Chromatogram Recording Errors

Timestamps. Extended periods of downtime due to system malfunction, power outage, or routine maintenance often led to system clock errors. Wildy anomalous clock errors were usually detected right away, but sometimes a field technician would mistakenly reset the clock with the wrong date (e.g. off by a day or even a month) or the wrong time (e.g. local instead of GMT) or both. This type of clock error might continue anywhere from a few hours to a few weeks before being discovered by a field technician, and it would lead to a segment of time-shifted data bounded by a data gap at one end and a time fold (region of overlapping chromatograms) at the other end. Not only would the data be shifted to the wrong place when processed into the areas/heights database, but data loss due to overwriting would occur at the time folded end. Many such episodes occurred and have been corrected.

Sample Source Labels. Occasionally, the procedure for resetting a RITS system by simultaneously powering down all of its separate components was not rigorously followed (e.g. when the computer was in need of rebooting), and the data recording system would lose track of the sample type being injected onto the columns. This would cause an anomalous phase shift between the actual sampling sequence and the sampling sequence assumed by the data recording system as it assigned sample type labels to the chromatograms. This problem was detected by plotting ratios of nearby environmental and calibration samples in the areas/heights database and checking for anomalous step jumps in the times series. Many such episodes have been corrected.