Flow Transmission Cell Options for Transparent Liquids Follow
A flow through cell can be a handy solution for continuous sampling and ease of measurement with a transparent, liquid product.
HunterLab offers both manual loading and flow transmittance cells in a range of path lengths.
|HunterLab Product Number||Path Length (mm)||Diameter of Measurement Face (mm)||Port OD/ID(mm)||Approximate Cell Volume Needed (mL)|
|D04-1015-179 (manual loading through single top port – no pump needed)||2||51||7/9||15|
Flow Cell Operation
- Two lengths of tubing are attached to the 9-mm OD of the cell port. At each end of the tubing, it is good idea to attach a piece of glass tubing or a dispensing wand to be lowered into a beaker of liquid sample.
- Fit the D02-1009-960 Flow Through Cell Holder in the transmittance compartment against the TTRAN (sphere side) port of the HunterLab sphere instrument.
- Place the flow cell in the holder using the spring-loaded guide to center it flush at the port. The cell is oriented in with the outlet port at the top.
- Loop the bottom length of tubing through the pump head.
- Lower both tubing ends into a beaker filled with distilled water.
- Turn the peristaltic pump on. The pump rubs on the outside of the tubing creating an internal vacuum within the tubing that pulls liquid into the cell. Air is automatically forced out of the flow cell through the top outlet port while liquid sample is drawn into the bottom port.
- The following is an optional but recommended PQ Performance Qualification step. As soon as the flow cycle is complete, take a measurement of the flow cell + DI water in EasyMatch QC. The color values should be L* = 100.0, a* = 0.0, b* = 0.0, Yellowness Index YI = 0. APHA/Pt-Co = 0, closely. If this is the case, the operator is performance-qualified to continue liquid sample measurements.
- Turn off the pump and drain the DI water from the flow cell and place inlet/out tubing into a beaker of liquid sample and make a measurement after the flow cycle is complete. One reading is usually sufficient for a transparent liquid. An averaged timed measurement of 2 or 3 readings is optimal to obtain repeatable measurements.
- To flush the system, turn off the pump and drain the liquid sample.
- Place the glass ends of the tubing into a beaker of water/solvent and cycle using the pump until clean.
Source: Peristaltic Pump and Tubing
For all path lengths, HunterLab flow transmission cells have inlet and outlet ports that are 7 mm ID and 9 mm OD. To keep costs low for this flow cell, the user can purchase any manual pumping system, direct drive or peristaltic (preferred) that will attach to those port dimensions.
Given the small volumes needed to fill these flow cells, a variable rate peristaltic pump has been found to work best. There are three components to a peristaltic pump system – a variable speed drive, pump head and tubing. While other suppliers are acceptable, MasterFlex pumps and tubing from Cole-Parmer have been found to work well and are available world-wide.
- MasterFlex L/S TW 07554-80 Controller Drive for 120V; TW 07585 for Controller Drive 230V has a variable rpm from 7 to 200. The 120V version will handle voltages from 90 volts to 130 volts, 50 or 60 Hz. The 220V version will handle voltages from 180 volts to 260 volts, 50 or 60 Hz.
- MasterFlex L/S Easy-Load 3 Pump Head 3 SS will accept tubing diameters appropriate for a 9 mm OD cell port and provide variable flow rates from 27 to 770 ml/minute.
- Tygon tubing is clear, quite robust, economical and has good product life as peristaltic tubing. It has an operational temperature range of -50 to 74 degrees C. MasterFlex 06509-18 Tygon LS/18 tubing (PVC-based) or HV-96419-18 Puri-Flex LS/18 tubing should provide a snug fit on the 9 mm OD cell port. If a higher sample operating temperature is required, other types of tubing can be used.
- MasterFlex 30619-09 size 36 Stainless Steel Dispensing Wand or less expensive 40610-02 Plastic Straight Connecting Barbed Fitting may be helpful in placing the tubing end into the beaker of liquid sample.
FAQ: "What applications do you use the flow cell option with?"
Flow cells will work with any situation where you are trying to automate measurements of transparent liquids. The best applications tend to be water-based for easy flushing, but mild chemical solvents like methanol can also be used. The application areas where we have sold several systems are
- Beverages such as colas and wine where fast measurement is a priority.
- Chemicals such as bleach and acids where the concern is to minimize operator exposure.
A key element is that you have to use a solvent to flush the system. A flow cell will not work with a sticky sample were the solvent flow will not completely clean the cell.
FAQ: HunterLab Sales Representative comments on Flow Cell Operation
"My initial suggestion to them was to include a pump with both tubing ends in a beaker of liquid product (http://www.masterflex.com/). That way the sample could recirculate. Or switch beakers. Then rinse with water then take the next sample. This worked effectively with a large wine producer."
"My customers who use the flow cell have 3 beakers, one with their product, one with water, one empty for waste. They use a hand pump (rubber squeeze balls) or low pressure peristaltic pumps and fill up the cell as overflow goes to waste through exit tube until filled cell with no air. They then clamp the exit tube. Then the entrance and read sample. No need to close door on the sphere sensor or a slot cut-out can be made in the transmittance door for the entrance and exit tube. They then squeeze or vacuum pump out the read sample to waste beaker and run water through to clean. In the case of one my chemical companies, they run an alcohol through like methanol.
These guys do it several times a day easily and no big issues. Also, remember, if the product covers the bottom 75% of the cell and air in the top part, the light path is probably seeing product only and it really doesn’t matter that a little air is in the system at the unread top part of the cell. But to be safe, I understand their desire to have a full cell with no air.
Again, I may be all wet on this but I really do have several users of flow through and they have all done it very easily as a bench top, and off a live stream."
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