The development and inter-laboratory verification of LC–MS libraries for organic chemicals of environmental concern

Abstract

The development, verification, and comparison study between LC-MS libraries for two manufacturers' instruments and a verified protocol are discussed. Compounds in the libraries are among those considered by the U.S. EPA Office of Water as threats to drinking water including pesticides, drugs of abuse, and pharmaceuticals. The LC-MS library protocol was verified through an inter-laboratory study that involved Federal, State, and private laboratories. The results demonstrated that the libraries are transferable between the same manufacturer's product line, and have applicability between manufacturers. Although ion abundance ratios within mass spectra were shown to be different between the manufacturers' instruments, the NIST search engine match probability was at 96% or greater for 64 out of 67 compounds evaluated.

Protocol for an Electrospray Ionization Tandem Mass Spectral Product Ion Library: Development and Application for Identification of 240 Pesticides in Foods

“…Several attempts have been made to create LC-MS libraries − and search algorithms that can be used for the identification of chemicals in LC-MS/MS analysis. In a CID experiment, analytical standards were introduced into different MS/MS systems through a syringe pump , or a LC through an ESI interface. ,− Fragment-rich EPI spectra were collected via ion trap, , triple quadrupole, Q-LIT, − and quadrupole time-of-flight (Q-TOF) MS with CID experiment utilizing single or multilevel CE − or a tuning point protocol to build EPI spectral libraries.…”

“…Several attempts have been made to create LC-MS libraries − and search algorithms that can be used for the identification of chemicals in LC-MS/MS analysis. In a CID experiment, analytical standards were introduced into different MS/MS systems through a syringe pump , or a LC through an ESI interface. ,− Fragment-rich EPI spectra were collected via ion trap, , triple quadrupole, Q-LIT, − and quadrupole time-of-flight (Q-TOF) MS with CID experiment utilizing single or multilevel CE − or a tuning point protocol to build EPI spectral libraries. Due to the ionization process of different ESI sources, including but not limited to clustering of neutral species and in-source fragmentation, and the lack of standardized protocols, there was limited success in creating an EPI spectral library with features similar to the NIST GC-MS library () that can be used independent of LC-MS/MS instrument platforms.…”

Evaluation of the comparability of spectra generated using a tuning point protocol on twelve electrospray ionisation tandem‐in‐space mass spectrometers

“…Bristow and coworkers [10] suggested the attenuation of the precursor [M + H] + ion to between 50% and 10% of its initial abundance and a similar procedure was used by Rosal and co-workers. [5] However, in practice this is difficult to apply for the creation of large libraries, due to issues with the data acquisition automation. Other standardisation procedures have been described where a model compound is used to tune the instrument prior to spectra acquisition.…”

“…In addition, a common approach used for assessing the degree of agreement between product ion spectra is the use of library search algorithms, where a query spectrum can be matched to all or some of the spectra contained in the library. For each comparison, search algorithms generate a fit score or match score that gives an indication of the degree of spectral agreement.…”

“…Many attempts at standardisation have been reported previously. Bristow and coworkers suggested the attenuation of the precursor [M + H] + ion to between 50% and 10% of its initial abundance and a similar procedure was used by Rosal and co‐workers . However, in practice this is difficult to apply for the creation of large libraries, due to issues with the data acquisition automation.…”