Thermogravimetry coupled to an atmospheric pressure photo ionization quadrupole mass spectrometry for the product control of pharmaceutical formulations and the analysis of plasticizers in polymers

Coupled and Simultaneous Thermal Analysis Techniques in the Study of Pharmaceuticals

Reliable interpretation of the changes occurring in the samples during their heating is ensured by using more than one measurement technique. This is related to the necessity of eliminating the uncertainty resulting from the interpretation of data obtained by two or more single techniques based on the study of several samples analyzed at different times. Accordingly, the purpose of this paper is to briefly characterize thermal analysis techniques coupled to non-thermal techniques, most often spectroscopic or chromatographic. The design of coupled thermogravimetry (TG) with Fourier transform infrared spectroscopy (FTIR), TG with mass spectrometry (MS) and TG with gas chromatography/mass spectrometry (GC/MS) systems and the principles of measurement are discussed. Using medicinal substances as examples, the key importance of coupled techniques in pharmaceutical technology is pointed out. They make it possible not only to know precisely the behavior of medicinal substances during heating and to identify volatile degradation products, but also to determine the mechanism of thermal decomposition. The data obtained make it possible to predict the behavior of medicinal substances during the manufacture of pharmaceutical preparations and determine their shelf life and storage conditions. Additionally, characterized are design solutions that support the interpretation of differential scanning calorimetry (DSC) curves based on observation of the samples during heating or based on simultaneous registration of FTIR spectra and X-ray diffractograms (XRD). This is important because DSC is an inherently non-specific technique. For this reason, individual phase transitions cannot be distinguished from each other based on DSC curves, and supporting techniques are required to interpret them correctly.

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 (T_max ).

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 T_max .

Impact of Thermal Stress on Abrasive Dust from a Carbon Fiber-Reinforced Concrete Composite

Recently, a novel corrosion-resistant construction material, Carbon Concrete Composite (C3), consisting of coated carbon fibers embedded in a concrete matrix, was introduced. However, thermal exposure during domestic fires may impact the release of organic pollutants and fibers during abrasive processing and/or demolition. Consequently, the objective of this study was to explore the emission characteristics of toxic compounds and harmful fibers during the dry-cutting after exposure to 25–600 °C (3 h, air). These parameters mimic the abrasive machining and dismantling after a domestic fire event. Mass spectrometry and chromatography served as analytical methodologies, and no organic pollutants for exposure temperatures ≥ 400 °C were found. In contrast, significant amounts of pyrolysis products from the organic fiber coating were released at lower temperatures. Studying the morphology of the released fibers by electron microscopy revealed a decrease in fiber diameter for temperatures exceeding 450 °C. At ≥550 °C, harmful fibers, according to the World Health Organization (WHO) definition, occurred (28–41 × 104 WHO fibers/m3 at 550–600 °C). This leads to the conclusion that there is a demand for restraining and protection measures, such as the use of wet cutting processes, suction devices, particle filtering masks and protective clothing, to handle thermally stressed C3.

Development of a fast-switching dual (ESI/APCI) ionization source for liquid chromatography/mass spectrometry

RATIONALE

High-throughput liquid chromatography/mass spectrometry (LC/MS) is an increasing topic in analytical chemistry. Especially the idle time of a mass spectrometer should be reduced for an efficient and cost-saving use. Therefore, a fast-switching dual ion source was developed, which uses the most important ionization techniques at atmospheric pressure, electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), with one or more LC systems.

METHODS

The performance of the developed ion source is shown by infusion experiments and chromatographic analyses of different standard substances. A high-throughput method is demonstrated by coupling two UHPLC systems to the dual ion source with a triple quadrupole mass spectrometer.

RESULTS

No decrease in the ion abundance and a stable performance of the mass spectrometer are presented while using the dual ion source. Instrumental limits of detection are 30 ng L^-1 for testosterone using ESI and 1 μg L^-1 for vitamin D₃ using APCI. A fast switching between two UHPLC systems and the dual ion source leads to a high sample throughput of 50 samples in 75 min with relative standard deviations for testosterone and vitamin D₃ of 1.5% and 3.8%, respectively.

CONCLUSIONS

This work presents the development of a dual ESI and APCI ion source operating simultaneously or in switched mode. The results show sensitive and reliable performance as well as the hyphenation to one or more HPLC systems.

Application of Molecularly Imprinted Polymers (MIP) and Flowing Atmospheric-Pressure Afterglow Mass Spectrometry (FAPA-MS) to Analysis of Nonsteroidal Anti-Inflammatory Drugs (NSAIDs)

In recent years, the rapid development of the pharmaceutical industry and the extensive and illicit use of painkillers have led to increased levels of nonsteroidal anti-inflammatory drugs (NSAIDs) in the environment. In view of the significant impact of NSAIDs on living organisms, including humans, their presence in the environment needs to be continuously monitored at trace levels. For this purpose, a combination of molecularly imprinted solid-phase extraction (MISPE) and HPLC-MS analysis is commonly used. MISPE has been utilized in direct, fast, and ecological analysis of drugs using a flowing atmospheric-pressure afterglow ion source for mass spectrometry (FAPA-MS). The new method was applied herein in the determination of naproxen, diclofenac, and ibuprofen. The linear dependence of the intensity of analytical signals on the amount of drugs is in the range of 0.2 μg to 1 g and the method detection limit (MDL) for all drugs is 0.2 μg in environmental samples. The new method also decreased the number of analytical stages, the time and cost of analysis, and the organic solvent consumption, besides being environmentally friendly.

Analysis of volatile metabolites from in vitro biofilms of Pseudomonas aeruginosa with thin-film microextraction by thermal desorption gas chromatography-mass spectrometry

Cystic fibrosis (CF) is an autosomal recessive inherited disease which leads to a production of thickened mucus in the airways. These conditions are conducive to poly-microbial infections, like chronic lung infection, in which Pseudomonas aeruginosa (P. aeruginosa) is the major pathogenic bacterium colonizing CF lungs at the end of the lifetime of CF patients. This in vitro study uses a P. aeruginosa biofilm model under partly cystic fibrosis conditions, with a sampling of volatile extracellular metabolites. The gas sampling was done with thin-film microextraction (TFME) and commercial polydimethylsiloxane (PDMS) films, whereas the analysis of loaded films was done by gas chromatography coupled to quadrupole mass spectrometry and thermodesorption (TD-GC-qMS). For this purpose, two commercially available films were characterized by means of thermogravimetry coupled to a qMS with atmospheric pressure photo ionization (TG-APPI-qMS), regarding homogeneity and temperature stability. The selected film was cleaned using a method developed in this study. The TD-GC-qMS method was successfully used for standards of volatile metabolites which were known to be produced by P. aeruginosa. Limits of detection and quantification of the method for middle and less polar compounds in low nanomolar range (0.5 nM and 1.5 nM) were achieved. The developed method was finally applied to investigate the extracellular volatile metabolites produced by biofilms of the strain P. aeruginosa DSM 50071 under aerobic and anaerobic conditions. In sum, eleven metabolites could be found under both conditions. Furthermore, it was shown in this study that different oxygen conditions (aerobic and anaerobic) resulted in emitting different extracellular volatile metabolites. Specific metabolites, like 1-undecene (aerobic) and 2-undecanone (anaerobic), could be identified. The results are promising, in that the biofilm model may be applicable for the identification of P. aeruginosa under clinical conditions. Furthermore, the model could be the basis for studying extracellular volatile metabolites from different mono- or co-cultures of various bacteria, as well as the implementation of pulmonary conditions, like these in CF lungs. This possibility allows the development of a non-invasive “at-bedside” breath analysis method for CF patients in focus of various bacterial infections.