Thermogravimetry combined with electrospray and atmospheric pressure chemical ionization mass spectrometry for characterization of synthetic polymers.

RATIONALE: Thermogravimetry (TG) combined with electrospray and atmospheric chemical ionization (ESI+APCI) mass spectrometry (MS) was developed to rapidly characterize thermal decomposition products of synthetic polymers and plastic products. The ESI-based TG-MS method is useful for characterizing thermally labile, nonvolatile, and polar compounds over an extensive mass range; and the APCI-based TG-MS counterpart is useful for characterizing volatile and nonpolar compounds. Both polar and nonpolar compounds can be simultaneously detected by ESI+APCI-based TG-MS. METHODS: Analytes with different volatility were produced from TG operated at different temperatures, which were delivered through a heated stainless-steel tube to the ESI+APCI source where they reacted with the primary charged species generated from electrospray and atmospheric pressure chemical ionization (ESI+APCI) of solvent and nitrogen. The analyte ions were then detected by an ion trap mass spectrometer. RESULTS: A semi-volatile PEG 600 standard was used as the sample and protonated and sodiated molecular ions together with adduct ions including [(PEG)n + 15]+ , [(PEG)n + 18]+ , and [(PEG)n + 29]+ were detected by TG-ESI+APCI-MS. The technique was further utilized to characterize thermal decomposition products of nonvolatile polypropylene glycol (PPG) and polystyrene (PS) standards, as well as a PS-made water cup and coffee cup lid. The characteristic fragments of PPG and PS with mass differences of 58 and 104 between respective ion peaks were detected at the maximum decomposition temperature (Tmax ). CONCLUSIONS: The information obtained from the TG-ESI+APCI-MS analysis is useful in rapidly distinguishing different types of polymers and their products. In addition, the signals of the additives in the polymer products, including antioxidants and plasticizers, were also detected before the TG temperature reached Tmax .

Flame-induced atmospheric pressure chemical ionization mass spectrometry.

RATIONALE: Charged species such as formylium (CHO(+) ), hydronium (H3 O(+) ), and water clusters [H3 O(+) (H2 O)n ] are commonly found in flames. These highly reactive species can react with analytes via ion-molecule reactions (IMRs) to form analyte ions. A new mass spectrometric technique, named flame-induced atmospheric pressure chemical ionization mass spectrometry (FAPCI-MS), was developed to characterize organic compounds via these mechanisms. METHODS: A commercial corona-discharge atmospheric pressure chemical ionization (APCI) source was modified by replacing the corona needle with a flame to make a FAPCI source. Liquid samples were vaporized in a heated tube and delivered to the IMRs region by nitrogen to react with the charged species generated by a flame. Analytes on surfaces were directly desorbed and ionized by a flame using the technique called desorption-FAPCI-MS (DFAPCI-MS). RESULTS: Intact molecular ions of various chemical and biological compounds were successfully characterized by FAPCI-MS. The FAPCI mass spectra are nearly identical to those obtained by traditional APCI-MS. The limit of detection (LOD) of reserpine by FAPCI-MS was 50 µg L(-1) with a linear calibration curve (R(2) = 0.9947) from 100 µg L(-1) to 10 mg L(-1) . The LOD for ketamine by DFAPCI-MS was estimated to be less than 0.1 ng. CONCLUSIONS: In FAPCI, analytes are not incinerated but vaporized and introduced into the ion source to react with the reactive charged species generated by a flame. The features of the FAPCI source include: configuration is very simple, operation is easy, high voltage or inert gas is unnecessary, and the source is maintenance free. Various combustible gases, solvents and solids are useful flame fuels for FAPCI. Copyright © 2016 John Wiley & Sons, Ltd.

Simultaneous detection of polar and nonpolar compounds by ambient mass spectrometry with a dual electrospray and atmospheric pressure chemical ionization source.

A dual ionization source combining electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) was developed to simultaneously ionize both polar and nonpolar compounds. The source was constructed by inserting a fused silica capillary into a stainless steel column enclosed in a glass tube. A high dc voltage was applied to a methanol solution flowing in the fused silica capillary to generate an ESI plume at the capillary tip. A high ac voltage was applied to a ring electrode attached to the glass tube to generate plasma from the nitrogen gas flowing between the glass tube and the stainless steel column. The concentric arrangement of the ESI plume and the APCI plasma in the source ensured that analytes entering the ionization region interacted with both ESI and APCI primary ion species generated in the source. Because the high voltages required for ESI and APCI were independently applied and controlled, the dual ion source could be operated in ESI-only, APCI-only, or ESI+APCI modes. Analytes were introduced into the ESI and/or APCI plumes by irradiating sample surfaces with a continuous-wavelength laser or a pulsed laser beam. Analyte ions could also be produced by directing the dual ESI+APCI source toward sample surfaces for desorption and ionization. The ionization mechanisms involved in the dual ion source include Penning ionization, ion molecule reactions, and fused-droplet electrospray ionization. Standards of polycyclic aromatic hydrocarbons, angiotensin I, lidocaine, ferrocene, diesel, and rosemary oils were used for testing. Protonated analyte ions were detected in ESI-only mode, radical cations were detected in APCI-only mode, and both types of ions were detected in ESI+APCI mode.

Rapid characterization of chemical compounds in liquid and solid states using thermal desorption electrospray ionization mass spectrometry.

Rapid characterization of thermally stable chemical compounds in solid or liquid states is achieved through thermal desorption electrospray ionization mass spectrometry (TD-ESI/MS). A feature of this technique is that sampling, desorption, ionization, and mass spectrometric detection are four separate events with respect to time and location. A metal probe was used to sample analytes in their solid or liquid states. The probe was then inserted in a preheated oven to thermally desorb the analytes on the probe. The desorbed analytes were carried by a nitrogen gas stream into an ESI plume, where analyte ions were formed via interactions with charged solvent species generated in the ESI plume. The analyte ions were subsequently detected by a mass analyzer attached to the TD-ESI source. Quantification of acetaminophen in aqueous solutions using TD-ESI/MS was also performed in which a linear response for acetaminophen was obtained between 25 and 500 ppb (R(2) = 0.9978). The standard deviation for a reproducibility test for ten liquid samples was 9.6%. Since sample preparation for TD-ESI/MS is unnecessary, a typical analysis can be completed in less than 10 s. Analytes such as the active ingredients in over-the-counter drugs were rapidly characterized regardless of the different physical properties of said drugs, which included liquid eye drops, viscous cold syrup solution, ointment cream, and a drug tablet. This approach was also used to detect trace chemical compounds in illicit drugs and explosives, in which samples were obtained from the surfaces of a cell phone, piece of luggage made from hard plastic, business card, and wooden desk.

Building blocks for the development of an interface for high-throughput thin layer chromatography/ambient mass spectrometric analysis: a green methodology.

Interfacing thin layer chromatography (TLC) with ambient mass spectrometry (AMS) has been an important area of analytical chemistry because of its capability to rapidly separate and characterize the chemical compounds. In this study, we have developed a high-throughput TLC-AMS system using building blocks to deal, deliver, and collect the TLC plate through an electrospray-assisted laser desorption ionization (ELDI) source. This is the first demonstration of the use of building blocks to construct and test the TLC-MS interfacing system. With the advantages of being readily available, cheap, reusable, and extremely easy to modify without consuming any material or reagent, the use of building blocks to develop the TLC-AMS interface is undoubtedly a green methodology. The TLC plate delivery system consists of a storage box, plate dealing component, conveyer, light sensor, and plate collecting box. During a TLC-AMS analysis, the TLC plate was sent to the conveyer from a stack of TLC plates placed in the storage box. As the TLC plate passed through the ELDI source, the chemical compounds separated on the plate would be desorbed by laser desorption and subsequently postionized by electrospray ionization. The samples, including a mixture of synthetic dyes and extracts of pharmaceutical drugs, were analyzed to demonstrate the capability of this TLC-ELDI/MS system for high-throughput analysis.

Effects of matrix, electrospray solution, and laser light on the desorption and ionization mechanisms in electrospray-assisted laser desorption ionization mass spectrometry.

Electrospray-assisted laser desorption ionization (ELDI) is a technique which combines laser desorption with subsequent electrospray ionization. It is useful for directly detecting small and large molecules in solid or liquid samples under ambient conditions. In this paper, the detection of the protein molecules desorbed on a dry protein spot by using pulse laser energies of up to 300 microJ was demonstrated. The influences of organic and inorganic matrices, the laser energy, the laser wavelength, and the sample plate material on desorption of protein molecules from sample plates were discussed. In addition, the effects of the composition of the electrospray solution on the ionization of the desorbed protein molecules were studied.

Electrospray laser desorption ionization (ELDI) mass spectrometry for molecular imaging of small molecules on tissues.

The use of an ambient ionization mass spectrometry technique known as electrospray laser desorption ionization mass spectrometry (ELDI/MS) for molecular imaging is described in this section. The technique requires little or no sample pretreatment and the application of matrix on sample surfaces is unnecessary. In addition, the technique is highly suitable for the analysis of hard and thick tissues compared to other molecular imaging methods because it does not require production of thin tissue slices via microtomes, which greatly simplifies the overall sample preparation procedure and prevents the redistribution of analytes during matrix desorption. In this section, the ELDI/MS technique was applied to the profiling and imaging of chemical compounds on the surfaces of dry plant slices. Analyte distribution on plant slices was obtained by moving the sample relative to a pulsed laser and an ESI capillary for analyte desorption and post-ionization, respectively. Images of specific ions on sample surfaces with resolutions of 250 µm were typically created within 4.2 h for tissues with sizes of approximately 57 mm × 10 mm.