On-line, Batch, & On-site Liquid Samples

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In the section, you can find detailed methods for collecting, preparing, and analyzing liquid samples on line, on site, or in batch mode. Click the appropriate links below to read each set of methods:

On-line Sample Collection and Filtration

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Quick disconnect valve fitted in horizontal position into piping.
If the liquid you plan to test is under pressure (between 10 and 100 psi), you can filter the samples directly at the sampling point. To do this, use an Merck Sampler Assembly and a clean disposable Fluid Contamination Cassette containing an Merck filter. The Fluid Sampling Kit is portable and self-contained. The kit consists of a stainless steel sampler, the connecting valves and everything else needed for frequent on-site sampling in pressurized systems. Connecting valves and additional equipment are sold separately. Using the kit eliminates the need for sample bottle cleaning and prevents cross contamination.

Plug the sampler assembly, containing a cassette, into a stainless steel quick-release valve installed in the system line. The operating pressure (100 psi max.) forces liquid through the assembly. The initial volume is directed through a bypass line to flush the valve and inlet hose. The sample volume then passes through the filtering cassette and into a graduated container. Alternatively, you may transfer the fluid to a collection vessel by means of a sampling tube.

After sampling, either send the filter cassette to the laboratory for analysis or evaluate it on site using the appropriate method.

Refer to the online guide to regulated analytical methods.

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Quick-Release Valve Installation

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Fluid sampling kit with contamination monitors
Install the quick-release valve horizontally or on top of a pipe where there is a high velocity flow during flushing. We recommend a permanently installed quick release valve to avoid test variation and non-repeatability. Do not mount on the bottom of a pipe or tank where particles can collect and will not all be rinsed away with the initial flush. One stainless steel quick-release valve is supplied with the Fluid Sampling Kit.

You can purchase additional valves and install them permanently at appropriate sampling points on systems throughout a given facility. Once permanent sampling valves have been installed, an operator may tour the facility with the sampling kit and filter samples directly using a new filter cassette at each point.

When installing the quick-release valves:
  • Do not omit the dust plug supplied with each valve.
  • Regulate the pressure immediately upstream of the valve to a maximum of 100 psi if necessary.

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Monitoring Cassette Sampling Procedure

After installing the quick-release sample valves at the appropriate points in the system, use the following instructions for all analytical procedures performed using the Fluid Sampling Kit.

Click here for the instructions to the Monitoring Cassette Sampling procedure:

Monitoring Cassette Sampling Procedure
  1. Unscrew the sampler. Remove the protective plugs from the 2-piece filter cassette and save the plugs for reuse.
Two-piece preloaded monitoring cassette.
Two-piece preloaded monitoring cassette.

Install the cassette into the sampler with the filter facing up.

NOTE: For gravimetric analyses, we recommend the MAWP037PM matched weight contamination monitoring cassettes to eliminate the need to preweigh the filters.
Installing cassette (plugs removed) into body of sampler.
Installing cassette (plugs removed) into body of sampler.

  1. Screw the sampler tightly together. Connect the bypass hose from the three-way inlet valve to the hole in the side of the sampler.
     
  2. Screw the hose with the grounding wire into the bottom of the sampling unit.
     
  3. Place the three-way inlet valve in the “off” position and remove the dust caps from the quick-release sample valve and the inlet hose nipple. Retract the valve collar and insert the nipple firmly into the valve. Release the collar when the nipple is seated.
Connecting bypass hose from valve to bypass port of standard sampler.
Connecting bypass hose from valve to bypass port of standard sampler.

  1. Place the outlet of the hose into a container.

    Turn the three-way valve to the “flush” position and allow fluid to flow through the bypass tubing to flush contaminants from the sampling valve, the hose and the three-way valve (typically about 100 mL for hydraulic fluids and one gallon [3.8 liters] for aircraft fuels).
     
  2. Hold the sampler upright, turn the valve to the “test” position, and allow the desired sample quantity to flow through the cassette and into the graduated container. Turn the three-way valve to “off” when the desired sample volume has been collected.
CAUTION: Some pumping systems (e.g. aircraft refuelers) develop a vacuum when stopped, which can cause backflow and rupture the filter in the cassette. Always turn the sampler three-way valve to “off” before pumping is discontinued.
  1. Retract the valve collar, remove the sampler and replace the dust caps.

  1. Disconnect the bypass hose from the side of the sampler, unscrew the sampler and remove the cassette (keep upright). Insert the syringe valve into the bottom of the cassette and pump it dry.
Removing fuel from cassette using 2-way syringe unit.
Removing fuel from cassette using 2-way syringe unit.




Replace the cassette protective plugs, label it and return it to the laboratory for analysis. For ASTM Method D2276: Place the filter in a PetriSlide™ device and compare to ASTM standards booklet.

When performing a colorimetric method, remove filter from cassette and place in a PetriSlide™ device. Compare the color of the filter to the color standard chart. Report color rating and volume tested.

When using matched weight filters, remove both filters from the cassette and weigh each filter. The result is the weight of the bottom filter subtracted from the top.

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Batch Sample Collection and Filtration

As an alternative to in-line monitoring, you can collect liquid samples in containers and then analyze them on site or send them to the laboratory for analysis. Cleanliness of the sample collection containers is critical. Containers should be graduated and preferably slightly larger than the sample volume.
Proper Cleaning of Sample Containers
Before each use, clean the sample containers as follows:
  1. Wash thoroughly with a standard laboratory cleaning solution. For critical work, check bottle cleanliness by filling and shaking with filtered solvent to dislodge particles. Then filter and analyze the solvent. If the standard cleaning procedure is not effective, you may need to clean with dilute acid or a low surface tension fluid (CFC-Free Contact Cleaner).
     
  2. Rinse each container twice with Milli-Q® water. In this and in all other rinsing operations, a solvent filtering dispenser is especially convenient. By squeezing the bulb on the flask, a stream of solvent is forced from the flask, through an Merck filter, and out of the flexible dispenser tip.
Flushing sample container with solvent filtering dispenser.
Flushing sample container with solvent filtering dispenser.

  1. When you need to clean many containers at one time, the Filterjet™ solvent dispenser is especially effective and convenient. When connected to a pressurized solvent tank, it provides a strong jet or spray of ultraclean solvent in a continuous or trigger-controlled action. 
Filterjet™ solvent dispenser connected to pressure vessel and vacuum/pressure pump.
Filterjet™ solvent dispenser connected to pressure vessel and vacuum/pressure pump.

  1. Rinse the sample containers with membrane-filtered isopropyl alcohol to remove residual rinse water. A final rinse of membrane filtered CFC-Free Cleaning solvent (miscible with isopropyl alcohol) is desirable if you are going to use the containers to collect oil or hydraulic fluid samples.
     
  2. Place a small square of Saran® or Mylar® plastic film, rinsed with membrane filtered solvent, over the mouth of the sample container before replacing the cap. This minimizes the danger of contaminating the container with particles from the screw cap. After closure, any residual rinse solvent evaporates in the empty sample container and creates a slight vapor pressure in it. This pressure tends to blow particles away from the mouth when the container is opened for sampling.
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ESP (engineered synthetic polymer) Valve fitted in horizontal position into PVC high purity water line.

Location of Sampling Valves

The best sampling valves, such as ball or plug valves, provide a straight fluid path when open In-line sampling valves must be made of a non-corrosive material, such as stainless steel. They should be flushed clean when first installed. If connected at a tee in the system, the valve should be oriented upward or horizontally so that any sediment in the fluid stream will not tend to settle into the tee and valve.

In dynamic systems, sampling valves should be located at points where baffles or changes in direction or pipe dimensions create turbulence. If possible, they should be installed just upstream of the most contamination-sensitive components in the system.

In static systems, such as storage tanks, the sampling valve should be located at the outlet connection. In the case of drums and similar fluid containers, the conventional stopcock or drain valve will usually suffice for sampling purposes.

Sample Collection

Dynamic systems should be operated for several minutes before taking the sample. This ensures that contaminants are evenly distributed throughout the system.

Sample Collection
  1. Open the sampling valve while the system is operating and allow sufficient liquid to flow into a waste container to flush out the valve. Never collect the sample immediately upon opening the sampling valve.
     
  2. Remove the cap from the sample bottle and hold it in your free hand.
     
  3. Place the bottle into the liquid stream immediately and collect the desired volume. Do not “rinse” the container in the sample fluid.
Collecting water sample from ESP Valve fitted into D.I. (deionized) water line.
Collecting water sample from ESP Valve fitted into D.I. (deionized) water line.

  1. Remove the container from the stream and replace the plastic film and cap.
     
  2. Turn off the sampling valve.
NOTE: Avoid wiping the sampling valve or the neck of the bottle with a cloth or paper towel since this may introduce fibers into the sample.
  1. Label the container.
     
  2. Return the sample bottle to the laboratory promptly for filtration and analysis.
NOTE: If you would rather analyze your samples on-site, see the “Patch Test Kit Collection and Filtration” section.
Fluid Contamination Kit
Fluid Contamination Kit

Filtration Equipment Preparation

Before using the laboratory filter apparatus, you should carry out the following cleaning procedure:
  1. Wash the filter holder in a standard laboratory cleaning solution. Rinse with hot water.
     
  2. Rinse twice with laboratory grade water, dispensed from either a solvent filtering dispenser or a Filterjet™ solvent dispenser.
     
  3. Rinse with membrane-filtered isopropyl alcohol (dispensed from either a solvent filtering dispenser or Filterjet™ solvent dispenser) to remove water and allow to dry.
For critical applications, check filter holder cleanliness by passing clean (already filtered) fluid through the filter holder and inspecting the filter for particles. If particles are visible, the cleaning procedure should be repeated or modified.
Flushing inside walls of glass filter funnel with solvent filtering dispenser.
Flushing inside walls of glass filter funnel with solvent filtering dispenser.

Filtration Procedure

This procedure should be carried out on a sanitary surface or under a laminar flow hood.
  1. Remove the membrane disc from the packing using forceps and rinse its surface with membrane-filtered petroleum ether or a CFC-Free Cleaning Solvent.
Flushing filter with solvent filtering dispenser.
Flushing filter with solvent filtering dispenser.

  1. Place it on the filter holder base. When using a gridded filter, place grid-side up.
     
  2. Attach the funnel to the base with the spring clamp.
▲ WARNING: If you are filtering petroleum ether or other flammable solvents, you must ensure that the Hydrosol™ unit (XX2004720) is grounded to prevent arcing from static electricity created during filtration.
Placing membrane filter on base of 47 mm glass filter holder.
Placing membrane filter on base of 47 mm glass filter holder.

  1. Pour the entire contents of the sample bottle into the funnel.
Pouring liquid sample into funnel of 47 mm glass filter holder.
Pouring liquid sample into funnel of 47 mm glass filter holder.

  1. Rinse the sample bottle with membrane-filtered solvent and pour into the funnel.
     
  2. Apply vacuum to the filter flask. When filtration is almost complete, release the vacuum.
     
  3. Use some membrane-filtered solvent to carefully rinse the funnel walls while some liquid still remains in the funnel. Do not direct the solvent stream onto the filter surface— it will disturb the particle distribution. Use a solvent that evaporates readily so that the filter dries quickly. You can obtain information on recommended quick drying CFC-Cleaners from Technical Service.
Rinsing the funnel walls.
Rinsing the funnel walls.

  1. Apply vacuum and pull the remainder of the fluid through the filter disc.
    • For gravimetric analysis only: While vacuum is applied, rinse the surface of the filter with a jet of filtered solvent, moving the accumulated sediment towards the center of the filter.
    • For microscopic particle counting: Do not rinse the funnel walls or the filter surface to avoid disturbing the even distribution of particles on the filter surface.
       
  2. Release the vacuum.
     
  3. Remove the funnel from the holder. Using forceps, immediately place the filter in a clean plastic PetriSlide™ device identified with the sample number.

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On-site Analysis Patch Test Kit Collection and Filtration

If you need to analyze your sample on site, use the Patch Test Kit, a portable filtration system that includes filter color rating and particle assessment scales that correspond to recognized standard contamination levels.

Jump to each step:

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Equipment Preparation

Before using the Patch Test Kit, you should carry out the following assembly and cleaning procedure:

Assembly and Cleaning Procedure
  1. Assemble test filtration apparatus. Remove 47 mm filter holder assembly from vacuum filtration flask, if necessary using butt end of forceps to pry against flask rim at cut-out slot. Invert holder assembly and install in flask with funnel up, seating holder base flange evenly against flask rim.
Remove 47 mm filter holder assembly from vacuum filtration flask.
Remove 47 mm filter holder assembly from vacuum filtration flask.

  1. Wash down inside of funnel. Close vent hole in solvent dispenser cap with your finger tip and squeeze bottle to direct jet of filtered solvent against all inner surfaces of funnel. Use enough solvent to carry all contaminants through filter holder screen and into flask.
Wash down inside of funnel.
Wash down inside of funnel.

  1. Install test filter. Remove funnel from test filter holder by turning knurled ring to left until free, then lifting. With forceps, center a 47 mm white test filter disc on wire mesh support screen. Replace funnel, and retighten knurled ring to seal filter in place.
Center 47 mm white test filter disc on wire mesh support screen.
Center 47 mm white test filter disc on wire mesh support screen.

  1. Attach syringe vacuum pump. The free end of the flexible tube attached to the syringe is fitted with a small nylon adapter. Insert adapter firmly into small hole on side of filter holder base. Tube and adapter are normally left attached to syringe for storage, but can be removed for cleaning.
Insert adapter in the end of the syringe tube into hole on side of filter holder base.
Insert adapter in the end of the syringe tube into hole on side of filter holder base.


Sample Collection
  1. Using filtered solvent, rinse out the inside of the clear plastic bottle you will use to hold test fluid sample, then properly discard the used solvent. Fill the sample bottle to the shoulder point with fluid to be tested, and cap securely.
Rinse inside of sample collection container.
Rinse inside of sample collection container.




Filtration Procedure
  1. Filter test sample. Shake sample bottle, and pour contents into funnel, pouring against funnel walls to distribute fluid evenly over filter. Then work syringe plunger to draw vacuum inside flask, until level of fluid in funnel just begins to fall, showing start of filtration.
Work syringe plunger to draw vacuum inside flask.
Work syringe plunger to draw vacuum inside flask.

  1. Rinse contamination from sample bottle. Fill test sample bottle 1/3 full with filtered solvent, shake thoroughly, and pour into funnel as soon as level of fluid permits. Operate syringe again to sustain filtration if necessary.
Rinse contaminant from sample bottle and pour into funnel.
Rinse contaminant from sample bottle and pour into funnel.

  1. Rinse contamination from funnel walls. When sample level in funnel drops to narrow neck of funnel, wash down inner surfaces of funnel with stream from filtered solvent dispenser. Do not let solvent stream directly strike test filter. Work syringe to draw all fluid through filter.
     
  2. Check test filter against standard. Remove funnel from base, lift off test filter with forceps, place face-up in uncovered PetriSlide™ device, and let dry completely in still air. Replace PetriSlide™ cover, and compare filter appearance with standard to determine the contaminant level. If trichloroethane or dry cleaning fluid is used as solvent, filter must be dry before placing in the PetriSlide™ device, to avoid clouding plastic.



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