Liquid chromatography-mass spectrometry of trace compounds with a moving-belt interface and multi-dimensional chromatography

A high-performance liquid chromatographic method with on-line mass spectrometric detection is described for the structural analysis of a number of synthetic impurities, present at trace levels in almitrine. To obtain mass spectra with various ionization methods and high-resolution mass measurements, a moving-belt liquid chromatograph-mass spectrometer interface is used. A two-column switching system allows the injection of large amounts of almitrine, from which the trace compounds are trapped on a second column, while discarding the major component. This permits the introduction of the impurities into the mass spectrometer by elution of the second column, without the risk of introducing too large an amount of the major compound into the mass spectrometer. The mass spectra thus obtained are of sufficient quality to permit a correct structural assignment of the impurities.     

Infrared study of HDTMA+ intercalated montmorillonite

In this paper, FTIR spectroscopy using attenuated total reflection (ATR) and KBr pressed disk techniques has been used to characterize sorbed water and HDTMA+ in organo-clay. Sorbed water content decreases with the intercalation of HDTMA+. With the decrease of the sorbed water content, the position of the nu2 mode shifts to higher frequency dramatically while the stretching vibration shifts to lower frequency slightly, indicating that H2O is less strongly hydrogen bonded. This might be resulted from the polarization of H2O molecules by the changeable cations and HDTMA+. FTIR spectra show that both antisymmetric and symmetric CH2 stretching absorption bands shift to low frequencies with increase of amine concentration within the galleries of montmorillonite, elucidating the increase of ordered conformation. Furthermore, the present study demonstrates that the antisymmetric CH2 stretching mode is more sensitive to the conformational ordering than the symmetric stretching mode. When KBr pressed disk technique used, two well resolved absorption bands at 730 and 720 cm(-1), and at 1473 and 1463 cm(-1), corresponding to the methylene scissoring and rocking modes, respectively, could be observed in FTIR spectra of organo-clays with relative higher concentration of surfactant. However, the FTIR spectra using ATR technique only display singlets and they are independent of amine concentration and chain conformation. Our present study demonstrates that FTIR spectroscopy using KBr pressed disk technique is more suitable to probe the conformational ordering of surfactant in organo-clays than that suing ATR technique does.     

Qualitative and quantitative evaluation of chrysotile and crocidolite fibers with IR-spectroscopy: application to asbestos-cement products

Infrared (IR) spectrophotometry allows simple and quick qualitative and quantitative evaluations of different kinds of asbestos, as well as of other inorganic particles. In particular, chrysotile and crocidolite have characteristic IR spectra and optical density measures of 2,710 nm band for chrysotile, of 12,820 nm band for crocidolite permit quantitative evaluation of each fiber alone or in mixture. IR spectra also give informations about changes of fiber structure and of chemical composition due, for example, to thermal treatment or acid leaching. The analytical method we developed can detect levels as low as 0.1 mg of fiber in a 300 mg disk of KBr using a low cost IR spectrophotometer. The use of a Fourier Transform IR spectrophotometer (FTIR) improves dramatically the sensitivity and selectivity. Computer assisted analysis of spectra offers the possibility to reduce matrix interferences and to compare different spectra. Examples of IR technique applied to asbestos-cement products and insulating materials are presented.     

The mechanism of the dissolution,spray and deposition technique--a novel infrared sampling method

The dissolution, spray and deposition (DSD) technique, a novel infrared (IR) sampling technique, gives very sharp spectra for amino acids and peptides. The mechanism of this unique technique has been established by scanning electron microscopy (SEM) studies and found to be due to the formation of several layers of fairly large KBr crystals in situ on an IR transparent window. The zwitterions of the amino acids and dipeptides are adsorbed on the surface of these large KBr crystals, which ensures the isolation of monomers of the amino acid or dipeptide zwitterions in the KBr matrix, thereby leading to sharp and well-resolved IR spectra. This methodology provides a powerful IR sampling technique, akin to matrix isolation, with the added advantage of being extremely cost effective as it does not require low-temperatures or a sophisticated experimental set up.     

Characterization of kaolinite of the Baten El-Ghoul region/south Jordan by infrared spectroscopy

The infrared spectra (3700-500 cm-1) have been recorded for kaolinite obtained from the Baten El-Ghoul region/south Jordan. The spectra were recorded for raw and dried samples, using KBr disk and nujol methods. The vibrational assignments of the basic fundamental modes were proposed, which were supported by the spectra obtained from the two methods used. The results obtained were compared with other related studies.     

付里叶变换红外光谱仪的操作参数对光谱的影响

本文以二苯基甲酮的ＫＢｒ压片为标样，在Ｂｒｕｋｅｒ ＩＦＳ １２０ＨＲ付里叶变换红外光谱仪上系统考察了该仪器折一些重要操作参数（光源光栏、切趾函数、扫描速度）对光谱质量（信噪比，分辨率）的影响。从而获得了测样时的优化操作条件。     

Renaissance of gas chromatography-time-of-flight mass spectrometry. Meeting the challenge of capillary columns with a beam deflection instrument and time array detection

This report describes the use of a unique beam deflection time-of-flight mass spectrometer to address some of the demands made on mass spectrometry by new developments in high-resolution capillary column gas chromatography. An integrating transient recorder is used in combination with this beam deflection time-of-flight instrument to apply the concept of time array detection in capturing all of the mass spectral information available from the ion source, thereby greatly enhancing the signal-to-noise ratio quality of the mass spectral data. The applicability of the time array detection approach to gas chromatography-mass spectrometry is demonstrated in the context of an analysis of the standard Grob mixture for assessing performance of capillary column chromatography. During analysis of the Grob mixture by gas chromatography-mass spectrometry, mass spectra were recorded at a rate of 20 scan files per second. The data indicate that this rate of mass spectral scan file generation is adequate to provide a suitable data base for reconstruction of the chromatographic profile. In addition, the effective scan rate is high enough that there is no distortion in the relative peak intensities throughout the individual mass spectra of components regardless of the relatively high dynamic changes in partial pressure of the analyte as reflected by the sharp peaks in the chromatographic profile. The experimental results indicate that the beam deflection time-of-flight mass spectrometer can provide mass spectra at a scan file generation rate much higher than that possible with the conventional quadrupole or magnetic sector mass spectrometer, but at comparable detection limits.     

Procedure for preparing infrared spectra on gas chromatographic fractions

A convenient technique is described for the preparation of microinfrared spectra on materials which elute from a gas chromatograph. The technique involves trapping the sample on KBr and then pressing this material in a die between two portions of pure KBr. Samples as small as 10 μg grams and as low boiling as 150 °C produce acceptable spectra. Since no solvents are employed, solvent band compensation is unnecessary.     

A study of background signals in graphite-furnace atomic absorption spectrometry

The non-specific absorption from inorganic and organic molecules between 190 and 400 nm are measured using a graphite furnace and an atomic absorption spectrometer with a deuterium source.The molecular absorption spectra of NaCl, KCl, RbCl and CsCl are very similar, with two maxima at ca. 200 and 250 nm. That of LiCl is very weak, as is that of NaF. The spectra of NaBr, NaI, KBr, KI, CaCl₂, MgCl₂, SrCl₂, FeCl₃, LaCl₃ are also reported.The non-specific absorption spectrum arising from albumin decreases fro 190 to 400 nm, and that for plasma is similar to albumin, although a contribution from inorganic salts can also be seen. To decrease the non-specific absorption from metal chlorides or biological samples of mainly inorganic composition such as urine, addition of HNO₃ is satisfactory. Oxygen introduction during low temperature charring is better for removing contribution from organic molecules.     

Laser Raman and IR spectra and force fields for 2,6-difluorobenzonitrile

Raman spectrum of 2,6-difluorobenzonitrile in the powder form has been recorded in the region 50–4000 cm⁻¹ on a Jasco K-500 spectrophotometer using the 488.0 nm radiation from an argon laser. IR spectra in the region 200–4000 cm⁻¹ have been recorded in KBr pellet and nujol mull on a Nicolet DX spectrometer and in liquid and vapour phases on a Jasco FTIR/7000 spectrometer. Using these observed frequencies force field calculations for the planar and non-planar modes have been carried out assuming a general valence force field.     

Membrane approach to solid-phase extractions

A novel material for separations has been developed in which efficient chromatographic particles are enmeshed in a network of PTFE fibrils to form a strong, porous sheet or “membrane”. The membrane can have a variety of sorptive or reactive properties, which are determined by the characteristics of the particulate chosen. The membranes, in the form of 47- or 25-mm disks, are used with standard filtration equipment. The use of hydrophobic octyl- and octadecyl-bonded silica particulates for reversed-phase extractions of environmental pollutants from an aqueous matrix, replacing conventional liquid-liquid extraction (LLE) is described. The water sample is filtered through the disk and adsorbed organic species are eluted from the disk with a small volume of an appropriate solvent for subsequent chromatographic separation. The technique is rapid, less labor intensive then LLE and eliminates the need for large volumes of hazardous and expensive solvents. Specific applications investigated include the analysis of ground, surface and tap waters for pesticides, polychlorinated biphenyls and phthalates at the μg l^?1 level.     

A computer program in ALGOL-60 for the location and evaluation of peaks in Ge(Li) gamma ray spectra

A program is presented for the analysis of γ-ray spectra from Ge(Li) multichannel spectrometer systems. The program is written in ALGOL-60 for off-line working with a large Philips Electrologica X8 computer. It has been extensively used in thermal neutron activation analysis practice.     

A New Approach to High Sensitivity Liquid Chromatography-Mass Spectrometry of Peptides using Nanoflow Solvent Assisted Inlet Ionization

Liquid chromatography (LC) solvent assisted inlet ionization (SAII) mass spectrometry (MS) was previously reported to give good chromatographic resolution and MS detection injecting 66 ng of a BSA tryptic digest. In analogy to nano-electrospray ionization (nESI), we extend SAII LC/MS to nano-SAII (nSAII) operating at nL min^–1 flow rates and demonstrate good quality ion chromatograms and mass spectra from injection of as little as 0.7 ng of BSA digest onto a capillary LC column. Data dependent fragmentation is demonstrated for injection of 7 ng of a BSA digest. This method has advantages over nESI in ease of use and low cost as it requires no voltage and is operational without the necessity of connectors or fragile nESI emitters, although similar constricted tips can be helpful in nSAII to stabilize the signal at low nanoliter flow. At a flow rate of 0.8 μL min^–1, the only requirement for nSAII is that the exit-end of the capillary LC column be adjusted near the aperture of the heated inlet of the mass spectrometer.     

Coupling of narrow-bore liquid chromatography to thin-layer chromatography : Part 2. Application of fluorescence-based spectroscopic techniques for off-line detection

The effluent from a narrow-bore liquid chromatographic (l.c.) separation can be immobilized on thin-layer chromatographic (t.l.c.) plates with little loss of resolution. The deposited compounds are then available for further inspection. For off-line detection, direct fluorescence emission, fluorescence excitation emission spectra, and fluorescence line-narrowing spectroscopy are investigated with tetracene and benz[k] fluoranthene as model compounds. Detection based on direct emission measurements and on measurements for which complete spectra are obtained for the separated compounds, is suitable for identification and determination. Detection limits are of the same order of magnitude as those for on-line detection in narrow-bore l.c. The fluorescence spectra of immobilized compounds can be obtained with a conventional fluorescence spectrometer equipped with a solid-sample accessory. No other special apparatus is needed. The immobilized chromatogram is also suitable for techniques incompatible with flow systems, e.g., fluorescence line-narrowing spectroscopy, which yields fluorescence spectra via laser excitation of low-temperature solid samples. Very selective narrow-line fluorescence spectra were obtained for tetracene deposited on t.l.c. plates in amounts down to the low picogram level.     

Component reconstruction in the primary space of spectra and concentrations. Alternating regression and related direct methods

A set of methods that extract the spectral components in a chromatographic run is considered. The methods do not need libraries of previously known spectra or retention times. The methods have been developed for two-dimensional spectra but they can also be used for chromatographic analyses with a single-channel detector. The methods are direct; they do not use principal components as the starting point. Alternating regression (AR) remains in the primary space of spectra and concentrations during the calculations. Random numbers are used as the starting spectra. Regression is used to solve first for the concentrations, then for the spectra. The method uses two kinds of constraints: all spectra and concentrations are forced to be positive; and all concentration profiles are forced to a unimodal shape with a single local maximum. It is assumed that all observations are a linear sum of components. Compact alternating regression (CAR) is a new variant of the basic AR. The idea is to replace multiplication of a large matrix by two multiplications of smaller matrices. This typically speeds up the iterations by a factor of ten. AR and CAR have been successfully used with combined techniques such as gas chromatography—mass spectrometry and liquid chromatography with UV—visible detection. The reliability of the solution is checked by repeatedly injecting noise and performing the analysis several times. This produces estimates of confidence intervals. AR and CAR have recently been extended to handle single-dimensional signals. Examples are single-channel detectors such as the flame ionization detector in gas or liquid chromatography with a fixed-wavelength UV detector. A batch of samples is used as the observation matrix. As a result, one obtains both the concentrations and the elution shapes of individual chromatographic peaks.     

Derivatization in mass spectrometry --7. On-line derivatisation/degradation

The review describes on-line derivatization/degradation methods employed in mass spectrometry to solve some structural and analytical problems. Advantages and applications of various positions of reaction systems connected mainly to a mass spectrometer or a gas chromatograph/mass spectrometer are considered. Among these are reaction systems connected directly to the mass spectrometer (reaction mass spectrometry, pyrolysis-mass spectrometry or direct pyrolysis-mass spectrometry); flash-heaters as reactors in gas chromatography/mass spectrometry (GC/MS); in-line chemical reactors located before the chromatographic column [pre-column derivatization/degradation with the use of catalytic reactions, pyrolysis (pyrolysis-GC/MS), degradation in elemental analyzers-isotope ratio mass pectrometry (EA-IRMS)]; on-column derivatization and deuteration; reactor located between the chromatographic column and a mass spectrometer [post-column catalytic derivatization, gas chromatograph-combustion-isotope ratio mass spectrometer (GC-c-IRMS)]. Post-column derivatization in high performance liquid chromatography/mass spectro-metry is briefly mentioned. Application of such on-line methodology to structure elucidation of low molecular mass compounds and polymers, to the determination of isotope ratios of the most common elements, to the investigation of catalytic reactions is discussed..     

Structure elucidation of β-carotene isomers by HPLC-NMR coupling using a C30 bonded phase

The separation of cis/trans isomers of β-carotene has been performed with a C₃₀ stationary phase employing ¹H NMR spectroscopy as an on-line detection technique. 1D as well as 2D NMR spectra have been recorded in the stopped-flow mode for the predominant chromatographic peaks. Structural assignment of the five identified isomers was performed via comparison of simulated 1D ¹H NMR spectra on the basis of the structures of β-carotene cis/trans isomers with the experimental data, and also by the analysis of the proton-proton connectivities in the 2D NMR spectra of three isomers with the highest concentration. The chromatographic retention behaviour of the isomers agreed well with previously reported data. The advantage of the applied hyphenated coupling technique compared to conventional off-line techniques lies in the fact that chromatographic separation and NMR detection are performed in a closed system, so that reisomerization of the separated compounds is inhibited. Received: 29 May 1996 / Revised: 1 July 1996 / Accepted: 4 July 1996     

Structure elucidation of β-carotene isomers by HPLC-NMR coupling using a C30 bonded phase

The separation of cis/trans isomers of β-carotene has been performed with a C₃₀ stationary phase employing ¹H NMR spectroscopy as an on-line detection technique. 1D as well as 2D NMR spectra have been recorded in the stopped-flow mode for the predominant chromatographic peaks. Structural assignment of the five identified isomers was performed via comparison of simulated 1D ¹H NMR spectra on the basis of the structures of β-carotene cis/trans isomers with the experimental data, and also by the analysis of the proton-proton connectivities in the 2D NMR spectra of three isomers with the highest concentration. The chromatographic retention behaviour of the isomers agreed well with previously reported data. The advantage of the applied hyphenated coupling technique compared to conventional off-line techniques lies in the fact that chromatographic separation and NMR detection are performed in a closed system, so that reisomerization of the separated compounds is inhibited. Received: 29 May 1996 / Revised: 1 July 1996 / Accepted: 4 July 1996     

Reaction gas chromatography/mass spectrometry. 4—structure elucidation of cyclic sulphides by gas chromatography/mass spectrometry with the use of on-line hydrodesulphurization

A method for structure determination of cyclic sulphides within mixtures is described. It involves the use of a vapour phase hydrodesulphurization micro-reactor (Raney nickel) located between the chromatographic column and the mass spectrometer (hydrogen and deuterium are used as carrier and reagent gases). A comparative examination of the mass spectra of the cyclic sulphides, as well as of the hydrocarbons and their deuterio analogues (deuterium atoms are bonded to carbon atoms which had been attached to sulphur) derived from the sulphides under the catalytic conditions employed, permits unambiguous determination of the size of the heterocycle and the position of the substituents.     

Determination of 3,3′-Dichlorobenzidine and its degradation products in environmental samples with a small low-field Fourier transform ion cyclotron resonance mass spectrometer

3,3'-Dichlorobenzidine (DCB) and its degradation products, 3-chlorobenzidine (MCB) and benzidine, are of environmental concern because of their carcinogenic nature. The suitability of a small Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer for the analysis of these environmental contaminants in different types of matrices was explored. All the measurements were carried out by depositing the sample solution directly on a disk that was introduced into the mass spectrometer. This approach is very fast and simple because it requires no prior chromatographic separation or derivatization. Calibration curves determined by collecting 70-eV electron ionization mass spectra of neat samples yielded lower limits of detection of 29 and 17 pg (total amount on the solids probe) for DCB and benzidine, respectively (based on a signal to noise ratio of > or = 2:1), while chemical ionization with ammonia resulted in lower limits of detection of 21 pg for DCB and 9 pg for benzidine (total amount on the solids probe). FT-ICR analysis of sediments collected from Lake Macatawa (Holland, MI) verified the presence of DCB in this complex, environmentally significant sample matrix. Laboratory experiments designed to probe biodegradation and photodegradation pathways showed that DCB undergoes sequential dehalogenation to yield MCB and then benzidine under exposure to microorganisms and under simulated tropospheric solar radiation. The ability of the FT-ICR to determine elemental compositions of compounds introduced as described above was demonstrated for one of the degradation products.