BI-MwA Molecular Weight Analyzer for GPC/SEC Calibration

Characterization of dilute polymer solutions using static light scattering (SLS) is now easier and more accurate with better value. The BI-MwA uses a 30 mW, 660 nm diode laser and seven angles to establish the intensity of scattered light as a function of angle and polymer concentration. Based on this information, one of the three plots is developed with the basic BI-MwAZP software: Berry, Zimm, or Debye.

From such plots, calculation of the root-mean-square radius (radius of gyration), R_g, the weight average molecular weight, M_w, and the second viral coefficient, A2, can be done. The BI-MwA can be used in flow or batch mode, as a chromatography detector, or for following the kinetics of polymerization using time-dependent static light scattering (TDSLS). Overall, the BI-MwA ideally has the maximum performance/price ratio of any light scattering detector employed for M_w determination.

• Proteins
• M_w of polymers
• Natural and synthetic
• Study aggregation

Why Seven Angles?

A single, low angle is adequate, theoretically, to establish Mw. But, calibration is still needed without dust or flare light interfering. This necessitates an extra 90° measurement. A minimum two angles are needed to establish R_g from a straight line fit. However, two points always establish a straight line, without any room for error. Thus, three angles are the absolute minimum for a least squares fit. What if dust alters one of the angular intensity values? What if more accuracy is needed? For these reasons, the basic BI-MwA optical configuration comprises of seven angles. Other configurations can be availed upon request.

Figure 1. Static Light Scattering: Zimm Plot for M_w

Rugged Design, Small Footprint

About a polymer handbook size, the BI-MwA design avoids the drawbacks of similar machines. The flow path is vertical, not horizontal, shunning trapped bubbles. There are no sharp corners within the cell, just conical shapes. Earlier solutions are more effortlessly flushed. The cell can endure much greater pressures than previous instruments of this type, up to 3.5 MPa, reducing the chance of a costly repair.

Unique Microcontroller and Detector Design

The exclusive microcontroller used in the BI-MwA supports four analog inputs as basic, 16 optional, all having 24-bit resolution. Two-way communication is achievable using a USB port. The BI-MwA is fully re-programmable via flash memory. In this manner, as necessities vary, so does the instrument with least bit of effort. The ultra-sensitive CCD detector is consistent in its response, and, together with the microcontroller, permits automatic gain adjustment across many decades of scattered intensity. The cell can endure much greater pressures than previous instruments of this type, up to 3.5 MPa, reducing the chance of a costly repair.

Applications

The BI-MwA is suitable for exploring natural and synthetic polymers in solution, including polysaccharides and proteins. It allows examination of oligomerization, stability, aggregation, complex formation, and conformation. SLS is an absolute method for M_w determination; while, viscosity measurements need calibration and too many assumptions about the polymer/solvent system that may not be correct in a specific case. Even shape may be established in certain cases by plotting log M_w vs log R_g. The slope of the line can show whether the molecule is coiled, rod-like, or spherical.

Specifications*

*A policy of continual improvement may lead to specification changes.