Characterization of fuel samples by on-line LC-GC with automatic group-type separation of hydrocarbons

Characterization of fuels by LC-GC is possible by use of automatic successive transfer (multiple transfer) of HPLC fractions to a GC via an on-column interface. This paper describes the instrumentation and the methodology for the HPLC separation of the hydrocarbons (aliphatic and aromatic) into separate groups and the on-line transfer of these groups to a capillary GC column. Two HPLC methods were used with the same valve configuration: single column (silica) with column back-flush to detector; and double column (silica and amino-bonded silica) with multiple fraction transfer and back-flush. The first method was used for the analysis of total saturated compounds and total aromatic compounds; the second was used for the separation of the one-, two-, three-, and four-ring aromatic compounds present in diesel fuels. Examples are shown of the characterization of diesel fuels, and the repeatability of the data.     

油品族组成的详细分析和燃油中芳烃的分析

用毛细管液相色谱-毛细管气相色谱联用方法详细分析了航空煤油、各种柴油、润滑油、抽出油和塔底油的族组成。在毛细管液相色谱上分离得到的单环、双环、三环、四环和稠环芳烃族,经过多位存储接口后,顺序进入毛细管气相色谱,通过毛细管气相色谱对每个族组分作详细分析及定量。用单检测器的二维毛细管气相色谱切割-反吹方法定性定量分析汽油、航空煤油中的各种芳烃,从第一维柱流出的组分和第二维柱流出的组分都先后进入同一氢火焰离子化检测器中,因此能用质量校正响应因子归一化方法准确定量分析而不需要标准样。用上述技术分析实际样品,证明了     

Determination of total biodiesel fatty acid methyl, ethyl esters, and hydrocarbon types in diesel fuels by supercritical fluid chromatography-flame ionization detection

A method for determining total biodiesel methyl and ethyl ester content in diesel fuels by supercritical fluid chromatography-flame ionization detection (SFC-FID) is developed. A silica column typically used for determining aromatics in conventional diesel fuels by ASTM D5186 is back-flushed after separation of the hydrocarbons to allow elution of the various esters as a single "total biodiesel" distinct peak. The modification concurrently allows the determination of total aromatic hydrocarbons and their distribution as mono- and polynuclear compounds, as described in the current version of D5186. The instrument response is linear from 1.0% to 50% biodiesel esters with a signal-to-noise ratio of 25 at the 0.1% level. The short-term relative standard is 0.8%. Normalized percent quantitation using a hydrocarbon response factor of 1.00 and an ester response factor of 1.19 provide an average percentage error of 1.8% when measuring actual biodiesel/hydrocarbon fuel blends. The ester response factor is the average of the response factors of 10 pure ester compounds. These responses are calculated from respective solutions of each ester and the four compounds, hexadecane, toluene, tetralin, and naphthalene, as used for the D5186 response factor mixture.     

Multiresidue determination of organochlorine pesticides and polychlorinated biphenyls in milk by gas chromatography with electron-capture detection after extraction by matrix solid-phase dispersion

A multiresidue analytical method based on matrix solid-phase dispersion was developed to analyze liquid milk for 22 organochlorine pesticides (OCPs) and 6 polychlorinated biphenyls (PCBs). Initial extraction is performed by loading 3 mL milk onto a 2.0 g octadecyl (C18)-bonded silica cartridge with n-hexane as the eluant. Neutral alumina column chromatography with sodium sulfate as the drying agent is used for further cleanup. The eluate is concentrated to 0.5 mL, and target analytes are determined by capillary gas chromatography with electron-capture detection. The optimized method was validated by determining accuracy (recovery percentages), precision (repeatability and reproducibility), and sensitivity (detection and quantitation limits) from analyses of milk samples fortified at 10 and 1 microg/L levels. Average recoveries were between 74 and 106% for all residues except beta-HCH, beta-endosulfan, and endosulfan sulfate. Both repeatability and reproducibility relative standard deviation values were < 22% for all residues. Detection limits ranged from 0.02 to 0.12 microg/L and quantitation limits were between 0.02 and 0.62 microg/L. The proposed analytical method may be used as a fast and simple procedure in routine determinations of OCPs and PCBs in milk.     

Determination of polychlorinated biphenyls in human blood plasma by on-line and off-line liquid chromatography–gas chromatography

A method for the determination of non-, mono- and di-ortho substituted polychlorinated biphenyls in human blood plasma is presented. The non-ortho CBs are isolated from the bulk of PCBs by HPLC on a dinitroanilino-propyl silica column and collected as a heart-cut fraction that is transferred on-line to GC-MS utilizing concurrent solvent evaporation technique. The on-line coupling serves to lower the limit of determination and to partly automate the sample clean-up. The di- and mono-ortho CBs are analyzed by off-line GC-ECD using two different columns. Sample pre-treatment is performed by extraction with organic solvents and fractionation on silica gel. A high reproducibility and an absolute over-all recovery of approximately 70 % is demonstrated. The method is applied to samples of blood from 5 individuals. All the samples demonstrated a similar relative concentration profile. It was also shown that three CB congeners (CB 126, CB 156 and CB 170) contributed to the major part of the toxic equivalent quantity of the PCB content in the blood.     

Carbon nanotube field effect transistor biosensor for the detection of toxins in seawater

Disposable field effect transistors (FET) biosensors (bio-FET) based on carbon nanotubes were fabricated for detection of domoic acid (DA), which belongs to the group of biotoxins associated with the amnesic shellfish poisoning. The analytical results obtained with the bio-FET were compared with those obtained with a traditional methodology (enzyme-linked immunosorbent assay) in order to validate the bio-FET for DA detection. Standard solutions of DA with concentrations between 10 and 500 ng L^?1 were tested in order to construct the calibration curve, where five bio-FET were used for reproducibility estimation and two analytical measurements were performed for each bio-FET for repeatability estimation. Ten spiked artificial seawater samples were used to validate the bio-FET. The obtained reproducibility (0.52–1.43%), repeatability (0.57–1.27%), limit of detection (10 ng L^?1) and recovery range (92.3–100.3%) reveal an adequate analytical performance of the bio-FET for the detection of DA in environmental samples such as seawater samples.     

Development of miniaturized multi-channel high-performance liquid chromatography for high-throughput analysis

We have developed miniaturized multi-channel high-performance liquid chromatography (HPLC) system. With this system, we can simultaneously separate multiple samples, using a single high-pressure gradient pump, a chip-based sample injection unit, a monolithic silica capillary column array, and a multi-channel UV detection unit based on fiber optics. The injection unit has a simplified structure composed of brass housing and a quartz microchip having microchannels and access ports, which enable a direct injection of sample to multi-channel by commercial multichannel micropipette. Moreover, that possesses a function of microvalve, and on-chip definition of sample injection plugs achieved with a cross channel injection method, providing each column of monolithic silica capillary array. The substances in channels were simultaneously detected with UV having multiple cells. Standard samples were analyzed for characterizing newly developed system, and sharp peaks were obtained with reproducibility data of < 0.9% (R.S.D.). Analysis of tryptic digestion of casein was also employed. These results show that the novel multi-channel HPLC system has the benefits for the high-throughput analysis in the post-genomic analysis/combinatorial chemistry.     

Determination of total sulfur in diesel fuel employing NIR spectroscopy and multivariate calibration

A method for sulfur determination in diesel fuel employing near infrared spectroscopy, variable selection and multivariate calibration is described. The performances of principal component regression (PCR) and partial least square (PLS) chemometric methods were compared with those shown by multiple linear regression (MLR), performed after variable selection based on the genetic algorithm (GA) or the successive projection algorithm (SPA). Ninety seven diesel samples were divided into three sets (41 for calibration, 30 for internal validation and 26 for external validation), each of them covering the full range of sulfur concentrations (from 0.07 to 0.33% w/w). Transflectance measurements were performed from 850 to 1800 nm. Although principal component analysis identified the presence of three groups, PLS, PCR and MLR provided models whose predicting capabilities were independent of the diesel type. Calibration with PLS and PCR employing all the 454 wavelengths provided root mean square errors of prediction (RMSEP) of 0.036% and 0.043% for the validation set, respectively. The use of GA and SPA for variable selection provided calibration models based on 19 and 9 wavelengths, with a RMSEP of 0.031% (PLS-GA), 0.022% (MLR-SPA) and 0.034% (MLR-GA). As the ASTM 4294 method allows a reproducibility of 0.05%, it can be concluded that a method based on NIR spectroscopy and multivariate calibration can be employed for the determination of sulfur in diesel fuels. Furthermore, the selection of variables can provide more robust calibration models and SPA provided more parsimonious models than GA.     

Prediction of FCC gasoline octane numbers using FT-MIR and PLS

A method for predicting octane numbers (RON and MON) in fluid catalytic cracking (FCC) gasolines is proposed. Using FT-MIR and PLS, improvements have been obtained in sample throughput, reduced delay times, accuracy (repeatability and reproducibility), amounts of samples and reagents and environmental working conditions when compared with current standard methods. A total number of 140 daily production samples were taken; and from there, a learning group was prepared (44 samples); a validation set (96 samples) was prepared, as well. Sample spectra were recorded from 4000 to 600 cm^-1 at 4 cm^-1 intervals (traditional sealed NaCl cells). The PLS technique was used in its two variants (1 and 2-block). Both provided similar results. Their predictive characteristics are very good: SEP_RON=0.38; SEP_MON=0.40; repeatability <0.1 O.N.; reproducibility <0.3 O.N. (SEP=Standard Error of Prediction).     

On-line determination of fuel quality parameters using near-infrared spectrometry with fibre optics and multivariate calibration

Near-infrared spectrometry with multivariate calibration has been widely used in the food and chemical industries for the determination of quality parameters. The use of fibre optics opens the possibility of using this technique for on-line analysis. With fuels such as gasoline and diesel, most of the parameters used for their characterization are measured using empirical and sometimes subjective tests. These tests might also require costly and complicated equipment as in the measurement of octane number, cetane number and paraffin, olefin, naphthene and aromatics content (PONA). Near-infrared spectrometry using fibre optics in combination with multivariate calibration was used for the determination of fuel quality parameters. The octane number of gasolines was measured. The sampling problems encountered when this method is implemented on-line were evaluated by monitoring the research and motor octane numbers in a gasoline line. Other applications, such as the determination of PONA in gasolines and the measurement of cetane number in diesel fuels, are discussed. In all instances the results obtained by the proposed technique agree with the values measured with conventional methods.     

Interlaboratory comparison of melt flow rate testing of moisture sensitive plastics

The current standard for melt flow rate testing, ISO 1133, does not adequately cover the measurement of materials that degrade or further polymerise at the melt flow rate test conditions. Materials such as PET, PBT and PA tend to degrade, sometimes rapidly, at melt temperatures if they contain absorbed water. This results in poor repeatability and reproducibility of melt flow rate results. The ISO Plastics Melt Rheology Working Group (TC61/SC5/WG9) is currently developing a modified melt flow rate test method for reliable measurement of moisture sensitive materials, thereby providing an alternative to intrinsic viscosity measurements. The modified method controls more tightly the time–temperature history experienced by the material during testing and, thus, the resultant variability in measured properties due to degradation.The results of an intercomparison of testing of moisture sensitive polymers using the melt volume flow rate (MVR) and melt mass flow rate (MFR) methods are reported. A polypropylene (PP), used as a benchmark material, and five moisture sensitive materials were tested by a number of laboratories measuring either MVR or MFR, or both. For standard testing of the PP material, the repeatability and reproducibility of measurements of MVR were up to 5% and 11%, respectively, and for MFR were 7% and 21%, respectively (95% confidence level, outliers excluded). For the moisture sensitive materials the repeatability and reproducibility of measurements varied significantly, with repeatability values up to 26% and reproducibility values up to 114% being obtained. By imposing moisture and temperature control criteria in accordance with the proposed testing standard, the repeatability and reproducibility limits were significantly reduced to approximately 10% and 60%, respectively. The results suggest that both the moisture and temperature criteria were important for improving the repeatability of MVR measurements. However, the moisture content criterion was more important for improving the reproducibility of MVR measurements.The need to tightly control the sample preparation, in particular the drying and subsequent sample handing procedures, and the time–temperature history of the sample throughout the test is considered critical to further improve the precision of measurements of such materials.     

Determination of the acid value of instant noodles: interlaboratory study

An interlaboratory study was performed to evaluate the method for determining the acid value of instant noodles, based on the Japanese Agricultural Standard (JAS), with extraction of lipid using petroleum ether at a volume of 100 mL to the test portion of 25 g. Thirteen laboratories participated and analyzed 5 test samples as blind duplicates. Statistical treatment revealed that the repeatability (RSDr) of acid value was <6.5%, and the reproducibility (RSDR) of acid value was <9.6%. The HorRat values (RSDR/predicted RSDR) were 1.2-1.8, where the RSDR and the predicted RSDR were obtained in terms of free fatty acids in the noodles per unit weight, using the equation [acid value = percent free fatty acids (as oleic) x 1.99] and the extracted lipid contents. This method was shown to have acceptable precision by the present study.     

CCD近红外光谱快速测定柴油中的芳烃含量

研究了采用电感耦合器件（ＣＣＤ）近工外光谱仪在短波近红外区域（７００－１１００ｎｍ）、利用偏最小二乘回归（ＰＬＳ）测定柴油中芳烃含量的方法。考虑样品颜色对短波近红外光谱的影响,对波长范围的选择和基线处理方式进行了研究。考察了样品进入光路的时间对测定结果的影响。将ＣＣＤＮＩＲ对未知样品的预测结果与傅里叶变换近红外光谱（ＦＴ－ＮＩＲ）在长波近红外范围（１０００－２０００ｎｍ）的预测结果及液相色谱的测定     

Uncertainty in spectrophotometric analysis--"error propagation break up", a novel statistical method for uncertainty management

In this work, is given the Combined Standard Uncertainty (CSU) calculation procedure, which can be applied in spectrophotometric measurements. For the assessment of the computations, different approaches are discussed, such as the contribution to the Combined Standard Uncertainty of the reproducibility, the repeatability, the total bias, the calibration curve, and the type of the measurand. Results of inter-laboratory measurements confirmed the assumptions. For the minimization of the errors propagation a controlled experimental procedure was applied by this laboratory, called “errors propagation break-up” (ERBs). The uncertainty of sample concentration from a reference curve dominates the Combined Standard Uncertainty. The contribution of the method and the laboratory bias (total bias) to the CSU is insignificant under controlled conditions of a measurement. This work develops a simple methodology that can be utilized to evaluate the uncertainty and errors control on routine methods used both by academic researchers or the industrial sector.     

化学反应-顶空气相色谱法测定气相二氧化硅表面硅羟基

建立了一种基于化学反应-顶空气相色谱测定气相二氧化硅表面硅羟基含量的新方法.实验取气相二氧化硅放入顶空瓶中于105℃烘箱中加热2 h去除水分,将甲苯稀释的格氏试剂注入密闭的顶空瓶中,格氏试剂与气相二氧化硅表面硅羟基快速反应产生甲烷(CH4),甲烷量与气相二氧化硅表面硅羟基含量成正比.经过气相色谱-氢火焰离子化检测器测定...     

Prediction of FCC gasoline octane numbers using FT-MIR and PLS

A method for predicting "octane numbers" (RON and MON) in fluid catalytic cracking (FCC) gasolines is proposed. Using FT-MIR and PLS, improvements have been obtained in sample throughput, reduced delay times, accuracy (repeatability and reproducibility), amounts of samples and reagents and environmental working conditions when compared with current standard methods. A total number of 140 daily production samples were taken; and from there, a learning group was prepared (44 samples); a validation set (96 samples) was prepared, as well. Sample spectra were recorded from 4000 to 600 cm(-1) at 4 cm(-1) intervals (traditional sealed NaCl cells). The PLS technique was used in its two variants (1 and 2-block). Both provided similar results. Their predictive characteristics are very good: SEP(RON)=0.38; SEP(MON)=0.40; repeatability <0.1 O.N.; reproducibility <0.3 O.N. (SEP=Standard Error of Prediction).     

Quantification of trace fatty acid methyl esters in diesel fuel by using multidimensional gas chromatography with electron and chemical ionization mass spectrometry

Measurement of contamination of marine and naval diesel fuels (arising from product mixing or adulteration) with biodiesel or fatty acid methyl esters can be problematic, especially at very low levels. A suitable solution for this task for trace amounts of individual fatty acid methyl esters with resolution and quantification can be achieved by using a multidimensional gas chromatographic approach with electron and chemical ionization mass spectrometric detection. A unique column set comprising a 100 m methyl‐siloxane nonpolar first dimension column and high‐temperature ionic liquid column in the second dimension enabled identification of individual fatty acid methyl esters at below the lowest concentrations required to be reported in a diesel fuel matrix. Detection limits for individual fatty acid methyl esters compounds ranged from 0.5 to 5.0 mg/L, with excellent linearity up to 5000 mg/L and repeatability of the method from 1.3 to 3.2%. The method was applied to the analysis of diesel fuel samples with suspected biodiesel contamination. Contamination at 568 mg/L was calculated for an unknown sample and interpretation of the results permitted the determination of a likely source of the contamination.     

An optimized setup for determining the bitumen content in asphalt concrete by the neutron reflection method

Summary A setup was developed in order to determine the bitumen content in asphalt concrete by neutron reflection. The main parts of this setup are an Am-Be neutron source of 37 GBq and a ³He neutron detector. To avoid geometrical effects of the measurements, the optimum volume of the samples was determined by plotting the reflected neutron response versus the sample volume. For the calibration of the system, the American Standard Method (ASTM) was used when preparing aggregate and asphalt concrete samples. The method was then compared to the conventional chemical method by analyzing unknown samples taken from an asphalt comcrete producing plant and finally the method was assessed in terms of reproducibility, sensitivity and precision.     

The characterization of silica microparticles by electrophoretic mobility measurements

Summary Electrophoretic mobility measurements in the pH 2‐10 range are described for several commercial HPLC silica microparticles and a laboratory-produced product. The content of metal impurities for the silicas was also determined by AAS. An acidic/hydrothermal treatment was used to generate a more homogenous surface for some of the silicas. The zero points of charge (zpc) for both a native and a treated silica plus several commercial HPLC silicas were compared. The electrophoretic mobility method may be useful in predicting the utility of certain types of silica supports for chromatographic separations.     

Influence of silica gel humidity on the determination of hydrocarbon types in gasoline by the ASTM D 1319 standard test method in relation to proficiency test reproducibility

The results obtained for the olefin content of gasoline with the ASTM D1319 Standard Test Method show a strong increase with the humidity of the silica gel used, while such an increase is absent for the aromatic hydrocarbon content. These results seem to suggest that the increased experimental reproducibility, compared to the value of the ASTM D1319 Standard Test Method, which is often observed for the olefin content in proficiency tests, may be due to the use of insufficiently dry silica gel.