Comparative evaluation of software for retention time alignment of gas chromatography/time-of-flight mass spectrometry-based metabonomic data

In chromatography-based metabonomic research, retention time (RT) alignment of chromatographic peaks poses a challenge for the accurate profiling of biomarkers. Although a number of RT alignment software has been reported, the performance of these software packages have not been comprehensively evaluated. This study aimed to evaluate the RT alignment accuracy of publicly available and commercial RT alignment software. Two gas chromatography/mass spectrometry (GC/MS) datasets acquired from a mixture of standard metabolites and human bladder cancer urine samples, were used to assess three publicly available software packages, MetAlign, MZmine and TagFinder, and two commercial applications comprising the Calibration feature and Statistical Compare of ChromaTOF software. The overall RT alignment accuracies in aligning standard compounds mixture were 93, 92, 74, 73 and 42% for Calibration feature, MZmine, MetAlign, Statistical Compare and TagFinder, respectively. Additionally, unique trends were observed for the individual software with regards to the different experimental conditions related to extent and direction of RT shifts. Conflicting performance was observed for human urine samples suggesting that RT misalignments still occurred despite the use of RT alignment software. While RT alignment remains an inevitable step in data preprocessing, metabonomic researchers are recommended to perform manual check on the RT alignment of important biomarkers as part of their validation process.     

Multiresidue screening of pesticides in foods using retention time locking, GC-AED, database search, and GC/MS identification

Fruit and vegetable extracts were screened for over 400 pesticides by gas chromatography with atomic emission detection (GC-AED) and an experimental database. A technique called retention time locking was used to match GC-AED and GC with mass spectrometry (MS) retention times to those of the database. Samples were analyzed for sulfur, nitrogen, phosphorus, and chlorine by GC-AED. Possible pesticides were suggested by database search and identified by GC/MS. Forty-four pesticide standards were analyzed to determine the precision of retention time matching and the accuracy of the database search. Analytical retention times matched database retention times within 0.32 min. Using elemental criteria, the database search identified the correct compound for 41 of 44 pesticide standards. For blind spikes of fruit and vegetable extracts, the database suggested 22 of 26 spiked pesticides as matches. Nineteen were identified by GC/MS. The combination of retention time locking, GC-AED, database search, and GC/MS can be a powerful tool for identifying pesticides in a complex matrix.     

Study of the interdependency of the data sampling ratio with retention time alignment and principal component analysis for gas chromatography

An in-depth study is presented to better understand how data reduction via averaging impacts retention alignment and the subsequent chemometric analysis of data obtained using gas chromatography (GC). We specifically study the use of signal averaging to reduce GC data, retention time alignment to correct run-to-run retention shifting, and principal component analysis (PCA) to classify chromatographic separations of diesel samples by sample class. Diesel samples were selected because they provide sufficient complexity to study the impact of data reduction on the data analysis strategies. The data reduction process reduces the data sampling ratio, S(R), which is defined as the number of data points across a given chromatographic peak width (i.e., the four standard deviation peak width). Ultimately, sufficient data reduction causes the chromatographic resolution to decrease, however with minimal loss of chemical information via the PCA. Using PCA, the degree of class separation (DCS) is used as a quantitative metric. Three "Paths" of analysis (denoted A-C) are compared to each other in the context of a "benchmark" method to study the impact of the data sampling ratio on preserving chemical information, which is defined by the DCS quantitative metric. The benchmark method is simply aligning data and applying PCA, without data reduction. Path A applies data alignment to collected data, then data reduction, and finally PCA. Path B applies data reduction to collected data, and then data alignment, and finally PCA. The optimized path, namely Path C, is created from Paths A and B, whereby collected data are initially reduced to fewer data points (smaller S(R)), then aligned, and then further reduced to even fewer points and finally analyzed with PCA to provide the DCS metric. Overall, following Path C, one can successfully and efficiently classify chromatographic data by reducing to a S(R) of ～15 before alignment, and then reducing down to S(R) of ～2 before performing PCA. Indeed, following Path C, results from an average of 15 different column length-with-temperature ramp rate combinations spanning a broad range of separation conditions resulted in only a ～15% loss in classification capability (via PCA) when the loss in chromatographic resolution was ～36%.     

色谱-质谱技术测定蔬菜、粮食中四种挥发性N-亚硝基化合物含量

N-亚硝基化合物是强致癌物,它仅以痕量状态存于某些食品中。T.A.Gough等曾提出用电子轰击源质谱高分辨峰匹配法对其测定,本实验也用此法测定了白莱、玉米等78份样品中四种挥发性N-亚硝基化合物含量,并对测定结果进行了讨论与评价。     

A straightforward algorithm to estimate the dead time in GC from the retention behavior of homologous series

Summary A new and very quick algorithm for the determination of the dead time t₀ in GC is described. It is based on the relationship between the carbon chain length n_c and the net retention time for homologous series. The shortcoming of former algorithms is overcome: it can also be applied if some not directly consecutive members of the homologous series are used for the calculation.     

Phenomenological characterization and thermal analysis of flame spread over jet fuel: influence of radiant exposure time

Journal of Thermal Analysis and Calorimetry - The high-temperature objects widely exist in industrial and civil building such as the nearby burning pool fires, the heated walls and the hot smoke...     

Speciation and GC retention indices of some organotin compounds in water

Analytical methods have been developed for the quantitative determination of Bu₄Sn, Bu₃Sn⁺, Bu₂Sn²⁺, BuSn³⁺, Me₃BuSn, Me₂Bu₂Sn, MeBu₃Sn, MeBuSn²⁺, Me₂BuSn⁺ and MeBu₂Sn⁺ in water. Organotin compounds are extracted from water with tropolone at 0.1 % in n-pentane, derivatized with n-pentylmagnesium bromide and determined by gas chromatography with flame photometric detection or flame ionization detection. Absolute detection limits are 0.05-0.12 ng and 1.2-13 ng as tin, respectively. The method was applied to the analysis of spiked tap-water containing 0.3-1000 ng cm^?3 of each of the organotin compounds.     

The use of GC x GC with time-of-flight mass spectrometry to investigate dienes and Diels-Alder polymerisation products in high-temperature Fischer-Tropsch-based fuels

Comprehensive GC in the reversed polarity mode i.e. a polar main column and an apolar secondary column have been used to differentiate cyclic olefins, dienes and cyclic dienes in high temperature Fischer-Tropsch (FT)-based fuels. The elucidation of the blobs in the contour plot was based on spectral data obtained by TOF-MS. The effectiveness of selective catalytic hydrogenation in transforming dienes into olefins could be studied. Dienes are prone to polymerisation by Diels-Alder reactions and dimers and trimers were detected in the 2-D plot by operating the MS in the ion extraction mode. Polymerisation is thought to be partially responsible for gum formation in high temperature FT-derived products.     

Identification of organic residues in tertiary effluents by GC/EI-MS,GC/CI-MS and GC/TSQ-MS

A method was developed for the analysis of non-volatile dissolved organic residues in tertiary treated wastewater effluents. This method involved concentration of samples by rotary evaporation, propylation using propanol/formic acid/acetyl chloride, and separation, detection and quantitation by capillary GC/EI and CI-MS and GC/TSQ-MS analysis. Ethylenediamine tetraacetic acid (EDTA) was the most prominent compound found in both granular activated carbon (GAC) and chlorinated GAC effluents (110 and 140 μg/L, respectively). Other compounds identified included nitrilotriacetic acid (NTA), carboxyalkylphenoxy ethoxy carboxylates, poly(propoxy), poly(ethoxy) or poly(ethoxy)(propoxy) compounds, small aliphatic dicarboxylic acids and aldehydes, all at lg/L levels. Approximately 80% of all chromatographically separated compounds were positively or tentatively identified. The identified compounds are estimated to account for approximately 10% of the dissolved organic carbon. Received: 8 August 1994/Revised: 14 February 1995/Accepted: 16 February 1995 Correspondence to: W.-H. Ding     

Determination of total and polycyclic aromatic hydrocarbons in aviation jet fuel

The aviation jet fuel widely used in turbine engine aircraft is manufactured from straight-run kerosene. The combustion quality of jet fuel is largely related to the hydrocarbon composition of the fuel itself; paraffins have better burning properties than aromatic compounds, especially naphthalenes and light polycyclic aromatic hydrocarbons (PAHs), which are characterised as soot and smoke producers. For this reason the burning quality of fuel is generally measured as smoke fermation. This evaluation is carried out with UV spectrophotometric determination of total naphthalene hydrocarbons and a chromatographic analysis to determine the total aromatic compounds. These methods can be considered insufficient to evaluate the human health impact of these compounds due to their inability to measure trace (ppm) amounts of each aromatic hyrcarbon and each PAH in accordance with limitations imposed because of their toxicological properties. In this paper two analytical methods are presented. Both are based on a gas chromatographic technique with a mass detector operating in be selected ion monitoring mode. The first method was able to determine more than 60 aromatic hydrocarbons in a fuel sample in a 35-min chromatographic run, while the second was able to carry out the analysis of more than 30 PAHs in a 40-min chromatographic run. The linearity and sensitivity of the methods in measuring these analytes at trace levels are described.     

Identification of Dinocap in water using GC/IR and GC/MS

The determination of Dinocap, one of the most often used acaricides and contact fungicides, is complicated by the fact that it consists of several isomeric alkyldinitro-phenyl-crotonates. In a first step, GC/IR and GC/MS has been used to separate the mixture, to determine the chromatographic behaviour and to fully characterize the six different isomeric compounds. The structures of additional impurities in the commerical preparation were shown to be the correlating phenols. An extraction/preconcentration method has been devised based on Carbopack B, yielding recoveries between 75 and 98%. A qualified estimation of the total Dinocap content of drinking water can be made by this approach for concentrations well below the limits set by the European drinking water regulations. The development of a complete analytical procedure based on these results appears to be feasible.Dedicated to Professor Dr. Dr. h.c. mult J. F. K. Huber on the occasion of his 70th birthday     

Two-dimensional gas chromatography analysis of components in fuel and fuel additives using a simplified heart-cutting GC system

Multidimensional gas chromatography (MGC) using heart cutting is an old idea that can benefit from the performance of modern instruments and capillary columns to provide fast, reliable separation of target analytes from complex sample matrices. A simplified heart-cutting switch is described that uses these improvements to provide very narrow precise heart cuts between columns of different selectivity. This system is used to analyze ppm levels of 4,6-dimethydibenzothiophene in diesel fuel using a standard flame ionization detector instead of a complex sulfur-selective detector. MGC systems also offer the possibility of faster analysis speed by using two short columns of different selectivity instead of very long columns to resolve compounds from complex matrices. The analysis of alcohols in denatured fuel ethanol using the MGC system is performed over six times faster than the standard American Society for Testing and Materials methodology.     

调味品中氯丙醇的GC/ECD和GC/MS/MS衍生化检测方法研究及应用

报道了调味品中氯丙醇的衍生化气相色谱(GC／ECD)和衍生化气相色谱双串联质谱法(GC／MS／MS)测定。GC／ECD测定酱油中3—氯—1，2—丙二醇(3—MCPD)的检出限达到0．01mg／kg，回收率为91％～104％，变异系数为2．27％～7．96％；GC／MS／MS同时测定酱油中1，3—二氯—2—丙醇、2，3—二氯—1—丙醇和3—氯—1，2—丙二醇，1，3—二氯—2—丙醇、2，3—二氯—1—丙醇的检出限为0．02mg／kg，3—氯—1，2—丙二醇的检出限为0．01mg／kg，回收率在92％～106％，变异系数为3．51％～13．33％。     

MgO/NaY催化糠醛和丙酮合成航空燃料中间体的性能研究

采用"机械混合-焙烧"方法制备了负载型固体碱催化剂MgO/NaY,研究了糠醛与丙酮在水-乙醇体系中的羟醛缩合反应,考察了催化剂负载量、原料配比、反应温度、反应时间等因素对催化剂性能的影响。结果表明,20%MgO/NaY催化剂表现出最佳的催化性能,在85℃条件下反应8 h后,糠醛转化率达到99.6%,亚糠基丙酮(FA)和二亚糠基丙酮(F₂A)选择性分别达到42.2%和57.1%,缩合产物的总收率为98.6%。高温促进反应中间体向产物的转化,有利于提高产物的总选择性。改变糠醛/丙酮的摩尔比可调控两种缩合产物的选择性,较高的糠醛/丙酮摩尔比有利于提高F₂A的选择性,但会降低整体反应速率。重复性评价表明,催化剂具有较好的再生性能。     

Pyrethroid soil extraction,properties of mixed solvents and time profiles using GC/MS-NICI analysis

Ultrasonic extraction was used to develop a suitable binary solvent system for the analysis of synthetic pyrethroid pesticides and mirex on soil. The analysis was carried out by gas chromatography with negative ion chemical ionization mass spectrometry (GC/MS-NICI). In the initial experiments, accurately weighed soil samples were spiked with a mixture of standard solution pyrethroids and mirex and shaken for 24?h to ensure homogeneity, then extracted with solvent. The extracts were evaporated to dryness before the volumetric internal standard was added.

The binary solvents used in this study were various mixtures of hexane?:?acetone, hexane?:?dichloromethane (DCM), isooctane?:?acetone and isooctane?:?dichloromethane, representing different classes of polarity. The recoveries of all pyrethroids and mirex were satisfactory over three solvent systems: hexane?:?acetone, hexane?:?DCM and isooctane?:?acetone, but results of isooctane?:?DCM produced low recoveries. The average recovery increased with the extraction time, but the increase was not statistically significant. A 30-min optimum extraction was deemed sufficient for recovering pyrethroids from soil. After 30?min, extraction decreased owing to the re-distribution of the analyte on the soil matrix.     

Comparison of GC/MSD and GC/AED for the determination of organotin compounds in the environment

Summary Methods are described for the analysis of environmental samples like water, sediment and suspended matter for the determination of all organotin compounds (OTs) that are currently used as biocides: tributyltin (TBT), triphenyltin (TPT), tricyclohexyltin (TCT) and fenbutatin oxide (FBTO). In water also five degradation products (di and mono substituted analogs) can be determined. Alkylation using a Grignard reagent was used to obtain OT derivatives amenable to gas chromatography (GC). Both methylation and pentylation have been employed for derivatization prior to GC analysis. The present results show that derivatization efficiencies for TPT, TCT and FBTO at trace levels are higher using methylation than pentylation. Detection limits for each type of sample matrix were determined using GC/Mass Selective Detection (GC/MSD) and GC/Atomic Emission Detection (AED). In sediment and suspended matter only tri-substituted OTs (i.e. the parent compounds) could be determined. Detection limits ranged from 0.2 to 10 ng/g dry weight. FBTO, not previously detected in environmental samples, was found at levels of 4 and 11 ng/g in a suspended matter sample and a sediment sample, respectively. In water the OTs and their degradation products were determined at levels of 1–10 ng/l (as tin) using 200 ml water samples.     

Prediction of retention time of cutinases tagged with hydrophobic peptides in hydrophobic interaction chromatography

Hydrophobic interaction chromatography (HIC) is an important technique for protein purification, which exploits the separation of proteins based on hydrophobic interactions between the stationary phase ligands and hydrophobic regions on the protein surface. One way of enhancing the purification efficiency by HIC is the addition of short sequences of peptide tags to the target protein by genetic engineering, which could reduce the need for extra and expensive chromatographic steps. In the present work, a methodology for predicting retention times of cutinases tagged with hydrophobic peptides in HIC is presented. Cutinase from Fusarium solani pisi fused to tryptophan-proline (WP) tags, namely (WP)2 and (WP)4, and produced in Saccharomyces cerevisiae strains, were used as model proteins. From the simulations, the methodology based on tagged hydrophobic definition proposed by Simeonidis et al. (Phitagged), associated to a quadratic model for predicting dimensionless retention times, showed small differences (RMSE<0.022) between observed and estimated retention times. The difference between observed and calculated retention times being lower than 2.0% (RMSE<0.022) for the two tagged cutinases at three different stationary phases, except for the case of cut_(wp)2 in octyl sepharose-2 M ammonium sulphate. Therefore, we consider that the proposed strategy, based on tagged surface hydrophobicity, allows prediction of acceptable retention times of cutinases tagged with hydrophobic peptides in HIC.