Feasibility of gas chromatography--ion trap tandem mass spectrometry for the determination of polychlorinated biphenyls in food

The different parameters affecting the ionisation and fragmentation of selected polychlorinated biphenyls (PCBs) in an IT detector working in the MS/MS mode, ITD(MS/MS), have been optimised for maximum selectivity and sensibility. The low LODs (in the range 0.03-0.3 microg/L), the satisfactory repeatability (RSDs in general below 11%) and reproducibility (RSDs below 17%) obtained when analysing standard solutions ensured proper determination of the PCBs studied at the concentrations typically found in food samples. Foodstuffs naturally contaminated with varying levels of PCBs have been analysed using the optimised GC-ITD(MS/MS) method. The results obtained compared favourably with those found using more conventional detectors, such as (micro-)electron capture detection (for ortho-PCBs) and high-resolution MS (for non-ortho-PCBs), as well as with the consensus PCB levels established for these particular samples via an international interlaboratory exercise. The relative merits of these three detectors have been discussed.     

Comparison of the response of four aerosol detectors used with ultra high pressure liquid chromatography

The responses of four different types of aerosol detectors have been evaluated and compared to establish their potential use as a universal detector in conjunction with ultra high pressure liquid chromatography (UHPLC). Two charged-aerosol detectors, namely Corona CAD and Corona Ultra, and also two different types of light-scattering detectors (an evaporative light scattering detector, and a nano-quantity analyte detector [NQAD]) were evaluated. The responses of these detectors were systematically investigated under changing experimental and instrumental parameters, such as the mobile phase flow-rate, analyte concentration, mobile phase composition, nebulizer temperature, evaporator temperature, evaporator gas flow-rate and instrumental signal filtering after detection. It was found that these parameters exerted non-linear effects on the responses of the aerosol detectors and must therefore be considered when designing analytical separation conditions, particularly when gradient elution is performed. Identical reversed-phase gradient separations were compared on all four aerosol detectors and further compared with UV detection at 200 nm. The aerosol detectors were able to detect all 11 analytes in a test set comprising species having a variety of physicochemical properties, whilst UV detection was applicable only to those analytes containing chromophores. The reproducibility of the detector response for 11 analytes over 10 consecutive separations was found to be approximately 5% for the charged-aerosol detectors and approximately 11% for the light-scattering detectors. The tested analytes included semi-volatile species which exhibited a more variable response on the aerosol detectors. Peak efficiencies were generally better on the aerosol detectors in comparison to UV detection and particularly so for the light-scattering detectors which exhibited efficiencies of around 110,000 plates per metre. Limits of detection were calculated using different mobile phase compositions and the NQAD detector was found to be the most sensitive (LOD of 10 ng/mL), followed by the Corona CAD (76 ng/mL), then UV detection at 200 nm (178 ng/mL) using an injection volume of 25 μL.     

Separation, characterization, and quantitation of process-related substances of the anti-hypertensive drug doxazosin mesylate by reversed-phase LC with PDA and ESI-MS as detectors

A simple and rapid reversed-phase liquid chromatography (LC) method with photodiode array (PDA) and electrospray ionization (ESI)-mass spectrometry (MS) as detectors was developed and validated to separate, identify, and quantitate the related substances of Doxazosin mesylate (DXZN) for monitoring the reactions involved during process development. The high-performance liquid chromatography profiles of related-substances of DXZN are used as fingerprints to follow the procedures used in the manufacturing units. The separation is accomplished on an Inertsil ODS-3 column with acetonitrile-ammonium acetate (10 mM, pH 4.0) as the mobile phase, using a gradient elution mode and monitoring the eluents by a photodiode array detector at 265 nm at ambient temperature. LC-ESI-MS-MS is used to identify the additional impurities formed during the synthesis. The identified impurities were synthesized and characterized by UV, Fourier transform-IR, 1H NMR, and MS data. The detection limits for the impurities are 0.74 - 4.14 x 10(-9) g, and the method is found to be suitable not only for the monitoring of synthetic reactions, but also for quality assurance of DXZN in bulk drugs and formulations.     

The Effects of the Electrode System Geometry on the Properties of Contactless Conductivity Detectors for Capillary Electrophoresis

The basic analytical parameters of contactless conductivity detectors with planar, semi‐tubular and tubular electrodes have been compared. It has been found that the differences in the analytical parameters of the detectors are not significant for analytical use. The mean values of baseline peak‐to‐peak noise of 0.27, 0.35 and 0.33 mV, sensitivities of 0.97, 2.08 and 2.27 mV/pg (for K⁺ ion), limits of detection of 0.93, 0.65 and 0.53, and the heights equivalent to a theoretical plate of 2.83, 2.39 and 2.40 μm were obtained for the detectors with planar, semi/tubular and tubular electrodes, respectively. Modifications of the basic detectors, namely a detector with thinned capillary wall and planar electrodes, and a detector with semi‐tubular electrodes placed one against the other on the opposite sides of the capillary were also tested. The configuration with the electrodes placed one against the other permits detector construction with zero gap between the electrodes without increasing the noise; when the electrodes overlap, the detector begins to operate as a permittivity detector.     

气相色谱分析中是否一定要用质谱检测器？

The detector, as well as being an essential supporting device for the gas chromatography (GC) has also played a critical role in the development of the technique as a whole. The mass spectrometer (MS) is still the commonly praised detector as before. In fact, the information of fragmentation patterns is seldom used in practice, and the GC-MS instrument is even more expensive. For today’s analytical problems, it seems that element specific detectors can and should be used for many applications rather than GC-MS.     

Development of a ginkgo biloba fingerprint chromatogram with UV and evaporative light scattering detection and optimization of the evaporative light scattering detector operating conditions

A fingerprint chromatogram of a standardized Ginkgo biloba extract is developed on a monolithic silica column using a ternary gradient containing water, iso-propanol and tetrahydrofuran. For the detection, UV and evaporative light scattering (ELS) detectors are used, the latter allowing detection of the poor UV absorbing compounds as ginkgolides (A-C and J) and bilobalide in the extract. The complementary information between the UV and ELS fingerprint is evaluated. The ELS detector used in this study can operate in an impactor 'on' or 'off' mode. For each mode, the operating conditions such as the nebulizing gas flow rate, the drift tube temperature and the gain are optimized by use of three-level screening designs to obtain the best signal-to-noise (S/N) ratio in the final ELS fingerprint chromatogram. In both impactor modes, very similar S/N ratios are obtained for the nominal levels of the design. However, optimization of the operating conditions resulted, for both impactor modes, in a significant increase in S/N ratios compared to the initial evaluated conditions, obtained from the detector software.     

A Comparative Study of Pyrolysis Liquids by Slow Pyrolysis of Industrial Hemp Leaves,Hurds and Roots

This study assessed the pyrolysis liquids obtained by slow pyrolysis of industrial hemp leaves, hurds, and roots. The liquids recovered between a pyrolysis temperature of 275–350 °C, at two condensation temperatures 130 °C and 70 °C, were analyzed. Aqueous and bio-oil pyrolysis liquids were produced and analyzed by proton nuclear magnetic resonance (NMR), gas chromatography–mass spectrometry (GC-MS), and atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS). NMR revealed quantitative concentrations of the most abundant compounds in the aqueous fractions and compound groups in the oily fractions. In the aqueous fractions, the concentration range of acetic acid was 50–241 gL⁻¹, methanol 2–30 gL⁻¹, propanoic acid 5–20 gL⁻¹, and 1-hydroxybutan-2-one 2 gL⁻¹. GC-MS was used to compare the compositions of the volatile compounds and APPI FT-ICR MS was utilized to determine the most abundant higher molecular weight compounds. The different obtained pyrolysis liquids (aqueous and oily) had various volatile and nonvolatile compounds such as acetic acid, 2,6-dimethoxyphenol, 2-methoxyphenol, and cannabidiol. This study provides a detailed understanding of the chemical composition of pyrolysis liquids from different parts of the industrial hemp plant and assesses their possible economic potential.     

Simultaneous determination of saponins and a flavonoid from aerial parts of Zygophyllum coccineum L

Triterpenoid saponins are a class of glycosides with a wide range of bioactivities, which make them interesting research candidates. Zygophyllum coccineum is an Egyptian desert plant rich in triterpenoid saponins. Reviewing the relevant literature, no data concerning the HPLC or ultra-performance LC (UPLC) analysis of Zygophyllum content were found. This paper presents two methods, HPLC-UV and UPLC-UV-evaporative light scattering detector (ELSD)/MS, for the simultaneous determination of 10 compounds in the alcohol extract of Z. coccineum. The HPLC method uses a C18 column and water-acetonitrile (both containing 0.1% trifluoroacetic acid) gradient system. The separation was achieved within 32 min. The developed UPLC method simultaneously detects and quantifies the 10 compounds using an Acquity UPLC BEH Shield RP18 column and reagent alcohol-acetonitrile (80/20, v/v) and water (both containing 0.5% formic acid) gradient system within 14 min with UV, ELS, and MS detectors. The methods were used to analyze another species, Z. simplex, and results revealed a great variation between the secondary metabolite pattern of both species.     

Polymer analysis using pyrolysis-GC-FTIR-MS and GC-AED

Volatile pyrolysates of a methyl methacrylate-butadiene-styrene copolymer (MBS) have been analyzed using a capillary gas chromatograph equipped with a Fourier transform infrared detector in tandem with a mass selective detector, and a gas chromatograph-atomic emission detector system. Among the volatile compounds observed were monomers used for synthesis of the polymer. Numerous oligomers of higher boiling point were also found; identification of these could be used to give structural information about the parent polymer. Combining information from these techniques was found to be extremely useful for the analysis of polymer pyrolysis products. In characterizing each compound it was found particularly helpful to juxtapose feature-specific chromatograms (e.g., single ion monitoring from the mass-selective detector and the selected wavelength chromatography from the infrared detector).     

Analytical methods for phenyltin compounds in polychlorinated biphenyl-based transformer oil samples

We present the first study on the analytical methods of phenyltin compounds (PTs) in polychlorinated biphenyl (PCB)-based transformer oil samples. Tetraphenyltin (TePhT) has been used as stabilizer for some kinds of PCBs-based transformer oil formulations. Monophenyltin (MPhT), diphenyltin (DPhT) and triphenyltin (TrPhT) could have been formed from TePhT during long-term use. TePhT was directly measured by gas chromatograph (GC) connected with three types of detectors, a mass spectrometer (MS), a flame photometric detector (FPD) and an atomic emission detector (AED) after dilution with hexane. MPhT, DPhT and TrPhT were propylated with Grignard reagent before measurement. The MS was the most sensitive of the detectors, with detection limits of phenyltin compounds of 30 ng/ml (MPhT), 9.8 ng/ml (DPhT), 5.5 ng/ml (TrPhT) and 0.60 ng/ml (TePhT), respectively. From the viewpoint of selectivity, MS was slightly worse than other detectors, but interference from PCBs matrices was not significant under ordinary analytical conditions. Two used transformer oil samples were analyzed using the analytical methods developed in this study. TePhT and TrPhT were found in both samples.     

Polyketide analysis using mass spectrometry,evaporative light scattering,and charged aerosol detector systems

In this study, a mass spectrometer (MS), an evaporative light scattering detector (ELSD), and a charged aerosol detector (CAD) were used to analyze an erythromycin precursor (termed 6-deoxyerythronolide B). The work highlights the capabilities of each detector to analyze a representative polyketide compound that does not possess a natural chromophore, and presents the first comparison to include a charged aerosol system. Each detector was evaluated based upon limit of detection (LOD), dynamic range, and precision in the context of polyketide analysis. Due to its low LOD, wide dynamic range, and ability to provide molecular weight information, the MS was deemed the best detection option for the analysis of low-concentration, poorly identified polyketide compounds. Alternatively, both the CAD and ELSD systems studied showed better precision and accuracy. The ELSD demonstrated the best precision at 3%, but its LOD was limited to concentrations primarily greater than or equal to 1 mg/L. The Corona CAD demonstrated a LOD (0.012 mg/L) and dynamic range comparable to mass spectroscopy and therefore serves as a more cost-efficient alternative for polyketide production schemes with low titers.     

A comparative study of commercial liquid chromatographic detectors for the analysis of underivatized amino acids

This study compares the main commercial detectors that can detect amino acids in their underivatized form. The detectors tested are: the chemiluminescent nitrogen detector (CLND), the evaporative light scattering detector (ELSD), the nuclear magnetic resonance spectrometer, conductivity detector, refractive index, UV, and electrospray quadrupole mass spectrometry (in simple and tandem MS mode). As ELSD, CLND and MS require a volatile mobile phase, an ion-pair reversed-phase liquid chromatographic system was selected, consisting of an octadecyl column and an aqueous mobile phase containing pentadecafluorooctanoic acid as volatile ion-pairing reagent. Underivatized taurine, hypotaurine, aspartic acid, hydroxyproline, asparagine, serine, glycine, glutamine, cysteine, glutamic acid, threonine and alanine were simultaneously analysed with each detector. In order to test the applicability of these detectors to "real world" samples, the amino acid stoichiometry of the tetrapeptide Gly-Gly-Asp-Ala was determined with each detector after acid hydrolysis. The detectors were compared in terms of linearity, limit of detection, advantages and disadvantages as well as special features (capacity to provide structural information, specificity, quantification with single calibration curve, etc.).     

毛细管电泳光学检测器的进展

对毛细管电泳的光学检测器作了简要评述。根据所采用的检测原理。光源检测器可分为紫外检测器，激光诱导荧光检测器、化学肆光检测器、荷耦合器件检测器、折射指数检测器等许多种类，具有简单方便、使用广泛，信息量较大等特点，是一类有良好诉检测器。     

Estimation of polyoxyethylene chain distribution of alcohol and alkylphenol ethoxylates

Summary Oxyethylated nonylphenol and alcohols were analyzed by HPLC on normal phases with mixtures of hexane, 2-propanol and water as mobile phases, using UV and evaporative light scattering (ELS) detectors. Effects of selected analytical conditions (type of detector, drift tube temperature and gradient) on determined distributions are discussed. The distributions of oxyethylated alcohols obtained in the presence of NaOH and calciumbased W7^TM catalyst and polyoxyethylene glycols present in products were compared. The distribution of oxyethylated alcohols and alkylphenols were fitted for normal distribution characterized by the mean and the standard deviation. It was found that the analytical results fitted the normal distribution quite well. The estimated mean agrees with the average degree of oxyethylation and the standard deviation can be used as a measure of the distribution broadness.     

Determination of seven compounds in Tang Maikang granule by high-performance liquid chromatography

An accurate and sensitive high-performance liquid chromatography method is developed and applied to the determination of seven compounds in a kind of traditional Chinese medicinal preparation of Tang Maikang Granule. The method is performed on Hypersil C(18) column (250- x 4.6-mm i.d., 5 microm), and different mobile phases and detectors are selected according to the various compounds. For astragaloside IV, an evaporative light scattering detector (ELSD) is used with a gradient of methanol-water at an eluent gas rate of 2.0 mL/min, under a drift tube temperature of 80 degrees C. Formononetin and calycosin are also eluted by a gradient of methanol-water, but a photodiode array (PDA) detector is used at a wavelength of 254 nm for formononetin and calycosin. A PDA detector at a wavelength of 230 nm is used for paeoniflorin, with methanol-water (30:70, v/v) as the mobile phase. For danshensu and protocate chualdehyde, an eluent of methanol-0.5% acetic acid (12:88, v/v) is used, with PDA detection at 280 nm. For berberine, methanol and water containing 0.1% sodium dodecanesulphonate (SDS) and 0.1% phosphorous acid (70:30, v/v) is employed as the mobile phase, also using a PDA detector, but the detection wavelength is 265 nm. The intra- and interrun precision (relative standard deviation) of this method is less than 5% for seven analytes.     

一种基于双工作电极-双通道的毛细管电泳电化学检测系统

报道了一种双工作电极-双通道毛细管电泳电化学检测系统，实现电导和安培 同时检测或者安培与安培检测联用，使两种方法相互补充，发挥各自的优势。其中 ，工作电极与检测池的制作工艺简单，操作简便，通过不锈钢针管和毛细管作为套 管，无需三维微调装置即可简单实现双工作电极的准确放置及分离毛细管与工作电 极的准确对接，并根据分析体系的需要采用不同类型的工作电极和检测器；同时采 用复式滤波电路解决了不同检测器之间的电场叠加对输出信号的干扰问题。采用该 装置可以同时检测复杂体系中的电活性和惰性物质，或同时测定只能氧化或只能还 原的物质，还可以对具有氧化还原性质的物质进行纯度的确证。将该装置应用于实 际样品的测定，节约了分析时间，提高了分析速度，扩大了检测范围，结果令人满 意。     

The mass detector: A new detection system for carbohydrate and lipid analyses

Summary The mass detector was investigated as an alternative to RI detection for carbohydrate and lipid analyses with high pressure liquid chromatography. The instrument was found to be more sensitive than most RI detectors and, as gradient elution could also be carried out, the resulting chromatograms showed improved resolution.     

Screening for anthocyanins using high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry with precursor-ion analysis, product-ion analysis, common-neutral-loss analysis, and selected reaction monitoring

A systematic method for anthocyanin identification using tandems mass spectrometry (MS/MS) coupled to high-performance liquid chromatography (HPLC) with photo-diode array detection (PDA) was developed. Scan for the precursor ions of commonly found anthocyanidins (cyanidin, delphinidin, malvidin, pelargonidin, petunidin, and peonidin) using LC/MS/MS on a triple quadrupole instrument allows for the specific determination of each category of anthocyanins. Further characterization of each anthocyanin was performed using MS/MS product-ion analysis, common-neutral-loss analysis, and selected reaction monitoring (SRM). The method was demonstrated for analysis of anthocyanins in black raspberries, red raspberries, highbush blueberries, and grapes (Vitis vinifera). Previous reported anthocyanins in black raspberries and red raspberries are confirmed and characterized. Common-neutral-loss analysis allows for the distinction of anthocyanin glucosides or galactoside and arabinosides in highbush blueberries. Separation and identification of anthocyanin glucosides and galactosides were achieved by LC/MS/MS using SRM. Anthocyanin isomers such as cyanidin sophoroside and 3,5-diglucoside were differentiated by their fragmentation pattern during product-ion analysis. Fifteen anthocyanins (all possible combinations of five anthocyanidins and three sugars) were characterized in highbush blueberries. Pelargonidin 3-glucoside and pelargonidin 3,5-diglucoside were detected and characterized for the first time in grapes. The present approach allows mass spectrometry to be used as a highly selective detector for rapid identification and characterization of anthocyanins and can be used as a sensitive procedure for screening anthocyanins in fruits and vegetables.     

Hyphenation of Curie-point-pyrolysis high-resolution gas chromatography with several spectroscopic methods for the analysis of cured epoxy resins

The coupling of Curie-point pyrolysis (Py) with gas chromatography (GC) and mass spectrometry (MS) or Fourier transform infrared spectroscopy (FTIR) has been widely reported. The approach reported in this paper combines chromatographic separation with eluent monitoring by use of three different spectroscopic detectors (MS, FTIR and Atomic Emission Detector [AED]). The features of these detectors, with different selectivities, are shown for the analysis of cured epoxy resins. Besides characterisation of major resin constituents by identification of the pyrolysis products, the usefulness of the AED is also revealed by the detection of minor compounds (such as coupling agents) in cured epoxy resins.