Impedance measurements, ITIES

In ac impedance measurement at ITIES, admittance due to the transfer of supporting electrolyte ions is significant even in the middle of the potential window, as was first suggested and treated quantitatively by Samec et al. [35]. This imposes a difficulty in accessing double layer capacitance from the admittance, particularly when the transfer of supporting electrolyte ions is not reversible. There is no straightforward way to deconvolute the admittance ascribable to double layer capacitance and that ascribable to ion transfer admittance [30]. A nonlinear least-squares... 

A number of other methods (chronopotentiometry [24], polarography with dropping electrolyte electrode [25], faradaic impedance measurement [26], current scan voltammetry [27] etc.) were also applied to the study of electrolysis at ITIES. 

The electrical double layer arising at the ITIES has been studied by measuring the surface tension [4, 7-16, 25] or the impedance [17-26] mainly of water/nitrobenzene [4, 7-15, 17, 19-24] and water/l,2-dichlorethane [12, 16, 18, 25, 26] systems. This contribution reviews the principles and the results of the impedance measurements, in particular those based on the AC impedance or galvanostatic pulse techniques, which have been used most frequently for the study of the double layer at the ITIES. The quantity, which can be inferred from the impedance measurements, and which is related to the double-layer structure, is the interfacial capacitance. We shall discuss first the thermodynamic background for the capacitance of the electrical double layer at the ITIES. 

The impedance data have been usually interpreted in terms of the Randles-type equivalent circuit, which consists of the parallel combination of the capacitance Zq of the ITIES and the faradaic impedances of the charge transfer reactions, with the solution resistance in series [15], cf. Fig. 6. While this is a convenient model in many cases, its limitations have to be always considered. First, it is necessary to justify the validity of the basic model assumption that the charging and faradaic currents are additive. Second, the conditions have to be analyzed, under which the measured impedance of the electrochemical cell can represent the impedance of the ITIES. 

It is often too expensive to have or maintain an inhouse descriptive sensory panel. Therefore, other ways of measuring flavor need to be developed. Off-flavor in many foods have been measured by using gas chromatography to assess the level of lipid volatiles associated with off-flavor development Chapters 5, 6, 9) such as hexanal or by direct chemical determination of thiobarbituric acid reactive substances Chapters 5, 6) as a marker of the degree of lipid peroxidation. A new method being tested for use in the assessment of food qu ity is impedance technology. This method is showing promise for use in the seafood industry Chapter 20),... 

The impedance or electrocapillary properties of the ITIES can be measured with the cell mentioned in Sch. 1. 

---