In-capillary microextraction for direct mass spectrometry analysis of biological samples

Arc-Induced Electrospray Ionization Mass Spectrometry

Arc-induced electrospray ionization mass spectrometry (AESI-MS) was developed during which alternating current electrospray is simply achieved through the arc plasma. The AESI source exploits the arc's temperature and charge properties to generate aerosols consisting of charged microdroplets. The electrospray region, in which organic molecules are contained within microdroplets, partially overlaps with the arc plasma region. Guided by the electric field, these molecules undergo ionization, yielding ionic target analytes. AESI represents a soft ionization method that combines the mechanisms of atmospheric pressure chemical ionization and electrospray ionization, facilitating the ionization of analytes with wide ranging polarities. The precisely targeted spraying area enhances ion entry into the mass analyzer, thereby enabling excellent ionization efficiency. The AESI source exhibits several notable advantages over the electrospray ionization source, including an elevated but comparable level of active species concentrations and types, simplified mass spectra for direct amino acid analysis, high salt tolerance, versatile analysis of compounds with varying polarities, and reliable quantitative analysis of amino acids in complex matrices. Overall, AESI broadens the methodologies employed to generate microdroplets, providing a technological and scientific framework for creating distinctive electrospray ionization techniques.

Slug-Flow Microextraction Mass Spectrometry for Enhanced Detection of Analytes in Human Tear Fluids using Noninvasive Microsampling and Nanoelectrospray Ionization via a Capillary

In vivo noninvasive sampling and sensitive analysis of human tear fluids at the microliter level is an important but challenging task in investigating eye health. In this work, capillary microsampling coupled with slug-flow microextraction mass spectrometry (SFME-MS) was developed for enhanced detection of analytes in human tear fluids. As low as 1.0 μL of human tear fluid could be directly sampled using a capillary, and extraction/spray solvent was then loaded into the capillary to perform slug-flow microextraction and direct nanoelectrospray ionization (nESI) of analytes. All analytical procedures, including tear microsampling, microextraction, and ionization of analytes, were performed using a capillary. Enhanced detection of therapeutic drugs and disease biomarkers in human tear fluids was successfully demonstrated. Acceptable analytical performances including sensitivity, reproducibility, and quantitation were obtained. It is found that the use of SFME could improve the nESI-MS detection of trace analytes over 100-fold that depends on the chemical properties of analytes. Overall, this study showed that SFME-nESI-MS is a highly effective method for enhanced detection of trace analytes in tear fluids and is expected to be a potentially powerful tool in significant biological and clinical applications.

Portable mass spectrometry system: instrumentation, applications, and path to 'omics analysis

Mass spectrometry (MS) is an information rich analytical technique and plays a key role in various 'omics studies. Standard mass spectrometers are bulky and operate at high vacuum, which hinder their adoption by the broader community and utility in field applications. Developing portable mass spectrometers can significantly expand the application scope and user groups of MS analysis. This review discusses the basics and recent advancements in the development of key components of portable mass spectrometers including ionization source, mass analyzer, detector, and vacuum system. Further, major areas where portable mass spectrometers are applied are also discussed. Finally, a perspective on the further development of portable mass spectrometers including the potential benefits for 'omics analysis is provided.

Covalent organic framework-based solid phase microextraction coupled with electrospray ionization mass spectrometry for sensitive screening and quantitative evaluation of carbamazepine and its metabolite in mice

Carbamazepine (CBZ) and its metabolite carbamazepine-10,11-epoxide (CBZEP) play vital role in the treatment of epilepsy. It is of great importance to develop a method for rapid and sensitive monitoring of CBZ and CBZEP due to their narrow therapeutic index. Herein, an imine-linked-based covalent organic framework was synthesized by using 1,3,5-tris (4-aminophenyl) benzene (TPB) and 1,3,5-triformylbenzene (TFB) (denoted as TPB-TFB-COF)，and applied as a solid-phase microextraction (SPME) probe for extracting CBZ and CBZEP. The TPB-TFB-COF showed large surface areas (371 m² g^-1), high regular porosity (1.23 nm) and extraordinary stability, which rendered it an ideal adsorbent for highly efficient enrichment of CBZ and CBZEP. Accordingly, an attractive strategy of the combination of the TPB-TFB-COF-based SPME probe and electrospray ionization mass spectrometry system (ESI/MS) was proposed for rapid screening and sensitive monitoring of CBZ and CBZEP. Under the optimized parameters, the developed method exhibited good linearity for CBZ and CBZEP in the range of 4-1000 μg L^-1 with correlation coefficient (r) no less than 0.9953, and the corresponding limits of detection (LODs) were 0.4 and 2.5 μg L^-1, respectively. Moreover, high enrichment factors (EFs, 202-351 folds) and satisfactory relative standard deviations (RSDs) of one probe (3.3-5.1%) and probe-to-probe (4.8-5.6%) were obtained. By using the proposed method, sensitive screening and quantitative evaluation of CBZ and CBZEP in mice whole blood and tissue homogenates were successfully achieved, indicating the promising applicability of the TPB-TFB-COF-SPME-AMIS as a powerful tool for drug monitoring.

Hyphenated sample preparation-electrospray and nano-electrospray ionization mass spectrometry for biofluid analysis

Stand-alone electrospray ionization mass spectrometry (ESI-MS) has been advancing through enhancements in throughput, selectivity and sensitivity of mass spectrometers. Unlike traditional MS techniques which usually require extensive offline sample preparation and chromatographic separation, many sample preparation techniques are now directly coupled with stand-alone MS to enable outstanding throughput for bioanalysis. In this review, we summarize the different sample clean-up and/or analyte enrichment strategies that can be directly coupled with ESI-MS and nano-ESI-MS for the analysis of biological fluids. The overview covers the hyphenation of different sample preparation techniques including solid phase extraction (SPE), solid phase micro-extraction (SPME), slug flow micro-extraction/nano-extraction (SFME/SFNE), liquid extraction surface analysis (LESA), extraction electrospray, extraction using digital microfluidics (DMF), and electrokinetic extraction (EkE) with ESI-MS and nano-ESI-MS.

In-tube solid-phase microextraction: Current trends and future perspectives

In-tube solid-phase microextraction (IT-SPME) was developed about 24 years ago as an effective sample preparation technique using an open tubular capillary column as an extraction device. IT-SPME is useful for micro-concentration, automated sample cleanup, and rapid online analysis, and can be used to determine the analytes in complex matrices simple sample processing methods such as direct sample injection or filtration. IT-SPME is usually performed in combination with high-performance liquid chromatography using an online column switching technology, in which the entire process from sample preparation to separation to data analysis is automated using the autosampler. Furthermore, IT-SPME minimizes the use of harmful organic solvents and is simple and labor-saving, making it a sustainable and environmentally friendly green analytical technique. Various operating systems and new sorbent materials have been developed to improve its extraction efficiency by, for example, enhancing its sorption capacity and selectivity. In addition, IT-SPME methods have been widely applied in environmental analysis, food analysis and bioanalysis. This review describes the present state of IT-SPME technology and summarizes its current trends and future perspectives, including method development and strategies to improve extraction efficiency.

On-site testing of multiple drugs of abuse in urine by a miniature dual-LIT mass spectrometer

There is an increasing need for rapid and on-site detection of emerging drugs of abuse. In this work, we developed a method using a miniature dual-LIT (linear ion trap) mass spectrometer recently developed with comprehensive tandem mass spectrometry analysis capability, for qualitative and quantitative analysis of multiple drugs of abuse. Paper-capillary spray cartridges were used with related workflow established to simplify overall analysis procedure. Quantitation of ketamine and methamphetamine was achieved by beam-type collision-induced dissociation on the miniature dual-LIT mass spectrometer and a linear concentration range of 100-5000 ng/mL was obtained. The system has been applied in analysis of real urine samples from individuals addicted to morphine and methamphetamine use. The changes of the ratio of cocaine to its metabolite benzoylecgonine were also explored to estimate the time of cocaine intaking.

High-Throughput Liquid-Liquid Extractions with Nanoliter Volumes

Current methods for liquid-liquid extractions generally require microliter to milliliter volumes of solvents and sample, long equilibration times, and manual procedures. Extraction methods for samples in microfluidic systems have been limited as this tool is difficult to implement on the nanoliter or smaller scale. We have developed slug-flow nanoextraction (SFNE), a method based on droplet microfluidics that allows multiple liquid-liquid extractions to be performed simultaneously in a capillary tube, using only 5 nL of sample and extraction solvent per extraction. Each two-phase slug is segmented from the others by immiscible carrier fluid. We found rapid extractions (<5 s), partition coefficients matching those achieved at larger scale extractions, and potential to preconcentrate samples through volume manipulation. This method was used to accurately and rapidly determine octanol-water partition coefficients (Kow), determining identical Kow as the shake-flask method for acetaminophen, Kow = 2.48 ± 0.02. The measurement, along with calibration and 12 replicates, was complete within 5 min, consuming under 150 nL of solvent and sample. The method was also applied to extract analytes from complex biological samples prior to electrospray ionization-tandem mass spectrometry (ESI-MS/MS) at a rate of 6 s per sample, allowing for simultaneous determination of five different drugs spiked into human plasma, synthetic urine (SU), and artificial cerebral spinal fluid (aCSF) using ethyl acetate as the extraction phase. The signal-to-noise (S/N) for analytes improved up to 19-fold compared to direct ESI-MS of single-phase droplets (aqueous plugs segmented by carrier fluid), with limits of detection down to 7 nM (35 amol).

High-Precision Quantitation of Biofluid Samples Using Direct Mass Spectrometry Analysis

The transition of mass spectrometry for clinical analysis is highly desirable, and major progress has been made with direct sampling ionization for operation simplification. High-precision quantitation, however, remains a major challenge in this transition. Herein, a novel method was developed for direct quantitation of biofluid samples, using an extremely simplified procedure for incorporation of internal standards selected against the traditional rules. Slug flow microextraction was used for the development, with conditions predicted by a theoretical model, viz., using internal standards of partition coefficients very different from the analytes and large sample-to-extraction solvent volume ratios. Direct quantitation of drug compounds in urine and blood samples was demonstrated. This development enabled an extremely simplified protocol that is expected to have a significant impact on on-site or clinical analysis.

Direct sampling mass spectrometry for clinical analysis

Direct sampling mass spectrometry (MS) has been advancing aggressively, showing immense potential in translating MS into the clinical field. Unlike traditional MS analysis involving extensive sample preparation and chromatographic separation, quick and simple procedures with minimal sample pretreatment or purification became available with direct sampling. An overview of the development in this field is provided, including some representative ambient ionization and fast extraction methods. Quantitative applications of these methods are emphasized and their efficacy are highlighted from a clinical aspect; non-quantitative applications in clinical analysis are also discussed. This review also discusses the integration of direct sampling MS with miniature mass spectrometers and its future outlook as an emerging clinical tool for point-of-care analysis.