (Ghaedi et al. 2008;
Tuzen 2003a; Tuzen 2003b; Tuzen et al. (2008), Karadede and Unlu 2000). Jahromi et al. (2007) reports the determination of Cd in water samples by GAAS.
2.4.2 Inductively Coupled Plasma-Optical Emission Spectrophotometry and Inductively Coupled Plasma-Mass Spectrometry
Inductively coupled plasma (ICP) is a high temperature source used primarily for generating atomic vapour from an aqueous sample. Generally, ICP is used for the determination of trace metals in environmental samples. Inductively coupled plasma is commonly combined with atomic emission spectroscopy (AES) and mass spectrometry (MS). The advantage of using ICP- AES or ICP-MS is that the combination of these instruments eliminates the sample preparation time required in the absence of an ICP. The latter produces singly-charged positive ions for most of the elements and this makes it an effective ionization source for MS. The advantage of using ICP-MS over ICP-AES is that ICP-MS has the ability to distinguish between the mass of the various isotopes of an element where more than one stable isotope occurs (Bradford and Cook 1997).
Analysis of heavy metals in environmental samples using either ICP-OES or ICP-MS has been reported (Karami et al. 2004; Bettinelli et al. 2000; Rahmi et al. 2007). Determination of heavy metals (Al, As, Cd, Co Cr, Cu, Mn, Mo, Ni, Pb, Se, Sn, Sr, and Zn) in fish, water, sediment and tissues have been carried out using ICP-OES (Meche et al. 2010; Demirak et al.
2006). Pereira et al. (2010) reported the simultaneous determination of Ag, As, Ba, Bi, Ca, Cd,
Cr, Fe, K, Li, Mg, Mn, Mo, Ni, Pb, Rb, Se, Sr, Tl, V and Zn in crude oil by ICP-MS and ICP- OES.
Due to wide linear dynamic range, low detection limit (parts per billion, ppb to parts per trillion, ppt) and multi-element analysis capability of these techniques (ICP-OES, ICP-MS and AAS), Environmental Protection Agency (EPA) has recommended them to be the standard techniques for heavy metal analysis (McGaw and Swain 2006; Berezhetskyy et al. 2008).
However these techniques are not only unsuitable for in-situ analysis, they are also expensive, time consuming during sample preparation, sophisticated and require skilled operators (Ilangovan et al. 2006; Malitesta, and Guascito 2005; Wang et al. 2009; Han et al. 2001; Tsai et al. 2003; Berezhetskyy et al. 2008; Ghica and Brett 2008; Mohammadi et al. 2005; Stoytcheva 2002).For these reasons the development of alternative techniques is necessary.
CHAPTER 3
ELECTROCHEMICAL SYNTHESIS AND CHARACTERIZATION OF POLYANILINE