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FLOPP & FLOPP-e — Open FTIR Libraries for Microplastics

https://doi.org/10.1021/acs.analchem.1c02549
  • Open Data: Yes
  • Access: Open Access

Description

FLOPP and FLOPP-e Database Overview

The FLOPP and FLOPP-e databases are open-access μATR-FTIR spectral libraries developed to improve the identification of microplastics in environmental samples. Designed specifically for microplastics research, these libraries move beyond conventional commercial polymer references by including spectra from real-world plastic particles with diverse colors, morphologies, uses, and weathering histories.

FLOPP stands for FTIR Library of Plastic Particles, while FLOPP-e is the environmental companion library containing spectra from plastics recovered from real environmental samples. Together, they provide a more realistic reference set for researchers analyzing microplastics with attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR).

Be sure to check out the companion RShiny-based visualization app on Plastiverse.org!

Why FLOPP and FLOPP-e Matter for Microplastics Research

Accurate microplastics identification depends heavily on the quality and relevance of the reference library used during spectral matching. Traditional commercial libraries often rely on pristine standard materials that do not reflect the diversity of plastics actually found in the environment. The paper introducing FLOPP and FLOPP-e emphasizes that environmental plastic particles differ in additives, pigments, morphology, degradation state, and biofouling, all of which can influence spectral output.

These libraries were built to address that gap. The authors showed that including microplastics-specific reference spectra improved spectral matching performance compared with using commercial libraries alone, and that the best performance came from using FLOPP/FLOPP-e in combination with commercial and other open libraries.

For laboratories, monitoring programs, and researchers seeking more defensible polymer assignments, FLOPP and FLOPP-e are valuable additions to the FTIR toolkit.

What Is Included in the FLOPP Database?

The FLOPP library contains 186 spectra from common plastic items representing 14 polymer types. These spectra were collected from non-standard plastic materials and everyday consumer products, rather than only pristine manufacturer-grade materials. The library intentionally includes particles with different sources, colors, and morphologies to better reflect plastics encountered in microplastics studies.

According to the paper, FLOPP includes particles across 13 colors, with white, clear, and black among the most common, and spans morphologies such as fragments, fibers, foams, films, and spheres.

This makes FLOPP especially useful for analysts working with heterogeneous particles from packaging, textiles, foams, and other everyday plastic debris.

What Is Included in FLOPP-e?

The FLOPP-e library contains 195 spectra across 15 polymer types and focuses on plastics sourced directly from the environment. These particles came from environmental samples collected between 2017 and 2020, including surface waters and biota-associated samples from San Francisco Bay, Mimico Creek, Lake Simcoe, and Toronto Harbor.

FLOPP-e is especially important because weathered plastics often produce spectra that differ from unaged materials. The paper’s principal component analysis showed broader spectral variability among environmentally aged particles, confirming that weathering changes the infrared signature of plastics.

For researchers identifying field-collected particles, FLOPP-e helps bridge the gap between idealized laboratory references and real environmental debris.

File Formats and Accessibility

A major strength of the FLOPP/FLOPP-e resource is that the authors made the spectral libraries available in multiple commonly used formats. The supporting information specifies that the database is provided as OMNIC spectral files in .spa, .jdx, and .csv formats for each library.

These formats improve interoperability across workflows and make the resource useful for analysts using OMNIC-based systems as well as those working with more customized or open data-processing pipelines.

Performance and Validation

The study validated FLOPP and FLOPP-e using two separate microplastic datasets. Using commercial libraries alone, the mean hit quality index (HQI) was 73% for both datasets. When all available libraries were combined, including FLOPP, FLOPP-e, and the Primpke polymer library, average HQI increased to 84% for the Chesapeake Bay dataset and 81% for the Toronto dataset.

The paper also found that, in many ambiguous cases, adding FLOPP and FLOPP-e improved the ability to assign spectra to specific polymers. In one set of inconclusive results, 19 of 20 spectra were identified as a specific polymer when the FLOPP/FLOPP-e libraries were used.

The practical takeaway is clear: microplastics-specific FTIR libraries can materially improve identification workflows, especially when used alongside broader reference libraries.

Key Advantages of FLOPP and FLOPP-e

1. Built for real microplastics work

These libraries are based on plastic particles researchers actually encounter in environmental samples, not just idealized reference standards.

2. Includes weathered environmental plastics

FLOPP-e captures spectral variation caused by environmental aging, which is often missing from conventional libraries.

3. Open and reusable

The libraries are openly shared and distributed in accessible file formats, supporting reproducibility and harmonization across laboratories.

4. Improves spectral matching

Validation results indicate that adding these libraries can improve HQI and support more confident polymer assignment.

Best Use Cases

FLOPP and FLOPP-e are particularly relevant for:

  • Microplastics laboratories using ATR-FTIR for particle identification

  • Environmental monitoring programs analyzing diverse field samples

  • Researchers building harmonized spectral workflows

  • Method developers evaluating open-access microplastics reference resources

  • Students and new labs looking for accessible FTIR polymer databases without relying solely on expensive commercial products

Because the study found the best results when combining multiple library types, these databases are best treated as complementary resources, not necessarily standalone replacements for all commercial libraries.

Keywords

FLOPP database, FLOPP-e database, microplastics FTIR library, μATR-FTIR microplastics, open spectral library microplastics, polymer spectral database, weathered plastic spectra, microplastics identification tool, FTIR reference library, environmental plastic spectra

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