Capillary Probe Research Articles

Scanning mass spectrometer for quantitative reaction studies on catalytically active microstructures

We describe an apparatus for spatially resolving scanning mass spectrometry which is able to measure the gas composition above catalytically active microstructures or arrays of these microstructures with a lateral resolution of better than 100 mum under reaction conditions and which allows us to quantitatively determine reaction rates on individual microstructures. Measurements of the three-dimensional gas composition at different vertical distances and separations between active structures allow the evaluation of gas phase mass transport effects. The system is based on a piezoelectrically driven positioning substage for controlled lateral and vertical positioning of the sample under a rigidly mounted capillary probe connecting to a mass spectrometer. Measurements can be performed at pressures in the range of <10(-2)-10 mbars and temperatures between room temperature and 450 degrees C. The performance of the setup is demonstrated using the CO oxidation reaction on Pt microstructures on Si with sizes between 100 and 300 mum and distances in the same order of magnitude, evaluating CO(2) formation and CO consumption above the microstructures. The rapidly decaying lateral resolution with increasing distance between sample and probe underlines the effects of (lateral) gas transport in the room between sample and probe. The reaction rates and apparent activation energy obtained from such measurements agree with previous data on extended surfaces, demonstrating the feasibility of determining absolute reaction rates on individual microstructures.

Acuminatanol, the first 2′,2‴-bis-dihydrobiflavonol from the aqueous extract of Trichoscypha acuminata

One new 3′,4′,5′,5,7-pentahydroxy-2′,2‴-bis-dihydrobiflavonol, acuminatanol (1), was obtained from the aqueous extract of Trichoscypha acuminata. The structure elucidation process was performed primarily utilizing a capillary scale NMR probe. Acuminatanol (1) is the first example of a bis-dihydroflavonol linked exclusively via the B-rings at C-2′ and C-2‴ positions. To date, it is the first naturally-occurring compound reported from the genus Trichoscypha, and the first new natural product published from our compound libraries generated from the aqueous extracts of American and African plants.

Isoflavones from Psorothamnus arborescens via high-throughput Natural Product Chemistry Methods

One new isoflavone, arborestin (2), together with the known fremontin (1), were obtained from Psorothamnus arborescens via high-throughput natural product chemistry methods. The isoflavones were isolated and the structure elucidation was performed using a capillary scale NMR probe and HR-/LR-ESIMS data.

Identification of Natural Products Using HPLC-SPE Combined with CapNMR

Two major development areas in HPLC-NMR hyphenation are postcolumn solid-phase extraction (HPLC-SPE-NMR) and capillary separations with NMR detection by means of solenoidal microcoils (CapNMR). These two techniques were combined off-line into HPLC-SPE-CapNMR, which combines the advantage of high loadability of normal-bore HPLC columns with high mass sensitivity of capillary NMR probes with an active volume of 1.5 microL. The technique was used for rapid identification of complex sesquiterpene lactones and esterified phenylpropanoids present in an essentially crude plant extract (toluene fraction of an ethanolic extract of Thapsia garganica fruits). Elution profiles of 10 x 1 mm i.d. SPE cartridges filled with poly(divinylbenzene) resin were found to be only marginally broader than those observed upon direct injection of 6-microL samples into the probe. Thus, the technique focuses analytes emerging in the HPLC elution bands of 0.5-1 mL into volumes of approximately 10 microL, compatible with the CapNMR probe. Using this technique, nine natural products (1-9) present in the plant extract in amounts varying from 0.1 to 20% were identified by means of 1D and 2D NMR spectra, supported by parallel HPLC-ESIMS measurements. Therefore, HPLC-SPE-CapNMR should be regarded as an attractive alternative to other applications of CapNMR for mixture analysis.

Modelling local bubble size distributions in agitated vessels

Photography and capillary suction probe were used to measure local bubble size distributions (BSDs) from Rushton turbine agitated (14/200 L) air–tap water and CO 2 – n -butanol dispersions. A multiblock stirred tank model with population balances (PBs) for bubbles was created to describe local BSDs in agitated vessels. Unknown parameters in breakage and coalescence models were adjusted by comparing the predicted and measured local BSDs. The BSDs from both investigated systems and varying vessel-operating conditions were included simultaneously to the fitting. The adjusted models were incorporated to MUSIG PB model in CFX-5.7 and tested for the laboratory stirred tanks. The multiblock model showed to be an optimal trade-off between the accuracy and CPU time for the investigation of gas–liquid hydrodynamics and validation of closure models. As a result of fitting, the adjusted model seems to describe local BSDs more accurately in agitated vessels than the model of Lehr et al. [2002. Bubble-size distributions and flow fields in bubble columns. A.I.Ch.E. Journal 48, 2426–2443], which has been successful in bubble column studies. This shows that phenomenological breakage and coalescence closures need experimental validation for various flow environments.

In vivo detection of secreted proteins from wounded skin using capillary ultrafiltration probes and mass spectrometric proteomics

The identification of in vivo secreted proteins is a major challenge in systems biology. Here we report a novel technique using capillary ultrafiltration (CUF) probes to identify the secreted proteins involved in wound healing. CUF probes, which use semipermeable membrane hollow fibers to continuously capture secreted proteins, were used to sample skin wound fluids. To identify low-abundance proteins, we digested the CUF probe-collected wound fluid with trypsin and then directly subjected it to MS without using 2-DE separation. Two protein fragments with masses of 1565.7 and 1694.8 Da were identified by MS as peptides of thymosin beta10 and beta4, respectively. This is the first identification of thymosin beta10 as an in vivo constituent of the skin wound fluid. The LKKTETQ peptide, a common actin-binding domain of thymosin beta4 and beta10, significantly enhanced skin wound healing in vitro and in vivo. Our data suggest that the enhancement of wound healing by LKKTETQ may be mediated by purinergic receptors. The technique of using CUF probes linked to mass spectrometric proteomics represents a powerful method to identify in vivo secreted proteins, and may be applicable for identification of proteins relevant in various human diseases.

Measurements of local bubble size distributions from various flexible membrane diffusers

Perforated and flexible aeration diffusers are widely used in biological wastewater treatment plants. Comparing to other aeration techniques, they have certain benefits in price, durability and replaceability. Bubble size from a diffuser should be small enough to achieve large interfacial area between air and water, and therefore sufficient oxygen mass transfer. Air compressing is a significant part of the operational costs of a wastewater treatment plant. Thus, by optimising bubble size and flow conditions savings can be achieved. These optima can be reached by the development of the membrane construction and by the means of state-of-the-art multiphase flow modelling. For both purposes, local bubble size distribution data is valuable. In the literature, bubble size data measured inside the dense bubble dispersions are scarce. In this work, local bubble size distributions were measured for five industrial membrane diffusers. The variables were hole specific gas flow rate, membrane hole density and hole diameter. Two apparatuses were used: small rectangular vessel of height 0.6 m and rectangular bubble column of height 3.0 m. Axial and radial variation of bubble size distributions was investigated by a capillary suction probe (CSP) and by digital photography. Inside the dense bubble dispersion, where most of the measurement techniques are not applicable, CSP was found to be a successful technique. Bubble size variation was notable, both axially and radially. Increasing the gas flow rate increased the bubble size. Same effect was found when increasing the hole density. The effect of hole size variation was not observed that clearly with these membranes. Minimum in the bubble size was detected 19 cm above the flexible membrane. This indicates that the tailoring of the bubble size should be made according to situation there, not at the surface of the membrane.

A comparison of capillary‐scale LC–NMR with alternative techniques: spectroscopic and practical considerations

Experimental and practical details for the use of capillary LC (CapLC)-NMR are reported. The capillary NMR probe has high sensitivity and excellent flow characteristics and we found CapLC-NMR to be best suited to samples that are truly mass limited. CapLC-NMR relies on good capillary-scale chromatography where highly concentrated peaks with a volume closely matched to the NMR flow cell are achievable. Provided that the loading capacity of the capillary column is not limiting, the combination of high sensitivity and high solvent suppression quality makes CapLC-NMR an excellent choice. For many real samples, however, the loading is limiting and we found the combination of LC-SPE-MS-NMR with a cryoprobe enables more material to be purified for NMR analysis, while retaining sensitivity.

Validation of bubble breakage, coalescence and mass transfer models for gas–liquid dispersion in agitated vessel

Bubble breakage and coalescence phenomena and multicomponent gas–liquid mass transfer were studied in a 194dm3 Rushton turbine agitated vessel. Local bubble size distributions (BSD) were measured from air–tap water system at several agitation conditions with capillary suction probe (CSP) technique. The CSP was compared to the digital imaging (DI) and phase Doppler anemometry (PDA) techniques in a 14dm3 stirred vessel. The volumetric BSDs between the CSP and DI were in agreement, but number BSDs showed notable deviation. The limitations of measurement techniques seem to be the main reason.A multiblock stirred tank model with discretized population balances for bubbles and two-film Maxwell–Stefan multicomponent mass transfer between gas and liquid was created for the 194dm3 agitated vessel. The model considers local mass transfer conditions in the vessel and is simple enough for the mathematical optimization of unknown model parameters. Unknown parameters in the mechanistic bubble breakage and coalescence models were fitted against measured local BSDs. After this, a parameter in the liquid film mass transfer correlation was adjusted against absorption and desorption experiments of oxygen. Local gas–liquid mass transfer areas were calculated from the population balance model. The simulations with the validated models show good agreement against experiments. On the other hand, the fitted parameters deviate from the theoretical values, which emphasizes the need of model validation against accurate experiments. Due to their fundamental character and the validation process, the fitted models seem to be useful tools for the design and scale-up of agitated gas–liquid reactors.

Development of Ultrahigh-Throughput NMR Spectroscopic Analysis Utilizing Capillary Flow NMR Technology

An ultrahigh-throughput method for acquiring 1H NMR spectra is described. By constructing a continuous flow system utilizing an HPLC pump, autosampler, and a capillary flow NMR probe, it was possible to inject samples into the NMR spectrometer every 30 s using a continuous flow rate of 30 microL/min. 1H NMR spectroscopic data were acquired continuously into a pseudo-2D data file, with a 96-well-plate completed in <50 min. Spectra in continuous flow mode were readily obtained from approximately 3.4 mug (500 MHz), while the LOD was <850 ng. There was found to be little variation in either sample broadening within the flow system or signal intensities between multiple injections. This system offers several advantages over more conventional NMR spectroscopic analyses, notably the limited solvent required, high sensitivity, high speed, and improved spectral quality as a result of reduced spectral "dead" regions resulting from residual solvent levels.

High-Throughput Nanoliter Sample Introduction Microfluidic Chip-Based Flow Injection Analysis System with Gravity-Driven Flows

In this work, a simple, robust, and automated microfluidic chip-based FIA system with gravity-driven flows and liquid-core waveguide (LCW) spectrometric detection was developed. The high-throughput sample introduction system was composed of a capillary sampling probe and an array of horizontally positioned microsample vials with a slot fabricated on the bottom of each vial. FI sample loading and injection were performed by linearly moving the array of vials filled alternately with 50-microL samples and carrier, allowing the probe inlet to enter the solutions in the vials through the slots sequentially and the sample and carrier solution to be introduced into the chip driven by gravity. The performance of the system was demonstrated using the complexation of o-phenanthroline with Fe(II) as a model reaction. A 20-mm-long Teflon AF 2400 capillary (50-microm i.d., 375-microm o.d.) was connected to the chip to function as a LCW detection flow cell with a cell volume of 40 nL and effective path length of 1.7 cm. Linear absorbance response was obtained in the range of 1.0-100 microM Fe(II) (r2=0.9967), and a good reproducibility of 0.6% RSD (n=18) was achieved. The sensitivity was comparable with that obtained using conventional FIA systems, which typically consume 10,000-fold more sample. The highest sampling throughput of 1000 h-1 was obtained by using injection times of 0.08 and 3.4 s for sample and carrier solution, respectively, with a sample consumption of only 0.6 nL for each cycle.

Local bubble size distributions in agitated vessels

Local bubble size distributions (BSD) were measured from 12, 14 and 194 dm3 agitated vessels with capillary suction probe (CSP) technique. The four investigated systems were air–water, air–aqueous NaCl, air–aqueous starch and CO2–n-butanol. Several gassing rates and stirring speeds were investigated to find their effect on local BSDs. The reproducibility tests and the comparison against photography showed that Sauter mean bubble sizes and volumetric BSDs can be measured accurately from the air–water system with the capillary probe. In the CO2–n-butanol experiments the variation of BSDs with the agitation conditions was reasonable, although the majority of bubbles was likely smaller than the capillary diameter. In the air–water system, bubble size varied more in the Rushton turbine than in the flat-blade turbine (FBT) agitated vessel because of differences in flow fields. The addition of a small amount of NaCl caused a sharp decrease of bubble size in the vicinity of liquid surface. In the impeller discharge flow, bubble size decreased less. The lower coalescence rates due to higher apparent viscosity likely explain the smaller bubbles in the air–aqueous starch system than in the air–water system. In the CO2–n-butanol system, bubbles were notably smaller compared to other systems and the bubble size decreased unexpectedly in the flow from the impeller discharge to the liquid surface. The measured local BSDs are useful for the validation of population balance models that are, as connected to a computational fluid dynamic code, useful tools for the simulation of local mass transfer areas in agitated gas–liquid reactors.

Local Bubble Size Distributions in Agitated Vessel: Comparison of Three Experimental Techniques

Local bubble size distributions (BSD) were measured at multiple locations and agitation conditions in a Rushton turbine agitated 14 dm3 vessel. Experiments were made with air–deionized water and CO2–n-butanol systems. Three commonly used measurement techniques, capillary suction probe (CSP), phase Doppler anemometry (PDA) and digital imaging (DI), were tested, allowing critical evaluation of measurement techniques. All techniques revealed qualitatively reasonable variation of BSDs with the measurement point and agitation conditions. The quantitative comparison of techniques, instead, revealed a notable deviation. The main reason was related to the limited detectable bubble size range of each technique. The DI detected 0.1–8.0 mm bubbles, PDA 0.005–1.4 mm bubbles and CSP 0.4–8.0 mm bubbles. The sampling errors in the CSP, the identification errors of bubbles from the images in the DI and the optical distortions in the PDA were other reasons for the deviations. It appeared that the shape of number BSDs and arithmetic mean bubble sizes were captured better with the PDA than with DI or CSP. The DI and CSP techniques instead detected the volumetric BSDs and Sauter mean bubble sizes better than PDA. The comparison indicates that the limitations of measurement techniques are a major reason for the spread between bubble size studies for stirred tanks.

An automated electrokinetic continuous sample introduction system for microfluidic chip-based capillary electrophoresis

An automated and continuous sample introduction system for microfluidic chip-based capillary electrophoresis (CE) was developed in this work. An efficient world-to-chip interface for chip-based CE separation was produced by horizontally connecting a Z-shaped fused silica capillary sampling probe to the sample loading channel of a crossed-channel chip. The sample presentation system was composed of an array of bottom-slotted sample vials filled alternately with samples and working electrolyte, horizontally positioned on a programmable linearly moving platform. On moving the array from one vial to the next, and scanning the probe, which was fixed with a platinum electrode on its tip, through the slots of the vials, a series of samples, each followed by a flow of working electrolyte was continuously introduced electrokinetically from the off-chip vials into the sample loading channel of the chip. The performance of the system was demonstrated in the separation and determination of FITC-labeled arginine and phenylalanine with LIF detection, by continuously introducing a train of different samples. Employing 4.5 kV sampling voltage (1000 V cm(-1) field strength) for 30 s and 1.8 kV separation voltage (400 V cm(-1) field strength) for 70 s, throughputs of 36 h(-1) were achieved with <1.0% carryover and 4.6, 3.2 and 4.0% RSD for arginine, FITC and phenylalanine, respectively (n = 11). Net sample consumption was only 240 nL for each sample.

Numerical and experimental investigations on supersonic ejectors

Supersonic ejectors are widely used in a range of applications such as aerospace, propulsion and refrigeration. The primary interest of this study is to set up a reliable hydrodynamics model of a supersonic ejector, which may be extended to refrigeration applications. The first part of this work evaluated the performance of six well-known turbulence models for the study of supersonic ejectors. The validation concentrated on the shock location, shock strength and the average pressure recovery prediction. Axial pressure measurements with a capillary probe performed previously [Int. J. Turbo Jet Engines 19 (2002) 71; Conference Proc., 10th Int. Symp. Flow Visuzlization, Kyoto, Japan, 2002], were compared with numerical simulations while laser tomography pictures were used to evaluate the non-mixing length. The capillary probe has been included in the numerical model and the non-mixing length has been numerically evaluated by including an additional transport equation for a passive scalar, which acted as an ideal colorant in the flow. At this point, the results show that the k–omega–sst model agrees best with experiments. In the second part, the tested model was used to reproduce the different operation modes of a supersonic ejector, ranging from on-design point to off-design. In this respect, CFD turned out to be an efficient diagnosis tool of ejector analysis (mixing, flow separation), for design, and performance optimization (optimum entrainment and recompression ratios).

Variation of bubble size distribution in a protein foam fractionation column measured using a capillary probe with photoelectric sensors

Bubble size is used to characterize not only bubble-specific interfacial area but also bubble coalescence in a foam column. The bubble size distributions were obtained in a continuous foam fractionation process for concentrating ovalbumin using a developed photoelectric probe. When the continuous process reached steady state, the bubble size distribution pattern remained stable. Bubble size distribution data above (+1 cm) or below (−1 cm) the bulk liquid–foam interface showed symmetry along the diameter of the column (14 cm ID). The bubble size distribution was affected by the column wall. The nearly constant protein concentration distribution across the column cross-section indicated that the bubble flow distribution approached a flat profile across the column. A log-normal bubble distribution pattern best fit the weighted range of bubbles in the column at column lengths above and below the liquid–foam interface. These observations may prove to be useful in understanding the mechanisms underlying the foam fractionation of proteins.

Measurement of the Adsorption of Drug Ions at Model Membranes by Scanning Electrochemical Microscopy

We present quantitative measurements of the adsorption of drug ions at Langmuir monolayers, which are considered as a model for biological membranes. The technique we have employed is based on scanning electrochemical microscopy using a capillary probe filled with organic electrolyte solution and operated in an inverted submarine arrangement in a Langmuir trough. In this experimental arrangement, we have made potential step chronoamperometric measurements, with the probe adjacent to the Langmuir monolayer deposited at the air/water interface, to extract information on the adsorption process. We have measured the adsorption of a cationic β-blocker drug, propranolol, at a Langmuir monolayer of stearic acid. By developing a theoretical simulation that assumes that the equilibrium at the interface is controlled by the competition between the acid/base equilibrium of the stearic acid molecules at the surface and the electrostatically induced adsorption of the positively charged propranolol ion, we have been able to extract from our data a drug adsorption constant of (5 ± 1) × 10-5 mol dm-3 at the monolayer surface pressure of 10 mN m-1.

The effect of capillary ultrafiltration probes on skin flap edema.

Edema clearly has deleterious effects on the microcirculation and, consequently, cell viability. Prior work from this laboratory demonstrated that hyperosmolar microdialysis can reduce tissue edema, but this method is technically challenging. A new, simpler technique of microdialysis using capillary ultrafiltration probes (CUPs) has been studied to determine if CUP microdialysis is as effective in reducing tissue edema in the same animal model. Twenty-four Sprague-Dawley rats were studied using a modified McFarlane skin flap. Microdialysis was accomplished using a catheter constructed of four 4-cm hollow fibers that were connected to polyethylene tubing. Catheters on the experimental side of the flap were attached to a vacuum manifold for 8 hours. The control side was treated in 2 ways. In group 1, catheters were placed but not applied to suction. In group 2, no catheters are placed on the control side. Tissue water content was determined by a biopsy-drying technique. Tissue water content was significantly reduced (by paired t test) in both groups by a mean of 3.2 mL/100 g of wet tissue. CUP microdialysis reduced tissue water content as effectively as did hyperosmolar microdialysis, but in a simpler and therefore more cost-effective method. The technique could be easily adapted for clinical application.

Effect of pH on the Startup of a Continuous Foam Fractionation Process Containing Ovalbumin

The effect of pH on the bubble size distribution, void fraction, and enrichment ratio of a continuous foam fractionation column containing ovalbumin was investigated. The bubble size and void fraction were measured using a photoelectric capillary probe for different solution pHs (3.5, 4.5, 6.5, and 9.7). The bubble diameters for pH 3.5 and 4.5 were the largest of the four pHs studied. At these two pHs, the foam was less stable and formed aggregates, leading to lower enrichment and mass recovery. For the nearly neutral pH 6.5 or the more basic pH 9.7, the bubble size was smaller and the foam was more stable, resulting in both high enrichment and high mass recovery. The void fraction was smallest for pH 6.5, but the effect of pH on void fraction was not significant. In the lower foam phase, the calculated specific area increased as the pH increased from 3.5 to 9.7, which may partially contribute to the higher enrichments at pH 6.5 and 9.7.

High-resolution capillary tube NMR. A miniaturized 5-microL high-sensitivity TXI probe for mass-limited samples, off-line LC NMR, and HT NMR.

A new triple-resonance (TXI) (1H, 13C, 15N) high-resolution nuclear magnetic resonance (NMR) capillary probe with 2.5-microL NMR-active sample volume (V(obs)) was built and tested for applications with mass- and volume-limited samples and for coupling of microbore liquid chromatography to NMR. This is the first microliter probe with optimized coil geometry for use with individual capillary tubes with an outer diameter of 1 mm. The 90 degree pulse lengths of the 1-mm microliter probe were below 2 micros for proton, below 8 micros for carbon, and below 20 micros for nitrogen, and a spectral line width at signal half-height below 1 Hz was obtained. Compared to a conventional 5-mm probe, the new 600-MHz 1-mm TXI microliter probe with z-gradient shows an increase in mass sensitivity by a factor of 5, corresponding to a 25-fold reduction in measuring time. The consumption of costly deuterated solvent is reduced by at least 2 orders of magnitude. The 1-mm TXI microliter probe with z-gradient allows the measurement of one-dimensional 1H NMR and two-dimensional heteronuclear NMR spectra with a few nanomoles (micrograms) of compound with high sensitivity, speed, and quality. This is a breakthrough for discrete sample NMR spectroscopy with paramount importance for structure elucidation in natural compound chemistry and metabolic research. It offers also advantages for linking chromatographic methods to NMR in a nindustrial environment. Capillary tube NMR may find new applications in areas where high sample throughput is essential, e.g., in the quality control of large sample arrays from parallel chemistry, screening, and compound depositories. It has the potential to increase the sample throughput by 1 order of magnitude or more if new hardware for fast sample handling and exchange becomes available.