Detection of Al 2 O 3 particles in toothpaste by FFF- ICP-MS - - PowerPoint PPT Presentation

Detection of Al2O3 particles in toothpaste by FFF- ICP-MS (confirmatory method)

Manuel Correia, Katrin Loeschner National Food Institute, Technical University of Denmark (DTU) manco@food.dtu.dk

NanoDefine Outreach Event

Brussels, September 2017

NanoDefine is funded by the European Community's Seventh Framework Programme under Grant Agreement-604347

Background

Why Al2O3 particles in toothpaste?

• Relevant in terms of risk assessment and labelling

for cosmetics

• Al2O3 particles not widely covered in other projects
• Complex mixture containing different types of

nano/micro-particles (e.g. SiO2, Al2O3)

Aims of the work:

• Develop a suitable sample preparation method for

analyzing Al2O3 in toothpaste by FFF-ICP-MS

• Develop the FFF-ICP-MS method and determine

particle size and number concentration of Al2O3 particles in toothpaste

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Ingredients: Aqua, Hydrated Silica, Sorbitol, Alumina, Olaflur, Hydroxyethylcellulose, Aroma, PEG-40 Hydrogenated Castor Oil, Stearic Acid, Sodium Saccharin, Cocamidopropyl Betaine, Citric Acid, Limonene, CI 77891, 3- (N-hexadecyl-N-2-hydroxiethylammonio)propyl-bis(2-hydroxiethyl)ammoniumdifluorid (1400 ppm F-)

Courtesy of BAM Al2O3 TiO2 SiO2

Concentration (mg/g, N=3)

19.7 ± 4.5 8.7 ± 0.6 238.4 ± 6.8

• Crystall. phases

(XRD, BAM)

Corundum Anatase

• Crystall. size

(nm, XRD, BAM)

26 36

• Al2O3

(abrasive)

SiO2

(abrasive)

TiO2

(pigment)

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Characteristics of the test toothpaste

DLS and zeta-potential TEM-EDX

Zave = 267 nm Zeta pot: -42 mV

Toni Uusimäki, EAWAG

• Complex and polydisperse NP mixture
• Proper separation and identification of the different

NPs is required → FFF-ICP-MS

Pre-characterization of the toothpaste

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FFF-MALS/ICP-MS method development

5 Carrier liquid (SDS, FL70, etc) Channel and membrane charact. Cross flow rate Focus/injection parameters Injected mass AF4 separation parameters Tested on-line detectors UV-vis absorption Dynamic light scattering (DLS) Multi angle light scattering (MALS) ICP-MS ICP-MS required for element- specific information! Sample preparation Matrix dilution Chemical oxidation with H2O2

Results: Sample preparation

Matrix dilution vs Chemical oxidation with H2O2 (MALS data)

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• Matrix dilution: unusual elution profile

for and lower overall MALS signal

• Chemical oxidation: ~60% recovery

in comparison to flow injections (based on light scattering) → Chemical oxidation with selected as sample preparation procedure for analysis by FFF-MALS-ICP-MS

Results: AF4-MALS and AF4-ICP-MS

Toothpaste after H2O2 digestion, minj = 10 µg

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ICPMS (27Al) MALS

• Three particles types (SiO2, Al2O3 and TiO2) contribute to the light

scattering → elemental specific detection by ICP-MS is required

Results: FFF method development

Optimization of FFF conditions (for optimal recovery and conversion to number distributions (noise level, removal of void peak)

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Cross-flow optimization Carrier liquid composition

• Other parameters tested: membrane composition, carrier liquid (SDS,

FL70, focus conditions), injection mass/volume

Results: FFF method performance

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Linear response (5, 10, 25 µg inj. toothp.) Good reproducibility (6 different membranes)

• Method can provide reproducible AF4-ICP-MS fractograms for Al2O3
• Drawback: low Al recoveries -15-20 % AF4-ICPMS recovery (losses

to membrane, large particles)

Presence of artifact in mass-based PSD (no particles detected by sp- ICPMS after analysis of AF4 fractions → log-normal fit) If log-normal fit is applied→ d50 = 155 nm, analysed Al2O3 not consid. nanomaterial

Results: FFF method performance

Conversion to number-based particle size distribution

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Mass-based PSD Number-based PSD

Artifact

Summary and conclusions

• A FFF-ICP-MS method was sucessfully developed for

separating and analyzing unknown Al2O3 particles in toothpaste

• Mass recoveries were not satisfactory in certain cases this

is difficult to avoid (loss of large particles)

• Secondary confirmatory method is required (e.g. artifacts)

→ FFF-ICP-MS requires fine tuning for specific particle/matrix combinations

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Thank you for your attention!

Research Group for Nano-Bio Science

“This project has received funding from the European Union’s Seventh Programme for research, technological development and demonstration under grant agreement No 604347”.

12 Toni Uusimäki New address since Easter 2017: DTU´s new building for Life Science & Bioengineering