Detection and Identification of Microplastic Particles in Cosmetic Formulations Using IR Microscopy

Introduction
It is estimated that there is in excess of 150 million
tons of plastic materials in the world’s oceans1
.
Much of this pollution consists of large items such
as discarded drink bottles and plastic bags. However,
there is increasing research into the amount of much
smaller materials, termed microplastics, in the river
and ocean systems which present a different type of
problem for marine life.
Many cosmetic products, such as facial scrubs, toothpastes, and shower gels, currently
contain microplastic beads as abrasive materials. These microplastics, which are typically sub-
millimetre in size, get washed down the sink and are too small to be filtered by sewage
treatment plants consequently ending up in the river systems and ultimately in the oceans.
These microplastics can be ingested by marine organisms and fish and end up in the human
food chain.
In 2014 a number of U.S. states banned the use of microplastics in cosmetic formulations
and most cosmetic companies are voluntarily phasing out their use.
Infrared (IR) spectroscopy is the established technique for identifying polymer materials and
has been used extensively for identifying large (over 100 micrometer) polymer materials. The
Spectrum Two™
is a portable FT-IR spectrometer that can operate from a battery pack and
has been used on boats for immediate identification of these polymers.1
For microplastics,
down to a few micrometers in size, an IR microscope can be used for the detection and
identification of these materials.
Detection and
Identification of
Microplastic Particles in
Cosmetic Formulations
Using IR Microscopy
A P P L I C A T I O N N O T E
Author:
Ian Robertson
PerkinElmer, Inc.
Seer Green, UK
Infrared, IR Microscopy

2
Two commercially available products were tested using the
Spotlight™
200i IR microscope system in order to determine
whether microplastics were present as the exfoliant and to identify
the types of plastics used.
Product 1 is a commercially available facial scrub. Product 2 is a
commercially available body scrub. Each of these products was
mixed with hot water in order to dissolve the soluble ingredients
in the formulation. The resulting solution was filtered through a
50 micrometer mesh, capturing any insoluble components greater
than 50 micrometers in size. The filter was then allowed to dry in
air prior to IR microscopy measurements. The samples were
measured both directly on the mesh and also after transferring the
residual particles onto an IR transmitting window on a microscope
holder. Visible images of the collected microplastics are shown as
Figures 1a and 1b.
It is clear from these images that Product 1 has irregular-shaped
microplastics with particles of two different colors. The particles
from Product 2 are regular spheres with those visible in Figure 1b
being approximately 50 and 80 micrometers in diameter. Infrared
spectra of these materials can be measured in either transmission
or reflectance on the IR microscope. Spectra measured on one of
the particles in Figure 1a, in-situ on the mesh, are shown as
Figure 2.
The transmission spectrum has a much higher signal than the
reflectance spectrum and gives better sensitivity for this
measurement. In addition, the bands in the reflectance spectrum
are more intense due to the fact that the IR beam is effectively
passing twice through the sample, known as transflectance. For
smaller particles this does not cause any problems; but for larger
particles the path length may be too large leading to totally
absorbing bands, thus making identification more difficult.
However, in this case, it would be possible to identify the material
from either the transmission or reflectance spectrum. The mesh
may interfere with the transmission measurement, slightly
decreasing the amount of energy reaching the detector. This
explains the baseline slope observed in the spectrum, but it does
not significantly impact the overall measurement. To obtain the
best quality spectrum of the material, the sample can be
transferred onto an IR-transmitting window material, such as
potassium bromide (KBr). A KBr window was placed onto the
mesh containing the sample and the mesh inverted thereby
transferring the microplastic particles directly onto the KBr window.
Figure 1a: Microplastics in Product 1 (facial scrub) collected on mesh.
Figure 1b: Magnified view of microplastics collected from Product 2 (body scrub).
Figure 2: Spectra from a microplastic particle in Product 1. Transmission spectrum
(black) and reflectance spectrum (red).

3
A “Visible Image Survey” was collected over the area containing
the majority of the particles in Product 1. Selecting the “Analyze
Image” function in the Spectrum 10 software invokes the
intelligent automated routine for detecting particles within this
Visible Image Survey, which is displayed as “analyze image
result” shown in Figure 3.
The results show that Product 1 has two different types of
polymers present, polypropylene and polyethylene. Product 2
contains only particles of polyethylene. Representative spectra
are shown in Figure 5. Small differences are observable in the
spectra of the polyethylene between the two different products,
most likely due to additives present.
This routine will automatically detect any particles present in the
visible image and mark them as regions of interest. It will then
calculate the maximum rectangular aperture size that can fit
wholly inside each of the particles, thus maximizing signal-to-noise
when the data is scanned. In the past, manual selection of the
regions of interest and setting of apertures took a considerable
amount of time. Clicking “Scan Markers” initiates the collection
of transmission spectra (using equivalent apertures for the
background) for each particle, displaying ratioed sample spectra in
real time as they are collected. Automatic processing of the
spectra, using software routines such as Search, Compare, or
Verify, can be performed during data collection. In this case, the
analysis of the microplastics, a spectral search was performed
against a library of polymer spectra to give the identity of each of
the particles as shown in the results screen in Figure 4.
Figure 5: Top – spectrum of polypropylene in Product 1. Middle – spectrum of
polyethylene in Product 1. Bottom – spectrum of polyethylene in Product 2.
Figure 3: The Analyze Image software routine detects the particles in Product 1.
Figure 4. Results screen for the detection and identification of particles.

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Summary
Microplastics are a major concern regarding their impact on the
environment and as such their use in consumer products is
increasingly being prohibited. An automated IR microscopy system
has been shown to be an invaluable method for the detection and
identification of a source of microplastics in cosmetic formulations.
The work presented here will be extended to analyze samples of
microplastics collected from European river systems to illustrate how
widespread this pollution problem is within marine environments.
References
1. Labo magazine – Oktober 2010 Wasserverschmutzung durch
Mikroplastikpartikel, www.labo.de

Detection and Identification of Microplastic Particles in Cosmetic Formulations Using IR Microscopy

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