Molecular Weight Analyzers
Particle Size Analyzer
Features at a glance
Rapid, Reliable and Accurate Analysis
The new 90Plus Particle Size Analyzer incorporates all you need for fast, routine, sub micron measurements. Based on the principles of Dynamic Light Scattering (DLS), most measurements only take a minute or two. Choose from the standard 35 mW laser for strong scatterers, or the avalanche photo diode for weak scatterers. And, at the time of manufacture, or as a future upgrade, add the BI-Zeta option for zeta potential measurements.
Two Scattering Angles: Most measurements will be made at the 90° scattering angle, however, the user may select the 15° detection angle where measurements are more sensitive to larger particles.
Principles of Operation
Dilute suspensions, on the order of 0.0001 to 1.0% v/v are prepared, using suitable wetting and/or dispersing agents. A small ultrasonicator is sometimes useful in breaking up loosely-held agglomerates. Two or three mL of suspension are required to make the measurements. Disposable, acrylic square cells are used for aqueous and simple alcohol suspensions. Disposable, glass round cells with reusable Teflon stoppers are used for aggressive solvent suspensions. Just a few minutes are required for the sample and cell to equilibrate with the actively controlled temperature environment inside the 90Plus. A square glass cell is available if desired and a special small-volume cell may be used to reduce the volume of material needed to just 150 µL or less. For aqueous samples this sample volume may be reduced to 50 µL with a new option , in both cases the sample is recoverable. For very small particles the high-sensitivity BI-APD detector is invaluable.
Perhaps the most important benefit for users is the reproducibility from sample-to-sample, operator-to-operator, and instrument-to-instrument. The figure below shows the results obtained for a polystyrene latex. Notice the Std. Error of the Effective (or Average) Diameter is less than 1% of the mean of the 10 repeated runs; the duration of each run was only five minutes. Such excellent repeatability is typical of the 90Plus for even routine QC analysis and ensures product quality time-after-time.
The following table shows several aspects of the inter-instrument repeatability found with routine Brookhaven dynamic light scattering equipment. To test the reliability of the information obtained with Brookhaven Instruments a customer subjected five instruments in five locations with different operators and using four different samples to examination. The tabulation below shows excellent reproducibility with recognized standard materials and superb internal agreement. You can be confident of the results you get with your 90Plus!
The 90Plus Particle Size Analyzer offers three choices. For routine determinations an average diameter (Eff. Dia.) and a measure of the distribution width (Polydispersity) are sufficient for many applications. This is illustrated above for the latex with a narrow size distribution. The second choice is to fit these values to a lognormal distribution, allowing the user to visualize the size distribution and to interpolate cumulative and differential results at 5% intervals.
Results from Test Bimodal Sample on 90Plus (diameters, in nm)
The figure above shows an example of the third choice, suitable for more complicated, multimodal size distributions. Here, a numerical algorithm, including Mie theory, is used. These results are for a mixture of known latex particles. Positions of the measured particle sizes on the accompanying graph are in excellent agreement with the known sizes of 98 and 270 nm.
During a measurement, the display can be switched interactively between any one of these — correlation function, lognormal, or multimodal — each shown “live” as data are accumulated. The live display is particularly useful in determining the end-point of a measurement where multimodal distribution shape may be important
Statistical Process Control
At the heart of process and quality control is the ability to measure, record, and track changes using statistical analysis. With the 90Plus, this procedure is now straightforward. Individual files, stored in user-defined folders, are simply marked for inclusion in a SPC chart. Files can be sorted by date/time or batch numbers. An SPC chart is automatically constructed using the mean and +/- 3 sigma (Std. Error) for the upper and lower control limits (UCL/LCL).
Alternatively, the user may select the mean and limits based on prior experience.
The Windows™-based software in the 90Plus allows the user to export the SPC chart into their favorite program. Of course, a direct printout is also available. The figure below shows a typical SPC chart for 18 runs. For this particular material the limits were manually set at 2 nm from the mean.
SPC Chart Display Selected on 90Plus
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