Polarimeter Sample Cells: Better By Design
Many Rudolph Polarimeter Cell designs offer significant advantages over traditional fused end glass cell designs as shown in Picture B. All glass, polarimeter cells are easily broken and often build up optically active residue on the inside of the glass ends. Also these cells do not have built in apertures so the light passing through the sample is easily affected by small air bubbles caught inside the cell as shown in Picture B. Rudolph does offer this style cell for those customers who prefer a fused glass end cell for use in their polarimeter or saccharimeter but doesn’t recommend them.
Rudolph Polarimeter Cells with built in apertures eliminate these problems because the stainless steel screw ends have apertures that are smaller than the internal diameter of the cell body to avoid the problem of the light being disturbed by small air bubbles along the surface of the cell. This design results in better optical rotation measurement stability (Figure 2).
As shown below, the screw caps have precision apertures which reduce the beam diameter to less than the internal diameter of the cell so that, when the cells are aligned with the beam, internal sidewall reflections and consequent depolarizing effects are minimized.
Polarimeter Samples Cells that are easy to clean
Another advantage over fused end cells is that screw caps, washers, and end plates are easily removed for cleaning the glass ends, sample cell interiors, or for replacement of the washers and end glass. To reassemble the cell requires following the configuration of Figure 2 and then applying finger tight pressure to the screw caps. As the screw caps are turned, the washers are compressed against the end glass creating a leak proof seal with the precision ground cell ends. Minimal screw cap pressure and the compressibility of the washer ensures a tight seal without causing stress induced birefringence in the glass end plates.
Sample Cell Selection
Cells That Meet Your Application
With over 50 cells to choose from, Rudolph Research Analytical has a cell to meet every application.
Rudolph Autopol™ Polarimeters Accept Sample Cells from 10mm to 200mm Long
Some polarimeters accept only special sample cells, with maximum lengths of 100mm. Rudolph’s Autopol™ accepts cells up to 200mm long. A 200mm sample cell offers twice the sensitivity when measuring the same solution in a 100mm cell. This additional optical path length is especially useful for solutions that have a small optical rotation. For precious samples and essential oils that have a large optical rotation, cells with only 0.05ml volumes and 10mm optical path lengths are available.
Access through gasketing in the top of the sample trough easily allows connection to a process stream (Figure 3). Readings can be downloaded via RS232 to a computer at fixed intervals or when prompted by an operator or an ASCI II command. Custom cells with special Swagelock® ferrules and fittings, and NEMA enclosures (as shown below) are available to allow connection to process streams.
Figure 3: Continuous Sampling Picture C: Pour In Sampling With Temperature Correction Picture D: Micro Volumes for HPLC
Sample solutions are either poured, injected with a syringe or pipetted into the center well, side well or side tubulation. Air bubbles are released by tilting the cells side to side or to one side while filling. Flexible tipped pipettes capable of reaching from the center well to either end of the sample can be helpful in filling narrow bore center fill cells.
Micro Volumes for Chiral Detection After HPLC
If your application demands 1ml or less, Type 32 Cells offer less than 0.5ml volumes. These cells come standard with HPLC fittings which transform your polarimeter into a chiral detector when connected to a chiral column after HPLC (Picture D).
Pour In Sampling Capability
Rapid operation is achieved by using a Type 31 or 33 Flow Through Polarimeter Sample Cell as seen in Picture C. Once the sample cell is filled, each successive sample poured into the funnel will displace the previous sample through the drain tube. This method eliminates opening and closing the polarimeter or saccharimeter sample chamber door and interchanging sample cells. Measurements can be made about as rapidly as successive samples can be poured.
For sucrose or other high volume applications where the temperature coefficient is known, a 33 Cell can be used as in Picture C. This cell has a built-in temperature port which, when the temperature probe is inserted, automatically measures the sample temperature inside the cell and sends the temperature to the Autopol™ IV or Autopol™ 880 for correction to 20°C, 25°C or any customer specified temperature.
Two Sample Temperature Control Solutions
Patented TempTrol™ Technology Eliminates the Need for a Water Bath
TempTrol™ heating and cooling transfer surface in the measurement trough of the Autopol™ Polarimeter.
Temperature is selected via an easy to read and easy to operate, LCD Touch-Screen.
TempTrol™ cell with mating heating and cooling transfer surface.
Place the Rudolph TempTrol™ cell in your TempTrol™ equipped Autopol™ IV or V sample chamber to measure to within ±0.2°C of the USP, EP, JP, or BP specified temperature (normally 20°C or 25°C ±0.5°C)
Rudolph provides a temperature validation cell with every TempTrol™ system. The temperature validation cell along with an optional NIST traceable thermometer is designed to validate the temperature control performance of the polarimeter and cell to ±0.2°C.
Sample Temperature Control With Water Bath
As seen above, almost all Rudolph Research Analytical jacketed cells come standard with quick release fittings which allow cells to be easily removed from the polarimeter or saccharimeter sample chamber. Tubing is held in place by rubber gasketing on top of the trough and the door. Optional stopper (choose “S” after the cell part no.) for evaporative samples (Picture A).
Temperature control is obtained through the use of an external water bath and a jacketed cell (Figure 1).