Anal. Chem. 2004, 76, 4349-4357
Comparison of Different Mass Spectrometric Techniques Combined with Liquid Chromatography for Confirmation of Pesticides in Environmental Water Based on the Use of Identification Points Fe´lix Herna´ndez,* Marı´a Iba´n˜ez, Juan V. Sancho, and O Ä scar J. Pozo
Analytical Chemistry, Experimental Sciences Department, University Jaume I, E-12071, Castello´ n, Spain
Three mass spectrometric techniques have been used and compared for the confirmation of the presence of several pesticides that had been detected in environmental water samples by a previously reported SPE-LC-MS/MS screening method. The 2002/657/EC European Comission Decision establishes the need to obtain at least three identification points (IPs) in order to confirm organic residues and contaminants in live animals and animal products. In this paper, a similar approach has been applied for confirmation of pesticides in water samples, using triple quadrupole mass spectrometry (QqQ), timeof-flight mass spectrometry (TOF), and hybrid quadrupole time-of-flight mass spectrometry (QTOF) to achieve the required IPs. The number of IPs collected, the sensitivity, and the practical advantages and disadvantages of these techniques have been discussed. In summary, the QqQ instrument allowed the confirmation of detected pesticides even at very low concentrations (ng/L) achieving between four and five IPs when adding confirmatory transitions. The direct confirmation with a TOF instrument was only feasible for those compounds showing sufficient sensitivity, isotopic pattern, or easy in-source fragmentation. In other cases, the required IPs could be reached by adding IPs earned with this technique to those obtained from the MS/MS screening method. Finally, the use of a QTOF instrument allowed obtaining up to 20 IPs in a single run at relatively high concentrations (submicrograms per liter) as no “ion shopping” was required. Additionally, the application of TOF and QTOF techniques made it possible to detect some nontarget organic contaminants, which were not included in the screening method. Several LC-MS(/MS) methods, based on quadrupole instruments, have been developed in the past few years in order to determine pesticides in environmental waters.1-4 Although these methods do not permit the determination of some important * To whom correspondence should be addressed. Tel: +34 964 728100. Fax: +34 964 728066. E-mail:
[email protected]. (1) Yu, K.; Krol, J.; Balogh, M. Anal. Chem. 2003, 75, 4103-4112. (2) Wang, N.; Budde, W. L. Anal. Chem. 2001, 73, 997-1006. (3) Herna´ndez, F.; Sancho, J. V.; Pozo, O.; Lara, A.; Pitarch, E. J. Chromatogr., A 2001, 939, 1-11. 10.1021/ac049768i CCC: $27.50 Published on Web 06/18/2004
© 2004 American Chemical Society
compounds, such as organochlorine pesticides and PCBs, they are chosen ahead of GC/MS-based methods as they present obvious advantages, for example, reducing sample pretreatment and having the capability to determine very polar compounds or transformation products (TPs). In the last years, applications in this field using tandem mass spectrometers have increased due to these instruments becoming more commercially affordable.5 These methods are usually based on the monitoring of one MS/ MS transition for each analyte. Although MS-based methods could be considered as highly selective methods, the occurrence of false positives is possible mainly in the analysis of relatively dirty samples, as some interferences can share the same MS properties as the analyte. This can also occur in water sample analysis and has been reported in some papers, producing some very constructive discussions on the subject.6-8 A new European Commission Guideline for identification and quantification of organic residues and contaminants has been proposed to guarantee effective and reliable control of residues in animals and fresh meat. The EC criteria are based on the use of identification points (IPs), a new approach to set up quality criteria for the spectrometric identification and confirmation of organic residues and contaminants. A laboratory is able to use any molecular spectrometric technique or combination of techniques in order to obtain the minimum number of IPs necessary for the identification of a compound. The number of IPs “earned” by the detection of a precursor/product ion depends on the technique used. If mass fragments are measured, the minimum number of points that must be obtained for group A (banned compounds) is set at four. For compounds with an established maximum residue level (group B), a minimum of three IPs is required for satisfactory confirmation of the compound’s identity. To qualify for the IPs, at least one ion ratio must be measured, all measured ion ratios must agree within specified tolerances (in LC-MS, maximum permitted tolerances range from (20%, for a (4) Hogenboom, A. C.; Hofman, M. P.; Kok, S. J.; Niessen, W. M. A.; Brinkman, U. A. T. J. Chromatogr., A 2000, 829, 379-390. (5) Reemtsma, T. Trends Anal. Chem. 2001, 20, 500-517. (6) Kolpin, D. W.; Furlong, E. T.; Meyer, M. T.; Thurman, E. M.; Zaugg, S. D.; Barber, L. B.; Buxton, H. T. Environ. Sci. Technol, 2002, 36, 1202-1211. (7) Ericson, J. F.; Laenge, R.; Sullivan, D. E. Environ. Sci. Technol. 2002, 36, 4005-4006. (8) Kolpin, D. W.; Furlong, E. T.; Meyer, M. T.; Thurman, E. M.; Zaugg, S. D.; Barber, L. B.; Buxton, H. T. Environ. Sci. Technol, 2002, 36, 4007-4008.
Analytical Chemistry, Vol. 76, No. 15, August 1, 2004 4349
Table 1. Relationship between Nature of MS Information, Mass Accuracy, and IPs Earned MS technique
IPs obtained for each iona
low-resolution (LR) MS LR-MS precursor ion LR-MS product ion high-resolution (HR) MS HR-MS precursor ion HR-MS product ion
1.0 1.0 1.5 2.0 2.0 2.5
mass accuracy error higher than 10 mDa single ion precursor ion product ion error between 2 and 10 mDa single ion precursor ion product ion error below 2 mDa single ion precursor ion product ion
IPs obtained for each ionb 1.0 1.0 1.5 1.5 1.5 2.0 2.0 2.0 2.5
a Criterion proposed by the Commision Decision. b Criterion proposed in this paper.
relative ion intensity of >50%, to (50%, for a relative ion intensity of
