Sample Preparation
| Digestion | Density Separation |
Reliable microplastic analysis begins with appropriate sample preparation. Environmental, industrial, and consumer product samples often contain complex organic and inorganic matrices that can interfere with particle detection, reduce analytical efficiency, or even prevent reliable polymer identification. Therefore, effective sample preparation is essential to isolate microplastic particles while preserving their physical and chemical integrity. At MIQALab, we have developed a modular sample preparation concept that can be adapted to the specific characteristics of each sample, ensuring high recovery, low contamination risk, and reproducible analytical results.
1
Cut-Off Filtration
Most environmental and industrial samples contain a large number of particles below 10 µm, which cannot be reliably detected by infrared spectroscopy. In this step, these particles are removed using our stainless steel cut-off filtration system.
2
Digestion
Different chemical digestion methods, including HCl, NaOH, H₂O₂, and Fenton reagent, are used to remove interfering matrix components prior to microplastic analysis. The appropriate treatment is selected based on the sample matrix and targeted polymers and can be combined or repeated for complex samples.
3
Density Separation
Density separation is used to separate microplastics from high-density inorganic matrix components, such as sediments, sand, and minerals. Depending on the targeted polymers and sample matrix, suitable density solutions are selected to efficiently isolate the microplastic fraction prior to analysis.
1. Cut-Off Filtration
| 10 µm | 20 µm |
Most samples contain large numbers of very small particles (<10 µm) that are below the reliable detection range of IR spectroscopy and can significantly increase the particle load on the analytical filter, leading to overload and particle agglomeration. Our stainless steel cut-off filtration removes particles below the selected size limit, with 10 µm and 20 µm cut-offs currently available. Additionally, it keeps the measurement time (overall particle load) within a certain range, allowing for faster analysis.
For particle transfer onto the analysis filter, we developed a custom glass apparatus that allows particles retained on the stainless steel sieve to be directly backflushed onto the gold-coated analytical membrane. No intermediate vessel is required, and the sample remains enclosed throughout the transfer process, helping to maximize particle recovery while minimizing the risk of airborne contamination.
2. Digestion
| Organic Contaminations | Inorganic contaminations |
Digestion is applied to remove organic and inorganic matrix components that are not microplastics but may interfere with filtration, spectroscopic analysis, or polymer identification. Depending on the sample composition, MIQALab offers a range of matrix-specific digestion protocols, including acidic (e.g. hydrochloric acid), alkaline (e.g. sodium hydroxide), oxidative (e.g. hydrogen peroxide or Fenton reagent), and enzymatic digestion. The most suitable protocol is selected individually to achieve efficient removal of organic material while preserving the physical and chemical integrity of the microplastic particles. For particularly challenging samples, multiple digestion steps can be combined or repeated to maximize purification efficiency prior to analysis.
2.1. HCl (10%) digestion
| Hydrochloric acid |
Treatment with 10% hydrochloric acid (HCl) is used to selectively remove acid-soluble matrix components prior to microplastic analysis. It is particularly useful for environmental and industrial samples containing mineral or corrosion-related residues.
Suitable for removal of:
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Carbonates (e.g. CaCO₃)
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Mineral deposits
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Rust and corrosion residues (e.g. iron oxides/hydroxides)
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Acid-soluble inorganic matrix components
Limitations and polymer considerations:
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Potential degradation or chemical alteration of polyamide (PA)
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Certain polyurethanes (PU) may be affected
2.2. NaOH (10%) digestion
| Sodium hydroxide |
Treatment with 10% sodium hydroxide (NaOH) is used for the alkaline digestion of organic matrix components. It is particularly useful for samples containing biological material, proteins, fats, and other alkali-degradable organic matter.
Suitable for removal of:
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Proteins and biological tissue
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Fats and lipid-rich components
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Cellular and other organic material
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Certain natural organic matrices
Limitations and polymer considerations:
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Potential degradation of polyester-based polymers, particularly PET (hydrolysis)
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Polyamide (PA) and certain polyurethanes (PU) may be affected
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Not suitable when quantitative recovery of alkali-sensitive polymers cannot be ensured
2.3. H₂O₂ (25%) digestion
| Hydrogen peroxide |
Treatment with 25% hydrogen peroxide (H₂O₂) is an oxidative digestion method used to remove organic matrix components while retaining microplastic particles for subsequent analysis. It is particularly useful for environmental and biological samples containing substantial amounts of degradable organic matter.
Suitable for removal of:
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Natural organic matter
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Biological residues and soft tissues
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Plant-derived organic material
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Other oxidizable organic matrix components
Limitations and polymer considerations:
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Prolonged exposure may cause surface oxidation or chemical alteration of certain polymers
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Particularly oxidation-sensitive or already weathered polymers may be more susceptible to modification
2.4. Fenton Reagent digestion
| H₂O₂ + Fe²⁺ |
Digestion using Fenton reagent (H₂O₂ + Fe²⁺) is a strong oxidative treatment based on the formation of highly reactive hydroxyl radicals. It is particularly effective for removing complex organic matrices and is commonly applied to environmental samples with a high organic matter content.
Suitable for removal of:
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Natural organic matter
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Biological residues and soft tissues
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Plant-derived organic material
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Organic matter in sediments and environmental samples
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Complex and persistent oxidizable organic matrices
Limitations and polymer considerations:
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Prolonged exposure may cause surface oxidation or chemical alteration of certain polymers
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Oxidation-sensitive and weathered polymers may be particularly affected
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Less suitable when preservation of the original polymer surface chemistry is essential
2.5. Enzymatic digestion
| Protease | Cellulase |
Enzymatic digestion using proteases and cellulases provides a mild and selective approach for removing organic matrix components while preserving microplastic particles. Proteases are used to degrade proteins and biological tissues, while cellulases specifically target cellulose and plant-derived material. Both enzymes can be applied individually or combined depending on the sample matrix.
CURRENTLY UNDER DEVELOPMENT
Suitable for removal of:
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Proteins and biological tissues
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Cellulose and cellulose fibers
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Plant-derived material
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Protein- and cellulose-rich organic matrices
Limitations and polymer considerations:
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Limited removal of lipids and other non-target organic compounds
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Longer treatment times compared with some chemical digestion methods
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Efficiency depends on pH, temperature, treatment time, and matrix composition
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Mild conditions minimize chemical alteration and degradation of polymer particles
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Protease treatment may affect polyamides (PA), including PA 6.6, depending on the enzyme and incubation conditions
3. Density Separation
| ZnCl₂ |
Zinc chloride (ZnCl₂) density separation is used to isolate microplastic particles from high-density inorganic matrix components. Due to the high achievable solution density, ZnCl₂ is particularly suitable when the analysis also targets high-density polymers such as PET, PVC, and PTFE.
Suitable for removal of:
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Sand and sediments
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Mineral and soil particles
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High-density inorganic material
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Inorganic residues in environmental samples
Limitations and polymer considerations:
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Very small particles may remain associated with sediment or mineral surfaces (low recovery values)
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Particle aggregation or incomplete settling may reduce separation efficiency