Quantitative Screening of Twenty Six Aromatic Amines Originated from Azo Dyes by LC/MS Method

Significance of the Topic

Textile and leather products often employ azo dyes for their vivid colors and durability. Under reductive conditions these dyes can break down and release aromatic amines, some of which are recognized human carcinogens. Regulatory bodies such as the European Union have therefore restricted certain azo dyes and set a maximum limit of 30 ppm for individual aromatic amines in consumer goods. Reliable analytical methods are essential to ensure compliance and protect public health.

Objectives and Study Overview

This application study presents a quantitative screening method for 26 aromatic amines derived from azo dyes. The approach combines sensitivity and confirmatory power by using simultaneous selected ion monitoring (SIM) and full scan acquisition on a Shimadzu LCMS-2020 platform. Although no sample conversion of dyes to amines is included, the method aims to detect and quantify the target compounds at levels compatible with EU regulations.

Methodology and Instrumentation

The analytical method couples reversed-phase liquid chromatography with electrospray ionization mass spectrometry in positive mode. Key parameters include:

• Column: Shim-pack XR-ODSIII, 150 × 2 mm
• Mobile phases: A = 10 mM ammonium acetate (pH 3.6), B = acetonitrile
• Gradient: 10 % B to 60 % B over 22 min, rise to 98 % B by 28 min, then re‐equilibration
• Flow rate: 0.20 mL/min, column oven at 40 °C
• Injection volume: 10 µL
• Mass spectrometer: LCMS-2020 single quadrupole, ESI interface
• SIM/Scan acquisition: positive mode, block temp 200 °C, desolvation line at 250 °C, nebulizing gas 1.5 L/min, drying gas 15 L/min

Main Results and Discussion

Retention times for the 26 amines spanned from 1.8 min (1,4-phenylene diamine) to 27.8 min (o-aminoazotoluene). The protonated molecular ion [M+H]+ was monitored in SIM for quantitation, while full‐scan spectra served to confirm identity and avoid false positives. Calibration curves constructed over 2–15 ppm exhibited excellent linearity (R2 > 0.94) for all compounds. Sensitivity varied: highly responsive analytes such as o-aminoazotoluene and p-cresidine showed low response factors (Rf ≈ 1–2 × 10^6), whereas less sensitive targets like p-chloroaniline (Rf ≈ 970 × 10^6) required attention during quantitation. Co-occurrence of M+ molecular ions in some benzidine derivatives was verified by high‐resolution MS/MS, underscoring the benefit of full‐scan confirmation.

Benefits and Practical Applications of the Method

This SIM/Scan LC–MS approach offers:

• Simultaneous screening and quantitation of all 26 amines in a single run
• High throughput compatible with regulatory limits (30 ppm)
• Enhanced selectivity via full‐scan confirmation to reduce false positives
• Flexible calibration enabling quantitative screening in complex matrices

Future Trends and Possibilities for Use

Further developments may include integration of on-line sample preparation to automate azo dye reduction and extraction. Expanding the method to high-resolution mass spectrometers could improve specificity for challenging matrices. Coupling with chemometric data analysis offers potential for rapid compliance screening in textile and leather manufacturing quality control.

Conclusion

A robust LC–MS screening protocol has been established for 26 aromatic amines relevant to EU azo dye regulations. Utilizing simultaneous SIM and scan acquisition on the Shimadzu LCMS-2020, the method achieves reliable detection, confirmation, and quantitation across the required concentration range. Adoption of this workflow supports regulatory compliance and consumer safety, pending validation with real sample matrices and tailored sample pretreatment.

Reference

1. Regulation (EC) No 1907/2006 of the European Parliament and of the Council, 18 Dec 2006
2. Directive 2002/61/EC of the European Parliament and of the Council, 19 July 2002
3. P. Sutthivaiyakit et al., Anal Bioanal Chem (2005) 381:268–276
4. M.C. Garrigos et al., J Chromatogr A (2002) 963:427–433