Instrumental Arrangement and Operation

A practical solution that allows both continuous flow from the HPLC column and a resting period of a sample fraction in the ESR spectrometer cuvette is depicted in Figure 2. In principle, a shunt is provided to short-cut the passage through the ESR spectrometer. It is opened while an ESR spectrum is in progress and closed at any other time. This allows the cuvette to be filled with a fraction, to leave it for the time of scanning a spectrum, and to flush the sample upon completion. A disadvantage of this procedure is that is does not allow spectra of fractions running closely together to be obtained since the spectrum of the first sample is still being recorded while the second one is starting to elute from the column. In this case, it is necessary to repeat the chromatographic separation step for the second fraction of interest.

In order to control the flow either through or bypassing the ESR spectrometer, a T-connector is inserted into the tubing between the HPLC detector and the ESR spectrometer for branching off to the shunt. Both the outlet tubing from the spectrometer and the shunt are connected to a valve which alternately opens or closes either way. This arrangement has two major advantages: on the one hand, unnecessary and irregularly shaped dead volume that may disturb the sample flow from the HPLC device to the spectrometer is avoided by placing the control valve after both devices, and on the other hand, it is not possible to close off both paths by control error, thus minimizing the risk of accidentally building up destructive pressure in the tubing system. In a simple set-up, the valve can be operated by hand via an electrical switch. The delay time from the appearance of the peak of interest in the monitor system of the HPLC to the moment of filling the ESR cuvette with the corresponding fraction can be measured exactly and is highly reproducible. In more standardized or routine applications, automatic control is possible. This whole arrangement makes the ESR spectrometer truly an additional HPLC monitor that analyses radicals.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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