Solartron claims Gamry's EIS measurement is "not
true high performance". We respond.
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Solartron Analytical has published a brochure entitled "Solartron CellTest® System". On page 4 of this brochure, they state that "Unlike copycat "FRAs", Solartron FRAs are true high performance analyzers not to be confused with soft-FRAs, sub-sampling FRAs, lock-in amplifiers or frequency detectors all of which are subject to one or more performance limitations (limited frequency bandwidth, limited frequency resolution, no FFT capability or limited frequency range for each measurement technique." We understand that Solartron is rightfully proud of their Frequency Response Analyzers (FRAs) that they use to make their Electrochemical Impedance Spectroscopy (EIS) measurement. But when they included "sub-sampling", they're criticizing Gamry, since Gamry uses Sub-Harmonic Sampling to perform EIS. Well, we're rightfully proud of our products, too, so we will respond to Solartron’s comments. Gamry's Sub-Harmonic Sampling technique is mathematically correct and is fully equivalent to the single-sine measurement made with FRA's from Solartron. Sub-Harmonic Sampling gives an accurate EIS result when implemented with any research-grade potentiostat. More importantly, we believe Solartrons’s emphasis on the FRA obscures the importance of the Potentiostat in an EIS experiment. An electrochemist doesn't make an EIS measurement with an FRA. He makes an EIS measurement with an FRA and a Potentiostat. It is Gamry’s opinion that the Potentiostat is the most critical device in any EIS System. There are several valid ways to make an EIS measurement, including Solartron’s FRA, a lock-in amplifier, and Sub-Harmonic Sampling. All of these techniques depend on the accurate application of an electrochemical signal and the accurate measurement of the electrochemical response by the Potentiostat. Designing a Potentiostat to faithfully apply high-frequency signals and measure the response is not trivial. Gamry is particularly skilled in potentiostat design. We are confident that Gamry Potentiostats do an excellent job in this regard and we guarantee that our specifications can be met in any laboratory in the world. In
truth, there probably is no "best" way to make the EIS
measurement. FRAs, lock-in amplifiers, and Sub-Harmonic Sampling all
do a good job, providing the potentiostat to which they are interfaced
is accurate. |
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