Maintenance of Flow Cell

Follow these instructions if you need to clean or replace the flow cell.  Be extremely careful when working with the flow cell and its fittings. Flow cells are made of quartz and are considered expendable. 

Flow Cell Cleaning (Interior)

There are two ways to clean a flow cell that has become coated with UV absorbing material:

1. Solvent Cleaning
2. Acid Cleaning

1.  Solvent Cleaning

• If you suspect that droplets of an organic-soluble contaminant or immiscible solvent contaminate the flow cell, draw or pump a series of miscible solvents through the cell.
• Either of these solvent series will remove contaminants with a wide range of solubilities:

1. Methanol, then tetrahydrofuran, then methylene chloride, and then methanol again
2. Hexane, then isopropanol, then methanol, then water.

2.  Acid Cleaning

• If you suspect that residual proteins contaminate the flow cell, draw 50% nitric acid through the cell. Acid cleaning is a more thorough technique, though much more care must be taken.

CAUTION! Take all necessary precautions to avoid contact with eyes, skin, clothing, and equipment surfaces.

• Using a 1/4-28 coupler, connect a Luer-lock end fitting to the 1/4-28 fitting on the outlet tubing.
• Attach a large glass syringe to the Luer-lock end.
• Place the end of the inlet tubing into a reservoir of 50% nitric acid.
• Draw nitric acid through the cell.

Note: Do not pump acid through the cell! You should never put acid under pressure. Use nitric acid. Do not use halogenated acid.

• After the acid flush, draw HPLC-grade water through the cell in the same manner.
• Reconnect the column to the inlet tubing. Redirect the outlet tubing to drain.
• Finish by pumping HPLC-grade water to cleanse the last traces of acid.
• To be sure that all acid has been removed, monitor the pH of the final outflow.

Flow Cell Removal/Replacement

• Proper maintenance of the detector includes periodic removal of the flow cell for cleaning. You should remove and clean the cell immediately if a leak occurs at the cell inlet or outlet.

Note: If you have experienced flow cell leakage, you should replace the ferrule on the end of the inlet tubing. 

ALSO READ: What is Peak Tailing?

Remove Faceplate

• Unscrew the thumbscrews on the front panel faceplate.
• Remove the entire flow cell assembly by sliding it towards you. You will feel some resistance as you remove it.
• From the right side of the assembly, you will see:

1. the flow cell, inserted into a rectangular hole
2. the reference aperture, in a circular hole

Loosen Fittings

• Loosen the 1/4-28 inlet and outlet fittings located above and below the flow cell.

Remove/Clean Cell

• Carefully invert the assembly until the cell drops into the palm of your hand. The reference aperture plate is secure and will not drop out.
• Moisten the quartz windows with alcohol or a laboratory cleaning solution. Then wipe the windows with a piece of lens paper or a lint-free towel.
• Clean the inside of the flow cell mounting area with a lint-free towel soaked in alcohol.
• Carefully dry all surfaces of the assembly.

Replace Cell

• Without touching the quartz windows, carefully insert the flow cell into its receptacle.

Note: One corner of the cell is beveled. Be sure to align that edge with the bevel on the receptacle.

• Seat the flow cell firmly. Push the cell as far into the hole as it will go. A poorly aligned flow cell may restrict or block flow.

Secure Tubing

Stainless Steel Inlet Tubing 

• Position a 1/4-28 fitting and a ferrule on the flow-cell end of the stainless steel tubing as shown in the image below. The tubing should extend about 1 mm beyond the ferrule.

• Finger-tighten the inlet fitting. As you tighten the fitting, the tubing will be pushed flush with the end of the ferrule.

Teflon Inlet Tubing

• Position a 1/4-28 fitting and an Omnifit gripper on the flow-cell end of the Teflon inlet tubing as shown in the next image. The gripper should be flush with the end of the tubing.
• Finger tighten the inlet fitting. Then firmly tighten the inlet fitting using a 5/16" wrench (1/8 turn).

Teflon Outlet Tubing

• Position a 1/4-28 fitting and an Omnifit gripper on the flow-cell end of the Teflon outlet tubing as shown in the previous image.

• Finger tighten the outlet fitting. Then firmly tighten the outlet fitting using a 5/16" wrench (1/8 turn).

ALSO READ: SOP for Agilent 1100 HPLC ChemStation

Inspect Flow Cell

• Inspect the quartz window again. If it is dirty, wipe once more with lens paper.

Check Flow

• Before you replace the flow cell assembly with the detector, test the integrity of the inlet and outlet fittings. Reconnect the inlet tubing to your system and initiate flow.
• If you notice leakage from the inlet or outlet fittings, you must remove, clean, and re-install the flow cell.
• Carefully install the fittings as described previously.

Replace Faceplate

• When no leaks are found, replace the flow cell assembly with the detector. Tighten the thumbscrews on the flow cell assembly faceplate. Reconnect the inlet and outlet tubings to your system.

Flow Cell Unclogging

• To try to eliminate a blockage from the cell or inlet or outlet tubing:

Remove Faceplate

• Unscrew the thumbscrews on the front panel faceplate.
• Remove the entire flow cell assembly by sliding it towards you. You will feel some resistance as you remove it.

Pump Solvent

• Very carefully pump solvent backward through the flow cell. Connect a high-pressure pump to the outlet and direct the inlet to waste.

CAUTION: Set the maximum pressure below 300 PSI (20 BAR)!

• Beginning at a flow rate of 0.1 mL/min, gradually increase the flow rate, in increments of 0.1 mL/min.
• A significant pressure drop indicates that the blockage has been removed.

Purchasing Other Flow Cells

• The standard quartz flow cell contains an 11 µL cavity with a 10 mm path length.
• With a choice of several flow cells, you can quickly and easily vary the detection limits and increase the versatility of the detector.
• Assemblies contain a flow cell, a reference aperture plate and tubing of the appropriate inner diameter (ID).

Inlet Tubing Replacement

Note: You should ensure that the inner diameter of your inlet tubing is appropriate for the flow cell that is installed.

• You can purchase pre-bent stainless steel inlet tubing for use with the standard HPLC flow cell [ID 0.010" (0.25 mm)] or with the microbore flow cell [ID 0.007" (0.18 mm)].

Remove Old Tubing

• To remove old stainless steel or Teflon inlet tubing, remove the fitting from the column end.
• Unscrew the thumbscrews on the front panel faceplate.
• Remove the entire flow cell assembly by sliding it towards you. You will feel some resistance as you remove it.
• Pull the old tubing through the inlet hole on the faceplate.

Secure New Tubing

• Push the new tubing through the inlet hole on the rear of the faceplate.

Stainless Steel Inlet Tubing

• Locate a new Upchurch ferrule from the detector accessory package. It is identical to the ferrule you just removed.

• Place the fitting and ferrule on the flow-cell end of the stainless steel tubing as shown in the image above. The tubing should extend about 1 mm beyond the ferrule.
• Finger-tighten the inlet fitting. As you tighten the fitting, the inlet tubing will be pushed flush with the end of the ferrule.

ALSO READ: SOP for Shimadzu LabSolutions

Teflon Inlet Tubing

• Position a 1/4-28 fitting and an Omnifit gripper on the end of the inlet tubing as shown below. Use a razor blade to cut the tubing and a needle-nosed plier to pull the tubing through the gripper.

Teflon Outlet Tubing

• Finger-tighten the outlet fitting. Then firmly tighten the outlet fitting using a 5/16" wrench (1/8 turn).

Check Flow

• Before you replace the flow cell assembly with the detector, test the integrity of the inlet and outlet fittings. Reconnect the inlet tubing to your system and initiate flow.
• If you notice leakage from the inlet or outlet fittings, you must remove, clean, and re-install the flow cell.
• Carefully install the inlet fitting as described above.

Replace Faceplate

• When no leaks are found, replace the flow cell assembly with the detector. Tighten the thumbscrews on the flow cell assembly faceplate. Reconnect the inlet and outlet tubings to your system.

Outlet Tubing Replacement

Remove Old Tubing

• Unscrew the thumbscrews on the front panel faceplate.
• Remove the entire flow cell assembly by sliding it towards you. You will feel some resistance as you remove it.
• Pull the old tubing through the outlet hole on the faceplate.

Secure New Tubing

• Push the new tubing through the outlet hole on the rear of the faceplate.
• Position a 1/4-28 fitting and an Omnifit gripper on the end of the outlet tubing as shown below. Use a razor blade to cut the tubing and a needle-nosed plier to pull the tubing through the gripper.

• Finger-tighten the outlet fitting. Then firmly tighten the outlet fitting using a 5/16" wrench (1/8 turn).

ALSO READ: SOP for ThermoFisher Scientific HPLC (Make: DIONEX, Model: ULTIMATE – 3000)

Check Flow

• Before you replace the flow cell assembly with the detector, test the integrity of the inlet and outlet fittings. Reconnect the inlet tubing to your system and initiate flow.
• If you notice leakage from the inlet or outlet fittings, you must remove, clean, and re-install the flow cell.
• Carefully install the inlet fitting as shown above.

Replace Faceplate

• When no leaks are found, replace the flow cell assembly with the detector. Tighten the thumbscrews on the flow cell assembly faceplate. Reconnect the inlet and outlet tubings to your system.

Lamp Replacement

• Caution! Never touch a hot lamp! After turning off the detector, wait 30 minutes or more before replacing the lamp.
• Before performing the maintenance described below, you must unplug the detector from its power source. Do not remove the cover until you have done this.

Remove Cover

• Remove the cover by removing the four screws from the sides of the unit. Lift the cover straight up.
• Place the detector in front of you, so you are facing the front panel.
• Locate the lamp/filter assembly below and to the right of the white plastic knob (the filter-block release). Use the following drawing as a reference.

• On the right-side panel of the detector is a cut-out that eases access to the lamp assembly.

Disconnect Connector

• The cable from the lamp/filter assembly terminates with a 6-pin connector that is visible at the right side of the unit. Disconnect the 6-pin connector.

Remove lamp/filter assembly

• To remove the lamp/filter assembly,

1. Unscrew and remove the 254/280 wavelength selection knob (standard units only)
2. Lift the white plastic knob and slide the lamp/filter assembly toward the rear of the unit

Detach old lamp (note old lamp type)

• To detach the mercury (or phosphor-coated mercury or 254/280 nm) lamp from the lamp/filter assembly, carefully remove the two screws that secure the lamp to the filter block. Do not touch the surface of the lamp.

Note: If you need to install a new filter, you should do that now, while the unit is dissembled. 

Install New Lamp

• To install a new 254/280 nm lamp:

1. Position the lamp so it is adjacent to the filter. Be sure that the lamp is not inverted relative to the filter block. (The new lamp is pre-aligned in a mounting block.)
2. Secure the lamp to the filter block with two screws
3. Replace the lamp/filter assembly (lift the white knob).
4. Reconnect the 6-pin connector.
5. Route the lamp cord beneath the fan at the rear of the detector.
6. Place the 254/280 nm wavelength selection knob shaft through the front panel hole into the lamp and secure it to the lamp/filter assembly (standard units only).

Replace Cover

• Replace and secure the detector's cover using the four screws you removed earlier.

Filter Replacement

• You must unplug the detector from its power source. Do not remove the cover until you have done this.
• Note: To replace a filter, you will need internal C-ring pliers.
• Unplug the 6-pin lamp connector and remove the lamp/filter assembly as described in Lamp Replacement.
• Using C-ring pliers, remove the C-ring from the circular chamber on the filter block.
• Invert the filter block and let the filter cartridge drop into the palm of your hand.
• Taking care not to touch the optical surface, place the new filter into its chamber. Secure the new filter cartridge with the C-ring.

ALSO READ: Column Restoration Procedures