Large Scale Pesticide Multiresidue Methods in Food Combining Liquid Chromatography– Time-of-Flight Mass Spectrometry and Tandem Mass Spectrometry

Abstract

Liquid chromatography tandem mass spectrometry (LC-MS/MS) and liquid chromatography time-of-flight mass spectrometry (LC-TOFMS) are powerful and complementary techniques that can independently cover the majority of the challenges related with pesticide residue food control. The sequential combination of both systems benefits from their complementary advantages and assists to increase the performance and to simplify routine large scale pesticide multiresidue methods. The proposed approach consists of three stages: (1) automated pesticide screening by LC-TOFMS; (2) identification by LC-TOFMS accurate mass measurements; and (3) confirmation and quantitation by LC-MS/MS. We have developed a fast comprehensive (identification/confirmation + quantitation) automated screening method for 100 target pesticides in crops. In the first stage, a set of data including m/z accurate mass windows (within 20 mDa width) and retention time is obtained (using a standard solution containing all the targeted pesticides) in order to build the automated screening procedure, which is created automatically by assigning retention time and the m/z mass window for each target pesticide. Samples are then analyzed, and the method enables the screening and preliminary identification of the species first by retention time and m/z mass window, followed by subsequent identification (only if positive results) by LC-TOFMS accurate mass measurements. After that, final confirmation of the positive findings using two MRM transitions and accurate quantitation is performed by LC-MS/MS using a hybrid triple quadrupole linear ion trap (QqLIT) mass spectrometer. In addition, the use of this QqLIT instrument also offers additional advantageous scanning modes (enhanced product ion and MS3 modes) for confirmatory purposes in compounds with poor fragmentation. Examples of applications to real samples show the potential of the proposed approach, including the detection of nonselected "a priori" compounds as a typical case of retrospective evaluation of banned or misused substances.

Full-scan accurate mass selectivity of ultra-performance liquid chromatography combined with time-of-flight and orbitrap mass spectrometry in hormone and veterinary drug residue analysis

“…Thus, a key question is whether the medium mass resolving power provided by time-of-flight (TOF) instruments is sufficient to enable the detection and accurate mass measurement of residues at low ng/g level in complex sample matrices. The utility of full-scan LC-TOFMS for the comprehensive screening of urine samples for drugs [3,4] and doping agents [5], crops for pesticide residues [6], and confirmation of antibiotics and fungicides in salmon [7] was demonstrated. Comparison of theoretical and measured isotopic patterns might be a useful additional tool to accurate mass determination and facilitates the identification process [8].…”

Aspectos analíticos e regulatórios na determinação de resíduos de macrolídeos em alimentos de origem animal por cromatografia líquida associada à espectrometria de massas

“…Estes espectrômetros de massas têm sido utilizados em métodos de rotina para triagem de multirresíduos de macrolídeos. 19,[86][87][88][89] Em um estudo para a determinação de seis macrolídeos em ovos, leite integral e mel, usando-se a técnica UHPLC-QToF obtiveram-se limites de detecção entre 0,1 e 1 mg kg -1 , adequados para atender os requisitos regulatórios em análises de rotina, e identificou a desmicosina (tilosina B) em mel, baseando-se na medição de massa precisa e usando o recurso de composição elementar. 19 A tilosina A sofre hidrólise e perde uma molécula de micarose, formando a tilosina B a pH 4, que é muito próximo ao pH médio típico do mel (entre 3,4 -6,1).…”

Highlights of Mass Spectrometric Methodologies in Environmental Pollution

“…This instrument retains classical QqQ modes for quantitative and qualitative analysis (SRM mode and neutral loss scan) and combines them with sensitive ion trap scan modes for the confirmation of analytes or characterization of unknowns, including enhanced product ion mode, time delayed fragmentation, and MS 3 with an ion accumulation capacity higher than a conventional three dimensional ion trap analyzer. The QqLIT analyzer can provide an improved sensitivity in these MS/MS studies and up to 200 compounds can be analyzed in a unique LC-MS/MS run, with 2 SRM transitions (Garcia-Reyes et al, 2007). The working modes (enhanced product ion and MS 3 ) are useful for the unambiguous confirmation of pesticides with poor fragmentation at low concentration levels, which cannot be easily confirmed by QqQ instruments due to the high SRM ratio between the two transitions (or absence of the second transition) for confirmatory purposes.…”