Direct Insertion Probe Research Articles

Characterization of fulgorid waxes (Homoptera:Fulgoridae:Insecta)

A series of waxes produced by three fulgorid species are shown to be mixtures of homologs indentical to those previously found in the unrelated cochineal insect Dactylopius confusus. Using direct insertion probe mass spectrometry, the intact wax was found to give characteristic spectra obviating the need for extensive hydrolysis. The utility of these compounds as taxonomic characters in Fulgoridae is discussed.

Characterization of polar polycyclic aromatic compounds in a heavy-duty diesel exhaust particulate by capillary column gas chromatography and high-resolution mass spectrometry

Polar normal-phase HPLC fractions of a heavy-duty diesel exhaust particulate, a National Bureau of Standards standard reference material 1650, were analyzed by capillary column GC coupled to both low- and high-resolution mass spectrometry (HRMS) using electron impact and negative ion chemical ionization (NICI). Over 80 polycyclic aromatic compounds (PAC), belonging to many different chemical classes (anhydrides, carbox-aldehydes, diazaarenes, cyclic imides, nitrohydroxy-PAC, nitroaza-PAC, nitrodiaza-PAC, nitrolactones, and quinones) were tentatively identified. Ten of them were positively identified by comparison of retention times with authentic standards. Among them, phenazine and phthalic anhydride were positively identified for the first time in diesel exhaust particulates. In addition, cyclic imides and their alkylated derivatives were tentatively identified for the first time. Other novel polar chemical classes of PAC were evidenced by NICI MS using a direct-insertion probe.

Pyrolysis-gas chromatography-mass spectrometry of two trimeric lignin model compounds with alkyl-aryl ether structure

Thermal degradation of ω-guaiacoxy-acetoguaiacone-benzylether (A) and ω-syringoxy-acetoguaiacone-benzylether (B) has been investigated for a better understanding of the thermolytic behaviour of lignins. Earlier differential scanning calorimetric studies revealed that degradation starts below 200° C. Direct insertion probe experiments also demonstrated that splitting of linkages between aroxy and acetoguaiacone-benzylether (C) moieties commences at 175° C. As a consequence the presence of the following compounds was observed: guaiacol and C (from A) and syringol and C (from B). Simultaneously to these splitting mechanisms a rearrangement occurs between the ω-carbon of compound C and the phenolic oxygen of the aroxy residues, resulting in the formation of 2-methoxybenzaldehyde and acetovanillone-benzylether (from A) and 2,6-dimethoxybenzaldehyde and acetovanillone-benzylether (from B). Pyrolysis-gas chromatography-mass spectrometry experiments between 240 to 600°C corroborated these results. The higher the pyrolysis temperature the more peaks are displayed in the pyrograms. The pyrograms obtained at 600° C show 40 to 70 major peaks which were evaluated. The relative retention times, M + values and in most cases the assignments to defined compounds are given. Many ‘unknown’ substances could be identified as condensation products derived from benzyl radicals. Flow diagrams illustrate the main splitting mechanisms of compounds A and B.

U.S. EPA reference standards and quality assurance materials for the analysis of environmental pollutants

quality of all analytical measurements rests ultimately upon the quality of reference materials This statement is especially appropriate in the determination of trace contaminant residues in environmental matrices. To support the need for a certified, quality-controlled, common database in the analysis of pollutant chemical agents in environmental substrates, the U.S. EPA's Environmental Monitoring Systems Laboratory (Las Vegas) and Environmental Monitoring and Support Laboratory (Cincinnati) jointly maintain several repositories of analytical grade reference materials under the Agency's Quality Assurance Reference Materials (QARM) Project. Operated under contract by Northrop Services in Research Triangle Park, NC, the Project currently offers standards of some 2700 compounds of environmental concern, including pesticides and their metabolites and degradation products; PCBs, chloroand bromodibenzodioxins and furans, and other halogenated organics; plasticizers; nitrosamines; polynuclear aromatics; and heavy metals and metalloids. Included among these are the Agency-identified compounds commonly known as the priority pollutants, those materials regulated under Appendix VIII (RCRA) and CERCLA (Superfund) legislation, and groundwater monitoring compounds. The program is currently being supplied by nearly 200 chemical manufacturing companies and 33 chemical supply houses. Additional commercially-unavailable compounds, especially select environmental reaction and degradation products, are synthesized and purified in-house. Standards are offered, without charge, to any and all laboratories worldwide engaged in environmental monitoring, research, and/or regulatory and enforcement activities. During 1986, more than 150,000 standards were distributed in response to 7,000 requests. The analyst using Project standards expects the highest quality materials at accurate purity values and concentrations (for solutions), often without knowledge of how the integrity of each is established and maintained. Prior to distribution, each compound is subjected to a rigorous quality assurance program, including (1) component identification, (2) purity assay of neat materials, (3) concentration verification of solutions, and (4) stability studies, using a variety of instrumental methods. Although acquired materials typically include a percent purity value, each is individually reanalyzed in a series of steps. Chemical identity is verified by mass spectrometry, introduced via gas chromatograph or alternately, by direct insertion probe. For select compounds, other spectroscopic methods-IR, NMR, and ultraviolet spectroscopy-are supplementally employed. Subsequently, chemical purity is assayed by (at least) two methods, normally one chromatographic (GC, HPLC, TLC) and one non-chromatographic (DSC, NMR, IR, etc.). Establishing purity of a neat material is often complicated by the lack of a uniform response for all components to a single mode of detection. Electron capture, flame ionization, nitrogen-phosphorus, Hall, or mass spectrometric detection are the chromatographic methods of choice for most compounds, whereas HPLC or TLC are used for highly polar or thermo-labile materials. Purity is established by the ratio of peak area of the compound of interest to the combined peak areas for all eluting components. Implicit in this procedure is the assumption that all components elute and produce equal response at the detector. For FID or MS (positive electron impact), the assumption of equal responses is reasonably accurate, although some differences in relative response are inevitable. Non-chromatographic methods of purity analysis include ultraviolet spectroscopy, NMR, melting point, and differential scanning calorimetry (DSC). The latter method is frequently used for highpurity compounds because the method is typically reliable at purities >97% and useful for a wide variety of compounds. In DSC analysis, purity is estimated using a van't Hoff plot of melting point data. Typically, agreement of results among methods is within 1-2% and an average value is reported. However, in some cases, a substantial discrepancy in results is observed, necessitating further analyses.

Isolation and characterisation of intact steryl ferulates from seeds

Approaches to the isolation and characterisation of intact steryl ferulates were investigated. Alkaline washing of the total lipid extract obtained from seeds allowed preliminary separation of a phenolic ester containing fraction from the abundant neutral lipids (comprising largely triacylglycerides, sterols and steryl fatty acyl esters). Subsequent thin-layer chromatography (silica gel) afforded purified steryl ferulates. Separation of individual molecular species was achieved by reversed-phase (ODS) high-performace liquid chromatography (HPLC) using the acetate derivatives of the steryl ferulates, or by high-temperature gas chromatography (GC) of the underivatised steryl ferulates or their acetates or trimethylsilyl ethers. Characterisation of intact individual molecular species was based on the electron impact mass spectra obtained by GC—mass spectrometry (MS) of the underivatised ferulates or their trimethylsilyl ethers, or by direct insertion probe MS of the acetates of the steryl ferulates obtained by preparative HPLC. The feasibility of the above approach was established using the well characterised steryl ferulate mixture γ-oryzanol obtained from rice bran oil. The methods were subsequently applied to the analysis of the steryl ferulates present in seeds of maize ( Zea mays).

Direct coupling of capillary supercritical fluid chromatography to high resolution mass spectrometry with minimum modification

The coupling of a capillary supercritical fluid chromatograph with a high resolution double focusing mass spectrometer has been accomplished without any modifications to the pumping or ion source systems. The interface utilizes a direct insertion probe (DIP), which was originally designed for the direct analysis of solid samples, together with a trit restrictor as a decompression device. The DIP is placed opposite to the SFC restrictor, and it provides sufficient heat to prevent cluster formation and cooling resulting from the expansion of the supercritical fluid into the vacuum environment. Excellent mass spectra of standard polycyclic aromatic hydrocarbons under chemical-ionization (CI) conditions using methane as the reagent gas, and under charge-exchange (CE) conditions using CO2 as the charge exchange medium were obtained.

Pyrolysis-mass spectrometric investigations of the mechanistic and kinetic aspects of thermal degradation of phenol-formaldehyde polycondensates

High-molecular-weight phenol-formaldehyde polycondensates, deuterium-labelled at the aromatic or methylene linkages, were subjected to pyrolysis in the direct insertion probe of a mass spectrometer or in separate pulse-mode pyrolysers interfaced to the mass spectrometer or to the gas chromatograph-mass spectrometer. The principal route of the thermal degradation in vacuum and in an inert atmosphere,involving the cleavage of phenol-methylene bonds and subsequent hydrogen abstraction and resulting in the ultimate formation of phenol and methyl-substituted phenols as volatile products, exhibited hydrogen-deuterium scrambling owing to the isomerization of themacroradicals. The degree of scrambling was found to be dependent on the pyrolysis conditions (temperature, rate of temperature rise). At higher temperatures, hydrogen abstraction is kinetically favoured over the scission of benzyl bonds.

Direct coupling of open-tubular liquid chromatography with mass spectrometry.

The design and performance of a probe that allows direct liquid introduction of the total effluent of an open-tubular liquid chromatography (OTLC) column into a mass spectrometer are described. No modification of the mass spectrometer source is required, and the probe is introduced through the direct insertion probe inlet. Because flow rates are less than 0.1 ..mu..L/min, this system can be used under both conventional electron impact and chemical ionization mass spectrometric conditions. The probe has been used with glass OTLC columns (0.5-mm o.d., 16-..mu..m i.d.) and fused silica columns (0.35-mm o.d., and 5- or 10-..mu..m i.d.). Tapering and heating the end of the column allow for the detection of compounds of low volatility while maintaining good peak shape and minimizing band broadening. A separation of five pesticides is shown, for which detection limits in the low picogram levels in the full-scan mode were obtained by using methane negative chemical ionization (MNCI). The analysis of two isomeric triazine herbicides by using OTLC with electron impact ionization mass spectrometry is also shown.

Microbore HPLC / mass spectrometry for the analysis of peptide mixtures using a continuous flow interface

Microbore HPLC techniques have been combined with fast atom bombardment mass spectrometry to provide HPLC/MS capabilities for the analysis of mixtures of peptides and small proteins. The interface between the liquid chromatograph and mass spectrometer is a continuous flow direct insertion probe which contains a fused silica capillary that delivers the eluting solvent to the FAB source of the mass spectrometer at a rate of 5–10 μL/min. Data are presented for the analysis of several mixtures of peptides ranging in molecular weights from about 900 to 6000 daltons. In addition, the analysis of 100 pmol of a tryptic digest of whale myoglobin is shown where 16 of the possible 19 peptides were identified in the mass range m/z 2200–250. The advantages of this approach to HPLC/MS are a relatively high sensitivity because of the low flow rates and low background, and the ability to detect high molecular weight compounds.

Thermal decomposition of tetraamineplatinum(II) chloride by simultaneous TG/DTG/DTA/MS and direct insertion probe mass spectrometry

Simultaneous thermogravimetry (TG), derivative thermogravimetry (DTG), differential thermal analysis (DTA), and evolved gas analysis (EGA) by mass spectrometry (MS) have been used to determine the decomposition path for tetraamineplatinum(II) chloride and cis- and trans-diamineplatinum(II) chloride. Unequivocal identification of the evolved gases was done by direct insertion probe mass spectrometry.The thermal decomposition of (NH3)4PtCl2 occurred in two steps. The first was endothermic loss of two moles of ammonia producing a mixture of cis- and trans-diaamineplatinum(II) chloride. The second step was decomposition of the diamine complex to metallic Pt and N2, HCl, and NH4Cl. Reduction of Pt(II) to metallic Pt was coupled with oxidation of ammonia to molecular nitrogen and protons.

Modular instrument for organic secondary ion mass spectrometry and direct chromatographic analysis

A secondary ion mass spectrometer has been constructed for the analysis of organic samples introduced via a direct insertion probe and for the direct analysis of chromatographic samples. For discrete organic samples, a level of performance commensurate with commercial instruments has been established. Novel spatially resolved spectra for organic samples are presented, as well as the results of the direct sputtering of samples from a chromatographic matrix. The use of a matrix cycled through the solid/liquid phase transition for the in situ extraction of material is also described.

Quantitative estimation of quaternary ammonium neuromuscular blocking agents in serum by direct insertion probe chemical ionization mass spectrometry.

A new method based on selected ion monitoring chemical ionization mass spectrometry was developed to measure the quaternary ammonium neuromuscular blocking agents, pancuronium and vecuronium, in serum. An ion-pair extraction procedure is utilized to separate the compounds of interest from biological fluids. The intensities of the ion currents produced by the bisamines formed from the drugs and the corresponding deuterated internal standards through thermolytic dequaternization are monitored. The assay shows good linearity over the range of 1-500 ng/ml. This assay has been utilized in a variety of clinical pharmacokinetic studies involving surgical pediatric, geriatric and obstetric patients requiring anesthesia.

Unexpected adduct ion formation under chemical ionization conditions.

As part of our efforts to characterize the in vivo metabolic fate of the antihypertensive agent alpha-methyldopa, we have examined the urine of alpha-methyldopa-treated rats with the aid of a direct insertion probe chemical ionization mass spectral assay. The mass spectrum of the sample obtained by chromatographic purification followed by treatment with ethanolic hydrochloric acid and pentafluoropropionic anhydride displayed an intense ion at m/z 812, consistent with the beta-ethoxy-N,O,O,O-tetrakispentafluoropropionyl derivative of 6-hydroxy-alpha-methyl-norepinephrine, a potential aromatic hydroxylation product of the known alpha-methyldopa metabolite alpha-methyl-norepinephrine. Comparison of this spectrum with the spectrum obtained with the corresponding synthetic 6-hydroxy-alpha-methylnorepinephrine, however, ruled out this possibility. A more thorough examination of the mass spectral data established that the ion at m/z 812 observed with the metabolic species was due to the formation of an unexpected adduct ion between a known metabolite of alpha-methyldopa and an impurity ion formed from a common constituent of urine. This paper summarizes the characterization of this adduct ion.

Measurement of the 6Li/ 7Li isotope ratio for lithium salts by FT NMR spectroscopy

We require a relatively fast and simple analytical method for direct determination of the ‘LQ7Li isotopic ratio in solution samples taken from chemical-exchange processes being studied for lithium isotope separation. In general, mass spectrometry is used for the measurement of isotopic ratios. This technique can provide very precise results under optimum conditions, but there are several drawbacks, including inevitable sample destruction, memory effects, and, occasionally, rather complicated sample prep aration procedures. In the case of lithium, a precision of f l-2% (1 a) is typical for 6Li/7Li analysis by thermionic source mass spectrometry (I). Various factors affecting the accuracy and precision of isotopic analysis of lithium samples by mass spectrometry have been reviewed recently (2). If an electron-impact ionization source instrument is used, lithium samples must first be converted to a “semivolatile” salt, such as LiI, before introduction by means of a heated direct insertion probe. Thermal ionization spectrometers are equally restrictive on the form of the sample since most compounds must first be converted to a suitable inorganic salt such as LiN03 (I). In addition, the occurrence of isotopic fractionation when the sample leaves the filament is a serious problem (I). As an alternative to mass spectrometry, we are investigating the application of 6Li and 7Li FT NMR spectroscopy to the measurement of lithium isotopic ratios. Since the 1960s there have been several successful applications of NMR spectroscopy to isotopic analysis. For the earliest cases, satellite peaks in the ‘H spectrum were used to determine concentrations of 13C (3, 4) “B and “B (4, 5), 199Hg (4) 29Si (4) and 207Pb (6). With the recent development of higher power multinuclear IT spectrometers direct measurement of the nucleus of interest is now possible. For example, the deuterium content at the natural abundance level in water has been measured by ‘H NMR with a reproducibility of + 1% (1 a?) (7). The accuracy of data obtained for boron both by ‘H satellite (5) and by “B spectra (8) compares very favorably with that obtained by mass spectrometry (8) and with a significant reduction in total sample analysis time. A cw NMR spectrometer was used about fifteen years ago to measure lithium isotope ratios; those tests involved sample tube substitution and conversion

A mass spectrometric study of copper(II) acetate

Electron and chemical ionization mass spectra of copper(II) acetate monohydrate have been obtained. Exact mass measurements resolve the previously disputed compositions of several cluster ions and new high mass cluster ions are reported. The majority of the ions are consistent with a Cu(I) oxidation state, but a few require Cu(II). The reported reduction of Cu(II) to Cu(I) on the direct insertion probe is confirmed, but is shown not to proceed to completion. The occurrence of intermolecular hydrogen transfer in electron ionization is conclusively established by exact mass measurement. The methane chemical ionization mass spectrum of copper(II) acetate is recorded for the first time; cluster ions with equal numbers of copper atoms and ligand groups are observed to incorporate hydrogen preferentially. Daughter and parent ion MS/MS experiments are used to establish ion relationships in the gas phase and, in particular, to highlight ions which incorporate additional hydrogen atoms.

Simultaneous determination of volatile trace elements in nickel-base alloys using a direct insertion probe and inductively coupled plasma-emission spectrometry

The direct determination of volatile trace elements in Ni-base alloys has been studied using direct insertion-inductively coupled plasma-atomic emission spectrometry. A graphite probe which accommodated mg quantities of alloy chips was raised, semi-automatically, into the ICP and the volatile elements Cd, Mg, Pb and Zn were rapidly vaporised from the involatile host matrix and underwent excitation. Emission response for the elements as a function of applied rf power and observation zone was examined. It was established that aqueous multielement standard solutions (non-matrix matched) could be used for calibration and the viability of the approach was tested using certified reference materials and previously analysed Ni-base samples. Limits of detection, based on a 5 mg sample were 0.004–0.08 μg g −1 and precision at the μg g −1 level was in the range 6–14 % RSD. The method was not applicable to the determination of As and Se.

Exact Mass FAB and EI/FAB MS with Peptides Using a Direct Insertion FAB Probe

Abstract We have successfully installed and tested the first direct insertion probe (DIP) fast atom bombardment (FAB) gun on a Kratos MS-80 mass spectrometer. the installation requires only minor modifications on the standard EI/CI source which do not interfere with normal EI or CI operation. A small 2 inch extender must be added to the solid inlet to accomodate the extra length of the probe tip; this can be replaced in a few minutes by the standard seal to accept the regular solid probe. We have operated the source under simultaneous EI/FAB conditions with excellent results. The use of sorbitol syrup helps to keep source contamination and background spectrum to a minimum making it possible to operate at sufficiently high resolution in order to make exact mass operation routine. The performance evaluation has been carried out with synthetic peptides and the results are presented here.

Secondary-ion mass spectra and fast-atom-bombardment mass spectra of liquid polymers: alkoxylated pyrazoles and hydrazines

The positive-ion secondary-ion mass (s.i.m.) spectra of polyalkoxylated hydrazines and pyrazoles contain series of ions that reflect the degree of polymerization of the parent compound, and also suggest the presence of several discrete polymeric series. The spectra of two examples of pyrazoles are interpreted in terms of a series of polymeric (M + H) + ions. Three alkoxylated hydrazines yield particle-bombardment spectra which contain polymeric ion series that extend to the mass limit of the analyzer. Positive-ion fast-atom-bombardment mass spectra are also recorded. These spectra also reflect the polymeric structures of the compounds studied, and are similar in almost every detail to the s.i.m. spectra, despite a difference in primary beam parameters and the use of a sector rather than a quadrupole mass analyzer. The liquid compounds are processed as neat samples on a direct-insertion probe for the production of both secondary-ion and fast-atom-bombardment mass spectra, and provide stable, long-lasting secondary-ion signals even under high fluxes of primary particles.

Identification of polymers by library search of pyrolysis mass spectra and pattern recognition analysis

A library of mass spectra of polymers containing about 200 entries is described. These spectra were obtained by direct pyrolysis-electron-impact mass spectrometry, i.e., by heating the polymers in the direct insertion probe for solid samples at a constant heating rate and recording repetitive mass spectra during the temperature rise. The library can be used both as a data base for library searches and as a training set for a pattern recognition analysis. The algorithm used to generate and search the files and a few applications of the library search and pattern recognition analysis are presented.

Modification of a packed column gas chromatograph/mass spectrometer

A packed-column gas-chromatograph/mass-spectrometer (GC/MS), Hewlett-Packard 5982, was modified to accommodate fused silica capillary columns. The original GC/MS interface and chemical-ionization sample-line in the ion-source were changed to allow the end of a fused silica capillary column to enter the ion-chamber directly. For chemical-ionization operation, the reagent gas was brought into the MS through the direct-insertion probe port. The calibration compound was introduced through the electron-impact sample-inlet, which simplified the operation. The modified system yields higher sensitivity and more efficient separation, as well as simpler operation, without sacrificing any original instrument functions.