Trace Detection of Diphenylamine in Baby Food

Significance of the Topic

Diphenylamine is widely used as a post-harvest preservative and antioxidant in agriculture and industry. Regulatory agencies in the US and EU set stringent maximum residue limits (5 µg/g for whole pears and 10 ng/g for processed baby foods) due to concerns over chronic dietary exposure, especially in infants.

Study Objectives and Overview

This work demonstrates a rapid, on-site surface-enhanced Raman spectroscopy (SERS) method for detecting trace levels of diphenylamine in pureed pears marketed as baby food. The goals are to establish sensitivity down to regulatory limits, validate reproducibility, and showcase field applicability.

Methodology and Instrumentation

• Sample Preparation: Pureed pear samples were spiked with diphenylamine at concentrations from 1 to 100 µg/g. Each sample was vortexed with chloroform, allowed to separate, and the organic phase was collected.
• Extract Concentration: The chloroform extract was evaporated on a hotplate, then redissolved in a mixture of gold nanoparticle (Au NP) colloid and NaCl to induce SERS-active aggregation.
• Spectral Acquisition: Measurements were performed on MISA with 5 s integration time, 10 averaged spectra per sample, 5 % laser power, and raster scanning enabled to enhance signal uniformity.

Used Instrumentation

• MISA Advanced (Metrohm Instant SERS Analyzer, firmware 0.9.33; software MISA Cal V1.0.15) with Orbital-Raster-Scan spectrograph
• MISA Vial Attachment and P-SERS Attachment for sample positioning
• ID Kit – Au NP (gold colloid solution, disposable spatula, pipettes, glass vials)

Main Results and Discussion

Baseline-corrected SERS spectra exhibited distinct diphenylamine fingerprint peaks at all tested levels, with a clear detection limit of 1 µg/g. Spectral overlays showed consistent intensity trends proportional to concentration, demonstrating method linearity and reliability for rapid screening.

Benefits and Practical Applications

• Enables fast, cost-effective on-site screening of diphenylamine residues in infant foods and produce.
• Offers a portable alternative to centralized laboratory techniques such as GC-MS and GC-NPD.
• Simplifies sample preparation and reduces analysis time to under one minute per measurement.

Future Trends and Potential Applications

Advancements in nanoparticle substrates and SERS data algorithms may push detection limits into the sub-ppb range. Integration with automated sampling systems and cloud-based spectral libraries could streamline monitoring of multiple pesticide residues. Expanding the approach to other food matrices and chemical hazards will broaden field-deployable quality control capabilities.

Conclusion

The MISA-enabled SERS assay provides sensitive, reliable, and field-ready detection of diphenylamine in baby food at levels relevant to regulatory standards, supporting improved consumer safety and rapid quality control in diverse settings.