Automated sample cleanup using on-line coupling of size exclusion chromatography to high resolution gas chromatography

A fully automated on-line sample cleanup system based on the coupling of size exclusion chromatography to high resolution gas chromatography is described. The transfer technique employed is based on fully concurrent solvent evaporation using a loop-type interface, early vapor exit and co-solvent trapping. Optimization of the LC-GC transfer was done visually via an all-glass oven door. To circumvent the problem of mixing within the injection loop, an adaptation was made to the standard loop-type interface. The determination of a series of additives in a polymer matrix is presented as one example of the vast range of applications opened up by this technique.     

Size exclusion chromatography of aluminium species in natural waters

Size exclusion chromatography was used in order to characterize organically bound aluminium in natural water samples. A Superose column was used, with 0.1 M acetate buffer (pH 4.6) as mobile phase. Three detection systems were used; graphite furnace atomic absorption spectrometry, post-column reaction with pyrocatechol violet and UV spectrometry at 254 nm. A single peak was obtained for organic aluminium in natural waters. The results indicated that aluminium binds with a broad size range of humic substances, and that the inorganic aluminium was present in polymeric form.     

Two‐dimensional chromatography as a tool for studying band broadening in size‐exclusion chromatography

Comprehensive 2‐D size‐exclusion chromatography (SEC×SEC) has been realized. SEC×SEC is not a useful technique for characterizing complex polymers. However, it is potentially an elegant tool to study band‐broadening phenomena. If narrow fractions can be collected from the first dimension, the band broadening in the second dimension is only due to chromatographic dispersion. This would allow a clear distinction to be made between chromatographic band broadening (column and extra‐column) and SEC selectivity (band broadening due to sample polydispersity). In comparison with MALDI‐MS, SEC×SEC allows the study of polymers across a much broader molar‐mass range.     

Progress in direct solid sampling analysis using line source and high-resolution continuum source electrothermal atomic absorption spectrometry

The literature about direct solid sample analysis of the past 10–15 years using electrothermal atomic absorption spectrometry has been reviewed. It was found that in the vast majority of publications aqueous standards were reported as having been used for calibration after careful program optimization. This means the frequently expressed claim that certified reference materials with a matrix composition and analyte content close to that of the sample have to be used for calibration in solid sample analysis is not confirmed in the more recent literature. There are obviously limitations, and there are examples in the literature where even calibration with certified reference materials did not lead to accurate results. In these cases the problem is typically associated with spectral interferences that cannot be corrected properly by the systems available for conventional line source atomic absorption spectrometry, including Zeeman-effect background correction. Using high-resolution continuum source atomic absorption spectrometry, spectral interferences become visible owing to the display of the spectral environment at both sides of the analytical line at high resolution, which makes program optimization straightforward. Any spectrally continuous background absorption is eliminated automatically, and even rapidly changing background absorption does not cause any artifacts, as measurement and correction of background absorption are truly simultaneous. Any kind of fine-structured background can be eliminated by “subtracting” reference spectra using a least-squares algorithm. Aqueous standards are used for calibration in all published applications of high-resolution continuum source atomic absorption spectrometry to direct solid sample analysis. This contribution is based on a presentation given at the Colloquium for Analytical Atomic Spectroscopy (CANAS ‘07) held March 18–21, 2007 in Constance, Germany.     

Investigation of phosphorus atomization using high-resolution continuum source electrothermal atomic absorption spectrometry

The atomization of phosphorus in electrothermal atomic absorption spectrometry has been investigated using a high-resolution continuum source atomic absorption spectrometer and atomization from a graphite platform as well as from a tantalum boat inserted in a graphite tube. A two-step atomization mechanism is proposed for phosphorus, where the first step is a thermal dissociation, resulting in a fast atomization signal early in the atomization stage, and the second step is a slow release of phosphorus atoms from the graphite tube surface following the adsorption of molecular phosphorus at active sites of the graphite surface. Depending on experimental conditions only one of the mechanisms or both might be active. In the absence of a modifier and with atomization from a graphite or tantalum platform the second mechanism appears to be dominant, whereas in the presence of sodium fluoride as a modifier both mechanisms are observed. Intercalation of phosphorus into the graphite platform in the condensed phase has also been observed; this phosphorus, however, appears to be permanently trapped in the structure of the graphite and does not contribute to the absorption signal.     

Size‐exclusion chromatography for the determination of the boiling point distribution of high‐boiling petroleum fractions

The paper describes a new procedure for the determination of boiling point distribution of high‐boiling petroleum fractions using size‐exclusion chromatography with refractive index detection. Thus far, the determination of boiling range distribution by chromatography has been accomplished using simulated distillation with gas chromatography with flame ionization detection. This study revealed that in spite of substantial differences in the separation mechanism and the detection mode, the size‐exclusion chromatography technique yields similar results for the determination of boiling point distribution compared with simulated distillation and novel empty column gas chromatography. The developed procedure using size‐exclusion chromatography has a substantial applicability, especially for the determination of exact final boiling point values for high‐boiling mixtures, for which a standard high‐temperature simulated distillation would have to be used. In this case, the precision of final boiling point determination is low due to the high final temperatures of the gas chromatograph oven and an insufficient thermal stability of both the gas chromatography stationary phase and the sample. Additionally, the use of high‐performance liquid chromatography detectors more sensitive than refractive index detection allows a lower detection limit for high‐molar‐mass aromatic compounds, and thus increases the sensitivity of final boiling point determination.     

Size exclusion chromatography sample pretreatment for GC-AED analysis of metalloporphyrins in crude oils

Size exclusion chromatography (SEC) has been demonstrated to be an effective and reproducible sample pretreatment procedure for removal of heavy oil matrices prior to GC-AED analysis of metalloporphyrins, and for the resolution of volatile metal species into clean and defined fractions. This paper also discusses the results obtained by SEC for determination of the distribution of metallopor-phyrins in crude oils and the correlation between total metal, metal-loporphyrin, and total distillable metal content.     

Determination of cadmium in coal using solid sampling graphite furnace high-resolution continuum source atomic absorption spectrometry

This work describes the development of a method to determine cadmium in coal, in which iridium is used as a permanent chemical modifier and calibration is performed against aqueous standards by high-resolution continuum source atomic absorption spectrometry (HR-CS AAS). This new instrumental concept makes the whole spectral environment in the vicinity of the analytical line accessible, providing a lot more data than just the change in absorbance over time available from conventional instruments. The application of Ir (400 g) as a permanent chemical modifier, thermally deposited on the pyrolytic graphite platform surface, allowed pyrolysis temperatures of 700 °C to be used, which was sufficiently high to significantly reduce the continuous background that occurred before the analyte signal at pyrolysis temperatures <700 °C. Structured background absorption also occurred after the analyte signal when atomization temperatures of >1600 °C were used, which arose from the electron-excitation spectrum (with rotational fine structure) of a diatomic molecule. Under optimized conditions (pyrolysis at 700 °C and atomization at 1500 °C), interference-free determination of cadmium in seven certified coal reference materials and two real samples was achieved by direct solid sampling and calibrating against aqueous standards, resulting in good agreement with the certified values (where available) at the 95% confidence level. A characteristic mass of 0.4 pg and a detection limit of 2 ng g^–1, calculated for a sample mass of 1.0 mg coal, was obtained. A precision (expressed as the relative standard deviation, RSD) of <10% was typically obtained when coal samples in the mass range 0.6–1.2 mg were analyzed.Dedicated to the memory of Wilhelm Fresenius     

原子吸收和原子荧光光谱分析

本文是《分析试验室》期刊定期评述中关于原子吸收光谱法 ( AAS)及原子荧光光谱法 ( AFS)分析的第 8篇综述文章。文中对 1 999年～ 2 0 0 0年 1 1月期间我国在 AAS/AFS领域所取得的主要进展进行评述。内容包括 :概述、仪器装置与数据处理、火焰原子吸收光谱法、电热原子吸收光谱法、化学蒸气发生技术以及原子荧光光谱法。共收集文献 2 96篇。     

High-resolution continuum source electrothermal absorption spectrometry of AlBr and CaBr for the determination of bromine

Molecular absorption spectra of AlBr and CaBr, produced in a graphite furnace, were investigated using a high-resolution echelle spectrometer equipped with a xenon short-arc lamp as continuum source. The analytical usability of the spectra for the determination of bromine was studied. To this end, the molecular absorptions of AlBr at 278.914 nm and CaBr at 625.315 nm were evaluated. Apart from strong absorption bands of CaF around 625.3 nm, which disturb the use of CaBr, no spectral interferences were observed for both AlBr and CaBr. Regarding chemical interference with matrix substances, the molecular absorption of AlBr and CaBr is influenced in a different way. While the sensitivity of the CaBr absorption is susceptible to chloride, aluminum, potassium and sodium ions, there is no significant effect on the AlBr absorption. In contrast, the inorganic acids (nitric, phosphoric, and sulfuric) have an influence on AlBr, but not on the CaBr molecular absorption. Therefore, the two methods complement each other and each has its own application area. Regarding real samples, a salt sample from the death sea and an organic pharmaceutical were evaluated. The results were in good agreement with those derived from two independent methods and with an existing reference value. Relative standard deviations were found in the range of 5%. The limit of detection for bromine was about 2 ng for both AlBr and CaBr molecular absorption; the dynamic range was linear at least up to 250 ng Br.     

Characterization of Klason lignin samples isolated from beech and aspen using microbore column size‐exclusion chromatography

The present study is focused on the separation and characterization of lignin samples isolated by Klason method from European beech (Fagus sylvatica) broadleaf hardwood and European aspen (Populus tremula) broadleaf softwood by size‐exclusion chromatography. The separation was carried out using dimethylformamide as major component of the mobile phase and a 3 mm id microbore column packed with hydroxyethyl methacrylate gel, calibrated with polystyrene standards. The influence of mobile phase composition and sample solvent composition on the chromatographic behavior and molar mass distributions was investigated.     

Differential size‐exclusion chromatography for the analysis of gelatin–polyelectrolyte complexes

Differential size‐exclusion chromatography (SEC) is used to characterize complexes formed between gelatin and two synthetic polyelectrolytes, sodium poly(styrenesulfonate) and sodium poly(2‐acrylamido‐2‐methylpropanesulfonate). The analysis is performed under aqueous, low‐salt conditions where maximum complexation between gelatin and the polyelectrolytes occurs. The adsorption effects that are commonly encountered in conventional SEC for gelatin and other charged polymers chromatographed under these solution conditions are minimized, because the columns are constantly equilibrated with the analytes in the mobile phase. Analyte solutions of identical composition, but of higher or lower concentration than that contained in the mobile phase, are injected, resulting in positive or negative detector responses, respectively. This method can separate the complexes from individual components, and can be used to determine relative sizes and stoichiometries of the complexes as a function of both the input ratio of gelatin to polyelectrolyte and the molecular weight of the polyelectrolyte. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 275–280, 1999     

Exploration of cardanol-based phenolated and epoxidized resins by size exclusion chromatography and MALDI mass spectrometry

Cardanol and cardanol derivatives are among the most important biobased materials currently investigated in green chemistry, as renewable and promising building blocks in lieu of traditional raw materials from non renewable resources, in particular owing to the olefinic linkages on the C15 alkyl side-chain. Despite the increasing interest they arouse, analytical chemistry dedicated to cardanol and associated resins has been rarely reported in the literature, found even poorer when dealing with chromatography and mass spectrometry. In this work, a thorough molecular characterization was conducted using matrix assisted laser desorption ionization (MALDI) mass spectrometry, size exclusion chromatography (SEC), and SEC–MALDI coupling to gain insights into the composition of phenolated, epoxidized, and epoxidized phenolated cardanol. A nomenclature was proposed to properly describe the numerous species found in these materials, while simulations of the unsaturation patterns and their comparison with the detected patterns in MALDI-MS gave useful details about the phenolation treatment expected to occur on the polyunsaturated C15 side chain. Finally, the SEC–MALDI off-line coupling allowed SEC peaks to be deconvoluted by mass spectrometry and MALDI artefacts related to matrix adduction to be pointed out.     

Estimation of boron isotope ratios using high resolution continuum source atomic absorption spectrometry

In the production of ¹⁰B enriched steels, the production–recycling process needs to be closely monitored for inadvertent mix-up of materials with different B isotope levels. A quick and simple method for the estimation of boron isotope ratios in high alloyed steels using high resolution continuum source flame AAS (HR-CS-FAAS) was developed. On the 208.9 nm B line the wavelength of the peak absorption of ¹⁰B and ¹¹B differs by 2.5 pm. The wavelength of the peak absorption of boron was determined by fitting a Gauss function through spectra simultaneously recorded by HR-CS-FAAS. It was shown that a linear correlation between the wavelength of the peak absorption and the isotope ratio exists and that this correlation is independent of the total boron concentration. Internal spectroscopic standards were used to compensate for monochromator drift and monochromator resolution changes. Accuracy and precision of the analyzed samples were thereby increased by a factor of up to 1.3. Three steel reference materials and one boric acid CRM, each certified for the boron isotope ratio were used to validate the procedure.     

Recent applications of gas chromatography with high‐resolution mass spectrometry

Gas chromatography coupled to high‐resolution mass spectrometry is a powerful analytical method that combines excellent separation power of gas chromatography with improved identification based on an accurate mass measurement. These features designate gas chromatography with high‐resolution mass spectrometry as the first choice for identification and structure elucidation of unknown volatile and semi‐volatile organic compounds. Gas chromatography with high‐resolution mass spectrometry quantitative analyses was previously focused on the determination of dioxins and related compounds using magnetic sector type analyzers, a standing requirement of many international standards. The introduction of a quadrupole high‐resolution time‐of‐flight mass analyzer broadened interest in this method and novel applications were developed, especially for multi‐target screening purposes. This review is focused on the development and the most interesting applications of gas chromatography coupled to high‐resolution mass spectrometry towards analysis of environmental matrices, biological fluids, and food safety since 2010. The main attention is paid to various approaches and applications of gas chromatography coupled to high‐resolution mass spectrometry for non‐target screening to identify contaminants and to characterize the chemical composition of environmental, food, and biological samples. The most interesting quantitative applications, where a significant contribution of gas chromatography with high‐resolution mass spectrometry over the currently used methods is expected, will be discussed as well.     

Oscillatory transverse electric field enhances protein resolution and capacity of size-exclusion chromatography

Protein separations by a novel size-exclusion electrochromatography (SEEC) are presented. The present SEEC, denoted as pSEEC, was established with an oscillatory low-voltage electric field perpendicular to the mobile-phase streamline. Retention experiments with different proteins indicated that the influence of electric field strength on the partition coefficient is different for different proteins as well as for the same protein under different mobile-phase conditions. These results of protein retention led to the experimental design of protein separations with binary mixtures of BSA and immunoglobulin G (IgG), myoglobin (Myo) and lysozyme (Lys), as well as ovalbumin (Oval) and Myo. The separation results for the binary protein systems sufficiently exhibited the applicability of the pSEEC for various separations in terms of their molecular weights (MWs) as well as pIs. For example, it was possible to separate the gel-excluded proteins (BSA/IgG) as well as gel-permeable and similar-molecular-weight proteins (Myo/Lys) by the pSEEC. Moreover, in the cases of Oval/ Myo, which could be partially separated by size-exclusion chromatography, the use of the pSEEC greatly improved the resolution and the separation became possible at high sample loading. The results indicate that the pSEEC technology is promising for preparative protein separations.     

The size exclusion chromatography calibration of ‘Mixed-A’ and ‘Mixed-D’ columns using various polymers and compounds: An application to coal-derived materials

This work attempts to obtain the calibration curves of two different size exclusion chromatography (SEC) columns operating with 1-methyl-2-pyrrolidinone (NMP) as eluent by using various standards. Polystyrene (PS) and polymethylmethacrylate (PMMA) standards were used for obtaining calibration curves, and checked against polysaccharide (PSAC) standards, some small aromatic polycyclic standards and miscellaneous polymers. Polystyrenes and polymethylmethacrylates gave identical calibrations while polysaccharides and miscellaneous polymers lay within 1 or 2 min of the polystyrene calibration. Small molecules of mass less than 1000 units lay on or near to the polystyrene calibration lines, with a shift to late elution for the smallest molecules. This shift may be caused by the interaction with the column packing. A sample has been examined by analytical size exclusion chromatography, which was calibrated using polystyrene and polymethylmethacrylate standards. Molecular mass (MM) distributions of the sample have been examined in terms of these calibrations.     

Determination of macro- and micronutrients in plant leaves by high-resolution continuum source flame atomic absorption spectrometry combining instrumental and sample preparation strategies

A method for determination of B, Ca, Cu, Fe, K, Mg, Mn, Mo, P, S and Zn in plant tissues by high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS) is proposed. This method is based on special features of HR-CS-AAS, such as side pixel registration, wavelength integrated absorbance, and molecular absorption bands, for determining macro- and micronutrients in foliar analysis without requiring several different strategies for sample preparation and adjustment of the analytes concentration ranges. Plant samples were analyzed and results for certified materials were in agreement at a 95% confidence level (paired t-test) with reference values. Recoveries of analytes added to plant digests varied within the 82–112% interval. Relative standard deviations (n = 12) were lower than or equal to 5.7% for all analytes in all concentration ranges.     

Use of high resolution continuum source atomic absorption spectrometry as a detector for chemically generated noble and transition metal vapors

Vapor generation and atomization conditions in a heated quartz tube to detect Ag, Cd, Co, Cu, Ni and Zn using High Resolution Continuum Source AAS (HRCSAAS), were optimized. Vapors were generated after mixing acidified solutions containing 8-hydroxiquinoline (oxine) with sodium tetrahydroborate. Afterwards, they were swept to the heated quartz cell by an argon flow.Reaction loop size and temperature of the quartz cell were optimized for each element. A temperature of 960 °C was selected as a compromise value to detect most of the metals. Afterwards, a Plackett–Burmann design was proposed to select which parameters were most important. Type of acid and its concentration were the most statistical significant variables. Optimum conditions for sequential detection of Cd, Cu, Ni and Zn were: 1 mg L^− 1 Co as catalyst, 250 mg L^− 1 oxine, 0.6 M nitric acid, 1.75% (w/w) sodium tetrahydroborate (prepared in 0.4 (w/v)% NaOH), a reaction loop of 250 µL, and a 25 L h^− 1 carrier Ar flow. Ag and Co were each detected in their own optimized conditions. Analytical performance of the system was evaluated in connection with a selected pixel number, and spectral correction was used to eliminate NO absorption bands interference in Zn detection. Detection limits were in the range of 1.5–18 μg L^− 1 for Ag, Cu, Cd and Zn, whereas sensitivity was worst for Co (169 μg L^− 1) and Ni (586 μg L^− 1). Atomization in a quartz cell of Co and Ni volatile species, generated by an addition of sodium tetrahydroborate to an acidified solution of the analytes, was reported for the first time in this paper. Precision expressed as RSD(%) had values lower than 10% except for Ni.