Fast Temperature Programming Research Articles

Front Cover: High‐throughput gas chromatography for volatile compounds analysis by fast temperature programming and adsorption chromatography

Front Cover: High‐throughput gas chromatography for volatile compounds analysis by fast temperature programming and adsorption chromatography

High-throughput gas chromatography for volatile compounds analysis by fast temperature programming and adsorption chromatography.

The synergy of combining fast temperature programming capability and adsorption chromatography using fused silica based porous layer open tubular columns to achieve high throughput chromatography for the separation of volatile compounds is presented. A gas chromatograph with built-in fast temperature programming capability and having a fast cool down rate was used as a platform. When these performance features were combined with the high degree of selectivity and strong retention characteristic of porous layer open tubular column technology, volatile compounds such as light hydrocarbons of up to C7 , primary alcohols, and mercaptans can be well separated and analyzed in a matter of minutes. This analytical approach substantially improves sample throughput by at least a factor of ten times when compared to published methodologies. In addition, the use of porous layer open tubular columns advantageously eliminates the need for costly and time-consuming cryogenic gas chromatography required for the separation of highly volatile compounds by partition chromatography with wall coated open tubular column technology. Relative standard deviations of retention time for model compounds such as alkanes from methane to hexane were found to be less than 0.3% (n = 10) and less than 0.5% for area counts for the compounds tested at two levels of concentration by manual injection, namely, 10 and 1000ppm v/v (n = 10). Difficult separations were accomplished in one single analysis in less than 2min such as the characterization of 17 components in cracked gas containing alkanes, alkenes, dienes, branched hydrocarbons, and cyclic hydrocarbons.

Rapid analysis of urinary opiates using fast gas chromatography–mass spectrometry and hydrogen as a carrier gas

A sensitive and specific fast gas chromatography–mass spectrometry (FGC–MS) analytical method using hydrogen as a carrier gas is developed for the rapid simultaneous determination of morphine, codeine, hydrocodone and hydromorphone in human urine. Urine samples were spiked with deuterated internal standards, morphine-d3, codeine-d3, hydrocodone-d3 and hydro-morphone-d3, subjected to acid hydrolysis, treated with hydroxylamine to convert the keto-opiates to oximes and then extracted using a positive pressure manifold and silica based solid phase extraction columns. The extracts were derivatized using BSTFA with 1% TMCS.Gas chromatographic–mass spectrometric analysis was performed in electron ionization mode by selective ion monitoring, using hydrogen as a carrier gas, a short narrow bore GC capillary column, and fast temperature program, allowing for a rapid analytical cycle to maximize the instrument time for high throughput laboratories. While maintaining specificity for these drugs, concentrations in human urine ranging from 50 to 5,000ng/mL can be measured with intraday and interday imprecision, expressed as variation coefficients, of less than 2.3% for all analytes within a run time of less than 3.5minutes.

Resolving overlapping GC–MS signals with a multistep screening chemometric approach for the fast determination of pesticides

For the rapid analysis of multicomponent mixtures using GC-MS, a chemometric multistep screening approach was proposed to extract the signals of the components from the overlapping signals measured with a very fast temperature program. At first, independent component analysis was used to find all the possible mass spectra from the overlapping signal in the moving windows along the retention time, and iterative target transformation factor analysis was employed to validate the existence of the extracted spectra from each window. Then, identical signals in the validated spectra were excluded using match ratio as a criterion. Finally, the chromatographic profiles for each spectrum were calculated using non-negative immune algorithm, and the spectra with a reasonable profile were taken as the identified components. A mixture of 53 pesticides was analyzed with a very fast temperature program of 7min. A total of 48 pesticides and 16 interferences were identified from the overlapping GC-MS signal.

Chemometric approach for fast analysis of prometryn in human hair by GC-MS

A method for the fast analysis of a specific component in complex samples by GC-MS was developed and used for the quantitative determination of prometryn in hair samples. In this method, the tedious and time-consuming sample pretreatment for purification was avoided, and a short capillary column and fast temperature program were employed to speed up the analysis. Although the measured total ion chromatogram is composed of overlapping peaks with interference and background noise, the signal of prometryn can be extracted by chemometric methods. Window-independent component analysis was used to extract the mass spectrum and a non-negative immune algorithm was employed to obtain the chromatographic profile of the interesting component from the measured data. Due to the complexity of the matrix, a standard addition method was adopted for the quantification. The applicability of the method was validated with spiked samples, and the recoveries were in the range of 99-105%.

Chemometric Resolution for Rapid Determination of Prometryn in Leek Samples Using GC–MS

Much effort has been made to analyze the pesticides in foods or vegetables due to the interferences in the sample matrix. In this work, taking the determination of prometryn in leek samples as an example, a simple method is proposed for fast analysis of the components in real samples using GC–MS and chemometric resolution. The purification step in preparing the samples was simplified, and a short capillary column and fast temperature program were employed in GC–MS measurement. Although the measured signal is composed of overlapped peaks with the interferences and background, the signal of prometryn can be extracted by chemometric resolution. Six leek samples from different markets were analyzed within an elution time of 6 min. Compared with the results by the standard method, the results by the proposed method were found to be reliable.

Temperature-Programmed Sputtered Micromachined Gas Chromatography Columns: An Approach to Fast Separations in Oilfield Applications

In a previous study, a new stationary phase deposition technique for micromachined gas chromatography columns was presented. The rerouting of the sputtering technique to this purpose enabled collective and reproducible fabrication of microcolumns in a silicon wafer. Silica-sputtered micromachined columns showed promising separations of light alkanes in isothermal conditions. In order to go beyond the limitations of isothermal separations, the columns were equipped with sputtered platinum filaments to enable high-speed and low-power temperature programming. The separation performances of temperature-programmed silica- or graphite-sputtered microcolumns were investigated: a separation of light alkanes (C1-C5) was completed in 9 s, and heavier alkanes (until C9), cyclic, isomeric, and unsaturated hydrocarbons were also successfully separated. Versatility of these microcolumns was demonstrated with a high-temperature C1-C2 separation and a C1-C5 separation with nitrogen as carrier gas instead of helium. By matching the requirements of a gas chromatography-based monitoring sensor, in terms of low-cost and industry-ready fabrication process, fast temperature programming and analysis, low power consumption, and good versatility (ambient temperature, carrier gas), these columns should be used in various applications related to oilfield gas analyses.

Rapid Temperature-Programmed Separation and Retention Prediction on a Novel Packed-Capillary Column in Gas Chromatography

Novel packed-capillary columns for gas chromatography were developed with a thin-wall stainless-steel capillary of 1.0 mm i.d.; and rapid temperature-programmed separations have been carried out after a basic evaluation concerning the compatibility of these columns to the temperature program. With a numerical integration method, the retention of several test analytes during temperature-programmed elution was successfully estimated. In order to confirm the suitability of the packed-capillary columns to relatively fast temperature programming up to 40 degrees C/min, theoretically predicted retention data were compared with that actually measured. The results suggested a good separation performance of the newly developed packed-capillary columns as a particle-packed column conventionally used. Also, the compatibility to a rapid temperature-programmed operation was quite satisfactory for almost all of the separations currently done in typical analytical laboratories.

Handling within run retention time shifts in two-dimensional chromatography data using shift correction and modeling

The use of PARAFAC for modeling GC × GC-TOFMS peaks is well documented. This success is due to the trilinear structure of these data under ideal, or sufficiently close to ideal, chromatographic conditions. However, using temperature programming to cope with the general elution problem, deviations from trilinearity within a run are more likely to be seen for the following three cases: (1) compounds (i.e., analytes) severely broadened on the first column hence defined by many modulation periods, (2) analytes with a very high retention factor on the second column and likely wrapped around in that dimension, or (3) with fast temperature program rates. This deviation from trilinearity is seen as retention time-shifted peak profiles in subsequent modulation periods (first column fractions). In this report, a relaxed yet powerful version of PARAFAC, known as PARAFAC2 has been applied to handle this shift within the model step by allowing generation of individual peak profiles in subsequent first column fractions. An alternative approach was also studied, utilizing a standard retention time shift correction to restore the data trilinearity structure followed by PARAFAC. These two approaches are compared when identifying and quantifying a known analyte over a large concentration series where a certain shift is simulated in the successive first column fractions. Finally, the methods are applied to real chromatographic data showing severely shifted peak profiles. The pros and cons of the presented approaches are discussed in relation to the model parameters, the signal-to-noise ratio and the degree of shift.

A New Method for Simultaneous Determination of Cyclic Antidepressants and their Metabolites in Urine Using Enzymatic Hydrolysis and Fast GC-MS

A method for the simultaneous determination of six commonly prescribed cyclic antidepressants and their major metabolites in urine is presented. This method can be used for quantitation of amitriptyline, nortriptyline, imipramine, desipramine, doxepin, desmethyldoxepin, and maprotiline in human urine, in addition to the qualitative determination of their hydroxylated metabolites. This method is suitable for confirmation of drug abuse in health care professionals and overdose cases where the identity of the abused cyclic antidepressant may not be known. Samples are spiked with internal standard and hydrolyzed with beta-glucuronidase from Escherichia coli. Hydrolysis is found to be essential to the extraction procedure as the tertiary cyclic antidepressants are found to be extensively conjugated in urine. The secondary cyclic antidepressants, on the contrary, are found to be minimally conjugated. Drugs are extracted from alkalinized urine into solvent and derivatized with MSTFA/ammonium iodide/ethanethiol reagent. This reagent produces more stable derivatives compared to reagents previously employed. Gas chromatographic (GC)-mass spectrometric analysis is performed in electron ionization mode by selective ion monitoring, using hydrogen as a carrier gas, a short narrow bore GC capillary column, and fast temperature program, allowing for a rapid analytical cycle. While maintaining specificity for these drugs, concentrations in human urine ranging from 50 to 20,000 ng/mL can be measured with intraday and interday precisions, expressed as variation coefficient, of less than 2.8% for all analytes.

Improvement of sample throughput using fast gas chromatography mass-spectrometry for biochemical diagnosis of organic acid disorders

Background Gas chromatograph mass-spectrometric (GC/MS) method of analysis for urinary organic acids is used for the diagnosis of a variety of metabolic disorders. The method is time-consuming and does not allow for improvements in sample throughput. Although the sample preparation and the data processing have been improved, the long GC/MS analysis time still remains to be problematic. Methods The fast-GC/MS method, which utilizes a short microbore capillary GC column and fast temperature programming, was applied to the analysis for urinary organic acids. Urine samples obtained from 15 patients with 9 different disorders and 16 healthy controls were analyzed using conventional GC/MS and fast-GC/MS. Results Analysis cycle time was shortened from 1 h to 15 min. The automated data system uses retention indices determined by conventional-GC/MS for the identification of 134 organic acids. These retention indices can also be used in data obtained by fast-GC/MS. New fast-GC/MS method with the automated data system gave the same diagnostic results as conventional-GC/MS except for 1 healthy control. Conclusions The combined system of fast-GC/MS and the automated data system will be powerful tools in clinical laboratories due to increased sample throughput and reduced analysis costs.

Gas chromatography with ballistic heating and ultrafast cooling of column

AbstractAn overview of the existing methods for minimization of the analysis time in gas chromatography (GC) is presented and a new system for fast temperature programming and very fast cooling down is evaluated. In this study, a system of coaxial tubes, a heating/cooling module (HC-M), was developed and studied with a capillary column placed inside the HC-M. The module itself was heated by a GC oven and cooled down by an external cooling medium. The HC-M was heated at rates of up to 330 °C min−1 and cooled at the rate of 6000 °C min−1. The GC system was prepared for the next run within a few seconds. The HC-M permits good separation reproducibility, comparable with that of a conventional GC, expressed in terms of relative retention times and peak areas of analytes reproducibilities. The HC-M can be used within any commercial gas chromatograph.

Fast temperature programming on a stainless-steel narrow-bore capillary column by direct resistive heating for fast gas chromatography

A direct resistive-heating fast temperature programming device for fast gas chromatography was designed and evaluated. A stainless-steel (SS) capillary column acted both as a separation column and as a heating element. A fast temperature controller with the deviation derivative proportional-integral-derivative (DDPID) control algorithm, which was suitable for ramp control using ramp-to-setpoint function, was used to facilitate the fast pulse heating. The SS resistive-heating column can generate linear temperature ramps up to 10 °C/s and can re-equilibrium from 250 °C down to 50 °C within 30 s. With n-alkanes as the test analytes, the relative standard deviations (RSDs) of retention time were between 0.19 and 0.59% and the RSDs of their peak areas were less than 4% for all but one. The results indicated that this technique could be used for both qualitative and quantitative analysis. Phenolic and nitroaromatic compounds were also analyzed by using the SS resistive-heated system. The combination of a short narrow-bore SS column and rapid heating rates provides sufficient separation efficiency for relatively simple mixtures at drastically reduced analysis time. The total analysis time including equilibration time was less than 2 min for all test mixtures in this study.

Rapid determination of C12–C26 non‐derivatized fatty acids in human serum by fast gas chromatography

The concentration of long-chain fatty acids (LCFAs) in human serum is closely related to human health. It is therefore important to develop a fast, low-cost, efficient method for their determination. In this study, by using fast temperature programming and micro-bore short capillary columns, a fast gas chromatography method was developed for the direct analysis of non-derivatized LCFAs including n-dodecanoic acid to n-hexacosanic acid (C12:0-C26:0, even numbers only), linoleic acid (C18:2), oleic acid (C18:1), and erucic acid (C22:1) within 4.0 min. Method optimization including extraction and separation conditions is considered, and the analysis of real serum samples is presented. The results show that ten LCFAs were well separated with sufficient resolution, and the detection limit was in the range of 2.8-9.6 microg/mL. The reproducibility (RSD) for both intra-day and inter-day determination was always less than 15%, and the recoveries for these LCFAs were from 63.1 to 97.0%.

Ultrafast Gas Chromatographic Separation of Organophosphor and Organosulfur Compounds Utilizing a Microcountercurrent Flame Photometric Detector

A microcountercurrent flame photometric detector (microcc-FPD) was adapted and optimized for ultrafast gas chromatographic (GC) separation and detection of organophosphor (OP) and organosulfur (OS) compounds on short chromatographic columns. Air and hydrogen are introduced to the microcc-FPD from opposite directions, creating a hydrogen-rich flame. In this microcc-FPD, combustion takes place between the burner tips without touching them. The separation between the tips and the flame reduces heat loss from the flame to the surrounding environment, resulting in low hydrogen consumption and a compact flame. The microcc-FPD is capable of detecting very narrow (13 ms) chromatographic peaks. An ultrafast GC separation of a group of six OP and OS compounds is achieved within less than 5 s using fast temperature programming of a 0.5-m-long microbore column. Very fast separations are also demonstrated on a 1-m-long microfabricated column consisting of 150-microm-wide, 240-microm-deep channels, etched in a 1.9-cm square silicon chip, covered with a Pyrex wafer, and statically coated with dimethyl polysiloxane. With a hydrogen flow rate of 10 mL/min, the detection limit for OP is 12 pg of P/s and 3 ng of S/s for OS compounds at a signal-to-noise ratio of 2. The coupling of a microfabricated column and a miniature FPD is an important step toward the development of a miniaturized GC-FPD capable of ultrafast detection of low levels of OP and OS compounds.

Ultrafast Gas Chromatography on Single-Wall Carbon Nanotube Stationary Phases in Microfabricated Channels

The key to rapid temperature programmed separations with gas chromatography are a fast, low-volume injection and a short microbore separation column with fast resistive heating. One of the major problems with the reduction of column dimensions for micro gas chromatography is the availability of a stationary phase that provides good separation performance. In this report, we present the first integration of single-wall carbon nanotubes (SWNTs) as a stationary phase into 100 mum x 100 mum square and 50-cm-long microfabricated channels. The small size of this column with integrated resistive heater and the robustness of the SWNT phase allow for fast temperature programming of up to 60 degrees C/s. A combination of the fast temperature programming and the narrow peak width of small-volume injections that can be obtained from a high-speed, dual-valve injection system allows for rapid separations of gas mixtures. We demonstrate highly reproducible separations of four-compound test mixtures on these columns in less than 1 s using fast temperature programming.

Fast screening of pesticide multiresidues in aqueous samples by dual stir bar sorptive extraction-thermal desorption-low thermal mass gas chromatography–mass spectrometry

A method for fast screening of pesticide multiresidues in aqueous samples using dual stir bar sorptive extraction-thermal desorption-low thermal mass gas chromatography–mass spectrometry (dual SBSE-TD-LTM-GC–MS) has been developed. Recovery of 82 pesticides – organochlorine, carbamate, organophosphorous, pyrethroid and others – for the SBSE was evaluated as a function of octanol–water distribution coefficients (log K o/w: 1.7–8.35), sample volume (2–20 mL), salt addition (0–30% NaCl), and methanol addition (0–20%). The optimized method consists of a dual SBSE performed simultaneously on respectively a 20-mL sample containing 30% NaCl and a 20-mL sample without modifier (100% sample solution). One extraction with 30% NaCl is mainly targeting solutes with low K o/w (log K o/w < 3.5) and another extraction with unmodified sample solution is targeting solutes with medium and high K o/w (log K o/w > 3.5). After extraction, the two stir bars are placed in a single glass desorption liner and are simultaneously desorbed. The desorbed compounds are analyzed by use of LTM-GC–MS with fast temperature programming (75 °C min −1) using a 0.18 mm i.d. narrow-bore capillary column and fast scanning (10.83 scan s −1) using quadrupole MS. The method showed good linearity ( r 2 > 0.9900) and high sensitivity (limit of detection: <10 ng L −1) for most of the target pesticides. The method was applied to the determination of pesticides at nanograms per liter levels in river water and brewed green tea.

Multi-element electrothermal AAS determination of 11 marker elements in fine ambient aerosol slurry samples collected with SEAS-II

Multi-element simultaneous electrothermal atomic absorption spectrometry (ETAAS) methods were developed for determining 11 elements, in three analytical groups (group-1, predominately crustal elements, Al, Cu, Fe, Mn, and Cr; group-2, tracers of coal and oil combustion as well as other anthropogenic sources, Se, As, Pb, and Ni; and group-3, tracers of municipal incinerator aerosol–Zn and Cd), in aqueous slurry of ambient fine airborne particles, collected, at 30 min intervals with the University of Maryland–Semicontinuous Elements in Aerosol Sampler-II (SEAS-II). Combined effects of acid (0.2% v/v nitric acid) and ultrasonic treatment (15 min) improved metals recovery and slurry stability. Linear calibration ranges were improved by using a 50 mL min −1 carrier gas flow (mini-flow) during the atomization stage. However, analytical sensitivity for group-1 and 3 elements was compromised. Palladium (4 μg) and hydrogen (5% in Argon) were found to be effective modifiers for group-1 and 2 elements. A fast furnace temperature program was developed for group-3. Detection limits for the eleven marker elements by the SEAS-II-ETAA approach were compared with traditional filter X-ray fluorescence, laser ablation-ICPMS, and instrumental neutron activation analysis (INAA) techniques used in air quality studies. The efficacy of the analytical method was evaluated by analyzing interim urban PM2.5 reference material, collected in Baltimore, by the National Institute of Standards and Technology (NIST) Gaithersburg, MD. Results obtained by the ETAAS methods agreed well with the results obtained by NIST using INAA.

Practical aspects of splitless injection of semivolatile compounds in fast gas chromatography

Possibilities and practical aspects of implementation of splitless injection of larger volumes for fast GC purposes utilizing narrow-bore column, hydrogen as carrier gas, fast temperature programming under programmed flow conditions and commercial instrumentation were searched. As a model sample semivolatile compounds of a broad range of volatility and polarity (7 n-alkanes and 19 pesticides) were chosen. Peak shapes, peak broadening and peak areas and its repeatability were evaluated under various experimental set-ups (liner/injection technique combinations). Various factors, such as liner design, injection technique, retention gap length, compound volatility and polarity, the solvent used, initial oven temperature influenced compound focusation and/or maximal injection volume. Combination of analytical column (CP-Sil 13 CB 25 m long, 0.15 mm i.d., film thickness 0.4 μm) with normal-bore retention gap (1 m long, 0.32 mm i.d.) allowed maximal injection volume 8 μl for 4 mm i.d. liner used without any peak distortion when solvent recondensation in the retention gap was employed.

High-speed gas chromatographic analysis of solvents in pharmaceuticals using solid phase microextraction

A simple, inexpensive and rapid analytical approach for the determination of organic volatile impurities in pharmaceutical drug substances is developed, where sample preparation step was conducted using solid phase microextraction (SPME), followed by a fast GC separation. With an extraction time between 3 and 5 min and separation of 13 solvents in less than 3 min employing fast temperature programming using resistively heated column, organic volatile impurities can be analyzed within a total analysis time of 6–9 min. Various SPME phases were evaluated towards sensitivity and selectivity for the extraction of 13 commonly found solvents in drug substances dissolved in dimethyl sulfoxide and water. A 2-cm Carboxen/polydimethyl siloxane/divinylbenzene (Carboxen/PDMS/DVB) phase and a 65-μm DVB/PDMS phase showed better sensitivity towards these solvents when extracted from organic and aqueous matrix in comparison with the sensitivity obtained with direct injection approach. Extraction parameters such as extraction time, extraction stir rate, etc. are discussed. %RSD of peak area of replicate extraction was between 2 and 10% when 100 μm PDMS was used for extracting solvents from aqueous matrix. When DVB/PDMS fiber was evaluated for precision, %RSD of peak area from replicate extractions of solvents from organic matrix was between 2 and 8%. One-hundred micrometer PDMS showed excellent linearity from 10 to 500 μg/ml for analytes extracted from water solutions. On the other hand, DVB/PDMS phase showed better linearity than Carboxen/PDMS/DVB fiber when it was used to extract analytes in the concentration range of 10–5000 μg/ml from organic matrix.