Conventional Capillary Column Research Articles

Precise measurement of 1,4‐dioxane concentration in cleaning products: A review of the current state‐of‐the‐art

Abstract1,4‐Dioxane, a co‐product that forms during the preparation of ethoxylated surfactants, particularly sulfated and phosphorylated ethoxylates, is classified as a potential human carcinogen whose occurrence in surface water and groundwater is of particular concern. As a result, the US state of New York has passed laws that will limit the concentration of 1,4‐dioxane to ppm levels in household cleansing, personal care and cosmetics products, all of which commonly employ ethoxylated fatty alcohol sulfate surfactants and California is considering such laws. This review first assesses the methodologies used to quantify 1,4‐dioxane in surface water and drinking water, then extends the assessment to commercially available products, which are more complex sample matrices than water. Our assessment indicates that gas chromatography using conventional capillary columns and mass spectrometric detection, and the employment of an internal standard, particularly 1,4‐dioxane‐d8, is the best approach. A means of isolating and concentrating 1,4‐dioxane from the commercial samples is critical to achieve resolution at the sub‐ppm level and to minimize interference from contaminants present in the sample matrix. We review the different concentration approaches, such as headspace analysis, liquid–liquid and solid‐phase extraction, purge‐and‐trap, and solid‐phase microextraction, and evaluate their advantages and disadvantages for the robust long‐term assessment of 1,4‐dioxane levels in commercial products.

Miniaturized micromachined gas chromatography with universal and selective detectors for targeted volatile compounds analysis

An effective analytical strategy for targeted analysis of volatile organic compounds which combines two orthogonal separation mechanisms and multiple tunable detection in a compact transportable analytical system is introduced. This strategy uses a commercially available micromachined gas chromatograph comprising a micromachined on-board thermal conductivity detector. The chromatograph capability is enhanced by incorporating a modified diode array detector and a radio frequency modulated ion mobility spectrometry microfabricated electromechanical system. The analytical platform offers powerful detection capabilities of individual compounds and various classes of volatile organic compounds with improved provisional confirmatory capability. The transportable micromachined gas chromatograph employs field replaceable conventional capillary columns for the separation of analytes. The use of a silicon micromachined sample introduction device affords fast injection to minimize band broadening with fast chromatographic separation rendered in the order of minutes. Advantaged synergy also includes leveraging the resolving power of gas chromatography to minimize charge exchange in the ionization chamber of the differential mobility spectrometer for improved detector performance. Performance of this scalable and transportable analytical system is demonstrated with relevant volatile compounds such as acetaldehyde, acetone, carbon disulfide, benzene, and ethyl butyrate having a day-to-day variability less than 5% and with a high degree of reliability.

Determination of persistent organic pollutants by gas chromatography/laser multiphoton ionization/time-of-flight mass spectrometry

An authentic mixture of polychlorinated biphenyls was measured using a short wide-bore capillary column for the group separation of major components present in an actual sample of Kanechlor. The limits of detection were improved by ca. 2 fold in comparison with those obtained using a conventional capillary column, since the retention time was reduced and the amount of analytes introduced into the mass spectrometer per unit time could be increased. On the other hand, surface-water and sediment samples containing polycyclic aromatic hydrocarbons (PAHs) were collected from the river located in the vicinity of a waste water treatment plant. Even acenaphthylene, a minor component of the mixture could be measured for the sediment sample, and the concentrations were determined for several heavy PAHs. As demonstrated, a technique involving laser multiphoton ionization/time-of-flight mass spectrometry was useful as a sensitive and selective analytical tool for the trace analysis of persistent organic pollutants in an environmental sample.

Microfabricated thermal modulator for comprehensive two-dimensional micro gas chromatography: design, thermal modeling, and preliminary testing

In comprehensive two-dimensional gas chromatography (GC x GC), a modulator is placed at the juncture between two separation columns to focus and re-inject eluting mixture components, thereby enhancing the resolution and the selectivity of analytes. As part of an effort to develop a microGC x microGC prototype, in this report we present the design, fabrication, thermal operation, and initial testing of a two-stage microscale thermal modulator (microTM). The microTM contains two sequential serpentine Pyrex-on-Si microchannels (stages) that cryogenically trap analytes eluting from the first-dimension column and thermally inject them into the second-dimension column in a rapid, programmable manner. For each modulation cycle (typically 5 s for cooling with refrigeration work of 200 J and 100 ms for heating at 10 W), the microTM is kept approximately at -50 degrees C by a solid-state thermoelectric cooling unit placed within a few tens of micrometres of the device, and heated to 250 degrees C at 2800 degrees C s(-1) by integrated resistive microheaters and then cooled back to -50 degrees C at 250 degrees C s(-1). Thermal crosstalk between the two stages is less than 9%. A lumped heat transfer model is used to analyze the device design with respect to the rates of heating and cooling, power dissipation, and inter-stage thermal crosstalk as a function of Pyrex-membrane thickness, air-gap depth, and stage separation distance. Experimental results are in agreement with trends predicted by the model. Preliminary tests using a conventional capillary column interfaced to the microTM demonstrate the capability for enhanced sensitivity and resolution as well as the modulation of a mixture of alkanes.

Two simple methods for enantiomeric analyses of urinary amphetamines by GC/MS using deuterium-labeled l-amphetamines as internal standards

Two simple methods for enantiomeric analyses of amphetamines in urine by gas chromatography-mass spectrometry (GC-MS) using l-amphetamine-d 3 and l-methamphetamine-d 6 as internal standards are presented. One method (method A) employs extractive derivatization on a diatomaceous column with (S)-(-)-N-(trifluoroacetyl)prolyl chloride (TPC) followed by separation with a conventional capillary column. The second method (method B) uses headspace solid-phase microextraction (HD-SPME) after derivatization with heptafluoro-n-butyryl chloride (HFB), followed by separation with an enantiomeric capillary GC column. By the two methods, all enantiomers were well separated in each chromatogram, and good linearity was obtained in practical concentration ranges (0.1–1.6μg/ml for method A and 0.05–1μg/ml for method B) for every compound by selected-ion monitoring. The precision studies indicated satisfactory coefficients of variation (<5%) for every enantiomer at 0.1μg/ml by both methods. Both methods were also evaluated by applying them to an actual poisoning case. Both methods are recommended for use in forensic analysis, because of their simplicity, high precision, and sufficient sensitivity.

Applications of Monolithic Silica Capillary Columns in Proteomics

The use and applicability of silica based capillary monolithic reversed-phase columns in proteomic analysis has been evaluated by liquid chromatography-mass spectrometry (LC-MS). Chromatographic performance of the monolithic capillaries was evaluated with a tryptic digest of cytochrome C showing very good resolution and reproducibility in addition to the known advantages of a low pressure drop over a time period of 6 months. Monoliths were subsequently tested for their suitability to separate proteins and peptides from samples typically encountered in proteomic research such as in-gel digested tryptic peptide mixtures or fractions of proteolytically digested human serum. The monolithic capillaries also proved useful in the analysis of phospholipid species in bronchoalveolar lavage fluid. Compared to particle-filled conventional capillary columns, rapid and highly efficient separation of peptides and proteins was achieved using these bimodal pore size distribution columns, and good quality collision induced dissociation (CID) mass spectra were obtained on an ion trap mass spectrometer. These novel monolithic separation media are thus a promising addition to the methodological toolbox of proteomics research.

Height Equivalent to a Theoretical Plate Theory for Rectangular GC Columns

The theory for the height equivalent to a theoretical plate (HETP) of a miniature rectangular gas chromatographic (GC) column is developed in analogy to Golay's theory for an open tubular GC column. The HETP is similar to that for an open tubular column except for the nonequilibrium or mass-transfer term. Unlike prior theories, the nonequilibrium or mass-transfer term is complexly related to column geometry. The theory successfully predicts the performance of fast chromatography, in the form of both short microbore and micromachined columns. For a given column length, rectangular columns have lower HETPs than conventional capillary columns and higher volumetric flow rates. A good rule of thumb is that the resolution can be adjusted by selecting the column height (provided it is much less than the column width), and the volumetric flow of carrier gas can be adjusted by selecting the column width (or cross-sectional area). A satisfactory compromise is to use a low inlet pressure that also provides an HETP that remains nearly constant over a range of pressures.

Preparation of continuous beds for electrochromatography and reversed-phase liquid chromatography of low-molecular-mass compounds

High-performance capillary columns for electrochromatography and reversed-phase liquid chromatography are often prepared from silica beads. However, the synthesis of the beads involves many expensive and complicated steps and the packing of reproducible, stable and uniform beds requires great experience. In this paper we propose a simpler and more cost-effective approach, not based on preformed beads but on continuous polymer beds synthesized in situ in the chromatographic tube. The continuous bed columns were prepared by polymerizing two different monomer solutions in two steps directly in the capillary, followed by effective derivatization with hydrophobic ligands (C 18). Electroendosmosis was created by embedding a long, charged polymer (dextran sulfate). The continuous beds, as synthesized previously for the separation of proteins by reversed-phase chromatography, showed low resolution for the separation of low-molecular-mass compounds owing to a relatively low ligand density. This disadvantage was overcome by a new method designed to increase the ligand density and, in addition, to achieve a more rigid gel matrix. For rapid removal of the Joule-heat generated in electrochromatography, it is mandatory to employ very narrow columns. Continuous polymer bed columns with an inner diameter of 25 μm or less are easy to prepare. The potential of this type of capillary column is demonstrated by the separation of non-charged polycyclic aromatic hydrocarbons at an efficiency of 120 000 plates/m for a retained solute using electro-driven buffer flow. The performance is thus comparable to that of electrochromatography columns of 40–50 μm I.D. packed with 3–5 μm silica beads. In accordance with theoretical considerations only a somewhat higher plate height was obtained when the same continuous bed column was eluted with a pressure-driven flow. The columns have the distinct advantage over conventional capillary columns packed with beads that air bubbles seldom form and spoil a run, partly due to the absence of a supporting frit.

Fast headspace analysis with short microcapillary columns

A new method of analysis using headspace gas chromatography with microcapillary columns is proposed. Small diameter (50 μm I.D.) fused-silica capillary columns with non-extractable SE-54 and PS-255 polysiloxane stationary phases were used for the analysis of low boiling organic compounds. The small diameter columns possess the usual very high efficiency so that the method can be employed for the headspace analysis of complex mixtures. The use of short microcolumns reduces the analysis times in comparison to conventional capillary columns. Good performances were obtained in the analysis of volatile compounds in some lemon essential oil, perfumes, and water samples.

Determination of selected principal organic hazardous constituents from incinerators using capillary column GC/MS

Abstract Laboratory and field experiments were conducted to evaluate the use of conventional capillary column GC/MS in the analysis of Volatile Organic Sampling Train (VOST) samples. The recovery of analytes and surrogates from replicate analysis was over 80% and the relative standard deviation less than 20 %. Field evaluations showed that the overall precision was less than 16% RSD; the recovery of surrogates was well within the system performance established by the EPA for a trial burn test of + 50% accuracy and 20% RSD precision.

Recent methods for the determination of volatile and non-volatile organic compounds in natural and purified drinking water

Four analytical protocols for the extraction and preconcentration of organic residues in natural or purified drinking water were investigated and compared: closed loop stripping analysis; simultaneous extraction—distillation; purge and trap analysis; continuous liquid—liquid extraction. Organic extracts were submitted to a variety of separation and identification techniques. Volatiles were determined by conventional capillary column gas chromatography with tandem mass spectrometry, using triple-stage quadrupole instruments. Non-volatile and thermally labile molecules were investigated by several different techniques (high-temperature gas chromatography, capillary column supercritical fluid chromatography, pyrolysis gas chromatography—mass spectrometry, thermospray liquid chromatography with tandem mass spectrometry and conventional fast-atom bombardment with tandem mass spectrometry). Several samples recently examined in the laboratory provide examples of this multitechnique approach for a more complete knowledge of the organic carbon distribution in water-dissolved organic matter, taking into account organic substances with widely different volatilities, polarities and thermal stabilities.

Determination of volatile fatty acids by gas chromatography on a capillary and a megabore column

Measuring the concentration of volatile fatty acids (VFA) in biological fluids is of clinical interest in renal failure [I], impaired liver function 121, inborn errors of metabolism [3-S], dental diseases ]6] and in anaerobic infections (71, in which faeces [8], pus 191, amniotic fluid [lo] and vaginal fluid [11,12] may be used for diagnosis of infection and bacterial identification. Vacuum distillation of the biological material was shown to be a suitable pretreatment method prior to gas chromatographic analysis of VFA [8,13,14]. The gas chromatographic analysis of VFA in aqueous solutions is complicated by the severe tailing which results when conventional column packing is used. To avoid this problem, the column packing may be pretreated with orthophosphoric acid [15-171 or the carrier gas may be saturated with formic acid [8,18]. In spite of stringent safety measures, there remains an explosion risk associated with the use of carrier gas saturated with formic acid. In addition, formic acid vapour or spatters are very corrosive and hazardous. In this paper, we describe a reliable and rapid method of analysis of VFA on a fused silica megabore column which does not require saturation of the carrier gas with formic acid. We have compared this method with gas chromatographic analysis of VFA on a packed and a conventional capillary column.

Separation of Low-boiling Hydrocarbons by Gas Chromatography using Packed Capillary Columns

BY modifying the method described by Desty et al.1 for drawing glass capillaries, we have succeeded in making packed columns having an inner diameter comparable with that of capillary columns, which will be referred to here as ‘packed capillaries’. A capillary packed with an adsorbant is particularly suited for separating low-boiling hydrocarbons at room temperature, an operation requiring very low temperatures when carried out with a conventional capillary column. Filling the capillary with an adsorbant is performed thus: a carefully cleaned steel wire of 1 mm. diameter is pushed through a glass tube having an inner diameter of 2.2 mm. and the empty space between the wire and the tube wall filled with the adsorbant. Then placing the tube in a horizontal position and removing the wire carefully the glass is drawn to a capillary of 0.3 mm. inner diameter, using Desty's method. The adsorbant used in our experiments was alumina produced by calcining for 9 hr. at 400° C. hydragillite (CAMAG Chemie-Erzeugnisse und Adsorptionstechnik AG., Muttenz, Switzerland) [γ-Al(OH)3], having a grain size of 0.10–0.15 mm. Afterwards the column was flushed for 24 hr. at 120° C. by a stream of dry hydrogen, in order to remove traces of water which might have been adsorbed by the alumina during the filling and drawing operation.