Microplastics（Microplastics，MPs）As a global environmental pollutant, it has a small particle size（1 Mm–5 mm）Widely distributed in the environment and complex polymer composition (such as polyethylene)PEPolypropylenePPPolystyrenePSEtc.) and other characteristics. Traditional detection methods such as optical microscopes can only observe particle morphology, while ordinary infrared spectroscopy cannot achieve micro area localization, making it difficult to meet recognition requirements. And the micro infrared spectrometer（Micro-FTIR） The innovative fusion of microscopy imaging and infrared spectroscopy technology, with micrometer level spatial resolution and molecular vibration characteristic analysis ability, has become the core "gold standard" technology in the field of microplastic detection. This article will provide a systematic and professional discussion from four aspects: technical principles, typical application scenarios, core advantages and challenges, and cutting-edge development directions.

1、 Technical principle: Micro spatial analysis of molecular vibration signals

The core value of a micro infrared spectrometer lies in The synergy between "micro positioning" and "molecular recognition" can be divided into two main modules: micro focusing and optical path design, and spectral acquisition and data analysis.

1. Microscopic focusing and optical path design

The system consists of an infrared microscope and a Fourier transform infrared spectrometer（FTIR）Coupling composition, with key hardware configurations designed around "high spatial resolution" and "multi scene adaptation":

Detector selection: liquid nitrogen cooling can be used MCTDetector (such as Northern Rayleigh)WQF-530AModel, suitable for high-sensitivity detection) or full band pyroelectric detector (covering4000–400 cm⁻¹ Complete spectral range, suitable for broad-spectrum analysis needs);

Microscopic objective lens: equipped with numerical aperture NA≥0.65 High magnification objective lens, capable of achieving1–10 MmFocused imaging of micro areas to meet the needs of detecting small particles;

Optical path mode: supports reflection, transmission, attenuation, and total reflection（ATR）Three working modes - reflection mode is suitable for opaque samples (such as soil particles), transmission mode is suitable for thin filter membrane samples,ATRThe mode can directly analyze microplastics in biological tissue slices without sample pretreatment.

2. Spectral Collection and Data Analysis

By using two core acquisition modes, it is possible to achieve Coverage from "single point recognition" to "global statistics":

Point scanning mode: for individual microplastic particles (such as 30 MmofPEParticle based fixed-point spectral acquisition, utilizingOMNIC PictaSoftware automatically deducts background interference (background media optional)KBrExtract polymer characteristic peaks (such as window or filter blank samples)PEof2920 cm⁻¹C-HStretching peak1467 cm⁻¹CH₂ bending peak), then compared with a standard spectral library (such asASTM D8401Comparing with the microplastic standard spectrum library, the accuracy of polymer identification can reach95%above;

MappingImaging mode: for samples (such as25 mmPerform grid scanning (typical step size) on a diameter filter membrane10 Mm）Generate a thermal map of the distribution of microplastic components, which can quickly calculate the proportion of different polymer types (such as in a certain seawater sample)PPproportion62%）Characteristics of particle size distribution (such as median particle size)D50=58Mm）Realize quantitative analysis of batch samples.

2、 Application scenario: Full chain coverage from environmental media to the fields of biology and food

Microscopic infrared spectrometer relies on The advantages of "in-situ, non-destructive, and high specificity" have been widely applied in the full scenario of microplastic research, solving the core detection needs in different fields.

1. Analysis of Microplastics in Environmental Media

Develop standardized testing procedures for typical environmental media such as water, soil, and atmosphere:

Water sample: Yes 100 LSeawater or freshwater samples are taken0.22 MmAperture polytetrafluoroethylene（PTFE）Membrane filtration, detecting microplastics trapped on the membrane through transmission mode, can identifyPE(Characteristic peak)2850 cm⁻¹)PS(Characteristic peak)700–800 cm⁻¹) and other polymers, with detection limits as low as0.1 Mg/L；

Soil sample: first remove organic matter interference from the soil by density flotation method, and then enrich the particle size by silica membrane filtration > 10MmMicroplastics, throughATRPattern analysis (such asPETof1720 cm⁻¹C=OStretching peak), effectively avoiding soil matrix interference, and controlling quantitative analysis errors within5%Within;

Atmospheric deposition: particle size collected using a Manta trawl 0.45–10 MmDetecting fibrous microplastics (such asPPfibrous1450 cm⁻¹CHCombined with regional wind speed data, the settlement flux of microplastics can be further calculated (unit:n/m²/d）Provide data support for tracing air pollution.

2. Research on microplastic risks in the biomedical field

Focusing on the migration, accumulation, and toxicity mechanisms of microplastics in living organisms, achieving Correlation analysis between "particle localization" and "molecular effects":

Particle localization in biological tissues: detected in the fetal side tissue of the human placenta 12 A polyethylene（PE）Microplastic particles (particle size)5–20 Mm）, throughMappingImaging clarifies the distribution of particles in placental tissue, directly indicating the potential health risks of microplastics crossing the placental barrier;

Study on the mechanism of cytotoxicity: observation A549Phagocytosis of pulmonary epithelial cells2 Mm PSAfter microplastics, micro infrared detection revealed cell membrane characteristicsC-HPeak (wavenumber)2960 cm⁻¹) Strength decrease15%Combined with biochemical testing to confirm intracellular reactive oxygen species（ROS）Level increase30%Established the "Microplastic Exposure-Cell membrane damage-Molecular correlation evidence chain of oxidative stress.

3. Microplastics and additive testing in the field of food safety

Provide quantitative methods for addressing issues such as food packaging migration and contamination risk:

Packaging material migration detection: for PETAfter ethanol extraction of the filter membrane sample in bottled water, free plasticizers (such as...) were detected by micro infrared spectroscopyDEHPof1720 cm⁻¹C=OPeak), quantification limit as low as0.01 mg/kg, in line with our countryGB 9685-2016Requirements of the "Standard for the Use of Additives in Food Contact Materials and Products";

microplastics -Analysis of pollutant complexes: targeting the adsorption of polycyclic aromatic hydrocarbons on the surface of microplastics in seawater（PAHs）The composite pollution scenario adopts the combined technology of micro infrared and Raman spectroscopy (such asHoriba LabRAM HR EvolutionSystem), synchronously obtaining infrared molecular vibration and Raman scattering signals, clarifyingPAHsThe adsorption configuration on the surface of microplastics (π)-The π stacking effect is dominant, providing a microscopic basis for the risk assessment of composite pollution.

3、 Technological Advantages and Existing Challenges: A Dialectical Perspective of Opportunities and Bottlenecks

1. Irreplaceable core advantages

Compared to other microplastic detection technologies such as Raman spectroscopy and thermogravimetric analysis, the core competitiveness of micro infrared spectrometers lies in three aspects:

High specificity: relying on the characteristic functional group peaks of polymer molecules (such as C=Oof1700 cm⁻¹C-O-Cof1100 cm⁻¹), distinguishablePEThePPThePETThePVCWait close20 Common microplastics with polymer misjudgment rate controlled within3%following;

In situ non-destructive testing: No pre-treatment operations such as acid digestion or high-temperature burning are required for the sample, and the morphological characteristics (such as fibrous and fragmented) and surface functional group information (such as hydroxyl groups generated by oxidative aging) of microplastics can be fully preserved, providing a basis for subsequent traceability research;

High throughput efficiency: mainstream commercial systems such as Thermo Fisher Scientific Spotlight 400）Support96 Automatic injection of orifice plate, capable of analysis in a single run2000 Microplastic particles with improved analytical flux compared to traditional manual point scanning mode50 Multiple, suitable for large-scale environmental sample testing needs.

2. Existing challenges that urgently need to be overcome

Despite its high level of technological maturity, it still faces three bottleneck constraints:

Particle size detection lower limit: The detection lower limit of conventional micro infrared is about 1 MmRegarding particle size< 100 nmNanoplastics need to be used in conjunction with atomic force microscopy（AFM-IRThe implementation of technology has significantly increased the cost and operational complexity of detection;

Complex matrix interference: Humic acid in soil (characteristic peak) 2500–3000 cm⁻¹), proteins in biological tissues (amide bond peak)1650 cm⁻¹) Easy to mix with plasticC-HPeak overlap requires correction through multivariate scattering（MSC）Algorithms such as first-order derivatives are still difficult to interfere with the optimization of spectral data;

Lack of standardization in testing: Different brands of instruments (such as Bruker, PerkinElmer, Thermo Fisher) have differences in spectral acquisition parameters (such as resolution, scanning frequency, background subtraction method), resulting in a decrease in comparability of testing results for the same sample on different platforms. There is an urgent need for an international standardization organization（ISO）Or American Society for Testing and Materials（ASTM）Develop unified testing method standards.

4、 Frontier progress and future direction: Technological innovation drives the upgrade of detection capabilities

In recent years, micro infrared spectrometers have been moving towards The direction of "integration, intelligence, and nanotechnology" is rapidly developing, constantly breaking through the boundaries of traditional technology.

1. Joint technology: expanding detection dimensions and sensitivity

Microscopic infrared -Raman spectroscopy: Microscopic infrared spectroscopy-Raman spectroscopy system breaks through the wavenumber range limitation of single spectral technology - infrared spectroscopy（4000–400 cm⁻¹) Identifying functional groups, Raman spectroscopy（50–3200 cm⁻¹) Supplement molecular skeleton information to significantly enhance fluorinated plastics (such as polytetrafluoroethylene)PTFE）Sensitivity of detecting inorganic doped plastics;

terahertz -Infrared combination: utilizing0.1–3 THzThe penetrability of terahertz waves can detect additives inside plastics, such as dioctyl phthalateDOPUV stabilizer, with spatial resolution of up to5 MmTo solve the problem of "surface detection cannot reflect internal components".

2. Intelligence: Improving Analysis Efficiency and Automation Level

AIAuxiliary Spectral Recognition: Based on Convolutional Neural Networks（CNN）Building a particle classification model (such asResNet-50Architecture), the training set covers5000 +The standard spectrum of polymer and the spectrum of actual environmental samples can achieve automatic classification of microplastic types, particle sizes, and aging degrees with an accuracy of98%Significantly reduce manual interpretation errors;

Cloud platform data integration: spectrometer support and laboratory information management system（LIMS）Docking, the detection data can be uploaded in real-time to the cloud database, supporting collaborative analysis among multiple laboratories and cross regional data comparison, providing technical support for the construction of a global microplastic pollution map.

Conclusion

Microscopic infrared spectrometer relies on The synergistic advantage of "molecular level identification" and "micrometer level localization" has become a core technical tool for microplastic pollution research, playing an irreplaceable role in environmental monitoring and health risk assessment. In the future, with the continuous innovation of combined technology, deep optimization of artificial intelligence algorithms, and improvement of detection standardization system, this technology will further break through the bottleneck of particle size limit and matrix interference, providing stronger support for the traceability and risk control of microplastic pollution.