Computerized frequency-analysis instrumentation

With modern computerized frequency-analysis instrumentation and software, it is possible to acquire impedance data on cells and extract the values for all components of the circuit models of Figure 2.>7, This type of analysis, w hich is called electrochemical impedance spectroscopy, reveals the nature t>f the faradaic processes and often aids in the investigation of the mechanisms of electron-transfer reactions. In the section that follows, we explore the processes at the electrode-solution interface that give rise to the faradaic impedance. 

Another factor which influences the speed in performing an analysis is calibration of the instrument. Calibration is especially time-consuming in cases where different elements are run on every analysis but even in cases where the same elements are determined time after time, the frequency of instrument calibration required to maintain a desired level of accuracy is an important consideration. Since manual data collection is not feasible in multielement determinations, the ideal system would undoubtedly be computerized. The computer would handle all data collection steps, the construction of calibration curves by mathematical curve-fitting methods, and the calculation of concentrations from these curves. 

Fourier analysis permits any continuous curve, such as a complex spectmm of intensity peaks and valleys as a function of wavelength or frequency, to be expressed as a sum of sine or cosine waves varying with time. Conversely, if the data can be acquired as the equivalent sum of these sine and cosine waves, it can be Fourier transformed into the spectrum curve. This requires data acquisition in digital form, substantial computing power, and efficient software algorithms, all now readily available at the level of current generation personal computers. The computerized instmments employing this approach are called FT spectrometers—FTIR, FTNMR, and FTMS instruments, for example. 

Havelock Ellis remarked that What we call progress is the exchange of one nuisance for another nuisance. The advent of computerized instruments has certainly made routine a number of difficult spectroscopic measurements. Unfortunately, the sophistication of the procedures now available can result in erroneous results or interpretations if they are not used with caution. A classic example is the use of curve-resolving techniques. There is always a suspicion that a good fit between an observed spectral profile and a number of bands can be obtained providing that a sufficient number of the latter are included in the analysis. Clearly, in such cases a prior knowledge of the number of bands and their frequency would significantly increase our confidence in the results. 

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