Determination of N-Nitrosamines by USEPA Method 521 using Triple Quadrupole Gas Chromatography Mass Spectrometry

This poster describes development of a Multiple Reaction Monitoring (MRM) instrument method using a commercially available triple quadrupole GC/MS/MS for detection and quantitation of N-nitrosamines after extraction as described by USEPA Method 521 (2004). GC/MS/MS in MRM mode produces significant improvements in selectivity and specificity, as well as dramatically lower detection limits than single quadrupole GC/MS, especially in complex matrices producing background interferences. In addition, this poster presents final instrument configuration and operating conditions, as well as instrument validation results, including estimated MDLs, and precision & accuracy as evaluated using standards at various concentration levels. Method 521 tandem MS with CI results are compared to the electron impact ionization triple quadrupole results. The intent was to create a determination step simpler than the techniques described in the method; therefore, this method uses 70 Electron Volt EI ionization, and simple syringe injection of 2 micro-liters of sample. Eliminating CI and LVI simplifies the method. The objective of this poster was to develop a simpler determination step than that described in the existing EPA 521 method and the various other N-nitrosamine experiments reported elsewhere. Because Method 521 is a drinking water method, there is very little modification allowed. Even though Section 6.11.3 of the method states: "The tandem mass spectrometer may be either a triple quadrupole or an ion trap", the same section also states "during the method development, only ion trap spectrometers were used". Changing a detector is not allowed unless there is sufficient data to support the change. Unlike the flexibility allowed with 40 CFR Part 136.6 for wastewater, modifications of drinking water methods must go through a full ATP evaluation; since drinking water regulations are national standards, single laboratory validations are not permitted. This poster demonstrates a “proof of concept” and demonstrates that the triple quadrupole MS/MS detection technique provides data that are as "equally effective" as tandem ion trap MS/MS.