Autosamplers trends

Sample solution instability or incomplete extraction/separation would show up if several aliquots from the same sample work-up were put in a series of vials that would be run in sequence that would cover at least the duration of the longest sequence that could be accommodated on the autosample/instrument configuration. For example, if an individual chromatogram is acquired for 5.5 minutes, postrun reequilibration and injection take another 2.75 minutes, and 10 repeat injections are performed for each sample vial in the autosampler, then at least 15 60/(5.5 -I- 2.75)/10 = 11 vials would have to be prepared for a 5 P.M. to 8 A.M. (=15 hour) overnight run. If there is any appreciable trend, then the method will have to be modified or the allowable standing time limited. 

This chapter presents an overview of current trends in high-pressure liquid chromatography (HPLC) instrumentation focusing on recent advances and features relevant to pharmaceutical analysis. Operating principles of HPLC modules (pump, detectors, autosampler) are discussed with future trends. 

The basic design of the gas chromatograph can be fitted with a range of specific injectors, columns and detectors to optimize the separation of components and aid their identification. Recent developments in computer control, the use of robotic autosamplers and the trend to couple instruments together for sequential procedures have lead to increased automation for routine analytical tasks performed by GCs in research, factory and quality control environments. 

This chapter provides an overview of modern HPLC equipment, including the operating principles and trends of pumps, injectors, detectors, data systems, and specialized applications systems. System dwell volume and instrumental bandwidth are discussed, with their impacts on shorter and smaller diameter column applications. The most important performance characteristics are flow precision and compositional accuracy for the pump, sampling precision and carryover for the autosampler, and sensitivity for the detector. Manufacturers and selection criteria for HPLC equipment are reviewed. 

In the second scenario shown by the data in Table 10.2, poor precision was encountered in both the retention time and peak area of an analyte. Scrutiny of the data showed that both retention time and peak area tended to trend upward. Troubleshooting the autosampler by replacing the sampling syringe yielded no improvements. The poor precision of retention time hinted to possible column problems. The column was therefore replaced and acceptable precision was restored. 

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