What information is available for the older acrylic Lachat diffusion blocks?

Document ID

Document ID TE4173

Published Date

Published Date 27/05/2017
Question
What information is available for the older acrylic Lachat diffusion blocks?
Summary
Information for Lachat acrylic diffusion/dialysis blocks
 
Answer
Many Lachat methods have moved to a new style of diffusion block.  However a few still use an older style acrylic diffusion block.  This article addresses the use of these older blocks. 
Definitions:
The terms Dialysis and Diffusion are used interchangeable. Dialysis is used to remove interferences, color or turbidity from the sample. Diffusion refers to the gas diffusing across the membrane but not the water
 
Parts list
 
Diffusion Blocks and Membranes
Note:  The blocks are measured by the path length, not the length of the block itself. To determine the path length, measure from the ports to end of the curve and multiply by 2.
 
 

 
Diffusion block
Dialysis Block, 6”  (Catalog Number/Order Code 50320)
Dialysis Block, 12”  (Catalog Number/Order Code 50321)
 
Diffusion membranes
Type C
Membrane, 6” - Type C (Catalog Number/Order Code 50304)
Membrane, 12” – Type C (Catalog Number/Order Code 50305)
Tape, ¾” Teflon Tape (Catalog Number/Order Code 50316) 
 
Block Mounting Bracket
Bracket, Flow Fit – 6” (Catalog Number/Order Code 50325)
Bracket, Flow Fit – 12” (Catalog Number/Order Code 50324)
 
Miscellaneous
Torque wrench, 25In-Lbs (Catalog Number/Order Code 50301)
Screw, Dialyzer w/Washer (Catalog Number/Order Code 50306)
 
Flow fit fitting (Catalog Number/Order Code 31077)
 
 
Assembly
 
Disassemble the block and remove the old membrane. Using the lab wipe, remove any residual Teflon from the block surface. Cut a 10 - 12 cm length of Teflon membrane and lay it on the bottom half of the block.
 
Using both hands, flatten the membrane so that the two small guide holes and the two large screw holes are visible through the membrane. While supporting the membrane with your fingers, puncture an “X” pattern through each of the four holes.
 
Place the top half of the block on the membrane being careful to line up the guide holes. Some wrinkling of the membrane will normally occur. Do not pull the membrane to try to straighten it.
 
Diffusion membrane, type C
Note: The membrane on the diffusion block (debubbler) should be changed daily. The diffusion membrane is packaged so that the membrane remains wet until it is used.
  1. Gather the required materials, including; diffusion block, membrane, a sharp scalpel (new is best), lab wipes and torque wrench.
  2. Place the diffusion membrane over the bottom half of the diffusion block .
  3. Pierce the membrane at the hole locations with a scalpel tip.
  4. Place the top half of the block over the bottom half of the block. Use the locating pins on the top half of the block as a guide to proper placement. The locating pins should pierce the membrane and sit in the holes of the bottom half of the block.
  5. Insert the screws in the holes and hand tighten.
  6. After the screws are hand tightened, use the torque wrench to tighten the screws. Turn the torque wrench until you hear two “clicks”.
  7. The membrane is now firmly set in the diffusion block.
  8. If necessary, the screws may be tightened an additional 1/8 turn using a pliers.
  9. After the pump tubing and manifold tubing are connected, check for leaks by pumping water for 10 minutes through the lines, manifold, and diffusion block. The water also rinses the diffusion membrane.
Stabilize system by pumping reagents for 3-4 minutes
 
“Supported Teflon membranes The Teflon membranes should be cut long and wide enough to cover the sample trough in the diffusion block with a little excess membrane extending beyond the block on all sides.
  1. Place the Teflon plumbers tape over the bottom half of the diffusion block.
  2. Place the Spectrapor PTFE “supported” membrane (0.20 micron pore size) over the Teflon plumbers tape. The smooth side of the Spectrapor membrane should be facing up.
  3. Press the membranes down on the block with your fingers in order to identify the locating pin and screw holes.
  4. Once the holes are located, pierce the Teflon membranes at the hole locations with a scalpel tip. By creating a smallcut or hole in the membranes, it will be easier to place the top half of the block over the membranes and push in the screws.
  5. After the screws are hand tightened, use the torque wrench to tighten the screws. Turn the torque wrench to tighten the screws. Turn the torque wrench until you hear two “clicks”.
The membrane is now firmly set in the diffusion block.
 
Condition the membrane
 
When the Teflon membrane is used for the first time in the diffusion block, it will be necessary to make 5 or 6 injections of the high standard to condition the membrane. The first peak will be small and by the 5th injection the peaks will become larger and start to level out.
 
Shutdown of the system
 
  1. Remove all transmission lines from the reagents and place them in deionized water.
  2. Pump water through the system for 25 minutes. During this time period, initiate a calibration sequence (using DI water as the standards) while all the lines are in the water. The calibration sequence will turn the valve from inject to load 5-8 times which will clear the valve of any concentrated material.
  3. Stop the pump and release tension on the pump tubing. Turn off the power to the instrument, but leave the lines in the deionized water overnight. The slow movement of water through the manifold will prevent clogs from forming.
     
    Maintenance:
     
    Diffusion Block:
     
    The block must be tighten down with the rachat wrench purchased with the block. If more pressure is applied to the block, it may warp the block and cause leaking.
     
    Gently clean the block with soapy water and rinse thoroughly to remove reagent build-up
     
    Membranes:
     
    Replace the Type C diffusion membrane every week. Keep the diffusion membrane wet overnight by keeping all the transmission lines in deionized water after the tension on the pump tubing has been released.
     
    The Teflon membranes are very durable and seldom have to be changed
     
    Troubleshooting:
     
    Leaking may be caused by a tear in the membrane, warp in the block something may be caught in the between block or leaky connectors
     
    If the sample contains particles, the sample must be filtered through Whatman No. 4 filter paper. It is very important not to have any particles in the sample or standards. The particles could clog the valve, or the connectors and dispersion coil on the manifold. Particles, which disrupt the flow, could ruin the results of the analysis. Particles could clog the valve and shut down the instrument for the repair of the valve.
     
    Torque Wrench fails to remove screws on diffusion block.  The torque has a feature that impedes the user to apply excessive force when tightening or loosening the screws. There is a limit force that can be applied before the torque disables itself. If the screws are stuck to the block, the torque will keep skipping the position to apply any force to the screws. Use a wrench on the torque to loosen the screws.  Do not use the handle of the torque to rotate it. Use the wrench instead. Once the screws are loose, you may proceed to use the handle as in a normal operation.