# Particle Metrology with ARCHIMEDES

**CHARACTERIZATION**: a description of qualities

**METROLOGY**: the science of measurement

**"How big are your particles?" ** This is a most basic question, yet most "particle characterization" instruments give at best an approximate answer. ARCHIMEDES measures the physical properties of particles by mass, an entirely new approach that gives true particle metrology, with results that are quantitatively superior to conventional methods such as light scattering.

## RESOLUTION

One of ARCHIMEDES' outstanding features is its high resolution, i.e., the ability to distinguish two particles of only slightly differing masses or sizes. The figure below shows a bimodal mixture of two µm-scale, NIST-traceable standards (Duke/Thermo Scientific 4009A and 4010A) that differ in size by only 4% (40 nm). ARCHIMEDES easily and completely resolves the two populations. In addition, the measured standard deviations are less than half of the manufacturer's specifications, and the standard error (uncertainty in the mean size) is measured at the single-Ångstrom level.

ARCHIMEDES' extraordinary resolution stems from its ultra-high frequency – and hence mass – resolution, combined with the cubic relationship between diameter and mass. For example, imagine a 1 µm diameter particle of density 1 g/cc. The mass of an outer shell weighing 1 femtogram (equivalent to ARCHIMEDES' mass resolution) is only 3 Å thick.

This resolution extends to the submicron scale. For example, ARCHIMEDES easily parses the tri-modal distribution of gold particles at right. Specified as 57 nm, 79 nm, and 100 nm, ARCHIMEDES finds these to be 57 nm, 81 nm, and 99 nm. Shown on the same scale is a dynamic light scattering measurement of the identical sample. Not only are the three populations not resolved, but the claimed sizes are significantly in error, as are the relative populations of the sample’s components.

## ACCURACY

ARCHIMEDES gives true accuracy at the 1% level. As an example, consider this mixture of four diferent NIST-traceable standards. ARCHIMEDES allows each sub-population to be analyzed separately, giving mean sizes that are within 0.1% to 0.5% of the manufacturer's specifications.

## REPEATABILITY and REPRODUCIBILITY

As must be expected of any metrology instrument, ARCHIMEDES possesses excellent repeatability. Using the simple, NIST-traceable calibration procedure, reproducibility is at the 1% level from sensor to sensor, as well as between instruments.

## CONCENTRATION and SAMPLE CONTENT

ARCHIMEDES' mass measurement is a true "counting" method: each particle is measured individually. And, its fluidics monitors the flow rate precisely throughout the measurement. From this information, ARCHIMEDES provides:

- Particle concentration [#/ml]
- Sample consumed [µl]
- Solid content [parts per billion]

This information is valuable in a number of applications, including:

- Monitoring content of aggregates in protein formulations
- Assessing agglomerates in inks that clog printheads