Time constant noise reduction

One final comment regarding the time constant in chromatographic detection limits concerns the noise level observed on the baseline. Large time constants serve as efficient filters for (high frequency) noise. Therefore, if a great reduction of the time constant is not... 

Therefore, a reduction in the time constant of current detection systems, without the accompanying effect of a great increase in the noise level, should have at least the same priority as the reduction of the extra-column dispersion in the design of future HPLC systems. 

With cw, the increase of the recording time constant is not as efficient as expected because the low-frequency components of the noise are stronger and the reduction of the sweep speed increases line saturation. But with digital memory oscilloscopes and computers it is now possible to repeat the sweeps and average the different recordings. The improvement on a given line is obvious. The experiment is relatively easy to set up and it has been used for Stark effect studies 14).But the stability and reproducibility needed in the search of new lines, with broader sweeps, make this technique somewhat difficult to use and no suclt experiment seems so far to have been reported for nitrogen. 

Appropriate software is available for all the noise reduction procedures, and the choice of approach depends on the aim of the particular analysis. The time constant approach (e.g., lengthening of the time... 

Regarding spectral noise, in addition to using the Altering time constants on the lock-in ampliflers, noise reduction in the calibration curve and the unknown spectra can also be accomplished by using measurement averaging on the computer. This is a very effective method. Multiple measurements of M number are made at the same wavelength and then averaged to become one reflectance data point, where R,ve( ) = (1/A ) (Ri(- ) +... 

Fig. 4 (Left) Difference between spectra obtained when CO was adsorbed on platinized Pt on a bulk Pt electrode before and after oxidation platinization was carried out with 0.072 M chloroplatinic acid at a constant voltage of 2.75 V for the times hsted. Note the changes in shape of the linearly bonded CO band as the platinization time increased the increased noise level is caused by the severe reduction in reflectance of the electrode as the amount of platinum black increased. (Right) Corresponding spectra obtained when platinization was effected at a constant current of 60 mA. Note that in Fig. 3 the spectrum of CO2 in solution was subtracted from the spectrum of adsorbed CO while the reverse process was performed for Fig. 4. [Reprinted from ref. 13 by permission of the American Chemical Society copyright 1999.]...

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