Technique for measuring our samples

Dynamic light scattering (DLS) is a technique in physics that can be used to determine the size distribution profile of small particles in suspension or polymers in solution. When light hits small particles, the light scatters in all directions (Rayleigh scattering) as long as the particles are small compared to the wavelength (below 250 nm). Even if the light source is a laser, and thus is monochromatic and coherent, the scattering intensity fluctuates over time. This fluctuation is due to small particles in suspension undergoing Brownian motion, and so the distance between the scatterers in the solution is constantly changing with time. This information received can be used to calculate different measurements of the fluid.

Nanoparticle tracking analysis (NTA) is a method for visualizing and analyzing particles in liquids that relates the rate of Brownian motion to particle size. The rate of movement is related only to the viscosity and temperature of the liquid; it is not influenced by particle density or refractive index. NTA allows the determination of a size distribution profile of small particles with a diameter of approximately 10-1000 nanometers (nm) in liquid suspension. The technique is used in conjunction with an ultramicroscope and a laser illumination unit that together allow small particles in liquid suspension to be visualized moving under Brownian motion. The rate of particle movement is related to a sphere equivalent hydrodynamic radius as calculated through the Stokes–Einstein equation. The technique calculates particle size on a particle-by-particle basis, overcoming inherent weaknesses in ensemble techniques such as dynamic light scattering. 

NTA adoption is more advantageous for the following reasons:

• NTA (10-2000nm) can detect samples 10 – 1000 times more diluted than DLS.
• Can give the number of aggregated particles (%) directly measuring without modelling or assumptions.

Since we at Type1 Water are working with the production of the purest water it is only natural that our testing methodology is capable of nanoscale measurements, henceforth we have adopted NTA as our basic testing methodology and we proudly claim that some NTA equipment manufacturer’s use our water to calibrate their instruments and recommend it to their respective customers.

Measurements

DLS & NTA was used on Xzero water, to determine the number of particles of each size distribution. Typical measurements per size fraction is below 10000. There is a long explanation why there seems to be a peak in the values around 300 nm (Mie Scattering), but this is due to the instrument and is not there in reality. However, the measurement even including this wrongful peak is still very low why it was not deducted. In total, the Xzero sample measured a total of 2,4 *10⁵ particles per ml size distribution <900 nm.

Current technologies are using reverse osmosis and deionization together with filtering techniques to mechanically block particles coming out of the reverse osmosis module. But the smallest filter used is 200 nm. Mechanical filters can not be used for smaller particles because of the enormous pressure drop they would create. Any particle smaller than 200 nm will pass right through.

The company performing the measurements could not provide detailed measurements of our competitors but stated that a standard number was in the region of 1*10⁸ particles per ml. This information together with the knowledge of no filtering below 200 nm and the fact that a normal particle distribution in a fluid has an increasing number for smaller sizes (Junge Distribution), enabled us to create this schematic diagram.

Standards that we are comparing against (ASTM D5127-07) states that the total weight of the particles must not exceed 1microgram/ liter (or 1 ppb, part per billion). To calculate the weight of all the particles we used the density of polyethene 1,3 g/ml times the size fraction and added it all up. The Xzero sample measured 1,35 microgram/ litre. The same procedure was made using available data for the current technologies, and the information was used to create graph number 2.

Ag+ and AU+ nanoparticles

1. Tap water spiked with Ag+ nanoparticles – 140mg/l with 80% 0,24nm particles and 20% 1-24nm particles. Result <0,1ug/l
2. Tap water spiked with 100% 2nm particles at a concentration of 37mg/l Au+ nanoparticles. Result < 0,1ug/l

Test by Swedish Environmental Research Institute in June 2014 with HPLC. The results for nanoparticles have later in the year been verified by tests done with equipment with even more stringent detection levels.

Since this first test was made; several tests have been made in co-operation with The Royal Institute of Technology (KTH), ALS Global, Swedish Environmental Research Institute (SERI), Manta Instruments, Clarkson University, and Anton Paar.
All tests have verified excellent results. The tests have been done with silver and gold nanoparticles to verify the technology and improve the practical implementation.

A program is underway in 2017 for testing other types of nanoparticles such as polystyrene sphere nanoparticles, silica nanoparticles, and other nanoparticles that are of interest in the industry. Since the method is not selective in regard to material or charge, it is expected that all nanoparticles will be removed in the same efficient way.

We welcome all major new technology leaders in nanotechnology and any other users of Type 1 Ultrapure Water to test our water as a challenge to the water they use today.

MORE TEST RESULTS