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Dr Patrick Sears

Senior Lecturer in Chemistry and Forensic Analysis
+44 (0)1483 689580
11 AZ 01


Affiliations and memberships

Royal Society of Chemistry
Fellow of the RSC (FRSC)
British Mass Spectrometry Society
Member of BMSS and committee member for the ambient ionisation special interest group


Research interests



Simone Mathias, Daniel Burns, Tabatha Hambidge, Bryan J. McCullough, Chris J. Hopley, David Douce, Ashley Sage, Patrick Sears (2023)Assessment of atmospheric solids analysis probe as a tool for the rapid determination of drug purity, In: Drug testing and analysis Wiley

The ability to determine the purity (% controlled compound) of drug‐of‐abuse samples is necessary for public health and law enforcement. Here, we describe the assessment of atmospheric solids analysis probe (ASAP) for the rapid determination of drug purity for a set of formulated pharmaceuticals, chosen due to their availability, uncontrolled status and consistency. Paracetamol and loratadine were used as models of high and low purity compounds being ~90% and ~10% active ingredient, respectively. Individual tablets were ground up and diluted in an internal standard solution. The resulting samples were analysed by ASAP coupled to a Waters QDa mass spectrometer followed by confirmatory testing by liquid chromatography–tandem mass spectrometry (LC–MS/MS). The inclusion of a non‐matched internal standard (quinine) improved linearity and repeatability of drug analysis by ASAP‐MS. Levels of drug purity using formulated pharmaceutical tablets were found to be highly comparable with results produced by the ‘gold standard’ LC–MS/MS technique. Rapid determination of drug purity is therefore possible with ASAP‐MS for highly concentrated samples with minimal sample preparation. It may be possible to use this deployable system to determine drug purity outside of a laboratory setting.

Nathaniel Bingham, James Wright, Simone C. Mathias, David Douce, Patrick Sears (2024)Atmospheric solids analysis probe mass spectrometry: An easy bolt‐on for the synthetic undergraduate teaching laboratory, In: Rapid communications in mass spectrometry38(5)e9689

Rationale High costs and student numbers can often hinder implementation of mass spectrometry (MS) in the undergraduate teaching laboratory, often with technicians running samples on students' behalf, and the implementation of MS only in discrete or isolated experiments. This study explores the use of atmospheric solids analysis probe MS (ASAP‐MS) as a relatively low‐cost, benchtop instrument, and its potential for application as a ‘bolt‐on’ to existing undergraduate organic chemistry experiments. Methods Thirteen products synthesised in undergraduate laboratory experiments were analysed by ASAP‐MS, along with their starting materials. Analysis was carried out with a Waters RADIAN ASAP mass spectrometer, at four different cone voltages simultaneously to provide fragmentation information. Results Out of the 13 undergraduate experiments, ASAP‐MS was shown to be complementary in 11 of these, either through simple analysis of the precursor ion or by a more complex analysis of the fragments. Conclusions ASAP‐MS provided spectra that both complement and enhance intended learning outcomes in existing organic chemistry experiments, showing its versatility as a bolt‐on technique. Moving forward, ASAP‐MS will be integrated into the University of Surrey's undergraduate teaching laboratory.

Simone Caroline Mathias, Marius Amerio-Cox, Toni Louise Jackson, David Douce, Ashley Sage, Peter Luke, Richard Sleeman, Carol Crean, Patrick Sears (2023)Selectivity of Explosives Analysis with Ambient Ionization Single Quadrupole Mass Spectrometry: Implications for Trace Detection, In: Journal of the American Society for Mass Spectrometry35(1)pp. 50-61 ACS

Ambient ionization (AI) is a rapidly growing field in mass spectrometry (MS). It allows for the direct analysis of samples without any sample preparation, making it a promising technique for the detection of explosives. Previous studies have shown that AI can be used to detect a variety of explosives, but the exact gas-phase reactions that occur during ionization are not fully understood. This is further complicated by differences in mass spectrometers and individual experimental set ups between researchers. This study investigated the gas-phase ion reactions of five different explosives using a variety of AI techniques coupled to a Waters QDa mass spectrometer to identify selective ions for explosive detection and identification based on the applied ambient ionization technique. The results showed that the choice of the ion source can have a significant impact on the number of ions observed. This can affect the sensitivity and selectivity of the data produced. The findings of this study provide new insights into the gas-phase ion reactions of explosives and could lead to the development of more sensitive and selective AI-based methods for their detection.

Mehrdad Zare, PELLO ALFONSO MUNIOZGUREN, Madeleine Jean Bussemaker, Patrick Sears, Efraím A Serna-Galvis, Ricardo A Torres-Palma, Judy Yu-Ting Lee (2023)A fundamental study on the degradation of paracetamol under single- and dual-frequency ultrasound, In: Ultrasonics Sonochemistry94106320 Elsevier

The degradation of paracetamol, a widely found emerging pharmaceutical contaminant, was investigated under a wide range of single-frequency and dual-frequency ultrasonic irradiations. For single-frequency ultrasonic irradiation, plate transducers of 22, 98, 200, 300, 400, 500, 760, 850, 1000, and 2000 kHz were employed and for dual-frequency ultrasonic irradiation, the plate transducers were coupled with a 20 kHz ultrasonic horn in opposing configuration. The sonochemical activity was quantified using two dosimetry methods to measure the yield of HO• and H2O2 separately, as well as sonochemiluminescence measurement. Moreover, the severity of the bubble collapses as well as the spatial and size distribution of the cavitation bubbles were evaluated via sonoluminescence measurement. The paracetamol degradation rate was maximised at 850 kHz, in both single and dual frequency ultrasonic irradiation. A synergistic index higher than 1 was observed for all degrading frequencies (200–1000 kHz) under dual frequency ultrasound irradiation, showing the capability of dual frequency system for enhancing pollutant degradation. A comparison of the results of degradation, dosimetry, and sonoluminescence intensity measurement revealed the stronger dependency of the degradation on the yield of HO• for both single and dual frequency systems, which confirms degradation by HO• as the main removal mechanism. However, an enhanced degradation for frequencies higher than 500 kHz was observed despite a lower HO• yield, which could be attributed to the improved mass transfer of hydrophilic compounds at higher frequencies. The sonoluminescence intensity measurements showed that applying dual frequency ultrasonic irradiation for 200 and 400 kHz made the bubbles larger and less uniform in size, with a portion of which not contributing to the yield of reactive oxidant species, whereas for the rest of the frequencies, dual frequency ultrasound irradiation made the cavitation bubbles smaller and more uniform, resulting in a linear correlation between the overall SL intensity and the yield of ROS.

Catia Costa, E.M. van Es, P. Sears, J. Bunch, Vladimir Palitsin, H. Cooper, M.J. Bailey (2019)Exploring a route to a selective and sensitive portable system for explosive detection– swab spray ionisation coupled to of high-field assisted waveform ion mobility spectrometry (FAIMS), In: Forensic Science International: Synergy1pp. 214-220 Elsevier

Paper spray mass spectrometry is a rapid and sensitive tool for explosives detection but has so far only been demonstrated using high resolution mass spectrometry, which bears too high a cost for many practical applications. Here we explore the potential for paper spray to be implemented in field applications with portable mass spectrometry. This involved (a) replacing the paper substrate with a swabbing material (which we call “swab spray”) for compatibility with standard collection materials; (b) collection of explosives from surfaces; (c) an exploration of interferences within a ± 0.5 m/z window; and (d) demonstration of the use of high-field assisted waveform ion mobility spectrometer (FAIMS) for enhanced selectivity. We show that paper and Nomex® are viable collection materials, with Nomex providing cleaner spectra and therefore greater potential for integration with portable mass spectrometers. We show that sensitive detection using swab spray will require a mass spectrometer with a mass resolving power of 4000 or more. We show that by coupling the swab spray ionisation source with FAIMS, it is possible to reduce background interferences, thereby facilitating the use of a low resolving power (e.g. quadrupole) mass spectrometer.

Holly-May Lewis, Roger Webb, Guido F Verbeck, Josephine Bunch, Janella De Jesus, Catia Costa, Vladimir Palitsin, John G. Swales, Richard J. A. Goodwin, Patrick Sears, Melanie Jane Bailey (2019)Nanoextraction coupled to liquid chromatography mass spectrometry delivers improved spatially resolved analysis, In: Analytical Chemistry91(24)pp. 15411-15417 American Chemical Society

Direct analyte probed nanoextraction (DAPNe) is a technique that allows extraction of drug and endogenous compounds from a discrete location on a tissue sample using a nano capillary filled with solvent. Samples can be extracted from a spot diameters as low as 6 µm. Studies previously undertaken by our group have shown that the technique can provide good precision (5%) for analysing drug molecules in 150 µm diameter areas of homogenised tissue, provided an internal standard is sprayed on to the tissue prior to analysis. However, without an isotopically labelled standard, the repeatability is poor, even after normalisation to and the spot area or matrix compounds. By application to tissue homogenates spiked with drug compounds, we can demonstrate that it is possible to significantly improve the repeatability of the technique by incorporating a liquid chromatography separation step. Liquid chromatography is a technique for separating compounds prior to mass spectrometry (LC-MS) which enables separation of isomeric compounds that cannot be discriminated using mass spectrometry alone, as well as reducing matrix interferences. Conventionally, LC-MS is carried out on bulk or homogenised samples, which means analysis is essentially an average of the sample and does not take into account discrete areas. This work opens a new opportunity for spatially resolved liquid chromatography mass spectrometry with precision better than 20%.

Catia Costa, Cecile Frampas, Katherine A. Longman, Vladimir Palitsin, Mahado Ismail, Patrick Sears, Ramin Nilforooshan, Melanie J. Bailey (2019)Paper spray screening and LC-MS confirmation for medication adherence testing: a two-step process, In: Rapid Communications in Mass Spectrometry Wiley

RATIONALE: Paper spray offers a rapid screening test without the need for sample preparation. The incomplete extraction of paper spray allows for further testing using more robust, selective and sensitive techniques such as liquid chromatography mass spectrometry (LC-MS). Here we develop a two-step process of paper spray followed by LC-MS to (1) rapidly screen a large number of samples and (2) confirm any disputed results. This demonstrates the applicability for testing medication adherence from a fingerprint. METHODS: Following paper spray analysis, drugs of abuse samples were analysed using LC-MS. All analyses were completed using a Q Exactive™ Plus Orbitrap™ mass spectrometer. This two-step procedure was applied to fingerprints collected from patients on a maintained dose of the antipsychotic drug quetiapine. RESULTS: The extraction efficiency of paper spray for two drugs of abuse and metabolites was found to be between 15-35% (analyte dependent). For short acquisition times, the extraction efficiency was found to vary between replicates by less than 30%, enabling subsequent analysis by LC-MS. This two-step process was then applied to fingerprints collected from two patients taking the antipsychotic drug quetiapine, which demonstrates how a negative screening result from paper spray can be resolved using LC-MS. CONCLUSIONS: We have shown for the first time the sequential analysis of the same sample using paper spray and LC-MS, as well as the detection of an antipsychotic drug from a fingerprint. We propose that this workflow may also be applied to any type of sample compatible with paper spray, and will be especially convenient where only one sample is available for analysis.

Stephanie Rankin-Turner, Patrick Sears, Liam M. Heaney (2023)Applications of ambient ionization mass spectrometry in 2022: An annual review, In: Analytical Science Advancespp. 1-21 Wiley

The development of ambient ionization mass spectrometry (AIMS) has transformed analytical science, providing the means of performing rapid analysis of samples in their native state, both in and out of the laboratory. The capacity to eliminate sample preparation and pre-MS separation techniques, leading to true real-time analysis, has led to AIMS naturally gaining a broad interest across the scientific community. Since the introduction of the first AIMS techniques in the mid-2000s, the field has exploded with dozens of novel ion sources, an array of intriguing applications, and an evident growing interest across diverse areas of study. As the field continues to surge forward each year, ambient ionization techniques are increasingly becoming commonplace in laboratories around the world. This annual review provides an overview of AIMS techniques and applications throughout 2022, with a specific focus on some of the major fields of research, including forensic science, disease diagnostics, pharmaceuticals and food sciences. New techniques and methods are introduced, demonstrating the unwavering drive of the analytical community to further advance this exciting field and push the boundaries of what analytical chemistry can achieve.

Direct analysis in real time is typically performed using helium as the ionisation gas for the detection of analytes by mass spectrometry (MS). Nitrogen and argon are found with abundance in the air and provide a cheaper and greener alternative to the use of helium as ionisation gas. This study explores the use of helium, nitrogen and argon as ionisation gas for detection of organic compounds. Four illicit drugs, 2 amino acids and 5 explosives were chosen as target analytes to understand selectivity, sensitivity and linearity when helium, nitrogen or argon was used as the ionisation gas with the direct analysis in real time (DART) source. Analysis was carried out on a Waters Acquity QDa single quadrupole mass spectrometer. Calibration curves over the range of 5 - 100 ng were produced for each analyte using the different ionisation gases to assess the instrument response. Nitrogen gave a higher response to concentration than helium or argon, however the lowest limits of detection were observed when helium was used. All the target analytes were detected using DART-MS with helium, nitrogen or argon as the ionisation gas. Whilst helium provides the highest sensitivity, nitrogen produced reasonable limits of detection and had good linearity across the concentration range explored, suggesting it provides a greener and cheaper alternative to helium.

DK Burns, Simone Mathias, Bryan J McCullough, Chris J Hopley, David Douce, NM Lumley, Steve Bajic, PATRICK SEARS (2022)Ambient ionisation mass spectrometry for the trace detection of explosives using a portable mass spectrometer, In: International Journal of Mass Spectrometry471116735 Elsevier

Five different classes of explosives were analysed by ambient ionisation mass spectrometry testing selectivity, sensitivity, and repeatability. We compare the effectiveness of two techniques (ASAP and SESI) for the trace detection of five explosives representative of the most common classes of high explosive: HMTD, RDX, PETN, Tetryl and TNT. Experiments also compared the effectiveness of sample loading via a glass fibre swab or glass rod. All analyses were carried out with a Waters Acquity QDa mass spectrometer, a small format mass spectrometer which can be operated in a transportable mode (using ambient air and a small diaphragm pump). Both ambient ionisation techniques, ASAP and SESI, successfully detected the five different explosives which could make them suitable for a screening method. By directly comparing a calibration range of 0.8–10 ng on both swabs and rods for each explosive, it appears that SESI produces less variability per repeat, particularly at the higher end of the range when compared to ASAP which typically has a lower limit of detection and better linearity.

Additional publications