Transmission Cells - an04_95r3 Follow

Please note that this is an archived application note and not all information may be current or up to date. If you have any questions regarding parts please reach out to the HunterLab Customer Experience team.

There are several types of transmittance cells available for containing samples while measuring the color of transparent liquids using HunterLab sphere instruments.

• HunterLab Glass Cells - rectangular, multiple path lengths, open top and capped, no compromise in performance

• Molded Glass Cells - rectangular, rugged, best for hot solutions, suitable for heating

• Plastic Cells - 20-mm Path Length, rectangular, come with caps, disposable

• Plastic Cells - 10-mm Path Length, rectangular, open top, disposable

• HunterLab Glass Flow Through Cells - multiple path lengths, for automatic operation

• HunterLab Small Volume Glass Cells - 10-mm path length, 5 mL volume of sample

• Round Glass Vials - 24-mm path length, rugged, suitable for heating, disposable

• Analytical and Semi-Micro Cells - 10-mm and 20-mm path lengths, glass or disposable plastic, open or capped, very small sample volume needed.

HunterLab Glass Cells - Open Top and Capped
The best measurement performance is achieved when HunterLab glass transmittance cells are used, as they are custom manufactured to HunterLab's specifications. Each cell is made of optical quality glass and is a three-piece construct that is first fused glass-to-glass, then annealed. Solvents will not affect these cells, as the three components are fused together at the edges, not glued. They have two flat windows and a U-shaped spacer that is abraded to minimize internal reflectance. HunterLab Quality Assurance monitors the path length, dimensions, and flatness of these cells. For critical measurements, these glass cells are recommended.

(illustrations)

FAQ: 'Can these cells be heated?' 
These cells, with sample contents, can be heated to a temperature of 275°C without injury provided the heating method is even and gradual (not directional heating like a hot plate). An air-circulating heater and gradual gradient heating are recommended at temperatures near the limit of 275°. To avoid condensation, liquid samples should be heated to those temperatures in the cell or else the cell should be preheated before adding the hot sample.

Molded Glass Cells for Hot Solutions
Unlike the three-piece construction of HunterLab cells, these Pyrex glass cells are produced by a one-step tubular injection molding operation on a stainless steel (Class A) mandrel. The molded construction makes them more robust for holding hot solutions. Another application is the heating of crystalline powders in these cells to a liquid form. Then the cell is transferred to a transmittance holder for measurement.

These molded glass cells are:

• Physically rugged for the measurement of hot solutions due to their molded construction.

• Rectangular in shape with standard path lengths.

• All molded cells will fit on the C02-1005-481 Transmittance Cell Holder or D02-1011-568 Transmittance Spill Tray and Cell Holder in the transmittance compartment of all HunterLab sphere instruments.

• These molded cells have performance characteristics (finish, repeatability, and reproducibility) that, while not as optimal as HunterLab glass cells, are acceptable for many applications.

• There is some thickness variation in the outside wall of these cells that can result in haze readings that are 2 haze units higher than those read using HunterLab cells. As an extra service, SGI will grind the outside faces of these cells. This will minimize the wall distortion and improve the haze measurement agreement with HunterLab transmittance cells.

Cells are available from:

SGI - Scientific Glass & Instruments, Inc. 2521 Fairway Park Drive, Suite 404 Houston, TX 77001
TEL: (703) 682-1481
FAX: (713) 682-3054
NET: www.sginstr.com

(data table)

Disposable Plastic Cells - 20-mm Path Length
Tissue culture flasks made of clear polystyrene with screw-on caps for volatiles can serve as inexpensive transmittance cells that are especially useful when measuring samples that are difficult to clean up or handle. These cells are also handy when large numbers of measurements are being made.
The performance of these cells is not as optimal as that of the HunterLab glass cells but is appropriate when the need for a disposable cell outweighs the small compromise in performance.

(illustration and Part # tables)

FAQ: 'Can these cells be used to measure opaque liquids or powders in reflectance?' 
Yes, the 10-mm plastic cells will cover the reflectance port using the sample clamp to position the cell and keep the cell flush at the port while maintaining a constant surround using the white ceramic backing if the sample is not fully opaque.

It is recommended that you standardize in RSEX LAV (Reflectance Specular Excluded, Large Area of View) mode to negate the specular reflectance off the plastic window from the measurement. The absorbance of the plastic window will still be part of the measurement, but it is a constant and less than 1% absorbance.

HunterLab Glass Flow Through Cells
A flow through cell can be handy for continuous sampling or ease of measurement with a transparent liquid product.

• All flow cells will fit in the transmittance compartment of all HunterLab sphere instruments using the D02-1009-960 Flow Through Cell Holder.
• The construction of the cells is clear annealed borosilicate, which can be heated (including the sample) in a water bath to 100 degrees Centigrade with no difficulty.
• The flow cells are aligned vertically in the holder and fed from the bottom to minimize air bubbles.
• The inlet and outlet ports are 7-mm ID and 9-mm OD to permit a high flow rate with port continuity at all path lengths so that the same tubing and pump can be used.

You will need to purchase tubing and a peristaltic pump appropriate for your needs from non-HunterLab sources. Tygon tubing is clear, robust, and has good product life as peristaltic tubing. Peristaltic pumps such as the MasterFlex line are acceptable. Both products are available from Cole Parmer (www.coleparmer.com). 

Flow Cell Operation
A length of tubing is attached to the 9-mm OD of each of the two cell ports. At the other end of each length of tubing, it is good idea to attach a piece of glass tubing to be lowered into a beaker of sample liquid. Place the flow cell in the D02-1009-960 holder. Turn the peristaltic pump on. The pump rubs on the outside of the tubing, creating an internal vacuum within the tubing that sucks liquid through and into the cell. The cell is oriented in the D02-1009-960 Flow Through Cell Holder with the outlet port at the top. Air is automatically forced out of the cell as the liquid comes in. As soon as the flow cycle is complete, a measurement can be taken. To flush the system, turn off the pump, place the glass ends of the tubing into a beaker of water/solvent and cycle until clean.

FAQ: 'What is the advantage of using the 2-mm flow cell?' 
Some liquid samples are so highly absorbing or translucent such that little light from the instrument's lamp can get through in transmittance. By using a very thin 2-mm path length with these samples, it is possible to differentiate lot differences in color that would not be possible with a regular path length cell.

• HunterLab Part # A13-1011-613 is a practical small volume transmittance cell for transmittance color measurements that was developed to measure the color of small volumes of very expensive development drugs in the pharmaceutical industry. It is a small, optically clear, manual loading,
10- mm path length round cell with a screw top.
• A13-1011-613 includes both an inject-a-cell top (that allows you to use a needle to load the cell through an injectable silicone membrane in the cell top) and second solid propylene top (good for volatile samples).
• A special D02-1011-886 Transmittance Holder is needed to hold these small volume round cells at either the TTRAN or RTRAN port.
• This 10-mm path length round glass cell has an OD of 28-mm and an ID of 25-mm which just covers the transmittance port. If you fill the cell to the top, 5-mL of sample is needed. If you fill the cell to the bottom of the screw top above the viewed sample area, the volume required is 4-mL of sample. By comparison, the standard rectangular HunterLab 10-mm cell uses 20-mL of sample.
• The throat has a 12-mm OD and an 8-mm ID, allowing the cell to be loaded with a pipette or needle.
• The 10-mm path length allows you to standardize to top-of-scale (100% transmittance) using the cell with distilled water as a blank, and yet still have sufficient path length to differentiate small amounts of chromofores in near-clear liquids, as well as measure the APHA/PtCo/Hazen color scale if desired.

Disposable Round Glass Vials - 24-mm Path Length
These round vials have the advantage of being made of borosilicate glass appropriate for corrosives. They come with caps to handle volatiles and are sufficiently cost effective to be disposable or recyclable.

• The HunterLab D02-1011-550 Transmittance Holder for 27 - 30-mm Vials positions the curved surface of the round glass vial consistently for measurement at the TTRAN port.
• The D02-1011-550 holder accepts all 20 mL, 40 mL and 60 mL round glass vials and fits in all HunterLab sphere instruments. There are 4 user-adjustable screws in the holder that can be employed to ensure that the vial does not wiggle in the holder.
• The 40-mL (1 1/3 oz) borosilicate glass threaded vial with a 27, 28 or 29-mm OD and 61-mm height is recommended for general use as a round disposable glass transmittance cell on HunterLab instruments.
• The 20-mL (2/3 oz) version is recommended for small sample volumes. These vials will fit in the transmittance compartment of the ColorQuest XE, ColorQuest XT, UltraScan XE, UltraScan PRO, or UltraScan VIS with the door closed.
• There is also a 60-mL high vial of the same diameter that fits above the door for exterior venting or external loading if required. The 60-mL size is recommended for measuring the color of hot solutions, as the extra height allows the tube to be more easily grasped by a set of tongs.
• In all cases, the internal diameter is 24-mm, defining the sample path length.
• These round tubes work well when the material must be centrifuged for mixing or separating, or if the materials need to be heated. The polypropylene caps and molded borosilicate glass can be autoclaved up to their melting points (450 degrees C), provided the heating and cooling is done slowly at a rate of 50 degrees per hour or less. There is the potential for cracking if the temperature is raised/lowered to high levels at rapid rates. For lower temperatures (< 150 degrees C), heating and cooling should be no problem.

Round glass vials can be ordered from:

Qorpak
Corporate One West
1195 Washington Pike Bridgeville, PA USA 15017-2808 TEL: 800-922-7558
TEL: 412-257-3100
FAX: 412-257-3001
NET: www.qorpak.com

Vial Options include:  

• Polypropylene caps in solid polypropylene and injectable silicone septa are available assembled with the vials or separate.
• A variety of internal cap liners can also be chosen, including metal, foamed polyethylene, polyethylene, vinyl and Teflon (minimal chemical reaction) disc liners.
• Individual barcode labels can be affixed for sample identification.
• There are a variety of cleaning procedures (vacuum ionization, particulate washing, and gamma sterilization) that can be done to ensure that there are no residual particulates (dirt, dust, carton lint, fine glass particulates, bacteria) or film (bottle release agents, aerosols, oil) on the glass surface. The most cost-effective is to order vials that are cleaned but do not have a certificate enclosed with each box. This provides an EPA-cleaning without the additional cost of certification.
• Some suppliers also have the same products available in HDPE: high-density polyethylene.
• These vials usually come shrink-wrapped with 72 or 144 in a case.

(See attached PDF fil for the complete article with illustrations, part numbers, and data tables).

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