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Capillary electrophoresis (CE) coupled with mass spectrometry (MS) through electrospray ionization (ESI) is a promising alternative technique to liquid chromatography-ESI-MS (LC-ESI-MS) due to its high separation efficiency and high detection sensitivity. A sensitive and robust interface is essential in CE-ESI-MS. Continued development of CE-ESI-MS interfaces in the last decade, including junction-at-the-tip interfaces and sheathless interfaces, has improved the sensitivity and robustness of CE-ESI-MS significantly. The limited loading capacity of CE, one of major reasons that limits the utility of CE as a routine separation method, has also been addressed effectively by the use of in-capillary sample preconcentration techniques, such as transient CITP/CZE and dynamic pH junction. CE-ESI-MS could yield higher sensitivity as compared with the conventional LC-ESI-MS, and, therefore, is capable of identifying more proteins and peptides when the sample amount is very limited, such as single cell analysis. To improve the protein sequence coverage, CE-ESI-MS can also be used as a complementary technique to LC-ESI-MS, or combined with reversed phase LC to form a two dimensional separation technique. CE-ESI-MS is also effective in quantifying targeted peptides/proteins in complex bio-matrix.

While portability is a key aspect of small mass spectrometers, they also need to be able to effectively screen the analytes from complex matrices. The accuracy and performance of mass spectrometers depend not only on the identification of parent ion signals in targets but also fragment ion signals. This paper reports on the construction of a device that uses a new time-domain excitation waveform called qualitative pre-scan waveform (QPSW) for its quadrupole ion trap mass spectrometry analyzer. This approach uses scanning to eliminate interfering ions, thus improving the sensitivity for the analyte and removing the cumbersome steps required to convert conventional stored waveform inverse Fourier transform (SWIFT) waveforms from the frequency domain to the time domain. Tests show that the target ions can be fragmented just by introducing air at the moment when the pinch valve is opened without any need for a carrier gas. This simplifies the equipment required, making the mass spectrometer more portable. Tests were undertaken to compare the performance with the use of conventional SWIFT waveforms and to optimize its experimental parameters so that the target ions were effectively accumulated in the ion trap. An approximate 5-fold improvement in sensitivity was achieved by QPSW compared to the SWIFT for 2 μg/mL ketamine. A 5-fold reduction in the limit of detection (LOD) to 20 ng/mL was also obtained for enrofloxacin. In addition, the stability was improved by QPSW with a relative standard deviation less than 13% compared to 16% for SWIFT. [ABSTRACT FROM AUTHOR]

The detection limit is one of the most important performance characteristics for portable mass spectrometers (MS). To significantly reduce the size and the weight, small vacuum pumps are used in portable MS which leads to the use of a discontinuous atmospheric pressure interface (DAPI). Multiple ion injections (M-DAPI), which accumulates ions through opening the DAPI pinch valve several times during the ion injection period while maintaining a radio frequency (RF) voltage continuously on the trap, was shown to improve the sensitivity of DAPI-based portable MS. A systematic investigation of the optimization of M-DAPI was performed. The primary parameters affecting the performance of M-DAPI were optimized and sensitivity and stability improvements are reported. An 11.6-fold improvement in sensitivity was achieved by M-DAPI compared to the single ion injection DAPI operation for 1 μg/mL enrofloxacin. A more than 10-fold reduction in the limit of detection (LOD) to 0.01 μg/mL was also obtained. In addition, the stability was improved by M-DAPI with a relative standard deviation of 14.4% compared to 4.6% for DAPI. [ABSTRACT FROM AUTHOR]

Rationale: Field asymmetric waveform ion mobility spectrometry (FAIMS) has a great potential to become a portable technology for rapid detection of chemical and biological agents. However, the ion current signals, measured at the exit of the planar FAIMS directly, may contain different types of noises. The peak information in the FAIMS spectrum, such as the compensation voltage (CV) value at the maximum peak intensity (CVP) and the peak width at half maximum (Wh), could not be accurately determined under the weak signal condition, which significantly limits the achievable instrument sensitivity, and there are no existing solutions to the problem. Methods: This study analyzed the noise type of FAIMS signal in detail, and three different signal processing algorithms, such as median filtering (MF), discrete wavelet transform (DWT), and zero‐phase digital filtering (ZDF), were evaluated for their performance in denoising the FAIMS signal. Results: The results show that the standard deviation of CVp obtained from the signal denoised using ZDF algorithm is at least 31.82% smaller as compared to using MF and DWT algorithms. The standard deviation of Wh is at least 45.45% smaller using ZDF algorithm. Moreover, only ZDF algorithm can keep the percentage error for the CV value of the denoised signal to be within 0.50 ± 0.47% of the true CV value, implying the effectiveness of ZDF algorithm in denoising while retaining the integrity of the signal. Conclusions: The ZDF algorithm greatly reduces the analyte peak extraction error and improves the limit of detection in FAIMS measurements. [ABSTRACT FROM AUTHOR]

This paper presents an electromechanical closed-loop interface for the high performance capacitive micro-accelerometer. To overcome the problem that the linearity of the traditional analogue force feedback scheme is sensitive to the mismatch in the MEMS transducer, a pulse-width-modulation (PWM) force feedback method is developed in this paper. Elaborate non-linearity analysis of the PWM force feedback and a comparison with traditional analog feedback method is presented. A prototype interface circuit is designed and fabricated in a standard 0.35 μm CMOS process which measures 6.25 mm. The noise floor of the system is 10 μg/√Hz and the signal bandwidth is 1.2 kHz, respectively. The system shows a DC nonlinearity of 1.6‰ without extra linearization circuit with an input range of ± 1.4 g when interface to a commercial accelerometer device. [ABSTRACT FROM AUTHOR]

A robust interface for coupling capillary electrophoresis (CE) to mass spectrometry (MS) was critical to maintain high separation efficiency of CE while achieving high sensitivity of MS. Current interfaces often suffer from problems such as reproducibility and ruggedness. For this purpose, a new polymetallic-coated sheathless interface was developed for the coupling of CE with MS. The electrical contact of the interface was achieved by etching one end of the fused silica capillary into a tapered tip using hydrofluoric acid (HF) solution, and then depositing a thin layer of chromium followed by a layer of platinum on it via physical vapor deposition technique. The performance of the new sheathless interface was systematically evaluated for the effect of flow rate and electrospray ionization (ESI) voltage on MS signal intensity, as well as the sample loading volume on CE separation efficiency and repeatability by using peptide standards and tryptic digest of bovine serum albumin (BSA). The interface was capable of generating stable electrospray even at ultra-low flow rate of 12.2 nL/min. In addition, the acid and alkali resistance of the polymetallic-coated emitter was tested by immersing it into 1 M HCL and 1 M NaOH solution, respectively. The results showed that polymetallic coating was still intact even after continuous immersion in the alkaline solution for 8 days (192 h) and a longer period in the acidic solution, indicating its excellent chemical stability. All the experimental results indicated that the sheathless interface fabricated by the new method in this study was robust and stable, making it promising for both sensitive and robust CE-MS sample analysis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)