Characterization of Silicon Dioxide Food Additives by Single Particle 

Inductively Coupled Plasma Mass Spectrometry

❖ Silicon dioxide (SiO2), in its amorphous form, is an approved

food additive (21 CFR 172.480) in the U.S., mainly used as

an anticaking agent in powdered food products, a chill

proofing agent in malt beverages, and a filter aid in wines,

beer, and juices. During production, particles of SiO2

aggregate to form nano-sized and larger particles, however,

there is currently no data concerning the particle size

distributions of food grade SiO2. This particle size metric is

important in evaluating the potential transformations of

nanoparticles (NPs) in food products.

❖ In 2006, the U.S. Food and Drug Administration (FDA)

initiated a Nanotechnology Task Force to address knowledge

gaps associated with the use of nanoscale materials in FDAregulated products. In this effort, FDA’s Center for Food

Safety and Applied Nutrition (CFSAN) has begun

collaborative work with the Inorganic Measurement Science

Group in National Institute of Standards and Technology

(NIST) to develop reliable analytical strategies for the

characterization of metal oxide NPs in food derivatives. Six

commercially available food grade SiO2 will be characterized

by a suite of analytical techniques.

Monique E. Johnson,

1 Sadia Afrin Khan,2 Timothy R. Croley,2 Antonio R. Montoro Bustos,1 

Ingo H. Strenge,

1 and Karen Murphy1

1 Chemical Sciences Division, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899

2 Center for Food Safety and Applied Nutrition (CSFAN), U.S. Food and Drug Administration, College Park, MD 20740

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Introduction

Research Goals

❖ Silicon content will be determined in test materials by

inductively coupled plasma mass spectrometry (ICP-MS)

following acid-assisted digestion.

❖ Particle size distribution information will be obtained using

dynamic light scattering, scanning electron microscopy, and

single particle (sp)ICP-MS analysis.

❖ Commercially available spherical SiO2 NPs, ranging from

300 nm to 500 nm in size, will be used as control materials to

optimize the challenging spICP-MS analysis.

Characterization of Commercial Silicon Dioxide Nanoparticles

Sample Z-Average (nm) via DLS

Average Diameter 

via spICP-MS (nm)

# of Particles Analyzed 

via spICP-MS (nm)

SiO2-A sonication 1362 419 ± 66 1,799

SiO2-B sonication 495 421 ± 65 2,209

SiO2-C1 sonication 156 323 ± 41 195

SiO2-C2 sonication 469 431 ± 63 2,011

SiO2-D1 sonication 277 451 ± 55 1,746

SiO2-D2 sonication 440 468 ± 65 697

✓Transmission- and scanning electron microscopy confirmed that the food grade silicon dioxide samples measured in this study contained nanosized particles when the materials were prepared

by a combination of sonication+filtration or shaken+filtration.

✓spICP-MS results show that probe sonication of the six food additive materials produced nanosuspensions containing particles in a size range from 300 nm to 700 nm. These sizes differ

significantly from the size of particles in the original material, demonstrating substantial transformations that silicon dioxide undergoes when they are used as food additives.

✓spICP-MS preliminary results also indicate that the filtration step caused a significant retention of nanoparticles larger than the 0.22 μm filter cutoff. Future work will seek to expand the linear

range of spICP-MS for SiO2 NP measurements in an effort to quantify and size NPs in the nanorange.

Sample Preparation and Analysis

✓Six food grade SiO2samples were procured from four

commercial distributors/manufacturers. These samples were

given unique names to ensure confidentiality.

✓0.1 % w/v dispersions of each food grade SiO2 material were

prepared in ultrapure water (18 MΩ) by three methods:

✓Sonication: 10 min, 55 % pulse amplification, pulse

mode: 20 s on and 20 s off

✓Shaken + filtration: 15 min at 250 RPM, followed by

filtration through a 0.22 μm filter.

✓Sonication + filtration: sonication procedure

mentioned above followed by filtration through a 0.22

μm polyethersulfone filter membrane.

✓Characterization of the bulk food additive material and

dispersions were carried out using a JEOL JEM-1400

Transmission Electron Microscope (TEM) and TESCAN

Mira3 Field Effect-Scanning Electron Microscope (FE-SEM).

✓Particle size distributions were measured via Malvern

Zetasizer Nano ZEN3600.

✓spICP-MS measurements were carried using a PerkinElmer

NexION 350D ICP-MS

✓Key instrument parameters: signal at m/z 28, 0.10 mL

min-1flow rate, 1 ms dwell time, 600 s measurement time

Sample*

High 

Resolution 

SEM (nm)

Average 

Diameter via

spICP-MS 

(nm)

# of Particles 

Analyzed via

spICP-MS (nm)

Particle 

Number 

Concentration 

Recovery (%)

300 nm SiO2

* 296 ± 16 312 ± 24 1,154 102 %

400 nm SiO2

* 367 ± 11 350 ± 33 1,413 97 %

500 nm SiO2

* 564 ± 22 473 ± 53 1,263 100 %Si Intensity (counts)

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SiO2A

Conclusions

CENTER FOR FOOD SAFETY & APPLIED NUTRITION

U.S. FOOD & DRUG

ADMINISTRATION

Characterization of Food Grade Silicon Dioxide

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SiO2C1

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FE-SEM of Bulk 

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