BI-MwA0 pages

■ MW of polymers ■ N atural & synthetic ■ P roteins ■ Study aggregation A New Beginning Characterizing dilute polymer solutions using static light scattering (SLS) has never been easier, more accurate, or a better value. The BI-MwA uses a 30 mW, 660 nm diode laser and 7 angles to determine the intensity of scattered light as a function of angle and polymer concentration. From this information one of three plots is constructed with the standard BI -MwAZP software: Zimm, Berry, or Debye. From such plots the weight-average molecular weight, Mw, the root-mean-square radius (radius of gyration), Rg, and the second viral coefficient, A2, are calculated. The BI-MwA can be used in batch or flow mode, as a chromatography detector, or for following the kinetics of polymerization using TDSLS, time-dependent static light scattering. Best of all, the BI-MwA has the highest performance/price ratio of any light scattering detector used for Mw determination. Why Seven Angles? A single, low angle is sufficient, theoretically, to determine Mw. However, calibration is still necessary without dust or flare light interfering. This requires an additional 90° measurement. At least two angles are required to determine Rg from a straight line fit. However, two points always determine a straight line, with no room for error. Therefore, three angles are the absolute minimum for a least squares fit. What if dust distorts one of the angular intensity values? What if more accuracy is required? For these reasons the standard BI-MwA optical configuration has seven angles. Other configurations are available on request. Rugged Design, Small Footprint About the size of a polymer handbook, the BI-MwA design avoids the pitfalls of similar machines. The flow path is vertical, not horizontal, avoiding trapped bubbles. There are no sharp corners inside the cell, only conical shapes. Previous solutions are more easily flushed. The cell can withstand much higher pressures than earlier instruments of this type, up to 3.5 MPa, minimizing the chance of an expensive repair. Unique Microcontroller and Detector Design The unique microcontroller used in the BI-MwA supports four analog inputs as standard, 16 optional, all with 24 bit resolution. Two-way communication is possible using a USB port. The BI-MwA is completely re-programmable via flash memory. In this way, as requirements change, so does the instrument with a minimum of effort. The ultra-sensitive CCD detector is uniform in its response, and, coupled with the microcontroller, allows for automatic gain adjustment over many decades of scattered intensity. The cell can withstand much higher pressures than earlier instruments of this type, up to 3.5 MPa, minimizing the chance of an expensive repair. Applications The BI-MwA is ideal for studying synthetic and natural polymers in solution, including proteins and polysaccharides. Investigate oligomerization, complex formation, aggregation, stability, and conformation. SLS is an absolute technique for Mw dtermination; whereas, viscosity measurements require calibration and too many assumptions about the polymer/ solvent system that may not be true in a particular case. Even shape may be deter-mined in some cases by plotting log Mw vs log Rg. The slope of the line can indicate whether the molecule is coiled, rod-like, or spherical.