May 28 - June 1, 2006 Washington State Convention & Trade Center Seattle, Washington http://www.asms.org/
CSS Analytical Poster Contribution:
Characterization of Di- and Tri-substituted Sulfonated Azo Dyes by LC/ESI/MS/MS, LC/EI/MS and LC/CI/MS
James M. Chapman1; Cagney Bennett1; Andrea Dolezal1; Scott Niemann2
1Rockhurst University, Kansas City, MO; 2CSS Analytical Company, Shawnee, KS
Introduction: Azo dyes have been used for a variety of purposes in the textile, colorant, and food industries. It is estimated that about 65 million pounds of sulfonated azo dyes are used annually by the textile industry. Azo dyes are also found as colorants in water-soluble markers and in certain types of processed foods. The general structure of an azo dye is Ar-N=N-Ar’. The addition of sulfonic acid groups to the aromatic rings enhances the solubility, but imparts a low volatility to the molecule. This low volatility significantly reduces, if not eliminates, the information that can be obtained from the standard electron-impact mass spectrometry techniques.
Methods: In order to gain a better understanding of the sulfonated dyes with regards to their mass spectral detection and characteristic fragmentation patterns, this study analyzed seven disulfonated and trisulfonated azo dyes using liquid chromatography electrospray ionization (ESI), liquid chromatography electron impact (EI), and liquid chromatography chemical ionization (CI) mass spectrometry. LC/ESI/MS/MS was conducted and recorded in alternating positive and negative modes on the commercially obtained dyes after chromatography with isocratic 35% acetonitrile: water with 0.1% formic acid on a C-18 column. LC/EI/MS or LC/CI/MS data was obtained under the same chromatographic conditions by utilizing a particle beam interface attached to an Agilent 5973 MSD.
Preliminary Results: The dyes selected for the study included Acid Violet 12, Acid Green 3, Acid Blue 9, Acid Yellow 17, Acid Yellow 23, Acid Red 52, and Yellow F.D. & C. #6. Our preliminary work has allowed us to develop predictive mechanisms of azo dye fragmentation that could prove useful in identifying the azo dyes under similar analytical conditions in clothing, colorants, foodstuffs, or as environmental bioaccumulants. The parent mass ions generated under ESI conditions for the dyes were consistently in higher abundance in the positive mode over the negative mode for all but two of the dyes which yielded no discernible parent mass ions in the negative mode. Many structurally important fragment ions were obtained through LC/ESI/MS/MS in positive and negative mode. The loss of SO3 was observed in the negative mode for the dyes whereas some fragments such as NCH2CH3, and SO3C6H4CH2 have been observed to form in either mode. These fragments and others that were observed will help to characterize and identify sulfonated azo dyes found in clothes, markers, and foodstuffs. Our experimentation with the dyes by LC/EI/MS utilizing a particle beam interface yielded principally low molecular weight structural fragments with no parent mass ions detected even in minor abundance. While volatilization of the dyes was obtained under the experiment conditions, the absence of parent mass ions seems to indicate that the energy in the EI proved to be too high for the analysis despite attempts with 70 and 35 keV. Additional work with the LC/CI/MS and particle beam interface will be carried out to investigate the utility of this softer ionization technique to generate parent mass ions.
Event Calendar
