Betty Petrillo, Product Specialist with Anton Paar, talks to AZoM about the new Litesizer™ 500, an instrument that gives a rapid and accurate insight into particle systems.
Could you please tell our readers why Anton Paar developed the Litesizer 500 and what it aims to address?
Anton Paar is a leading developer and manufacturer of high performance analytical instrumentation, constantly working to develop newer and better products.
With this in mind, we decide to expand our portfolio by introducing the Litesizer™ 500, an instrument that gives a rapid and accurate insight into particle systems; measuring particle size, zeta potential and molecular mass by light scattering technology with simple, easy to use software.
Figure 1. Litesizer™ 500
How has the novel omega-shaped zeta-potential cuvettes enabled highly stable and reproducible measurements compared to the more standard U-shaped tube?
Our R&D team has investigated the performance of the commercially available, traditional, U-shaped cells against the new Ω-shaped cells developed by Anton Paar. They demonstrated that when applying an electric field, the field remains constant in the omega cell but changes significantly in the U-shaped cell, depending on the measurement position within the capillary. The Ω-shape means that ELS measurements are independent of the measurement position because it facilitates a homogeneous electric field within the measuring channel. Thus, the results are highly stable and reproducible.
Figure 2. Omega cuvette
How has the development of cmPALS allowed for measurements with shorter duration and with lower electric field applied?
Zeta potential is a key indicator of colloid stability. The higher the magnitude of the zeta potential (that is, highly positive or highly negative), the more stable the colloid. A lower-magnitude zeta potential indicates a less stable colloid; in other words, the colloidal particles will tend to aggregate or coagulate. Thus, knowledge of zeta potential is important for optimizing processes and for quality control.
Our research team has developed a new patented technology called cmPALS (EP2735870) incorporated in the Litesizer™ 500 that results in dramatic enhancements in the sensitivity and stability of zeta-potential measurements.
The newly patented method, "continuously monitored PALS" (cmPALS) is a modification of PALS in which an additional modulator monitor is implemented. This extra modulator monitor detects the interference between the modulated and un-modulated (reference beam) laser light, thus, its beat frequency is solely the modulation frequency and is therefore independent of the electrophoretic motion of the particles. In other words, the frequency difference between sample interference and modulator monitor is exactly the Doppler shift caused by the electrophoretic motion of the particles. Any non-linearity of the modulator is automatically compensated, and does not influence the results. The quality of the results is also not affected by any longer-term deterioration in the modulator performance. Thus, the advent of cmPALS means that modulators with large movements can be used, despite their non-linearities. As a consequence the sensitivity and stability of laser Doppler electrophoresis measurements can be significantly enhanced because measurements of substantially shorter duration and lower electric field applied become feasible.
What differences does the Litesizer 500 offer for zeta-potential measurements?
The Litesizer™ 500 enables the ELS analysis of more sensitive samples because the user can keep the electric field as low as possible and apply it for as short a time as possible to reduce heating and decomposition, while still producing precise and reliable results.
In one of our technical notes we present a comparison of results between our device based on the cmPALS technique and a PALS instrument. The results show that cmPALS produces results with increased precision in a substantially shorter measurement time than that required by the PALS instrument.
The performance of cmPALS vs PALS was also tested at low electric field by measuring the zeta potential at decreasing voltages. At the lowest voltage, the Litesizer™ 500 measurements are still fast and also show a low standard deviation. In contrast, measurements with the PALS device take much longer and the standard deviation remains higher. Thus, the cmPALS measurements show better repeatability and are much faster than the PALS measurements.
How does the Litesizer 500 allow users to gain instant insight into the suitability of the sample for light scattering measurements?
In addition to dynamic, electrophoretic and static light scattering, the Litesizer™ 500 can measure the continuous transmittance for every sample. Transmittance measurements provide information about the sample transparency, and hence the degree of multiple scattering, allowing the user to get instant insight into the suitability of the sample for light scattering measurements. In addition, it enables the Litesizer to select the best measuring parameters for the material under analysis in terms of measurement angle and focus position.
How does the Litesizer 500 use SLS to measure the molecular mass of a sample?
The Litesizer™ 500 can be used in static light scattering mode to measure the absolute molecular mass of proteins, small particles, and polymers. The scattered light intensity of several sample concentrations c are measured at a single angle (90 °) and the results are then used to generate a Debye plot and the intercept of the Debye plot is used to determine the molecular mass and the slope is used to calculate the second virial coefficient.
How does the Litesizer allow users to resolve several different particle sizes in a single suspension?
One of the highlights of the Litesizer™ 500 is its capability to resolve multiple particle sizes in suspensions. Although many bi-disperse samples have been successfully characterized with various instruments on the market, to our knowledge there have been no reports of a mix of three particle sizes with a high level of accuracy (see Figure below).
Figure 3. Size (radius) distribution of sample 3, a tri-disperse polystyrene latex sample containing particles of 22, 100 and 700 nm
The improved resolution of the Litesizer 500 is due to a different method for data processing. This means that poor data are weighted in ways that have minor importance for the curve fitting. If the data are very noisy at low or very high correlation times, they are even cut off.
This noise reduction allows us to lower the "regularization parameter" which leads to more narrow distributions and hence separation of broad peak into individual ones.
Can you tell us about any case studies that you are particularly proud of?
We have established a long-lasting cooperation with Prof. Zimmer at Graz University and we are very proud of the preliminary results obtained with the Litesizer™ 500. The current study is aimed to develop miRNA drug-delivery systems that may represent a new therapeutic strategy to prevent metabolic complications associated with obesity. The first step of the project was to investigate the influence of different mass ratios (miRNA:protamine) on the nanoparticle assembly in terms of size and stability. These physicochemical properties were determined by using dynamic light scattering (particle size) and electrophoretic light scattering (zeta potential) and precise results were achieved using the Litesizer™ 500, despite the very low sample concentrations and low volumes.
How do you plan on developing the Litesizer 500 further?
Anton Paar works closely to the scientific community to provide highly precise devices and solutions to make their daily life in the laboratory easier. Therefore, we will soon introduce new accessories and features of the LitesizerTM 500 that will still be simple to operate while providing the most accurate results.
Where can our readers learn more?
More information about LitesizerTM 500 can be found on our website (http://www.anton-paar.com/corp-en/products/details/litesizerTM-500/) and also on other social networks, like Twitter and LinkedIn.
About Betty Petrillo
Betty Petrillo joined Anton Paar GmbH in 2013 as product specialist in Particle Characterization and as part of the development team for the Litesizer 500.
In the previous years, she worked at Thermo Fisher Scientific as European instructor on GC/GC-MS in 2008 and then she was appointed service manager in Italy in September 2010.
Mrs Petrillo has an Msc in pharmaceutical chemistry from Naples University (Italy) and a PhD in polymer chemistry and drug delivery from Cardiff University (Uk).
She is now candidate for an executive MBA at Politecnico of Milan.
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