Development of membrane inlet mass spectrometry for examination of fermentation processes

Membrane inlet mass spectrometry (MIMS) is useful for on-line monitoring of fermentation processes. However, readings are affected by the complex and dynamic matrix in which biological processes occur, making MIMS calibration a challenge. In this work, two calibration strategies were evaluated for measurement of typical products of acidogenic fermentation, i.e., ethanol, H₂, and CO₂ in the liquid phase, and H₂ and CO₂ in the gas phase: (1) “standard calibration”, which was performed independent of fermentation experiments with sterile standards in water with a N₂ headspace, and (2) “in-process calibration” whereby fermentation was monitored concurrent with off-line analysis. Fermentation was operated in batch and continuous modes. In-process calibration was shown to be most effective for measurements of H₂ and CO₂ in both gas and liquid phases; standard calibration gave erroneous results. In the gas phase, this was due to a lower sensitivity during experiments compared to the independent standard calibration, believed to be caused by formation of a liquid film on the surface of the probe. In the liquid phase, moving from the standard calibration environment to the fermentation caused the linear relationship between the H₂ concentration and MIMS signal to change in intercept, and the relationship for CO₂ to change in slope, possibly due to dissolved ions, and related non-ideality. For ethanol, standard calibration results were fairly consistent with in-process calibration results. The main limitation with in-process calibration is the potential for a lack of variability in target concentration. This could be addressed by spiking the targeted compound at the end of the experiment. Regardless, MIMS is an ideal instrument for analysing fermentation experiments, due to its ability to measure targeted compounds semi-continuously, and due to a lack of drift over long periods.     

Thermal decomposition of copper(II) and zinc carbonate hydroxides by means of TG-MS

Summary For the quantitative analyses of evolved CO₂and H₂O during the thermal decomposition of solids, calibration curves, i.e. the amounts of evolved gases vs. the corresponding peak areas of mass chromatograms measured by TG-MS, were plotted as referenced by the reaction stoichiometry of the thermal decomposition of sodium hydrogencarbonate NaHCO₃. The accuracy and reliability of the quantitative analyses of the evolved CO₂and H₂O based on the calibration curves were evaluated by applying the calibration curves to the mass chromatograms for the thermal decompositions of copper(II) and zinc carbonate hydroxides. It was indicated from the observed ratio of evolved CO₂and H₂O that the compositions of copper(II) and zinc carbonate hydroxides examined in this study correspond to mineral malachite, Cu₂CO₃(OH)₂, and hydrozincate, Zn₅(CO₃)₂(OH)₆, respectively. Reliability of the present analytical procedure was confirmed by the fairly good agreement of the mass fraction of the evolved gases calculated from the analytical values with the total mass-loss during the thermal decompositions measured by TG.     

CO2 isotope analyses using large air samples collected on intercontinental flights by the CARIBIC Boeing 767

Analytical details for ¹³C and ¹⁸O isotope analyses of atmospheric CO₂ in large air samples are given. The large air samples of nominally 300 L were collected during the passenger aircraft‐based atmospheric chemistry research project CARIBIC and analyzed for a large number of trace gases and isotopic composition. In the laboratory, an ultra‐pure and high efficiency extraction system and high‐quality isotope ratio mass spectrometry were used. Because direct comparison with other laboratories was practically impossible, the extraction and measurement procedures were tested in considerable detail. Extracted CO₂ was measured twice vs. two different working reference CO₂ gases of different isotopic composition. The two data sets agree well and their distributions can be used to evaluate analytical errors due to isotope measurement, ion corrections, internal calibration consistency, etc. The calibration itself is based on NBS‐19 and also verified using isotope analyses on pure CO₂ gases (NIST Reference Materials (RMs) and NARCIS CO₂ gases). The major problem encountered could be attributed to CO₂‐water exchange in the air sampling cylinders. This exchange decreased over the years. To exclude artefacts due to such isotopic exchange, the data were filtered to reject negative δ¹⁸O(CO₂) values. Examples of the results are given. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of variation in argon content of calibration gases on determination of atmospheric carbon dioxide

Carbon dioxide (CO₂) is a greenhouse gas that makes by far the largest contribution to the global warming of the Earth's atmosphere. For the measurements of atmospheric CO₂ a non-dispersive infrared analyzer (NDIR) and gas chromatography are conventionally being used. We explored whether and to what degree argon content can influence the determination of atmospheric CO₂ using the comparison of CO₂ concentrations between the sample gas mixtures with varying Ar amounts at 0 and 18.6 mmol mol⁻¹ and the calibration gas mixtures with Ar at 8.4, 9.1, and 9.3 mmol mol⁻¹. We newly discovered that variation of Ar content in calibration gas mixtures could undermine accuracy for precise and accurate determination of atmospheric CO₂ in background air. The differences in CO₂ concentration due to the variation of Ar content in the calibration gas mixtures were negligible (<±0.03 μmol mol⁻¹) for NDIR systems whereas they noticeably increased (<±1.09 μmol mol⁻¹) especially for the modified GC systems to enhance instrumental sensitivity. We found that the thermal mass flow controller is the main source of the differences although such differences appeared only in the presence of a flow restrictor in GC systems. For reliable monitoring of real atmospheric CO₂ samples, one should use calibration gas mixtures that contain Ar content close to the level (9.332 mmol mol⁻¹) in the ambient air as possible. Practical guidelines were highlighted relating to selection of appropriate analytical approaches for the accurate and precise measurements of atmospheric CO₂. In addition, theoretical implications from the findings were addressed.     

A system for high‐quality CO2 isotope analyses of air samples collected by the CARIBIC Airbus A340‐600

In 2007, JRC‐IRMM began a series of atmospheric CO₂ isotope measurements, with the focus on understanding instrumental effects, corrections as well as metrological aspects. The calibration approach at JRC‐IRMM is based on use of a plain CO₂ sample (working reference CO₂) as a calibration carrier and CO₂‐air mixtures (in high‐pressure cylinders) to determine the method‐related correction under actual analytical conditions (another calibration carrier, in the same form as the samples). Although this approach differs from that in other laboratories, it does give a direct link to the primary reference NBS‐19‐CO₂. It also helps to investigate the magnitude and nature for each of the instrumental corrections and allows for the quantification of the uncertainty introduced. Critical tests were focused on the instrumental corrections. It was confirmed that the use of non‐symmetrical capillary crimping (an approach used here to deal with small samples) systematically modifies δ¹³C(CO₂) and δ¹⁸O(CO₂), with a clear dependence on the amount of extracted CO₂. However, the calibration of CO₂‐air mixtures required the use of the symmetrical dual‐inlet mode. As a proof of our approach, we found that δ¹³C(CO₂) on extracts from mixtures agreed (within 0.010‰) with values obtained from the ‘mother’ CO₂ used for the mixtures. It was further found that very low levels of hydrocarbons in the pumping systems and the isotope ratio mass spectrometry (IRMS) instrument itself were critical. The m/z 46 values (consequently the calculated δ¹⁸O(CO₂) values) are affected by several other effects with traces of air co‐trapped with frozen CO₂ being the most critical. A careful cryo‐distillation of the extracted CO₂ is recommended. After extensive testing, optimisation, and routine automated use, the system was found to give precise data on air samples that can be traced with confidence to the primary standards. The typical total combined uncertainty in δ¹³C(CO₂) and δ¹⁸O(CO₂) on the VPDB‐CO₂ scale, estimated on runs of CO₂‐air mixtures, is ±0.040‰ and 0.060‰ (2‐σ values). Inter‐comparison with MPI‐BGC resulted in a scale discrepancy of a similar magnitude. Although the reason(s) for this discrepancy still need to be understood, this basically confirms the approach of using specifically prepared CO₂‐air mixtures as a calibration carrier, in order to achieve scale unification among laboratories. As important practical application and as a critical test, JRC‐IRMM took part in the passenger aircraft‐based global monitoring project CARIBIC ( http://www.caribic‐atmospheric.com ). In this way, reliable CO₂ isotope data for the tropopause region and the free troposphere were obtained. From June 2007 to January 2009, approximately 500 CARIBIC air samples have been analysed. Some flights demonstrated a compact correlation of both δ¹³C(CO₂) and δ¹⁸O(CO₂) with respect to CO₂ concentration, demonstrating mixing of tropospheric and stratospheric air masses. These excellent correlations provide an independent, realistic data quality check. Copyright © 2009 John Wiley & Sons, Ltd.     

An FTIR spectroscopic study and quantification of 2-amino-2-methyl-1-propanol,piperazine and absorbed carbon dioxide in concentrated aqueous solutions

This study reports the investigation of carbon dioxide (CO₂) absorption into an amine blend solution of 2-amino-2-methyl-1-propanol (AMP) and piperazine (PZ). The reaction in the liquid phase between CO₂ and the amines were qualitatively and quantitatively monitored by Fourier Transform Mid-Infrared spectroscopy (mid-FTIR). A multivariate partial least square regression (PLS2) model was obtained to quantify free or non-reacted AMP and PZ and absorbed CO₂ in all chemical forms, i.e. no differentiation was made into carbonates or carbamates. The calibration model was constructed using a single wide region and 270 calibration samples. The concentration of AMP, PZ and CO₂ from 568 samples were simultaneously predicted with low relative errors.     

Traceability in routine chemical measurements: an example of application in the determination of CO2 at atmospheric concentration

In routine chemical measurements traceability can be achieved by using analytical instruments calibrated against primary reference materials. In the present work the calibration of a CO₂ non-dispersive infrared (NDIR) analyzer with measuring range 0–2000 μmol/mol of CO₂ and a resolution of 5 μmol/mol is reported. A procedure with working reference gas mixtures (WRMs) has been adopted, which requires seven calibration points. Primary reference gas mixtures (PRMs) are used to validate WRMs in a narrower range around the average atmospheric CO₂ concentration value. In this range the relative uncertainty reached is of the order of some parts in 10³ and the corrections are between 1 μmol/mol and 5 μmol/mol. Received: 16 March 2000 Accepted: 27 November 2000     

Calibration transfer strategy to compensate for instrumental drift in portable quadrupole mass spectrometers

We report the use of a calibration transfer strategy to correct for drift in the quantitative sensitivity of a portable quadrupole mass spectrometer (QMS) aimed at process monitoring applications. Gas mixtures of CH₄/Ar/C₂H₆/CO₂ were studied with calibration phase measurements made of the pure gases for a univariate analysis and of 40 multi-component mixtures for a multivariate approach. To evaluate calibrations, test set spectra of a CH₄/Ar/C₂H₆/CO₂ gas mixture were recorded bi-weekly over a period of 12 months. As part of the strategy a standard of pure argon was measured during both calibration and test phases so that correction factors could be calculated for each measurement day. It was shown that in the absence of a calibration transfer strategy quantifications of test set spectra could be inaccurate by more than an order of magnitude over 12 months. Furthermore, due to the effects of drift in the sensitivity over the 6 days required to record the training set in the calibration phase it was found that the multivariate analysis quantified test spectra less accurately than the univariate analysis. However, by applying the calibration transfer strategy across all measurements (both calibration and test phases) it was shown that the errors in prediction using the multivariate analysis previously seen after 2 weeks were not observed until approximately 12 months later.     

External calibration in gas chromatography-combustion-isotope ratio mass spectrometry measurements of endogenous androgenic anabolic steroids in sports doping control

An alternative calibration procedure for the Gas Chromatography–Combustion–Isotope Ratio Mass Spectrometry (GC–C–IRMS) measurements of the World Antidoping Agency (WADA) Accredited Laboratories is presented. To alleviate the need for externally calibrated CO₂ gas for GC–C–IRMS analysis of urinary steroid metabolites, calibration using an external standard mixture solution of steroids with certified isotopic composition was investigated. The reference steroids of the calibration mixture and routine samples underwent identical instrumental processes. The calibration standards bracketed the entire range of the relevant δ¹³C values for the endogenous and exogenous steroids as well as their chromatographic retention times. The certified δ¹³C values of the reference calibrators were plotted in relation to measured m/z¹³CO₂/¹²CO₂ (i.e. R(45/44)) mass spectrometric signals of each calibrator. δ¹³C values of the sample steroids were calculated from the least squares fit through the calibration curve. The effect of the external calibration on δ¹³C values, using the same calibration standards and set of urine samples but different brands of GC–C–IRMS instruments, was assessed by an interlaboratory study in the WADA Accredited Laboratories of Sydney, Australia and Athens, Greece. Relative correspondence between the laboratories for determination of androsterone, etiocholanolone, 5β-androstane-3α,17β-diacetate, and pregnanediacetate means were SD(δ¹³C) = 0.12‰, 0.58‰, −0.34‰, and −0.40‰, respectively. These data demonstrate that accurate intralaboratory external calibration with certified steroids provided by United States Antidoping Agency (USADA) and without external CO₂ calibration is feasible and directly applicable to the WADA Accredited Laboratories for the harmonization of the GC–C–IRMS measurements.     

Galvanic solid electrolyte cells for the measurement of CO<Subscript>2</Subscript> concentrations

The first commercially offered CO₂ sensors with galvanic solid electrolyte cells have very different properties. A review of the numerous carbonate cells described in the literature shows that it is easy to obtain CO₂-sensitive systems with Au, Na₂CO₃ measuring electrodes. The problems of obtaining reproducible CO₂ sensors with long-term stability mainly concern the reference electrode. Only electrodes composed of pure solid substances, stable under the operational conditions, promise the desired properties. Reference electrodes with the oxides of Mo, W, Sn, Ti, Si and Ge have been tested, with different degrees of success. With silica and sodium silicate on β-alumina, a CO₂ sensor results that can be used also in reducing gas phases and without calibration because the evaluation of the signals is possible by a thermodynamically precalculated equation. The volatility of Na₂CO₃ is presumably caused by the vapor pressure of thin layers of the creeping substance and by the formation of gaseous Na₂(OH)₂. The properties of Na₂CO₃ are particularly unfavorable for planar sensors. The sensor signals are independent of the partial pressure of O₂ and H₂O, but the participation of O₂ in the electrode reactions causes cross sensitivities not only for carbon-containing gases but also, for example, for NH₃ and H₂. The cross sensitivities against halogens and SO₂ are irreversible. At sudden changes of the CO₂ concentration the sensor signal follows within less than a few seconds, but questions remain concerning the observable differences in the response times of differently arranged sensors. The response times are highly important for a sensor arrangement that is aimed at simultaneous measurements of CO₂ and O₂ in real time for each breath.     

Theoretical aspects of quantitative mass spectrometry of gas mixtures

The problem of calibration of mass spectrometers with standard gas mixtures is studied theoretically. The results obtained can be used in deciding the number and optimum composition of standard mixtures. An analogy is drawn between this calibration problem and the mathematical theory of experimental design when mixtures are considered. It is shown that calibration based on a number of standard mixtures is more accurate than calibration with pure gases. A procedure for correction of calibration coefficients is described; it can be applied during measurements on the composition of gas mixtures or gas flows. Application to gas mixtures containing CO, N₂ and CO₂ is discussed.     

Crystallization and morphology of star-shaped polyethylenoxyde-b-polycaprolactone under high pressure carbon dioxide

Atomic force microscopy（AFM）,wide-angle X-ray diffraction（WAXD） and differential scanning calorimetry are used to analyze the crystallization morphology and melting behavior of 4-arm PEO-b-PCL under high-pressure CO₂.It is demonstrated that CO₂ has certain effect on the melting and crystallization behavior of the samples.After crystallization under CO₂ at 4 MPa,spherulites with concentric ring-banded structure are formed which are composed of crystals with periodic thickness variation,and the band distance decreases with increasing treatment pressure.Due to the plasticization effect of CO₂,depression of the melting temperature is observed with sorption of CO₂ in polymers.     

Gas transport in poly [bis(trifluoroethoxy) phosphazene] above the T(1) transition

Gas permeation measurements were performed by the time-lag method for 13 gases in poly [bis(trifluoroethoxy) phosphazene] above the mesophase transition, T (1) transition, of the crystals. Hysteresis was found in the temperature dependence of the permeability coefficients for CO₂, O₂, and N₂ in the transition region as observed by dilatometry and differential scanning calorimetry. Independently the solubility of CO₂ was determined gravimetrically above and below T(1). Noticeable change and hysteresis were also observed in the temperature dependence of the solubility coefficients. Diffusion of CO₂ in the measophase is suggested from the permeation and sorption measurements. Gas transport parameters of CO₂ in the mesophase are estimated, and the contributions of the mesophase and the crystalline phase to gas transport are considered.     

Innovative method for carbon dioxide determination in human postmortem cardiac gas samples using headspace-gas chromatography–mass spectrometry and stable labeled isotope as internal standard

A novel approach to measure carbon dioxide (CO₂) in gaseous samples, based on a precise and accurate quantification by ¹³CO₂ internal standard generated in situ is presented. The main goal of this study was to provide an innovative headspace-gas chromatography–mass spectrometry (HS-GC–MS) method applicable in the routine determination of CO₂. The main drawback of the GC methods discussed in the literature for CO₂ measurement is the lack of a specific internal standard necessary to perform quantification. CO₂ measurement is still quantified by external calibration without taking into account analytical problems which can often occur considering gaseous samples. To avoid the manipulation of a stable isotope-labeled gas, we have chosen to generate in situ an internal labeled standard gas (¹³CO₂) on the basis of the stoichiometric formation of CO₂ by the reaction of hydrochloric acid (HCl) with sodium hydrogen carbonate (NaH¹³CO₃). This method allows a precise measurement of CO₂ concentration and was validated on various human postmortem gas samples in order to study its efficiency.     

In-House Absolute Calibration of Gamma-Emitting Radioactive Voluminous Samples: Detector Setups Using Natural Radionuclides

A method for the absolute calibrations of -rays spectrometers for voluminous samples using natural radionuclides is suggested. The method is based on relative calibration with a solution of ²³²Th salts and absolute calibration with K₂CO₃ or KCl.     

Determination of total carbon and total organic carbon from volatile air pollutants

Summary The method developed based on the determination of TC and TOC in the form of the total amount of CO₂ requires application of the proper techniques for the final determination of CO₂. The possibility of using a stream of carrier gas at a convenient flow-rate for desorbing quantitatively CO₂ concentrated on a molecular sieve permits use of a wide variety of known analytical techniques for the final determination of CO₂. Various methods were compared on the basis of both absolute and calibration measurements. The absolute methods chosen were gravimetric (classical or an automated version based on application of a gravimetric automat and automatic recording balance), thermogravimetric analysis and coulometry. The calibration methods included thermal conductivity, the flame-ionization detector (after conversion of CO₂ into methane) and infrared absorption. Usefulness of the methods was evaluated on the basis of comparative statistical analysis of experimental data with respect to precision (Snedecor'sF-test and Bartlett'sU ²-test) and accuracy (Student'st-test).

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Zusammenfassung Das entwickelte Verfahren zur Bestimmung des TC- und TOC-Gehaltes in Form der gesamten Menge CO₂ erfordert die Anwendung geeigneter Analysentechniken zur Endbestimmung dieser Verbindung. Die Möglichkeit einer Desorption des am Molekularsieb angereicherten CO₂ in einem Gasstrom mit geeignetem Durchfluß erlaubt zur Endbestimmung von CO₂ die Anwendung einer Reihe verschiedener Analysenverfahren. Die Anwendbarkeit verschiedener, auf Absolutverfahren und auch auf relativen Messungen beruhender Methoden wurde vergleichend untersucht. Die folgenden Methoden zur CO₂-Bestimmung wurden gewählt: die Gravimetrie (klassische oder automatisierte unter Einsatz eines Wägeautomaten und einer registrierenden Waage), die Thermogravimetrie und die Coulometrie. Von den relativen Methoden wurden die Thermokonduktometrie, der Flammenionisationsdetektor (nach Umsetzung von CO₂ zu Methan) und das IR-Absorptionsmeßverfahren geprüft. Die Anwendbarkeit der Methoden wurde mit Hilfe statistischer Prüfverfahren beurteilt, wobei die Präzision (SnedecorsF-Test und BartlettsU ²-Test) und die Genauigkeit (Studentst-Test) der erhaltenen Analysenwerte verglichen wurden.

     

Optical sensor for carbon dioxide combining colorimetric change of a pH indicator and a reference luminescent dye

A new optical CO₂ sensor based on the luminescence intensity change of the europium(III) complex tris(thenoyltrifluoroacetonato) europium(III) dihydrate ([Eu(tta)₃]) caused by the absorption change of various pH indicators—thymol blue, phenol red, or cresol red—with CO₂ was developed and its CO₂ sensing properties were investigated. For all the CO₂ sensors using pH indicators the observed luminescence intensity from [Eu(tta)₃] at 613 nm increased with increasing CO₂ concentration. The linear calibration method based on the plot of (I₁₀₀–I₀)/(I–I₀) versus the inverse of CO₂ concentration was suggested, where I₀ and I₁₀₀ were luminescence intensities at 613 nm of the CO₂ sensor film in 100% nitrogen and 100% gaseous CO₂. In all cases the plots showed good linearity and the correlation factors of the plots, r², were 0.991 for thymol blue, 0.990 for phenol red, and 0.998 for cresol red. The slopes of the plots (A/B) for thymol blue, phenol red, and cresol red were 2.2, 5.2, and 9.0%, respectively. The response times of the CO₂ sensor film were 4.0 s for thymol blue, 4.4 s for phenol red, and 8.8 s for cresol red for switching from nitrogen to CO₂, and the recovery times of films were 36 s for thymol blue, 39.2 s for phenol red, and 56.6 s for cresol red for switching from CO₂ to nitrogen. The signal changes were fully reversible and hysteresis was not observed during the measurements. The highly sensitive CO₂ sensor was developed using thymol blue as an indicator for the CO₂-sensing probe.     

The Electrocatalytic Oxidation of Thymine at α‐Cyclodextrin Incorporated Carbon Nanotube‐Coated Electrode

Electrocatalytic oxidation of thymine at α‐cyclodextrin (α‐CD) incorporated carbon nanotube‐coated electrode (CNT/CE) was thoroughly studied in alkaline media. CNT showed an electrocatalytic effect on the oxidation of thymine, formation of a supramolecular inclusion complex between α‐CD and thymine at CNT/CE further enhanced the sensitivity to thymine. The electrocatalytic behavior was further developed as a sensitive detection scheme for thymine by differential pulse voltammetry. A linear calibration over the concentration range from 2.5×10^?5 to 1.8×10^?3 mol/L in pH 10.8 NaHCO₃‐Na₂CO₃ buffer solution was obtained with a detection limit of 5×10^?6 mol/L.     

Four-component reciprocal system Na,K∥F,CO<Subscript>3</Subscript>, WO<Subscript>4</Subscript>

The four-component reciprocal system Na,K∥F, CO₃, WO₄ has been studied using differential thermal analysis in combination with projective and differential geometry. The a priori prediction of the crystallization path (CP) shows six quaternary invariant points; of them, three are eutectics and the others are peritectics. The dominant exchange and complexing reactions have been recognized. The following four-component systems have been studied: (NaF)₂-(KF)₂-K₂CO₃-K₃FWO₄ (1), (NaF)₂-K₂CO₃-K₂WO₄-K₃FWO₄ (2), (NaF)₂-Na₂CO₃-Na₂WO₄-K₂WO₄ (3),, and (NaF)₂-Na₂CO₃-K₂CO₃-K₂WO₄ (4); the coordinates of all quaternary invariant points have been determined.