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Postnova model 3621 Multi-Angle Light Scattering (MALS) detector

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Date of creation: 
1 October 2015
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Postnova 21-angle Multi-Angle Light Scattering (MALS) detector - the ideal detector for ultra-high molar mass

The Postnova 21-angle MALS detector has been especially developed for coupling with FFF systems – to the opposite of previously available MALS detectors which were designed with chromatography (SEC/GPC) in mind, that is for smaller molar mass.

Some unique features of the Postnova Multi-Angle Light Scattering (MALS) detector

• Highest number of angles and lowest working angles
• Best possible extrapolations when Debye plots are curved
• Most precise and accurate determination of molecular weight and radius of gyration for ultra-high molar mass

Laser design

The model 3621 MALS detector uses a high performance laser at 532 nm with a highly coherent collimated beam design. The 50 mWatt power exceeds the power of normal lasers in the 658 — 810 nm range as the power is proportional to 1 / λ4.  This provides an exceptional laser performance compared to conventional MALS which are not giving Rg values below 15 nm. This is the reason why Postnova are using a high performance pumped green 532 nm laser instead of a simple standard red laser diode, because with lower wavelength you can access lower sizes for Rg values going in the direction of 6-8 nm (depending on the sample, dn/dc and concentration).

Nanoparticle mix
Peak 1:   Rg = 6.3 nm
Peak 2:   Rg = 17 nm
Peak 3:   Rg = 33 nm
Peak 4:   Rg = 136 nm  

Measurement angles

The model 3621 features 21 static light scattering measurement angles. The following angles are used: 7, 12, 20, 28, 36, 44, 52, 60, 68, 76, 84, 90, 100, 108, 116, 124, 132, 140, 148, 156 and 164 degree.
Angle positioning

Angle positioning has been optimized to allow the most linear portion of the Debye fit for mass and size determinations, thus improving precision and accuracy without relying on model fits. The model 3621 design requires that, among the 21 detector angles, there are 14 angles between 7 and 108 degrees to achieve an optimal extrapolation to zero angle.
Reliable measurements at a 7 degree angle

7 degree measurements are considered extremely difficult to achieve by MALS but the model 3621 is capable of making these measurements.