Thermo Scientific NITON XL3t 500, User Manual

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To Prepare or Not to Prepare - In Situ vs. Ex Situ
Thermo Scientific NITON XL3 Analyzer User’s Guide 1-35
To Prepare or Not to
Prepare - In Situ vs.
Ex Situ
Bulk media are generally tested either on-site ( in situ ) for screening
purposes, or removed and prepared ( ex situ ) to enhance the accuracy of the
measurement. The degree of preparation may vary depending on the
accuracy desired, the characteristics of the sample, and the characteristics of
the site.
Understanding the advantages of in situ testing and of various degrees of
preparation is crucial to obtaining useful data. In situ measurements should
be used to profile an area, to locate areas of interest, to determine the
boundaries of such areas, or to gather data that will subsequently be used to
design a sampling plan.
In situ measurements are usually only approximations, though they may
correlate very well with lab analysis if the site tested is highly homogeneous.
If the site is non-homogeneous, as is often the case, then in situ
measurement results may differ greatly from laboratory obtained results.
Both sets of results may be correct. The difference arises from the fact that
actual samples tested were different.