Direct Inlet Probe Research Articles

Rapid Identification of Different Cinnamon Using Coated Direct Inlet Probe Coupled with Atmospheric-Pressure Chemical Ionization Mass Spectrometry

This study demonstrates a rapid method for the identification of volatile and endogenous compounds in cinnamon through a coated direct intracavity probe (CDIP) coupled to the atmospheric pressure chemical ionization (APCI) source for mass spectrometry direct injection. Sixty-seven molecular ions were screened from quadrupole-time-of-flight (Q-ToF) mass spectrometer data as fingerprint ions of four varieties of cinnamons. Electronic nose and gas chromatography-mass spectrometry (GC-MS) as comparisons were used to analyze the cinnamons. The principal component analysis (PCA) results showed that both GC-MS and CDIP-APCI-Q-ToF method could be used to identify different kinds of cinnamons effectively. Part of the fingerprint ions obtained via CDIP-APCI-Q-ToF could be matched to the compounds detected by GC-MS. These findings indicated that CDIP-APCI-Q-ToF direct injection considerably shortened sample analysis time and achieved a faster, more efficient, and sensitive identification of different varieties of cinnamons.

Cyclic Ion Mobility Spectrometry Coupled to High-Resolution Time-of-Flight Mass Spectrometry Equipped with Atmospheric Solid Analysis Probe for the Molecular Characterization of Combustion Particulate Matter.

Anthropogenic air pollution has a severe impact on climate and human health. The immense molecular complexity and diversity of particulate matter (PM) is a result of primary organic aerosol (POA) as well as secondary organic aerosols (SOAs). In this study, a direct inlet probe (DIP), i.e., atmospheric solids analysis probe (ASAP), with ion mobility high-resolution mass spectrometric detection is applied. Primary particulate matter emissions from three sources were investigated. Furthermore, photochemically aged emissions were analyzed. DIP introduction allowed for a direct analysis with almost no sample preparation and resulted in a complex molecular pattern. This pattern shifted through oxidation processes toward heavier species. For diesel emissions, the fuel's chemical characteristic is partially transferred to the particulate matter by incomplete combustion and characteristic alkylated series were found. Polycyclic aromatic hydrocarbons (PAHs) were identified as major contributors. Ion mobility analysis results in drift time profiles used for structural analysis. The apex position was used to prove structural changes, whereas the full-width-at-half-maximum was used to address the isomeric diversity. With this concept, the dominance of one or a few isomers for certain PAHs could be shown. In contrast, a broad isomeric diversity was found for oxygenated species. For the in-depth specification of fresh and aged spruce emissions, the ion mobility resolving power was almost doubled by allowing for three passes in the circular traveling wave design. The results prove that ASAP coupled with ion mobility spectrometry-mass spectrometry (IMS-MS) serves as a promising analytical approach for tackling the vast molecular complexity of PM.

Direct Inlet Probe Atmospheric Pressure Photo and Chemical Ionization Coupled to Ultrahigh Resolution Mass Spectrometry for the Description of Lignocellulosic Biomass.

Lignocellulosic biomass, in particular wood, is a complex mixture containing cellulose, hemicellulose, lignin, and other trace compounds. Chemical analysis of these biomasses, especially lignin components, is a challenge. Lignin is a highly reticulated polymer that is poorly soluble and usually requires chemical, enzymatic, or thermal degradation for its analysis. Here, we studied the thermal degradation of lignocellulosic biomass using a direct insertion probe (DIP). The DIP was used with two ionization sources: atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) coupled to ultrahigh-resolution mass spectrometry. Beech lignocellulosic biomass samples were used to develop the DIP-APCI/APPI methodology. Two other wood species (maple and oak) were analyzed after optimization of DIP parameters. The two ionization sources were compared at first and showed different responses toward beech samples, according to the source specificity. APPI was more specific to lignin degradation compounds, whereas APCI covered a larger variety of oxygenated compounds, e.g., fatty acids and polyphenolics compounds, in addition to lignin degradation products. The study of the thermodesorption profile gave information on the different steps of lignocellulosic biomass pyrolysis. The comparison of the three feed sample types (oak, maple, and beech), using principal component analysis (PCA) with DIP-APCI experiments, showed molecular level differences between beech wood pellets and the two other wood species (maple and oak).

Thermal Decomposition Behavior of a Chelating Resin Immobilizing Carboxymethylated Polyethyleneimine: Possibility of Estimation of Carboxymethylation Rate.

Chelating resins immobilizing carboxymethylated polyethyleneimine (CM-PEI) with different carboxymethylation rates were prepared. The thermal decomposition behavior of CM-PEI resins was investigated using thermogravimetry-differential thermal analysis/photo ionization-quadrupole mass spectrometry (TG-DTA/PI-QMS) and ion attachment ionization-quadrupole mass spectrometry equipped with direct inlet probe (DIP/IA-QMS). The obtained results suggested that the carboxymethyl group decomposed at relatively low temperature (150 °C - 300 °C); the peak areas at m/z 45 and 59 in TG-DTA/PI-QMS and m/z 58, 70, and 72 in DIP/IA-QMS significantly increased with increasing carboxymethylation rate. These relationships should be useful for estimating the carboxymethylation rate of CM-PEI resin.

Direct inlet probe – High-resolution time-of-flight mass spectrometry as fast technique for the chemical description of complex high-boiling samples

Comprehensive chemical investigation of non-volatile complex mixtures, without extensive sample pretreatment, remains challenging due to the high number of constituents with different chemical properties. In past years, direct high-resolution mass spectrometry established itself as powerful technique for the detailed molecular description of ultra-complex mixtures, but was mainly used with atmospheric pressure ionization. In this study, we present a direct inlet approach with vacuum ionization and high-resolution time-of-flight mass spectrometry. Exemplary, the non-volatile fractions of crude oil were directly inserted into the ion source and volatilized under reduced pressure conditions. An applied temperature gradient enabled thermal pre-separation, according to volatility, prior to electron ionization and mass spectrometric detection. With exact mass information, peaks were assigned to elemental compositions and grouped into component classes. Moreover, the application of supervised and unsupervised statistical tools allowed differentiation of the samples on a molecular level and the identification and attribution of significant chemical features.

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.

Direct inlet probe ion mobility spectrometry

Direct inlet probe (DIP) was used as an introduction and a pre-separation step for atmospheric pressure photoionization time-of-flight ion mobility spectrometry (APPI-TOF-IMS) for the first time. IMS is an analytical technique used to separate and identify ionized molecules in the gas phase and under atmospheric pressure based on their mobility. The utilization of DIP prior to IMS gives the possibility to introduce the analytes into the gas phase and provides an additional separation based on their vapor pressure. The proof-of-principle study was done on example of eight polycyclic aromatic hydrocarbons (PAHs) with the ring number from 2 to 5, namely naphthalene, fluorene, anthracene, phenanthrene, pyrene, fluoranthene, benzo[a]pyrene, and benzo[k]fluoranthene. All these compounds are included in EPA priority pollutant list. Moreover, benzo[a]pyrene and benzo[k]fluoranthene are marked by EPA as probably carcinogen compounds and also included into SCF and EU lists. To increase the sensitivity of DIP-APPI-IMS the analysis was performed using a dopant assisted ionization method (benzene, 74mgL−1 in N2). It was found that the heating rate of the interface plays a crucial role for the whole analytical procedure. To prove the ability of this method to analyze PAHs in the mixture, the mixtures containing up to five PAHs were analyzed. The LODs for the analyzed compounds obtained with DIP-APPI-IMS were found to be in the tens- or hundreds-of-microgram-per-liter range. The obtained results are promising enough to ensure the potential of DIP as an introduction and a pre-separation step for ion mobility based methods.

Application of direct analysis in real time (DART) and direct inlet probe (DIP-APCI) mass spectrometry in the context of industrial sample analysis

In today’s industry, quick and reliable analytical methods play an important role for quality control. On that account, two emerging techniques, namely direct inlet probe-atmospheric pressure chemical ionization (DIP-APCI) and direct analysis in real time (DART) mass spectrometry, are particularly promising. In case of a DIP-APCI source, small amounts of solid or liquid samples can be studied without sample pre-treatment. A similar system is the DART ion source. In addition to the analysis of solid and liquid samples without pre-separation, this ion source offers the possibility to scan the surface of a sample. A method for industrial sample analysis focusing on the study of delamination of coatings from a panel was developed using DIP-APCI-Q-TOF-MS and DART-Q-TOF-MS, respectively. Comparative studies based on the conventional pyrolysis–GC–MS were carried out.

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

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. 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. 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. 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.

Ag‐Cu Colloid Synthesis: Bimetallic Nanoparticle Characterisation and Thermal Treatment

The Ag‐Cu bimetallic colloidal nanoparticles (NPs) were prepared by solvothermal synthesis from metalloorganic precursors in a mixture of organic solvents. The nanoparticles were characterized by dynamic light scattering (DLS) and small angle X‐ray scattering (SAXS). The properties of metallic core and organic shell of the nanoparticles were studied by direct inlet probe mass spectrometry (DIP/MS), Knudsen effusion mass spectrometry (KEMS), double‐pulse laser‐induced breakdown spectroscopy (DPLIBS), and differential scanning calorimetry (DSC). The transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used for particle characterization before and after thermal analysis. The experiment yielded results that were for AgCu nanoparticles for the first time. The detected liquidus temperature has been compared with the prediction obtained from calculation of the phase diagram of Ag‐Cu nanoalloy. The experimental results show that of near‐eutectic composition AgCu nanoparticles possess the fcc crystal lattice. Surprisingly, spinodal decomposition was not observed inside the AgCu nanoparticles at temperatures up to 230°C. The depression of the eutectic AgCu melting point was calculated but not observed. The eutectic AgCu microparticles are formed before melting.

Ligand exchange reactions between Cu(II), Pb(II), Al(III), and Cr(III) acetylacetonates and dipivaloylmethanates: The possibility of using exchange reactions in estimation of standard enthalpies of formation of metal β-diketonates

Ligand exchange reactions between Cu(II), Pb(II), Al(III), and Cr(III) acetylacetonates and dipivaloylmethanates were studied by mass spectrometry with sample evaporation from an analog of the Knudsen effusion cell (direct inlet probe). It was shown that exchange reactions can be used to estimate the standard enthalpies of formation of metal β-diketonates.

Evolved Gas Analysis of Ti(C5H5)2Cl2 by Means of Li+ Ion Attachment Mass Spectrometry

Characterization of the compound Ti(C(5)H(5))(2)Cl(2) was studied using Li(+) ion attachment mass spectrometry (IAMS) as an analytical methodology. Since this target compound is used as an anticancer drug in the treatment of leukemia, accurate and rapid monitoring methods for the determination of titanium drugs in a hospital environment are desirable. A quadrupole mass spectrometry system along with a Li(+) ion attachment technique and a direct inlet probe (DIP) produced the Li(+) adduct of Ti(C(5)H(5))(2)Cl(2), Ti(C(5)H(5))(2)Cl(2)Li(+). The DIP also was used to study the temperature-resolved behavior of this compound. The slope of the plot of signal intensity of Ti(C(5)H(5))(2)Cl(2)Li(+) versus temperature for Ti(C(5)H(5))(2)Cl(2) sublimation from 60 to 100 °C was used to determine an apparent activation energy (E(a)) of 124.43 kJ/mol for the sublimation of Ti(C(5)H(5))(2)Cl(2). This value is comparable to the reported value of 118.8 kJ/mol for molar enthalpy of sublimation of Ti(C(5)H(5))(2)Cl(2). These results demonstrate that the IAMS methodology can be used to study the enthalpy of sublimation for d-metal complex materials.

Temperature-resolved thermal analysis of cisplatin by means of Li+ ion attachment mass spectrometry

Li(+) ion attachment mass spectrometry (IAMS) was evaluated as an analytical methodology for measurement of the thermally labile, nonvolatile, and insoluble compound cisplatin, which is used as an anticancer agent in the treatment of testicular and ovarian cancers. We aimed to develop an improved method for the mass spectrometric determination of cisplatin, particularly in its molecular ion form. A uniquely designed quadrupole mass spectrometry system along with a Li(+) ion attachment technique and a direct inlet probe provided cisplatin molecular ions as Li(+) ion adducts; to our knowledge this is the first reported instance of cisplatin Li(+) ion adducts. Full-scan spectra were obtained with approximately 10 microg samples. Infrared image furnace-ion attachment mass spectrometry (IIF-IAMS) also was used to study the temperature-programmed decomposition of this drug. The slope of the plot of signal intensity versus temperature for cisplatin decomposition from 225 to 249 degrees C was used to determine an apparent activation energy (E(a)) of 38.0 kcal mol(-1) for the decomposition of cisplatin. This decomposition parameter is useful for predicting drug stability (shelf life). In this study, we have demonstrated that IAMS can be a valuable technique for the direct mass spectral analysis and kinetic study of d-metal complex platinum anticancer agents.

Tert-Butyl 3-(4-Cyano-5-phenylisothiazol-3-yl)carbazate

3-Iodo-5-phenylisothiazole-4-carbonitrile 1 reacts with tert-butyl carbazate via a Buchwald C-N style coupling to afford tert-butyl 3-(4-cyano-5-phenylisothiazol-3-yl)- carbazate 2 in 70% yield. [...]

Comparison of isotopic dilution methods for determination of theophylline in the plasma and saliva of infants and children

Isotope-dilution mass spectrometry (IDMS) using the direct inlet probe and an isotope dilution gas chromatographic-mass spectrometric (GC-IDMS) technique are presented for determination of theophylline in paired specimens of plasma and saliva from infants and children treated with theophylline for idiopathic apnea of prematurity, or for asthma.15N-theophylline was used as internal standard. A non-invasive means of individualization of the dosage was achieved by analysis of levels of the drug in saliva secreted in response to stimulation with citric acid.

Furfuraldehyde resin pyrolysis in a closed system

The pyrolysis of two insoluble resins obtained by acid catalysis from furfuraldehyde and furfuraldehyde-dimethylketone was carried out in a closed system at 400 °C. The products of the pyrolysis were extracted under their vapor pressure. The compositions of the pyrolyzates were analyzed by mass spectrometry using a direct inlet probe technique under an electron impact of 70 eV. Thus, the main structural sequences of both resins were determined. Trifurylic sequences are the main component for the furfuraldehyde resin but the furfuralde-hydedimethyl ketone resin has two types of structural units: furfurylidene and furylmethylene.

Isolation and determination of paspalitrem-type tremorgenic mycotoxins using liquid chromatography with diode-array detection

A liquid chromatographic (LC) method is described for the isolation and determination of the tremorgenic mycotoxins paxilline ( Penicillium paxilli NRRL 6110), paspaline, paspalinine and paspalicine ( Claviceps paspali). Following a Soxhlet extraction of a mould-contaminated matrix using chloroform, the crude extract was partitioned between hexane and 80% aqueous methanol. The latter fraction, containing the desired toxin(s), was evaporated to dryness, the residue dissolved in methylene chloride and the solution analysed by liquid chromatography using a Supelcosil LC-Si column eluted with methylene chloride-diethyl ether (9 + 1, v/v). A mixture containing standards of these compounds was similarly analysed. All toxins were detected using a UV diode-array detector. The generated UV spectra and chromatographic data of the standard toxins were stored in a computer as a library and used to identify these toxins in a crude mixture. The purity of the separated peaks and the amount of toxin in the crude mixture were also determined. The toxins were isolated by selectively collecting the eluted peaks using a programmable fraction collector equipped with a peak level sensor. Further confirmation of compound identity was achieved by mass spectrometry using the direct inlet probe method. In comparison with methods used previously to isolate these toxins, the present technique is fast and allows the acquisition of complete UV spectral information and chromatographic data and the isolation of multiple toxins in a single chromatographic operation.

Comparison of tandem and conventional mass spectrometry using electron capture negative ionization in the detection of chemically oxidized dexamethasone in human plasma

Dexamethansone, a synthetic steroid, can be oxidized chemically to a ketonic steroid structure that is readily detected by electron capture negative ionization mass spectrometry (ECNI/MS). Previous work from this laboratory has demonstrated that the chemical oxidation procedure provides advantages of low detection limits and high selectivity for detection of oxidized dexamethasone against chemical background that would otherwise interfere with detection of this steroidal drug in biological samples using more conventional methodology. This report describes the extent to which tandem mass spectrometry (MS/MS) can further enhance the selectivity of the oxidation/ECNI methodology for the detection of dexamethasone during the analysis of human plasma and presents evidence that sample introduction by direct inlet probe (DIP) can be used successfully under ECNI conditions. For purposes of comparing the methodologies, the same human plasma samples are analyzed by ECNI, first with detection by conventional mass spectrometry using selected ion monitoring (SIM) and then by MS/MS using selected reaction monitoring (SRM) with sample introduction by the gas chromatographic (GC) inlet and by the DIP. The results indicate that use of the DIP is a viable means of sample introduction for ECNI when sample processing involves the specialized oxidation procedure described herein because the sample matrix does not compete significantly for the thermal electrons in the ion source. Whereas SIM and SRM provide comparable results when sample introduction is achieved by the GC inlet, the MS/MS approach offers the possibility for sample introduction using the DIP, which significantly simplifies and shortens the analysis.

Analysis of domoic acid and related compounds by mass spectrometry and gas chromatography/mass spectrometry asN-trifluoroacetyl-O-silyl derivatives

A method is presented for the analysis of shellfish tissue for domoic acid, a neurotoxic amino acid responsible for cases of amnesic shellfish poisoning. Tissue extracts are first taken through a two-stage solid-phase extraction clean-up, using reversed-phase and strong cation exchange cartridges. A two-stage derivatization, using N-methyl-bis-trifluoroacetamide followed by either N-methyl-tert-butyldimethylsilyltrifluoroacetamide or N, O-bis-trimethylsilyltrifluoroacetamide, is then used to produce an N-trifluoroacetyl-O-silyl derivative which can be analyzed by mass spectrometry with introduction via direct inlet probe, moving-belt liquid chromatograph/mass spectrometer interface, or capillary column gas chromatography. The N-trifluoroacetyl-O-tert-butyldimethylsilyl derivative, which has good stability towards hydrolysis, provides a spectrum well suited to gas chromatography/mass spectrometry (GC/MS) using selected ion recording. GC/MS data for two related compounds, kainic acid and dihydrokainic acid, are also reported. The latter is used as an internal standard for quantification of domoic acid, although the method reported is intended primarily for confirmation of the toxin and related compounds in shellfish tissue.

Serum theophylline analysis by isotope dilution mass spectrometry

Serum theophylline analysis was attempted using stable isotope dilution mass spectrometry. Theophylline 15N-labelled in position 7 was used as internal standard. The analysis was performed at resolution 3000 by selected ion monitoring with temperature programming. The sample was introduced in underivatized form by means of the direct inlet probe. Good linearity was obtained in the concentration range 5-40 micrograms ml-1 with relative standard deviations less than 6%. The method is simple and permits six samples to be run per hour. Sensitivity permits analysis at 0.5 micrograms ml-1 at a signal to noise ratio 4:1.