Introduction to Data Acquisition

Inexpensive integrator systems have made the chromatographer s life easier in one sense, but complicated it in another. The computer extends this dichotomy. I ll discuss briefly the variables that must be controlled in an integrator and how to use it in a research versus a clinical environment. I ll also explain when and why you might want to hook up to a computer, if that decision was not made for you when you bought your system. 

The computer handles data differently. It measures the voltage at a preset time interval and stores each displacement as a digital word, usually at a rate of 10-20 points/sec. The computer requires much more memory than the integrator to store a single chromatogram, however, it can use this raw data to report tables of peak maxima, areas, and heights versus time and recalculate, redisplay, and compare chromatograms. 

When you are in a clinical environment where reproducibility is critical, you need to know and understand the variables that the calibration selects. An integrator should be able to integrate close neighbors about four times more accurately than you can by hand. The integrator sets three variable levels peak width, slope rejection, and noise rejections. It also makes decisions on how to integrate unresolved peaks. As peaks widen (or narrow) in later parts of the chromatogram, the integrator doubles (or halves) the peak width value to include the whole peak. 

To achieve maximum reproducibility you must make these decisions instead of leaving them to the machine. You will have to do a methods development project. TUrn off the automatics, shoot a sample, adjust a variable, and then repeat until you have it right. When setting variables manually, we first set the peak width followed by slope rejection and then noise rejection. If peak width is correct, the print gap, left when the integrator prints the retention time, will fall half way down the backside of the peak. If it falls closer to the 

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