Rapid screening of illegally added drugs in functional food using a miniature ion trap mass spectrometer

Research advances in detection of food adulteration and application of MALDI-TOF MS: A review

Food adulteration and illegal supplementations have always been one of the major problems in the world. The threat of food adulteration to the health of consumers cannot be ignored. Food of questionable origin causes economic losses to consumers, but the potential health risks cannot be ignored. However, the traditional detection methods are time-consuming and complex. This review mainly discusses the types of adulteration and technologies used to detect adulteration. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) is also emphasized in the detection of adulteration and authenticity of origin analysis of various types of food (milk, meat, edible oil, etc.), and the future application direction and feasibility of this technology are analyzed. On this basis, MALDI-TOF MS was compared with other detection methods, highlighting the advantages of this technology in the detection of food adulteration. The future development prospect and direction of this technology are also emphasized.

A simple numerical simulation model can elucidate the key factors for designing a miniaturized ion trap mass spectrometer

BACKGROUND

Miniature ion trap mass spectrometer enables mass-to-charge ratio analysis of ions via quadrupole field in a low vacuum environment. It plays an important role in on-site detection due to its portability and specificity. In order to gain a deeper understanding of the analysis mechanism of miniature ion trap mass spectrometers, a quadrupole MS ion trajectory numerical simulation model (QITNS) is established in this paper for ions trajectory calculation under the action of quadrupole field, exciting field and neutral gas molecule collision. Compared with the existing methods, the model in this paper is simpler and more direct, which effectively explored the effects of dipole excitation and quadrupole excitation on ion manipulation under high background pressure.

RESULTS

The simulation results demonstrate that high RF amplitude, low auxiliary AC amplitude and quadrupole excitation can effectively improve the isolation resolution. Besides, it clarified the difference between the analysis mechanism of ion trap mass spectrometers under high background pressure (above 13.332 Pa) and absolute vacuum conditions. The relevant results are consistent with the conclusions of previous experiments and other theories, proving the applicability and accuracy of the proposed calculation model and solution method.

SIGNIFICANCE

This research bears the guiding significance for further understanding the mechanism of quadrupole mass spectrometry as well as designing and developing miniature mass spectrometers.

Rapid screening and identification of targeted and non-targeted illegal added drugs in functional foods by MRSIT-HRMS based on NIST screening database

The last few decades have witnessed the increasing consumption of functional foods, leading to the expansion of the worldwide market. However, the illegal addition drugs in functional foods remains incessant despite repeated prohibition, making it a key focus of strict crackdowns by regulatory authorities. Effective analytical tools and procedures are desperately needed to rapidly screen and identify illegally added drugs in a large number of samples, given the growing amount and diversity of these substances in functional foods. The MRSIT-HRMS (Multiple Sample Rapid Introduction combined with High Resolution Mass Spectrometry) without chromatographic separation, after direct sampling, utilizes NIST software (National Institute of Standards and Technology) matching with a home-built library to target identification and non-targeted screen of illegal additives. When applied to 50 batches of suspicious samples, the targeted method detected illegal added drugs in 41 batches of samples, while the non-targeted method screened a new phosphodiesterase-5 (PDE-5) inhibitor type structural derivative. The positive results obtained by the targeted method were consistent with LC-MS/MS (QQQ). The novel MRSIT-HRMS with a limit of quantification (LOD) of 1 μg/mL achieved 100 % correct identification for all 50 batches of actual samples, demonstrating its potential as a highly promising and powerful tool for fast screening of illegally added drugs in functional food, especially when compared to traditional LC-MS/MS methods. This is essential for ensuring drug safety and public health.

Direct Performance of Triple-Stage Tandem Mass Spectrometry Analysis Using Dual-Direction Dipolar Excitation in a Digital Linear Ion Trap

The ion trap mass spectrometer offers a unique advantage over other mass spectrometers by enabling multistage tandem mass spectrometry analysis with a single mass analyzer. It is employed to generate fragment ions through collision-induced dissociation (CID) usually by applying alternating current (AC) signals to a pair of electrodes for dipole excitation. The process of achieving double-stage tandem mass spectrometry analysis (MS/MS) in the mass spectrometer involves successive stages of injection, cooling, isolation, excitation, and scanning. For triple-stage tandem mass spectrometry analysis (MS/MS/MS), additional stages of isolation, cooling, and excitation need to be added based on the MS/MS analysis, resulting in a complex and time-consuming mass spectrometry workflow. In this study, a digital ion trap technology with the method of simultaneously applying dipole excitation signals to two pairs of electrodes in the ion trap was developed. This allows fragmentation of the precursor ion in one direction while exciting the first-generation product ions in the other direction, enabling direct acquisition of MS/MS/MS spectra. This approach simplifies the process of tandem mass spectrometry, as demonstrated by experimental studies on methamphetamine, which show that dual-direction excitation effectively reduces workflow and enhances the intensity of product ions. Additionally, the method of direct MS/MS/MS spectra achieved through dual-direction excitation in a digital ion trap mass spectrometer allows for a lower q value of the precursor ion owing to a pseudopotential well depth that is 1.648 times greater than that of a traditional sinusoidal ion trap. The experiments of analyzing high concentration n-butyl acetate and isobutyl acetate have shown that the implementation of MS/MS/MS analysis using dual-direction excitation can provide more mass spectral information and effectively distinguish between the two isomeric samples. The results of direct triple-stage spectra obtained by this technique for several typical volatile hazardous chemicals demonstrate the method's capability for rapid analysis and detection of such substances. In summary, the developed method of dual-directional excitation coupled with digital ion trap technology enables direct performance of triple-stage tandem mass spectrometry analysis, improving fragment ion intensities and providing more valuable mass spectral information. It offers advantages such as simplified workflows, faster analysis, and enhanced accuracy for analyzing compounds with low mass fragment ions.

Capillary self-aspirating electrospray ionization (CSESI) for convenient and versatile mass spectrometry analysis

Electrospray ionization (ESI) is one of the most widely used ionization techniques, and its simplification can benefit many interested users. In this study, sample introduction by capillary action was studied and used to develop a simple ESI source called capillary self-aspirating electrospray ionization (CSESI). A conventional CSESI source requires only a common capillary of appropriate diameter in addition to the support of high voltage (HV). No pumps and sample loading is needed because the solution can spontaneously climb across the capillary by capillary action. With the proper modification of the glass capillary, the operation of CSESI can be further simplified and efficient. Specifically, cold plasma processing of the capillary creates a more hydrophilic surface that can facilitate sample introduction. Moreover, sputtering a thin platinum layer on the capillary tip makes the application of HV more convenient, and it also eliminates the influence of air bubbles in the capillary to ensure a sustained and stable electrospray. Overall, CSESI exhibits multiple desirable features such as simple structure, self-aspiration ability, low sample consumption, and inherent physical filtration capability. Apart from the routine ESI-MS analysis, it has also been applied in real-time monitoring of the oxidative dimerization of 8-methyl-1,2,3,4-tetrahydroquinoline, as well as direct analysis of muddy soil solutions without pretreatment.

SR-Unet: A Super-Resolution Algorithm for Ion Trap Mass Spectrometers Based on the Deep Neural Network

The mass spectrometer is an important tool for modern chemical analysis and detection. Especially, the emergence of miniature mass spectrometers has provided new tools for field analysis and detection. The resolution of a mass spectrometer reflects the ability of the instrument to discriminate between adjacent mass-to-charge ratio ions, and the higher the resolution, the better the discrimination of complex mixtures. Quadrupole ion traps are generally considered as a low-resolution mass spectrometry method, but they have gained wide attention and development in recent years because of their suitability for miniaturization and high qualitative capability. For an ion trap mass spectrometer, the mass sensitivity and resolution can be mutually constrained and need to be balanced by setting an appropriate scanning speed. In this study, a super-resolution U-net algorithm (SR-Unet) is proposed for ion trap mass spectrometry, which can estimate the possible ions from the overlapping ion peaks of low-resolution spectra and improve the equivalent resolution while ensuring sufficient sensitivity and analysis speed of the instrument. By determining the mass spectra of a linear ion trap mass spectrometer (LTQ XL) in Turbo and Normal scan modes, the same unit mass resolution as that at a scan speed of 16,667 Da/s was successfully obtained at 125,000 Da/s. Also, the experiments demonstrated that the algorithm is capable of the mass-to-charge ratio and instrument migration. SR-Unet can be migrated and applied to a miniature mass spectrometer for cruise detection of volatile organic compounds (VOCs), and the identification of VOC species in Photochemical Assessment Monitoring Stations (PAMS) was improved from 31 to 50 species with the same monitoring and analysis speed requirement. Further, super-unit mass resolution peptide detection was achieved on a miniature mass spectrometer with the help of the SR-Unet algorithm, which reduced the full width at half-maxima (FWHM) of bradykinin divalent ions (m/z 531) from 0.35 to 0.15 Da at a scan speed of 375 Da/s and improved the equivalent resolution to 3540. The proposed method provides a new idea to enhance the field mixture detection capability of miniature ion trap mass spectrometers.

Swab-in-Capillary Electrospray Ionization and a Miniature Mass Spectrometer for In Situ Drug Analysis

In situ analysis of drugs has been in increasing demand in many fields. As an updated version of capillary-in-capillary electrospray ionization (CC-ESI) developed previously, a disposable swab-in-capillary electrospray ionization (SC-ESI) source was designed in this study. With a micro medical swab for sampling and an integrated filter membrane for online filtration, SC-ESI was able to directly sample and MS analyze complex samples without the need for pretreatment. Coupled with a miniature mass spectrometer, SC-ESI was applied for direct analysis of effective ingredients in therapeutic drugs (in tablet, capsule, and liquid droplet) and drugs in saliva and quantitation of therapeutic drugs in blood. The limits of detection in absolute amounts were obtained as 1 ng for fentanyl and 0.5 ng for cocaine in saliva. Combining with an internal standard method, SC-ESI acquired linear quantitation ranges of 100-5000 ng/mL for imatinib in whole blood and 100-2000 ng/mL for clozapine in serum with high accuracies and precisions. The entire analysis process, from sampling to data acquisition, can be completed in less than 2 min. As demonstrated as a cheap, portable, and sampling-effective ionization source, SC-ESI has shown great potential for in situ drug analysis, especially in border drug screening and clinical therapeutic drug monitoring.

Development and application of a miniature mass spectrometer with continuous sub-atmospheric pressure interface and integrated ionization source

For the miniature mass spectrometer (MS) with a continuous atmospheric pressure interface (CAPI), the gas in the multi-stage chambers directly affects the performance of the instrument. In this study, a sealed ionization chamber is designed to couple with a conventional mini CAPI-MS. In this configuration, the gas environment in the first ionization chamber can be flexibly changed to regulate the gas conditions throughout the entire instrument. By studying the effect of gas pressure on the performance of the instrument, we found that the instrument shows some unique advantages when the first ionization chamber is under sub-atmospheric pressure (SAP) conditions, such as reducing the load of the vacuum pump by 40%, achieving pump-free injection for gas and liquid samples, and improving the resolution by a factor of 2 without loss of detection sensitivity. Therefore, we propose a new integrated interface called continuous sub-atmospheric pressure interface (CSAPI) for building a miniature ion trap mass spectrometer. The CSAPI specially integrates sample introduction, gas/ions interface, and ionizations, including electrospray ionization (ESI) and secondary electrospray ionization (SESI), making this system more convenient for non-professional handlers to rapidly identify or monitor target analytes in gaseous- and solution-phase samples. We also use this system to study gas composition to further improve performance, being able to achieve a 5-fold sensitivity and 2-fold resolution improvement. At last, some custom applications of the current CSAPI-MS platform are explored and demonstrated, including real-time monitoring of chemical reactions in solution and long-distance sampling and analysis of dried Chinese herbs. In conclusion, this study provides a new approach to constructing a complete, versatile and practical miniature MS instrument.