Analysis of Sulfonated Anthraquinone Dyes by Electrospray Ionization Quadrupole Time-of-flight Tandem Mass Spectrometry

Min Li,Yufei Chen

doi:10.4172/2165-8064.1000236

Abstract

A tandem mass spectrometric method using a commercial quadrupole–time-of-flight (QTOF) mass spectrometer is described for the identification of sulfonated anthraquinone type dyes, having a 1-amino anthraquinone-2- sulfonate backbone. A total of 9 anthraquinone dye model compounds were evaporated and ionized via negative-ion electrospray ionization (ESI). Ionization of the sulfonated anthraquinone compounds primarily results in the formation of deprotonated molecules, [M-H]-. Once ionized, the ions were subjected to collision-activated dissociation (CAD). The type of neutral molecules or ions cleaved during CAD facilitates identification of the original compound. In most cases, a loss of 64 amu was observed for all dyes and was confirmed to be SO2 by high resolution mass spectrometry analysis. A unimolecular rearrangement of the sulfonate (SO3) group was triggered by CAD that allowed loss of SO2. Also, it was found that different group functionalities attached to the anthraquinone backbone (e.g., secondary aromatic amines and secondary alkyl amines) have specific fragmentation pathways that can be used to distinguish them under similar CAD conditions. For example, an anthraquinone having a secondary amine with an aromatic group attached to it (e.g., Acid Blue 25) can be differentiated from an anthraquinone having a secondary alkyl amine (e.g., Acid Blue 62) based on the product ions. The resultant fragmentation patterns could contribute to the identification of unknown dyes with similar chemical structures. The method was also successfully used in concert with targeted CAD for quantification purposes. The methodology presented here is the first stage in building a high resolution mass spectrometry dye database from the extensive uncatalogued Max Weaver Dye Library at North Carolina State University.

Highlights

The ability to identify unknown dyes in complex mixtures is of great importance in the areas of food, environment, human health, and forensics [1,2,3,4,5]
We report here the use of electrospray ionization (ESI) in combination with a quadrupoletime-of-flight (QTOF) Mass spectrometry (MS)/MS as a way to determine specific fragmentation pathways of commercial sulfonated anthraquinone dyes for identification purposes
The deprotonated molecules formed upon negative-ion ESI were subjected to collision-activated dissociation (CAD) events revealing fragmentation patterns that facilitated the identification of the anthraquinone derivatives

Summary

Introduction

The ability to identify unknown dyes in complex mixtures is of great importance in the areas of food, environment, human health, and forensics [1,2,3,4,5]. Acid dye manufacturing constitutes one of the highest production worldwide, and is normally used on nylon, synthetic polyamides, wool, silk, paper, inks and leather [6]. The continuous development of new products requiring improved dyeing properties (i.e., leveling characteristics, washfastness, and lightfastness) requires the use of suitable analytical tools for structural identification of new dyes, their byproducts and degradation products, as well as synthetic impurities. The chemical structures of dyes are often protected by patents, making their characterization a challenge. The same dye type may have a different structure depending on the colorant manufacturer. For this reason, we set about to develop a suitable methodology for the analysis of these compounds, both qualitatively and quantitatively

Methods

Results

Conclusion