In online analysis, as in all analytical chemistry, sampling is the most critical and least accurate step. In addition, 80

to 90% of all maintenance problems experienced by an online analyzer occur during sampling. Filtration and dilution may be required when the sample arrives at the analyzer; the more equipment used, the greater the potential for malfunctions.

All sampling techniques for online analysis fall into one of the three following general categories:

Direct insertion of the sampler into the process (inline or in situ analysis) Continuous extraction of process material for delivery to the analyzer via transfer lines (ex situ or extractive analysis)

Discrete or grab sampling (atline or nearline analysis)

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