HPLC Separation of Aryldiamine Transformation Products using a Polar-Modified RP-C₁₈ Column

Abstract

A high-performance liquid chromatography–UV/VIS detection–electrospray ionization single quadrupole mass spectrometry (HPLC–UV/VIS–ESI-MS) method was developed to separate oxidative and photolytic degradation products of aryldiamines, that is, para-phenylenediamine and para-toluenediamine. The separation was performed on a polar modified reversed phase-C₁₈ column which provided superior chromatographic resolution compared to conventional columns. Gradient elution was used with the mobile phases of water and acetonitrile containing 10 mM ammonium acetate. Various compounds including aryldiamines, benzoquinones, aromatic nitro compounds, and azobenzenes were selected for an optimization of the ESI-MS operation and the chromatographic separation conditions. Highly linear calibrations (r² > 0.999) were achieved for a subset of 5 standard substances. Using analyte-specific UV detection wavelengths, limits of detection and limits of quantitation of these substances ranged from 3.0 to 7.0 µg L⁻¹ and from 10.0 to 23.3 µg L⁻¹, respectively. The analysis of aqueous solutions of para-toluenediamine photolysis products confirmed the performance of the method. Up to 28 chromatographic signals were recorded and the change of their peak heights during the transformation process was monitored for 24 hours. The identities of the compounds were ascertained by means of MS detection correlations between molecular features and the chromatographic retention of the compounds.

Keywords:

• Aryldiamines
• Oxidation
• Para-phenylenediamine (PPD)
• Para-toluenediamine (PTD)
• Photolysis

Acknowledgments

The funding of the research by a grant of the Research Fund of the University of Trier is gratefully acknowledged by the authors.

Notes

^a Flow rate 0.3 mL min⁻¹, column temperature 25°C.

^b Flow rate 1.0 mL min⁻¹, column temperature 25°C.

^c Flow rate 0.3 mL min⁻¹, column temperature 20°C.

Note: Chromatographic conditions as in Figure 3. Detection at 234 nm with DAD, absorbances at other wavelengths measured with standard UV/VIS-detector.

LOD: 3 times S/N ratio; LOQ: 10 times S/N ratio.

Determination of peak height precision: 6 consecutive injections.

Wavelength 234 nm: DAD detector, all others: UV/VIS detector.

Analytical conditions as in Figure 3.

Notes: Analytical conditions as in Figure 3. Saturated aqueous PTD solutions were irradiated.

^a Relative to PTD peak height.

^b Most intense signal, omitting m/z 83.08, marked in bold; 2nd most intense signal noticed only if signal intensity ≥50% of most intense signal.

n.d.: not detectable.