Millipore Specifications Update – Extraction and Sample Preparation

“Millipore” testing evaluates cleanliness by extracting particulate contamination from a surface and then either weighing or counting and quantifying the collected particles to assess the cleanliness achieved by a prior cleaning means.  The first step in either case is to collect and prepare for analysis any particulate residue remaining on the surface after pervious cleaning.  Having received and read the most recent ISO specification regarding the testing procedure I find it interesting how they have more thoroughly defined the methods and limitations of the extraction process.  I will go on to address the evaluation processes in later blogs.

Better Definition

Although it would be difficult to fully explore all the updates from previous specifications it is remarkable that the overall “tone” of the present ISO specification has changed.  The specification is much more definitive and yet, at the same time, more lenient and flexible in many ways.  There are seven different means of extraction using liquids described.  This includes two which could be seen as extensions of those found in previous documents but defined in a new way.  The latest specification is much more specific in its description of the methods and procedures involved.  Among other things they describe in welcome detail

  • How samples should be selected and in what numbers to provide the most meaningful evaluation results.
  • How to measure, reduce and maintain blank test numbers as well as interpret their meaning.
  • How samples, extraction liquids and collecting devices should be prepared and handled to prevent inadvertent contamination resulting in false readings.
  • How to manage remote testing in cases where samples are collected some distance from the evaluation site.
  • Amplified discussion of how extractions are to be performed including, for example, evaluating the types of nozzles, pressures, liquid volumes and times to be used for spray extraction.  Also, the use of wash bottles for extractions is banned except for in the most rudimentary applications.
  • Limits to contaminant loading and distribution on sample collection filters.
  • Discussion of means to pretreat samples by soaking to remove wax and dried contaminants that may interfere with liquid extractions.
  • Allowance for “exceptional cases” where testing using the described procedures is not accurate or possible.

The Human Aspect

In addition, and arguably more important than all of the above, is a recognition that people play a major role in the testing process.  Starting with the extraction process, the importance of testing being carried out by well trained and competent personnel is stressed repeatedly not only in the section regarding sample extraction but throughout the document.  These statements include the following – –

  • “In order to perform cleanliness inspections, special equipment, suitable premises and skilled, experienced staff are required.”
  • ” . . . well trained and highly motivated staff members are essential . .  “
  • “Because the result of a cleanliness inspections highly dependent on the care with which the always manual extraction procedure is performed, it is essential that the inspection staff are well-trained.”
  • “Frequent staff changes should be avoided because the results of cleanliness analyses are highly dependent upon staff experience and consistent inspection procedures.”

The focus on the people doing the work is new and significant in the latest specification.  The testing procedure is, for the most part, tedious and time consuming.  This invites assigning relatively unskilled labor to the task.  There are,  however, decision points where critical and not always intuitive decisions are required to produce an accurate and meaningful test result. The skill to make these decisions is not inherent in entry level personnel.  The risk of error is further amplified by the fact that once the extraction has been done, there is no way to go back and verify it other than to start with new samples which may or may not be representative of the first ones.  An investment in the people doing the work is, therefore, an important consideration in testing of this nature.




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