Development, optimization, and use of an APCI source with temperature-controlled vaporization of solid and liquid samples

Coated direct inlet probe coupled with atmospheric-pressure chemical ionization and high-resolution mass spectrometry for fast quantitation of target analytes

The coated direct inlet probe (CDIP) is a new laboratory-made low-cost technology developed from a direct inlet probe (DIP), which has the advantage of quick enrichment/cleanup of an analyte from liquid samples. A capillary probe is coated with hydroxy-terminated polydimethylsiloxane (OH-PDMS), divinylbenzene (DVB), and β-cyclodextrin (β-CD) by a sol-gel method. This probe can be directly coupled with a commercialized atmospheric-pressure chemical ionization (APCI) ion source and high-resolution mass spectrometry, which are widely applicable, reliable, and durable. The ability to perform quantitative analyses with the use of a stable-isotope-labeled internal standard (SIL-IS) was tested by using different concentrations of acenaphthylene (ACY), acenaphthene (ACP), fluorene (FLR), fluoranthene (FLT), phenanthrene (PHE), and benzo[a]pyrene (B[a]P). Calibration curves with a coefficient of determination of R² ≥ 0.9982 for different polycyclic aromatic hydrocarbons (PAHs) were obtained. A limit of detection (LOD) of 0.008-0.04 ng mL^-1 for PAHs was determined. The entire workflow is solvent-free and can be completed in less than 5 min, which demonstrates the advantages of this technique for quantitative analysis.

High-Throughput, Rapid Quantification of Phthalic Acid Esters and Alkylphenols in Fish Using a Coated Direct Inlet Probe Coupled with Atmospheric Pressure Chemical Ionization

Intake of endocrine-disrupting chemicals (EDCs) by humans could disturb the metabolism of hormones, induce cancer, and damage the liver and other organs. Phthalate acid esters (PAEs) and alkylphenols (APs) are important EDCs and environmental contaminants. With the increasing use of plastics and nonionic surfactants worldwide, PAEs and APs have entered environmental water and accumulated in edible fish, which are finally consumed by humans. In this study, a coated direct inlet probe (CDIP) based on an atmospheric solid analysis probe, which can rapidly and simultaneously extract both PAEs and APs in fish, was developed. Twelve PAEs and APs were quantified by using a stable-isotope-labeled internal standard. Standard curves of the PAEs and APs having correlation coefficients of R² ≥ 0.9837 were obtained. The limit of detection of the PAEs and APs was distributed from 0.01 to 40 ng g^-1. The relative recovery of the method was 78-120% between low, medium, and high spiked levels. Combined with principal component analysis, PAE- and AP-contaminated Carassius auratus from different habitats could be identified. Multiple sample analysis mode allowed the extraction of up to 12 samples at once, and the total analysis time (including sample pretreatment, extraction, and analysis time) was less than 10 min per sample, which indicates that CDIP is useful for rapid quantitative analysis.

Analysis of volatile compounds by open-air ionization mass spectrometry

This study demonstrates a simple method for rapid and in situ identification of volatile and endogenous compounds in culinary spice samples through mass spectrometry (MS). This method only requires a holder for solid spice sample (2-3 mm) that is placed close to a mass spectrometer inlet, which is applied with a high voltage. Volatile species responsible for the aroma of the spice samples can be readily detected by the mass spectrometer. Sample pretreatment is not required prior to MS analysis, and no solvent was used during MS analysis. The high voltage applied to the inlet of the mass spectrometer induces the ionization of volatile compounds released from the solid spice samples. Furthermore, moisture in the air also contributes to the ionization of volatile compounds. Dried spices including cinnamon and cloves are used as the model sample to demonstrate this straightforward MS analysis, which can be completed within few seconds. Furthermore, we also demonstrate the suitability of the current method for rapid screening of cinnamon quality through detection of the presence of a hepatotoxic agent, i.e. coumarin.

Non-destructive plasticizer screening using a direct inlet probe-atmospheric pressure chemical ionization source and ion trap mass spectrometry

RATIONALE

In recent years, several ambient ionization techniques, where solid and/or liquid samples are brought directly into the ion source without any sample preparation and chromatographic separation, have been introduced for mass spectrometric (MS) analyses. Using the direct inlet probe-atmospheric pressure chemical ionization (DIP-APCI)-MS and DIP-APCI-MS(n) methods presented here, a non-destructive screening analysis for plasticizers directly from plastic articles can be performed.

METHODS

The DIP-APCI ion source developed in our laboratory uses a temperature-programmed push rod to introduce solid or liquid samples into a homemade APCI ion source. The DIP-APCI ion source was coupled to an ion trap (IT) mass spectrometer and selected source parameters were optimized. To enable a screening analysis for plasticizers, standards substances of several phthalates and other plasticizers were analyzed and their fragmentation behavior during collision-induced dissociation (CID) was studied.

RESULTS

Using DIP-APCI-ITMS, plasticizers can be detected directly from plastic articles and identification is possible through MS(n) experiments. For example, the isomeric phthalates di(2-ethylhexyl) phthalate and di-n-octyl phthalate can be differentiated according to their fragmentation behavior.

CONCLUSIONS

There are several advantages of the DIP-APCI source in comparison to many other ambient desorption ion sources: (i) well-defined gas phase matrix, (ii) precisely adjustable reagent gases (e.g. O2 for negative APCI), (iii) well-defined probe temperature, and (iv) fully automated operation.

Quantification of coumarin in cinnamon and woodruff beverages using DIP-APCI-MS and LC-MS

The use of the direct inlet probe-atmospheric-pressure chemical ionization (DIP-APCI) ion source developed in our laboratory coupled to a high resolution Q-TOF MS for the quantitative analysis of coumarin in different cinnamon samples was demonstrated in this study. Extraction of coumarin from various cinnamon samples was followed by DIP-APCI-mass spectrometry (MS) and liquid chromatography (LC)-MS analysis. For quantification, an external calibration with and without the use of stable isotope-labeled coumarin as internal standard was compared. The results obtained by DIP-APCI-MS and LC-MS were in good agreement. Even without the use of an internal standard satisfying linearity (R(2) > 0.997), recovery (94-104% for spiking levels between 100 and 5,000 mg/kg) and intra- and interday repeatability (2.2-13.8%RSD) was demonstrated using DIP-APCI-MS. To reduce the number of samples requiring quantitative analysis, the possibility of semi-quantitative screening of coumarin directly from powdered cinnamon using DIP-APCI-MS was shown. The analysis of woodruff-flavored beverages and cinnamon-flavored chewing gum by DIP-APCI-MS resulted in the formation of an artifact interfering with coumarin detection. As with other ambient ionization methods, special attention has to be paid to possible spectral interferences due to isobaric substances present in the sample matrix or formed from matrix components after ionization. The temperature-programmed vaporization in DIP-APCI-MS combined with the use of stable isotope-labeled coumarin as internal standard helped in recognizing this interference.