Received: 29 June 2017 Revised: 31 July 2017 Accepted: 3 August 2017 DOI: 10.1002/rcm.7952 RESEARCH ARTICLE Polymer‐spray mass spectrometric detection and quantitation of hydrophilic compounds and some narcotics Maria T. Dulay | Richard N. Zare Department of Chemistry, Stanford University, Rationale: High‐throughput screening of biofluids is essential in monitoring concentration of Stanford, CA 94305, USA a variety of drugs to determine their efficacy and toxicity. Organosiloxane polymers prepared by Correspondence R. N. Zare, Department of Chemistry, Stanford sol‐gel chemistry as sample supports, and electrospray ionization emitters in a single material and University, Stanford, CA 94305, USA. as an alternative to paper substrates, is described in this study. Email: [email protected] Methods: Hydrophobic drugs and hydrophilic streptomycin were analyzed by polymer‐spray mass spectrometry with an LTQ‐Orbitrap mass spectrometer. Drug samples in urine (1–2 μL) Funding information National Institute of General Medical Sciences, were deposited on an OSX polymer, allowed to dry, then electrosprayed from the polymer tip into Grant/Award Number: 1R41 GM113337‐01; the mass spectrometer without sample pretreatment. The OSX polymers, whose polarity and National Institute of Mental Health, Grant/ porosity can be controlled, were prepared by sol‐gel chemistry where methyl‐substituted Award Number: R01‐MH112188 alkoxysilanes were hydrolyzed in the presence of a pore template and an acid catalyst. Results: Five nanograms each of seven narcotic drugs were detected in <1 min (relative standard deviation (RSD) of response <1% for each drug). Calibration curves of cocaine and streptomycin in urine were used to establish the performance of the polymer. For sample 1 (n = 2), the mean recovery for cocaine was 81% with paper and 90% with polymer. Streptomycin is detected with polymer, not with paper; for samples 1 and 2 (n = 3), mean recovery was 97% and 95%, respectively. Conclusions: Organosiloxane polymers achieve more sensitive analysis than paper, allowing for more accurate quantitation of both hydrophobic and hydrophilic drug compounds. The ability to tailor the polymer polarity and porosity allows for the synthesis of a wide range of polymers, and thus opens many possibilities for further development and applications. 1 | INTRODUCTION hydrophilic interaction chromatography (HILIC), an alternative form of high‐performance liquid chromatography (HPLC), where uncharged Improving the management of a variety of diseases caused by polar compounds are separated on polar stationary phases coupled pathogenic organisms relies on the correct dosage of antibiotic drugs with mass spectrometry4 or matrix‐assisted laser desorption/ for a patient. Measuring the concentration of antibiotics administered ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS).5 to a patient as part of the dosing regimen is often done by repeated However, these analytical methods suffer from increased time of measurements of the drug concentration over time to determine the analysis because of sample pretreatment and labor‐intensive therapeutic range to sustain drug efficacy, avoid drug‐related toxicity, chromatographic procedures. Rapid analytical methods based on MS and decrease multiple‐drug resistance. Streptomycin, the most widely for high‐throughput analyses would provide important information on used aminoglycoside antibiotic used to treat infections in humans, is proper dosing of these drugs during antibiotic therapy and their a highly polar (hydrophilic) compound with narrow therapeutic index detection in commercial food products. (20–30 μg/mL) and toxicity (50 μg/mL), which may be severe or Electrospray ionization mass spectrometry (ESI‐MS) has been irreversible.1 Between 29% and 89% of the administered dose is shown to be an invaluable tool in the analysis of chemical compounds excreted unchanged in the urine within 24 h.2 Streptomycin is also in a variety of different matrices, including biological fluids. In used as a growth promoter in food‐producing animals with the conventional ESI, a small‐diameter capillary is used to generate the potential to develop streptomycin‐resistant pathogens.3 The detection electrospray that results in the formation of analyte ions. However, and quantitation of streptomycin in biofluids often requires the use of one of the drawbacks of using a capillary is the danger of clogging. Rapid Commun Mass Spectrom. 2017;31:1651–1658.wileyonlinelibrary.com/journal/rcm Copyright © 2017 John Wiley & Sons, Ltd. 1651 1652 DULAY AND ZARE Over the past two decades, improvements to sampling and ionization 2.2 | Preparation of organosiloxane (OSX) polymer have been made, including the development of ambient ionization OSX polymer was prepared by stirring 2.5 mL methyltrimethoxysilane techniques and ESI on solid substrates, such as metals and paper.6 (MTMS) with 0.72 mL water, 0.18 mL toluene, and 0.035 mL These improvements have led the way for the development of concentrated HCl for 15 min at room temperature. The reaction paper‐spray mass spectrometry, which is an appealing form of ambient solution was cast into the wells of a 24‐well polystyrene multiculture ionization mass spectrometry because only a small volume of analyte, plate at various volumes, ranging from 0.75 mL to 1.5 mL, then aged typically some biofluid, is deposited on the surface of the paper and cured at room temperature for 21 h. The polymers were cut into support, allowed to dry, and then electrosprayed from the tip of the triangles (base ~1.3 cm, each of the two sides ~1.6 cm, tip angle paper into a mass spectrometer.7-10 This technique, which requires ~49°) using conventional scissors. The polymer product was cleaned no pneumatic assistance to transport analytes to the mass of any unreacted starting materials by immersion in acetonitrile for spectrometer inlet, can be beneficial for use in on‐site therapeutic drug 2 h followed by immersion in water for approximately 18 h. The poly- monitoring in biofluids and in monitoring the quality of food products mer triangles were dried under ambient conditions before use. and can allow for high‐throughput analyses. Open‐surface sampling avoids the clogging problem of capillaries and allows for more choices of sampling support materials, such as a synthetic polymer. 2.3 | Sample preparation An important feature of sampling materials for ambient ionization Each drug stock solution was prepared by dissolving the drug in water. mass spectrometry is their polarity. Hydrophobic materials such as Drug‐spiked urine samples were prepared by directly adding the polymethylmethacrylate and polytetrafluoroethylene have been appropriate volume of drug stock solution into urine. shown to have enhanced signal intensity and stability over less hydrophobic materials used in desorption ionization techniques.11,12 Paper coated with a variety of different compounds has also been 2.4 | Calibration curves shown to have enhanced performance as sample support in paper‐spray mass spectrometry.13-22 We have found that hydrophobic Standard samples of streptomycin were prepared in urine. Linear polymer sample supports allow for the detection of hydrophilic drugs, regression analysis was carried out on known added concentrations such as streptomycin, that are not easily detected, if at all, using of streptomycin against the peak intensity of streptomycin to paper‐spray mass spectrometry. dihydrostreptomycin (internal standard). Standard samples of cocaine We describe here a modification of paper‐spray mass in urine were prepared in a similar manner, and linear regression spectrometry in which the paper support is replaced by a suitable analysis was carried out using isotope‐labeled cocaine‐d3 as the 2 organic‐inorganic hybrid organosiloxane (OSX) polymer whose internal standard. The regression coefficient (R ), slope, and intercept, porosity and chemical composition can be carefully controlled by use and equation of the resulting standard curves were determined. of a sol‐gel process,24 allowing for facile modification of the polymer Calibration curves for streptomycin in urine for polymer spray, and surface (e.g., control of the surface hydrophobicity). The sol‐gel cocaine in urine for both paper and polymer spray, are presented in process offers a simple, easy, and inexpensive route to make these the supporting information. OSX polymers. OSX polymers are used for the first time as a sampling support and an ESI emitter in a single material for the detection and 2.5 | Polymer‐spray mass spectrometry quantitation of hydrophobic narcotics (logP ~0.9 to 2.3, where logP is the partition coefficient of the concentration of the compound in Scheme 1 is a diagram of the polymer‐spray setup. Sample volumes of octanol to water),24 and for the detection and quantitation of 1to2μL were loaded near the tip of a polymer or paper triangle. The streptomycin (logP −6.4),24 a hydrophilic antibiotic drug, which is not sample droplet was dried under ambient conditions for 1 h. The tip of detectable using paper‐spray mass spectrometry. the polymer triangle was placed ~10 mm from the mass spectrometer inlet. All polymer materials used in the experiments were prepared by casting 0.75, 1.0, or 1.25 mL of reaction volume into molds. High 2 | EXPERIMENTAL voltage (5 kV) was applied by connecting the back end of the triangle to the HV power supply of the mass spectrometer via a flat stainless steel alligator clip. For paper‐spray experiments, Whatman filter paper 2.1 | Chemicals (Grade 1; Fisher Scientific, Waltham, MA, USA) was used and the Methyltrimethoxysilane (MTMS), streptomycin, dihydrostreptomycin, same process used for polymer‐spray was used for paper‐spray. The lidocaine, narcotic drugs and their deuterated analogs were spray solvent was a 1:1 (v/v) or 9:1 (v/v) combination of methanol purchased from Sigma‐Aldrich (St Louis, MO, USA) and used without and water with 0.1% by volume of formic acid. further purification. Narcotic drugs were purchased as 1 mg/mL in Mass spectrometry was performed with an LTQ‐Orbitrap XL methanol or acetonitrile: amephetamine, methamphetamine, 3,4‐ (Thermo Fisher Scientific, Waltham, MA, USA).