product degradation studies and shelf- life estimation ... · trace elements • toxic by-products...

Innovation with Integrity

Product degradation studies and shelf-life estimation using EPR spectroscopy Kalina Ranguelova EPR Applications Scientist Bruker Users’ Meeting Hilton Head Island, SC – March 2019


What is EPR?

• EPR is a magnetic resonance technique that detects unpaired electrons

• Unpaired electrons occur in free radicals and many transition metals

• Free radicals and transition metal ions are often present as impurities or participate in product degradation processes

EPR solutions EMXnano package

Detection


Why doing EPR?

EPR solutions EMXnano package

• There are many areas of interest where EPR spectroscopy is beneficial:

Detecting and evaluating degradation • Photo • Thermal • Chemical

Optimizing stability & shelf-life • Product stability • Antioxidant

effectiveness

Reaction monitoring • Yield

optimization • Green chemistry • Chemical

Post-sterilization QC • Irradiation • Thermal

Paramagnetic impurity profiling • Trace elements • Toxic by-products

Free radicals & Transition metals


Why doing EPR?

• Free radicals are the main source of damage in materials, organisms and food products!

• Transition metal ions are involved in catalysis, redox chemistry, electrochemistry, enzymatic reactions, etc.

watch the video: https://www.bruker.com/products/mr/epr/what-is-epr.html

https://www.bruker.com/products/mr/epr/what-is-epr.html






EPR solutions in food industry Lipid degradation

Window light exposure Window light exposure


EPR solutions in food industry Starch degradation

Kurdziel M. et al., Carbohyd. Polym. 210 339 (2019)

• EPR shows that thermal treatment causes depolymerization while UV-irradiation is effective in oxidation of oat and barley starches

• Barley starch is less stable than oat starch based on the quantitative EPR

• Three C-centered polysaccharide radicals were identified from the EPR spectra:

• The radical formation correlates with declining in starch crystallinity and molecular weight


EPR solutions in food industry Beverages degradation



Uchida M. and Ono M., J. Am. Soc. Brew. Chem. 58 30 (2000)



R. J. Elias et al., J. Agric. Food Chem. 2009, 57, 4359

Metal-catalyzed wine oxidation mechanism

Sulfite effect


EPR solutions in food industry Antioxidant properties of beverages

E. C. Pascual et al., J. Agric. Food Chem. 2002, 50, 6114 A. M. Maghraby, Topics from EPR Research, 2119


EPR solutions in pharma industry Drug degradation

Nifedipine

Photodegradation of Nifedipine after exposure to light shows the formation of N-based free radical. The amount of free radicals corresponds to the level of degradation!

Non-degraded

Degraded EPR

An example: Photodegradation of Nifedipine (a hypertension drug):

Light On

Degradation

Free Radicals


EPR solutions in pharma industry Drug degradation

• Polysorbates used in drug formulation as a stabilizer undergoes autoxidation • Autoxidation is catalyzed by transition metal ions and results in side-chain cleavage and

free radical formation • EPR detected, identified and quantified the three different free radical impurities


EPR solutions in pharma industry Stability and shelf-life optimization

An example: Polysorbate autoxidation • Stress testing is a form of forced

oxidation/degradation and is used to predict drug stability

• In stress testing the drug product is exposed to heat, light or chemical agents

• Some of the goals achieved by stress testing are:

Understanding degradation pathways

Determining the intrinsic stability and shelf-life

Developing stable formulations

Evaluating antioxidant efficiency


EPR solutions in cosmetic industry Antioxidant efficiency

An example: Antioxidants’ effect on a skin care product during UV-irradiation: • The efficacy of antioxidants depends on their

penetration kinetics, reactivity with non-radical components, and photo-stability

• EPR monitors the time-efficacy profile showing how fast an antioxidant can unfold its full potential in skin and how stable its activity is


EPR solutions in polymer industry Photodegradation

An example: Paint deterioration • Degradation of polymers due to light exposure

leads to discoloration and a decrease in the mechanical properties (elasticity, toughness, etc)

• To prevent this decomposition, hindered amine light stabilizers (HALS) are added to the polymer as radical scavengers

• EPR detects HALS nitroxyl radicals generated during paint oxidation upon UV exposure

• Quantitative EPR analysis shows correlation between the free radical concentration and the exposure duration confirming the effectiveness of HALS as an antioxidant

Initial reaction of a HALS with a polymer peroxy radical: this step stabilizes the polymer and converts the HALS to its aminoxyl form


EPR solutions in material science

Paramagnetic defects and impurities in photovoltaic materials include:

• Eˈ centers in SiO2

• Atomic H0 in SiO2 or c-Si

• D center defects in a-Si

• Pb centers at Si-SiO2 interfaces

• Vacancies

• Transition metals

• Free radicals

An example: Solar cell degradation


EPR solutions in material science

An example: Organic solar cell degradation

Polymerbatch

Spin density Spins/g

Power Conversion Efficiency,

%

Half Lifetime,

hrs

A 2.2e17 4.5 30

B 1.4e17 6.2 50

C 0.3e17 7.1 150

• Conjugated polymers are used as electron donors in organic solar cells (organic photovoltaics)

• The amount of free radical defects in polymers varies between different batches, synthesis, or vendors

• The EPR can detect, identify and quantify the free radical defects (impurities) • Quantitative EPR analysis (spins/g) correlates with solar cell efficiency (PCE) and stability


Degradation - a two-edged sword?

An example: Advanced Oxidation Processes (AOPs)


Degradation - a two-edged sword?

An example: Decomposition of pharmaceuticals

• Diclofenac was decomposed by pulsed corona plasma generated in water

• The degradation was measured by GC-MS is directly correlated to the increase in hydroxyl radical concentration over time

• Hydroxyl radicals detected by EPR are responsible for the decomposition of pharmaceutical compounds

• EPR measurement of hydroxyl radical concentration aids in optimizing the decontamination process.

Banaschik R. et al., J. Hazard Mater. (2018) 342 651


Degradation in biological samples


EMXnano The standard for bench-top EPR

• Automated tuning and measurement

• Software automated data collection, processing, and storage

• Integrated, motorized amplitude and field reference standard (marker)

• Fully-calibrated for quantitative analysis with dedicated application workflows. No need of calibration curve

SpinCount: Reference free quantification of EPR species

SpinFit: Spectrum fitting and identification of EPR species

Spin-trap library of EPR spectra

• Video how-to guide

• Low infrastructure requirement and low cost-of-ownership


EMXnano Full range of accessories

• UV irradiation system - provides in-situ irradiation of the

sample in the microwave cavity with simultaneous EPR

detection. A light guide is used for efficient transmission

to the sample.

• Variable temperature accessory (100 – 425 K) - the

digital temperature control system makes use of liquid or

gaseous nitrogen for stable temperature control. Easy

and quick sample exchange at any temperature offers

safe operation and high measurement throughput.


EMXnano Full range of accessories

• Reaction monitoring - the flow through cell is optimized to

offer high sensitivity for lossy and non-lossy samples.

Sample exchange is via static injection, continuous flow, or

auto-sampler.

• Aqueous samples – the flat cell maximizes the usable

sample volume for low concentration measures. Optical

access enables irradiation with the optional UV system.

• Biological tissue samples - the tissue cell is designed for

studies of plant, animal, and human tissues. Optical access

enables irradiation with the optional UV system.

product degradation studies and shelf- life estimation ... · trace elements • toxic by-products...

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