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Below please find the recommended membrane based on your contaminant:
Below please find the recommended membrane based on your test method:

AD030 Particle Monitoring Guide

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Originally published in 1965 as a technical manual for particle monitoring methods, the AD030 guide has been used by analysts worldwide for monitoring air and fluids in the workplace and frequently referenced in protocols and publications. This AD030 Learning Center is now your convenient, online resource for particle monitoring.

We reference recommended NIOSH, OSHA and ASTM methods for monitoring contamination using Merck filters. These methods incorporate the use of filter collection of particles for analysis by a variety of techniques, including but not restricted to gravimetric, atomic absorption (AA), spectrophotometric, inductively coupled plasma (ICP) and HPLC-UV analysis.

Regulated Analytical Methods: Choose the Correct Filter

Already planning to use a specific regulated analytical method? Many methods specify the use of particular filters. Use the filter selection wizard below to choose the correct filter for your method.

Particle Contamination in Industry Settings

Particle contamination is of special interest in several industries, for their impact during processing, manufacturing, packaging, and transportation of products, especially in systems with electronic and mechanical components. Further, checking particle levels in hydraulic systems or aircraft fuel is of critical interest. The levels of particle contamination that are tolerated in these systems are extremely low and must be monitored.
  • Particle volume and size factor into how well and how long a system will operate
  • Large particles cause a system to break down faster than small particles 
  • Large number of small particles can also cause premature system failure

What Fluid and Air Samples Are Monitored in the Workplace?

Fluids and fluid streams that are routinely monitored include fuels, gases, hydraulic oils, lubricants, water, chemicals, precision component rinses, cleaning tanks, boilers, and pharmaceutical products. Routine analysis of clean room environments, building abatements, and worker safety in an industrial environment relies on methodology for particle analysis of air. We manufacture a variety of analytical tools for collecting, identifying, and measuring particles in the air during a manufacturing process or for determining worker exposure by personal air monitoring.

We have specialized in providing products for occupational and environmental monitoring for over 40 years and continues to meet today’s demanding standards.
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General Sampling Guidelines

To sample for particle contamination in any system (gases, liquids, or component surfaces), you can apply direct batch or online collection method using a membrane filter. You should reliably adhere to the same sampling procedure to ensure reproducible results.
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Sampling variables can be categorized as follows:
  • Sampling Cross-Contamination: All sampling equipment, collection containers, analytical apparatus, and filters must be clean to use subsequent measurements as a valid index of the system you plan to test.
  • Sample Adequacy: The number of samples, sample volume, and sampling time are dependent on the level of system contamination and the type of measurement you are performing. You must sample sufficient material to clearly measure “critical” levels of contamination. As an example, 100 mL would be representative of a high performance hydraulic system by microscopic particle counting; 1 to 5 gallons (4-20 liters) would be a representative sample for gravimetric analysis of a turbine fuel system.

Fluid Sample Collection

The samples must represent the entire fluid system when the system is operating normally in order to obtain meaningful and reproducible data. You should take samples of viscous fluids from areas of high turbulence where particles are mixed throughout the fluid cross section. When you are sampling a static system and the system contents cannot be thoroughly mixed, take a multilevel sample.

Surface Sample Collection

You cannot remove all contaminating particles from a component surface by rinsing. It is important to use the same sampling (flushing) procedure every time you analyze the samples. The analytical results from such sampling do not indicate the total extent of surface contamination, but yield meaningful and reproducible data.  
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Analytical Methods for Determination of Particle Contamination

There are many test procedures for particle contamination. NIOSH, OSHA and ASTM have developed methods using filtration for sample collection, monitoring and preparation of particle and chemical contaminants. These procedures have been specifically designed for monitoring contaminants in the workplace and are dedicated to worker safety.
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The following analytical methods are described in detail:
  • Particle Counting: A quantitative method for determining particle contamination by counting the particles on a filter through a microscope.
  • Gravimetric Analysis: A quantitative method for determining contamination level by weight.
  • Patch Testing: The Patch Test is a colorimetric, semi-quantitative method that allows for visual evaluation of contamination levels based on the characteristic color of the particle matter.
Spectroscopy, HPLC-UV and x-ray diffraction are methods that will not be described in this text but may be applicable.  

Sampling Apparatus

Most sampling techniques require filters, filter holders and a pump with vacuum or positive pressure.

Filters

You can use different types of filters for particle monitoring: membrane filters and depth filters. The membrane filter is a uniform, continuous mesh of polymeric material with precisely defined pore size. These filters are available in nitrocellulose, nylon, polycarbonate, PTFE or PVC. The material type you use depends on its compatibility with the fluid you need to sample.
Cross section of membrane filter, particles retained on surface
Cross section of membrane filter, particles retained on surface
Depth filters have a matrix of randomly-oriented fibers pressed, wound, or bonded together into a random matrix of flow channels. Unlike membrane filters, depth filters have a nominal pore size, causing the filter to retain a range of particles during initial use. Due to the random orientation of fibers, depth filters do become saturated and eventually the pores become larger with use. Therefore, we recommend you use them for prefiltration or as a support pad in many of the monitoring procedures.
Cross section of depth filter, random entrapment of particles.
Cross section of depth filter, random entrapment of particles.


Factors such as the size of the particles, fluid/filter compatibility, and the filtration method determine which filter you should use. Refer to the section on selecting the right filter for the proper monitoring method. You can also refer to the compatibility guide in our sample preparation guide and our online chemical compatibility information.

Download chemical compatibility chart (PDF)
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Filter Holders

Use particle-monitoring filters as discs with an underlying support to protect the filter against pressure differentials achieved during filtration. You can install or clamp filter discs in the filter holders between parallel sealing surfaces or gaskets.

There are two types of Merck filter holders for use in contamination analysis:

Reusable Filter Holders: We provide a variety of reusable filter holders constructed of stainless steel, glass or polypropylene for both liquid and atmospheric sampling. We recommend these holders for many procedures performed in a laboratory benchtop environment.

Disposable Filter Holders: We also provide a variety of disposable filter holders for fluid contamination monitoring and air monitoring, depending on the specific method.

Air monitoring cassettes:
  • Available in 25 and 37 mm diameters in a two- or three-piece configuration
  • Available preloaded or empty
  • Different pore sizes are available for these cassettes to meet both unique and standard sampling requirements
  • Assembled in a clean room environment to minimize background particle contamination
  • For preloaded cassettes, average background particle count has been determined and is marked on the outside of each package
  • Matched weight membranes eliminate the need for preweighing test filters for gravimetric analysis
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The procedures described in this guide may involve hazardous materials, operations, and equipment. If you plan to follow these procedures, you are responsible for establishing appropriate safety and health practices and determining the applicability of regulatory limitations before you begin.

For example, if you use the Hydrosol™ Stainless Steel Filter Holder (XX2004720) for flammable liquids, you must ground it according to the directions provided with the product. The Hydrosol™ unit is fitted with a grounding screw and comes complete with a grounding lead fitted with an alligator clip.

▲ WARNING: If you are filtering petroleum ether or other flammable solvents, you must ensure that the Hydrosol™ unit is grounded to prevent arcing from static electricity created during filtration.
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