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Mass spectrometry (MS) has become an essential analytical method in every sector of science and technology. Because of its unique ability to provide direct molecular structure information on analytes, an extra method is rarely required. This review describes fabrication of a variable-pressure hollow cathode discharge (HCD) ion source for MS in detection, quantification and investigation of gas-phase ion molecule reactions of explosives and related compounds using air as a carrier gas. The HCD ion source has been designed in such a way that by altering the ion source pressures, the system can generate both HCD and conventional GD. This design enables for the selective detection and quantification of explosives at trace to ultra-trace levels. The pressure-dependent HCD ion source has also been used to investigate ion-molecule reactions in the gas phase of explosives and related compounds. The mechanism of ion formation in explosive reactions is also discussed. [ABSTRACT FROM AUTHOR]

Ambient ionization mass spectrometry (AIMS) is an emerging onsite rapid detection technique that has been applied in the area of public security. AIMS measurements of samples with complex matrices are characterized by poor reproducibility and complexity. Low reproducibility and complex background cause imprecise screening for trace drugs in hair. In this work, a rapid screening method of methamphetamine in hair is proposed. Firstly, the generalized weighted robust principal component analysis (GWRPCA) algorithm is used to remove background and extract the analytical signals. The similarity scores between the analytical signals and standard mass spectrum of methamphetamine were calculated based upon an improved Pearson's correlation coefficient combined with the preset matching threshold to achieve rapid screening of methamphetamine in hair. The results show that this method accurately screens for this drug hair and identifies actual false positives with 100% accuracy when the analyte threshold was 0.1 ng/mg and the matching threshold was 0.6. This study provides technical support for the rapid screening for drug abuse by AIMS. [ABSTRACT FROM AUTHOR]

AbstractThe capillary is a widely used atmospheric pressure interface in mass spectrometers that may be heated to enhance the desolvation of ions. In this study, the ion transmission efficiency of a portable ion trap mass spectrometer was investigated using capillaries with different inner diameters and temperatures, different vacuum pressures, and different ion optics designs. Due to the incomplete desolvation and the space charge effect inside the miniature ion funnel, the increase of ion intensities with the inner diameter of the capillary leveled off when the inner diameter of the capillary was larger than 0.37 mm. With the increase of capillary temperature, the ion intensities first increase due to better desolvation and then decrease due to greater diffusion loss. The optimal temperature of the capillary increases with the inner diameter of the capillary and the mass-to-charge ratio of ion. In addition, the pressures of different vacuum stages also exerted remarkable effects on the sensitivity of the portable mass spectrometer. From the perspective of instrument miniaturization, optimal transmission efficiency can be obtained when the first-stage vacuum pressure is maintained from 4 to 6 mbar. For a capillary with an inner diameter of 0.37 mm, the background of mass spectrum can be significantly reduced by replacing the pinhole behind the ion funnel with an off-axis skimmer. [ABSTRACT FROM AUTHOR]

According to the Report of Drug Situation in China (2020), the growth rate of the number of drug abusers in China has decreased, but the number of drug abusers is still large. An efficient screening method is necessary for controlling drug abuse. As an important type of biological sample, urine is widely used for the rapid screening of drug addicts. However, because of the complex composition, low content, and strong interference from the body's metabolism, the detection of drugs in urine remains a challenge. Traditional rapid screening techniques such as immunocolloidal gold analysis have a high false positive rate and insufficient quantitative capability. In addition, laboratory mass spectrometry methods require complicated time-consuming sample pre-processing and strict environmental conditions, and hence, are unsuitable for on-site rapid analysis. In recent years, various direct ionization mass spectrometry techniques such as direct analysis in real time (DART), desorption electrospray ionization (DESI), and dielectric barrier discharge ionization (DBDI) have advanced rapidly. These techniques have been applied to public safety, food safety, environmental detection, etc. In contrast to traditional ionization mass spectrometry methods, these direct ionization techniques allow for the in situ analysis of samples with simple or no pretreatment; moreover, they have the advantages of high analytical efficiency and sensitivity. In particular, pulsed electrospray ionization has the characteristics of less sample demand, compact, lightweight equipment, and no carrier gas. This paper presents a rapid method based on pulsed electrospray ionization mass spectrometry for the detection of urine samples. A rapid detection platform comprising a probe electrospray ionization source, a portable linear ion trap mass spectrometer (MS), and their coupling interface is adopted. The probe electrospray ion source includes a conducting metal wire, plastic handle, and silica glass capillary, whose tip has an inner diameter of 50 μm. The guide rail at the coupling interface is used to align the probe with the sample inlet of the portable mass spectrometer and maintain a distance of 10 mm between the probe tip and the sample inlet of the MS. The spray voltage of the probe electrospray ion source and the temperature of the MS inlet capillary are optimized at 1.8 kV and 205 ℃, respectively. In addition, rapid and efficient pretreatment techniques for urine samples have been developed. Buffer salts used for pH regulation and liquid-liquid extraction based on ethyl acetate were adopted for the pretreatment process. The linearity of the detection ability and the linear ranges of various drug-spiked solutions were also investigated. The results showed that the correlation coefficients for the quantitative detection of methamphetamine, ketamine, methylenedioxymethamphetamine (MDMA), and cocaine were greater than 0.99 at concentrations ranging from 1 to 100 ng/mL. Moreover, the limits of detection (LODs) for the five conventional drug-spiked urine were 0.5-30 ng/mL. The spiked recoveries ranged from 56.1% to 103.7%, with relative standard deviations (RSDs) of 9.0%-27.8%, implying that the combination of the instruments and the pretreatment method can lead to good accuracy. To validate the performance of the rapid detection method, 40 positive and 110 negative urine samples were tested and analyzed. The overall accuracy was over 99%, and the five conventional drugs in urine samples could be detected within 20 s. The research findings of this work could promote the development of rapid detection technology, accelerate the popularization and application of ambient direct ionization mass spectrometry, and improve the services of on-site law enforcement.