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July 11, 2017

4 M's – sources of error

By GE Life Sciences Support Team

When looking for potential sources of error in the lab, consider the 4 Ms – Man, Method, Machine, and Materials. Learn how evaluating these factors can maximize lab efficiency and lab productivity.

You might have heard about the four primary sources of potential error in a process; the so-called ‘4 Ms’:

  1. Man
  2. Method
  3. Machine
  4. Materials

In this post, we look at how the 4 Ms can be applied to sources of error in the laboratory. For example, you might find it helpful to refer to them in a failure investigation to assess what went wrong, or explain why something is not working as efficiently or as productively as possible.

Man (or woman)

This ‘M’ looks at the people involved and their relevant skills and experience for a particular process.

In the laboratory, this will likely include training on specialist equipment and instrumentation and ensuring that training is up-to-date. A good opportunity to check on responsibilities and capabilities is when a protocol is updated or a new method is introduced.

Visual aids such as step-by-step videos can be helpful for initial training or for a quick refresher. Check out our short “how-to” videos on these filtration topics:

Video: How to fold a cellulose filter and perform gravity filtration

Video: How to set up a trap and perform vacuum filtration


Evaluating your method, workflow, protocol, and technique can help identify whether any of these points are negatively affecting results.

Assessing each individual step in isolation can identify specific problems. Looking at the steps in relation to the whole process might also help to identify potential errors.

When applying this evaluation process to the laboratory, most steps in each method will involve one or more of the other three ‘M’ factors. So, considering them together can be useful.

Sometimes a simple error in one part of a method, such as omitting an initial wash step, could be the reason an analysis didn’t give the expected results. Double-checking the protocol to clarify even small details might be worthwhile.

If you’re using one of our filtration products in a specific application, you might find the detailed methods in our white papers to be helpful.

White paper: Environmental monitoring - a study using Whatman brand filtration products

White paper: HPLC sample preparation


This ‘M’ refers to the necessary machines, or equipment, and their suitability for the job. Performing regular maintenance and repair can help to identify and avoid potential sources of error.

In a laboratory setting, “machines” includes all equipment used in a process. General laboratory items, such as pipettes and filtration devices, would fit into this category. So would specialist equipment designed for particular applications (e.g., protein purification systems or spectroscopy instruments).

Analysis using the right filtration device for the sample will help you get the results you need. For example, if your samples are highly viscous or contain large particles you will probably experience challenges when using a filter of a single small pore size.

In these cases, prefiltration is a good idea. To maximize lab efficiency, we recommend using a specially designed syringe filter device with a prefiltration stack. A graded-density microfiber filter traps larger particles before they reach the membrane, enabling processing of larger sample volumes with less back pressure build-up.

For more information and tips on filtering viscous samples, look at our previous blog post.


The final ‘M’ considers the physical and chemical properties of your materials, including their chemical compatibility in your process.

Beyond ensuring chemical compatibility, you might consider how standardizing materials could benefit consistency in your lab. Using the same filter material across different sample types and filtration formats, such as syringes and flat papers, is one way to minimize variation in the laboratory. Regenerated cellulose is a candidate for such standardization.

Try our Whatman Filter Selector App to find out if you are using the most appropriate filtration solution for your samples. To discuss any challenges you are facing, please contact GE's Life Sciences Scientific Support.