Volume Of Liquid Sample Research Articles

Tolerance analysis of a micro-optical detection system for on-line monitoring of lubricant oils

We present a functional prototype of a micro-optical detection unit for both absorbance and laser-induced fluorescence analysis in fused silica capillaries. Absorbance detection allows concentration measurements ranging from 0.6 µM to 12 mM, whereas fluorescence detection enables concentration measurements from 6 pM up to 0.6 mM. We make use of non-sequential optical ray tracing simulations combined with statistical design methodology to perform a complete tolerance analysis for manufacturability and we demonstrate experimentally that the efficiency of the system is insensitive to reasonable misalignment and fabrication errors of its building blocks. The possibility of using standard fabrication techniques to prototype and replicate this miniaturized plastic detection system, as well as its wide measurement range make it a good candidate for applications where low-cost and portable systems are needed to measure small volumes of liquid samples with low-level concentrations. As an example we demonstrate the use of the system for the optical characterization and differentiation of nanoliter volumes of lubricant oils.

Three‐dimensional femtosecond laser micromachining of photosensitive glass for biomicrochips

AbstractInternal modification of transparent materials such as glass can be carried out using multiphoton absorption induced by a femtosecond (fs) laser. The fs‐laser modification followed by thermal treatment and successive chemical wet etching in a hydrofluoric (HF) acid solution forms three‐dimensional (3D) hollow microstructures embedded in photosensitive glass. This technique is a powerful method for directly fabricating 3D microfluidic structures inside a photosensitive glass microchip. We used fabricated microchips, referred to as a nanoaquarium, for dynamic observations of living microorganisms. In addition, the present technique can also be used to form microoptical components such as micromirrors and microlenses inside the photosensitive glass, since the fabricated structures have optically flat surfaces. The integration of microfluidics and microoptical components in a single glass chip yields biophotonic microchips, in other words, optofluidics, which provide high sensitivity in absorption and fluorescence measurements of small volumes of liquid samples.

The Role of Acidification for Antimicrobial Activity of Atmospheric Pressure Plasma in Liquids

AbstractWater disinfection by indirect plasma treatment was investigated using a surface dielectric barrier discharge (DBD). Liquid was neither part of the discharge electrode configuration nor stirred during plasma treatment. High concentrations (106–108 cfu·mL−1) of Escherichia coli and Staphylococcus aureus have been completely inactivated within 5–15 min, depending on liquid sample volume. Inactivation occurred in non‐buffered liquids, only, where pH decrease was found. Measurements of pH, nitrate, and nitrite concentrations after DBD plasma or NO gas treatment lead to the conclusion that nitric acid formation from plasma‐generated reactive nitrogen species are the main source of liquid acidification. Incubation of bacteria in nitric acid alone did not result in comparable inactivation effects. Increase of H2O2 concentration was found as a result of plasma treatment of liquids but not after treatment by NO gas. Therefore, synergistic action of both reactive oxygen and nitrogen species are discussed to be responsible for antimicrobial plasma effects.magnified image

Physical properties of the probe electrospray ionization (PESI) needle applied to the biological samples

Probe electrospray ionization (PESI) is a recently developed technique that uses a fine solid needle as a probe for sampling biological materials. In this study, we quantified the volume of liquid sample picked up by the solid needle with the tip diameter of approximately 700 nm and the apex angle of approximately 60 degrees. The amounts of low-viscosity samples (rat urine) loaded on the tip of the needle by a single stroke were 0.35 +/- 0.09 pl. Interestingly, the amount of liquid adhered to the tip did not significantly depend on the protein concentration, but viscosity and surface tension of the sample. Under these conditions, we successfully obtained mass spectra for each biological sample.

Heated-spray chamber-based low sample consumption system for inductively coupled plasma spectrometry

A systematic study about the effect of the heating of a modified version of the so-called Torch Integrated Sample Introduction System (TISIS) has been performed. The results showed that when working at liquid flow rates of 20–40 µl min−1, it was possible to raise the chamber wall temperature up to 100 °C without degradation of plasma thermal characteristics. Furthermore, a sheathing gas stream was added to the spray chamber so as to improve the aerosol transport towards the plasma. Under these conditions, sensitivity enhancements ranging from 8 to 15 with regard to those found under standard conditions (i.e., with neither chamber heating nor sheathing gas inlet) were reached for the different ionic and atomic emission lines studied. As a result, limits of detection at 20 µl min−1 were improved by a factor between 2.5 and 13. These LODs were only 1.7 to 2 times lower than for a cyclonic spray chamber at an uptake rate of 1 ml min−1. Two direct injection nebulizers were used for comparison: the conventional direct injection high efficiency nebulizer (DIHEN) and its demountable version (d-DIHEN). When TISIS was used under standard conditions quite similar results were found as those provided by d-DIHEN, although at low nebulizer gas flow rates (i.e., 0.1 l min−1), the DIHEN gave rise to higher sensitivities. However, by heating the TISIS chamber at 100 °C, sensitivities were enhanced by a factor up to one order of magnitude with respect to both the DIHEN and d-DIHEN. The result was ascribed both to the production of a finer tertiary aerosol and to the improved plasma excitation conditions. Furthermore, lower limits of detection were encountered for the hot chamber as compared to direct injection nebulizers. Hence, the developed system could be considered to be very promising for the analysis of very low liquid sample volumes through ICP techniques.

A New Transient Two-Wire Method for Measuring the Thermal Diffusivity of Electrically Conducting and Highly Corrosive Liquids Using Small Samples

The transient hot-wire (THW) technique is widely used for measurements of the thermal conductivity of most fluids, and some attempts have also been carried out for simultaneous measurements of the thermal diffusivity with the same hot wire. However, for some particular liquids like concentrated nitric acid solutions or similar nitric mixtures, for which the thermal properties are important for industrial or security applications, this technique may be difficult to use, because of possible technological incompatibilities between measurement probe materials and highly electrically conducting and corrosive liquids. Moreover, the possible highly energetic (explosive) character of these liquids requires minimum volume liquid samples and safety measurement devices and processes. It is the purpose of this paper to report on a modified THW technique (previously used for thermal-diffusivity measurements in soils), which is associated with a specific patented double-wire probe and is shown to be valid for direct thermal-diffusivity measurements in liquids. This method responds to the previous requirements and allows automatic and quasi-simultaneous thermal-conductivity and thermal-diffusivity measurements to be made safely on liquids compatible with the tantalum technology, with liquid sample volumes < 2 cm3. Low uncertainties are found for the thermal-diffusivity data when relative measurements are carried out with reference liquids like water or toluene.

A MEMS Thermal Biosensor for Metabolic Monitoring Applications

This paper presents a microelectromechanical systems (MEMS) differential thermal biosensor integrated with microfluidics for metabolite measurements in either flow-injection or flow-through mode. The MEMS device consists of two identical freestanding polymer diaphragms, resistive heaters, and a thermopile between the diaphragms. Integrated with polymer-based microfluidic measurement chambers, the device allows sensitive measurement of small volumes of liquid samples. Enzymes specific to a metabolic analyte system are immobilized on microbeads packed in the chambers. When a sample solution containing the analyte is introduced to the device, the heat released from the enzymatic reactions of the analyte is detected by the thermopile. The device has been tested with glucose solutions at physiologically relevant concentrations. In flow-injection mode, the device demonstrates a sensitivity of approximately 2.1 muV/mM and a resolution of about 0.025 mM. In flow-through mode with a perfusion flow rate of 0.5 mL/h, the sensitivity and resolution of the device are determined to be approximately 0.24 muV/mM and 0.4 mM, respectively. These results illustrate that the device, when integrated with subcutaneous sampling methods, can potentially allow for continuous monitoring of glucose and other metabolites.

Combined photolysis and catalytic ozonation of dimethyl phthalate in a high-gravity rotating packed bed

In this study, a high-gravity rotating packed bed (HGRPB) was used as a catalytic ozonation reactor to decompose dimethyl phthalate (DMP), an endocrine disrupting chemical commonly encountered. The HGRPB is an effective gas–liquid mixing equipment which can enhance the ozone mass transfer coefficient. Platinum-containing catalyst (Pt/-Al 2O 3) of Dash 220N and ultra violet (UV) lamp were combined in the high-gravity ozonation (HG-OZ) system to enhance the self-decomposition of molecular ozone in liquid to form highly reactive radical species. Different combinations of HG-OZ with Dash 220N and UV for the degradation of DMP were tested. These include HG-OZ, HG catalytic OZ (HG-Pt-OZ), HG photolysis OZ (HG-UV-OZ) and HG-UV-Pt-OZ. The result indicated that all the above four ozonation processes result in significant decomposition of DMP and mineralization of total organic carbon (TOC) at the applied ozone dosage per volume of liquid sample of 1.2 g L −1. The UV and Pt/γ-Al 2O 3 combined in HG-OZ can enhance the TOC mineralization efficiency ( η TOC) to 56% (via HG-UV-OZ) and 57% (via HG-Pt-OZ), respectively, while only 45% with ozone only. The process of HG-UV-Pt-OZ offers the highest η TOC of about 68%.

A New Transient Hot-Wire Instrument for Measuring the Thermal Conductivity of Electrically Conducting and Highly Corrosive Liquids using Small Samples

The transient hot-wire technique is widely used for measurements of the thermal conductivity of most fluids. However, for some particular liquids such as concentrated nitric acid solutions or similar nitric mixtures, for which the thermal properties are important for industrial or security applications, this technique can be difficult to use, which is essentially due to incompatibility between measurement probe materials and highly electrically conducting and corrosive liquids. Moreover, the possible highly energetic (explosive) character of these liquids requires minimum volume liquid samples, and safety measurement devices and processes. It is the purpose of this paper to report on a new patented instrument, based on tantalum short-hot-wire probe technology, which responds to the above requirements and allows safe automated thermal-conductivity measurements of concentrated acid nitric solutions and similar nitric mixtures for liquid samples less than 2 cm3, with uncertainties better than 5%.

Adsorption and elution characteristics of nucleic acids on silica surfaces and their use in designing a miniaturized purification unit

We report nucleic acid (NA) adsorption isotherms and elution profiles for silica surfaces and use these to design a miniaturized NA purification unit based on solid-phase extraction with silica beads. The procedure is based on a pressure drop equation for flow through a packed bed and allows estimation of key design parameters such as channel dimensions, liquid flow rates, sample volume, and amount of silica needed. The usefulness of this design procedure is demonstrated by applying it to a column-based NA purification device for influenza detection for a case study of Madin–Darby canine kidney cells infected with influenza A virus.

Sensitive determination of free benzophenone-3 in human urine samples based on an ionic liquid as extractant phase in single-drop microextraction prior to liquid chromatography analysis

Benzophenone-3 (BZ3), one of the compounds most commonly used as UV filter in cosmetic products, can be absorbed through the skin into the human body, since it can be found at trace levels in urine from users of cosmetic products that contain BZ3. Moreover, different undesirable effects have been attributed to this compound. Thus, sensitive analytical methods to monitor urinary excretion of this compound should be developed. This paper presents a selective and sensitive methodology for BZ3 determination at ultratrace levels in human urine samples. The methodology is based on a novel microextraction technique, known as single-drop microextraction (SDME). An ionic liquid (IL) has been used as extractant phase instead of an organic solvent. After the microextraction process, the extractant phase was injected into a liquid chromatography system. The variables of interest in the SDME process were optimized using a multivariate optimization approach. A Plackett–Burman design for screening and a circumscribed central composite design for optimizing the significant variables were applied. Ionic strength, extraction time, stirring speed, pH, ionic liquid type, drop volume and sample volume were the variables studied. The optimum experimental conditions found were: sodium chloride concentration, 13% (w/v); extraction time, 25 min; stirring speed, 900 rpm; pH, 2; ionic liquid type, 1-hexyl-3-methylimidazolium hexafluorophosphate ([C 6MIM][PF 6]); drop volume, 5 μL; and sample volume, 10 mL. The proposed method requires a standard addition calibration approach, and it has been successfully employed to determine free BZ3 in urine samples coming from human volunteers who applied a sunscreen cosmetic containing this UV filter. The limit of detection was in the order of 1.3 ng mL −1 and repeatability of the method, expressed as relative standard deviation, was 6% ( n = 8).

Fiber-optic ring-down spectroscopy using a tunable picosecond gain-switched diode laser

Visible and near-infrared laser light pulses were coupled into two different types of optical fiber cavities. One cavity consisted of a short strand of fiber waveguide that contained two identical fiber Bragg gratings. Another cavity was made using a loop of optical fiber. In either cavity ∼40 ps laser pulses, which were generated using a custom-built gain-switched diode laser, circulated for a large number of round trips. The optical loss of either cavity was determined from the ring-down times. Cavity ring-down spectroscopy was performed on 200 pL volumes of liquid samples that were injected into the cavities using a 100 μm gap in the fiber loop. A detection limit of 20 ppm of methylene blue dye in aqueous solution, corresponding to a minimum absorptivity of εC<6 cm-1, was realized.

Improved methods for fMRI studies of combined taste and aroma stimuli

Previous neuroimaging studies of the cortical representation of gustatory and olfactory stimuli have often delivered tastants to the mouth in very small quantities or stimulated olfaction orthonasally. In studies of retro-nasal olfaction, swallowing was generally delayed to reduce head motion artefacts. The present fMRI study aims to improve upon such methodological limitations to allow investigation of the cortical representation of flavour (taste and aroma combination) as it typically occurs during the consumption of liquid foods. For this purpose we used (1) a novel, automated, sprayed stimulus delivery system and a larger volume of liquid sample (containing sweet tastants and banana/pear aroma volatiles) to achieve more extensive stimulation of the oral cavity taste receptors, (2) a pseudo-natural delivery paradigm that included prompt swallowing after each sample delivery to obtain physiological retro-nasal olfactory stimulation, (3) fMRI acquisition with wide brain coverage and double-echo EPI to improve sensitivity. We validated our paradigm for the delivery of volatiles using atmospheric pressure chemical ionisation mass spectrometry. This showed that the main retro-nasal delivery of volatiles in the paradigm occurs immediately after the swallow. Several brain areas were found to be activated, including the insula, frontal operculum, rolandic operculum/parietal lobe, piriform, dorsolateral prefrontal cortex, anterior cingulate cortex, ventro-medial thalamus, hippocampus and medial orbitofrontal cortex.

Vapor−Liquid−Liquid Equilibria of Pentafluoroethane and Ionic Liquid [bmim][PF6] Mixtures Studied with the Volumetric Method

In this article, we investigate vapor-liquid-liquid equilibria (VLLE) of binary systems using a simple volumetric method. Being different from the usual cloud-point method for the determination of liquid-liquid separation boundaries, the present volumetric method is able to determine the direct VLLE properties, such as equilibrium compositions, as well as molar volumes of the two liquid phases, by measuring only weights and volumes of liquid samples. The theory behind this method is described, and detailed error analyses for our simple apparatus are discussed by using well-established systems in the literature: water + 2-butanol and 1-butanol + 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]). Then, results for mixtures of [bmim][PF(6)] and pentafluoroethane (R-125) are provided, as well as those of the test systems above. As predicted in our earlier work, this binary system shows liquid-liquid separations in the R-125-rich side solutions with a lower critical solution temperature. In addition, we have found very large negative excess molar volumes in this system.

Elemental analysis of liquid microsamples through inductively coupled plasma spectrochemistry

The elemental analysis of very low liquid sample volumes through plasma spectrometry (i.e. inductively coupled plasma atomic spectrometry (ICP-AES) and ICP mass spectrometry (ICP-MS)) is a challenging research subject because, in many fields, the sample volume is the limiting factor for the analysis. The system for introducing liquid samples has been modified in order to perform this kind of analysis and different choices have appeared. Two general solutions are reviewed: (i) the continuous introduction of the solution into the plasma as an aerosol; and, (ii) the discrete introduction of the sample into the system. Included in the first group are several nebulizers, spray chambers and desolvation systems that have been developed to work at low liquid-flow rates (i.e. below 100 μl/min). The second group includes electrothermal vaporization (ETV) of a low sample volume and its further transport to the plasma. We review these systems and discuss the analytical problems associated with each.

Influence of the spray chamber design for vapor-based liquid sample introduction at room temperature in ICP-AES

This paper describes a new concept for the introduction of very low liquid sample volumes in ICP-AES. Three single pass low inner volume spray chambers have been designed and characterized: two cylindrical ones of different inner volumes, 4 and 8 cm3, and a spherical type one, with 11 cm3. In every case a high efficiency nebulizer (HEN) has been used to generate the aerosol, and comparison with a conventional cyclonic spray chamber has been performed. The chambers were designed to enhance solvent evaporation within the spray chamber at liquid flow rates below 100 µl min−1, and to obtain a simple aerosol path. The aim was to combine the advantages of a spray chamber and those of a so-called direct injection nebulizer (DIN). The best analytical results, viz., repeatability, signal-to-background ratio and limits of detection, were obtained with the 8 cm3 single pass chamber. Results were usually improved when compared with the conventional cyclonic spray chamber. It has also been found that the interferences due to organic solvents (ethanol, formic and acetic acid), aqueous solutions and mixtures thereof (water–ethanol solutions) were less severe for the single pass spray chamber than for the cyclonic one.

Use of Ar–He mixed gas plasmas for furnace atomisation plasma ionisation mass spectrometry (FAPIMS)

The effect of Ar–He mixed gas plasmas on analyte signal intensities generated in a furnace atomization plasma ionization mass spectrometry (FAPIMS) source is presented. Analyte is introduced as a volatile headspace gas effluent (I2(g) and Hg(g)) and in discrete liquid sample volumes (Fe, Rb, Pd, In, Cs, Yb, Pt, Pb and Bi). The presence of as little as 2–10% (v/v) Ar increases the signal intensity of analytes having first ionization potentials greater than 6 eV by up to 10-fold. This may be attributed to the formation of more energetic plasmas whose electron density, ionization temperature and gas kinetic temperatures increase with Ar content. Consistent with this, elements with the highest ionization potentials showed the greatest enhancements. Analytes with ionization potentials of less than 6 eV, which are already presumed 100% ionized, are unaffected. Further increases in Ar content (50–100% v/v) can lead to plasma instability and accelerated erosion of graphite surfaces within the source. Most of the analytes studied showed slight improvements in the limits of detection for plasmas containing ≈5% v/v Ar; the increased signal intensity was accompanied by little or no increase in the background signal. Although Ar can significantly affect conditions within the source, the composition of the Ar–He mixture can also influence the transmission of analyte into the free jet expansion and to the MS detector. The appearance and intensity of Ar-based spectral interferences, such as ArC+, ArO+ and Ar2+, increase with Ar content and source temperature, degrading the determination of species such as 52Cr+, 56Fe+ and 80Se+. The amount of Ar required to generate significant signal enhancements is small (<10% v/v) and therefore does not significantly ease the pumping requirements on the interface.

Semiquantitative bioluminescent assay of glutathione.

A novel technique has been developed for semiquantitative detection of glutathione (GSH) in small volumes of liquid samples. GSH is detected via enzymatic linkage to the NADP/NADPH + H+ redox system through glutathione reductase. Accumulated NADPH is measured via the bioluminescent FMN oxidoreductase bacterial luciferase reaction. A linear correlation is obtained between bioluminescence intensity of the luciferase reaction and the GSH content of the liquid sample. Possible applications of this procedure are discussed.

Simple and versatile injection system for capillary gas chromatographic columns Performance evaluation of a system including mass spectrometric and light-pipe Fourier-transform infrared detection

Abstract A cryogenic concentrator, a pre-trap, and ancillary systems were developed to facilitate the introduction of large volumes of either gaseous or liquid samples to a capillary GC column. This large-volume injection system, referred to as LVIS, is used in conjunction with the conventional split/splitless injector of a gas Chromatograph. The performance of the split/splitless injector is essentially unchanged by the installation of the cryogenic concentrator; thus, the gas Chromatograph can be operated as usual. Reproducibility, accuracy, and inertness were demonstrated while performing injections of a hydrocarbon mixture (n-C7–C22) and the Grob-programmed test mixture. Liquid samples, up to 100 μl, were conveniently handled by the system. Applicability to gas-phase analyses was demonstrated by sampling perfume components in the headspace of a granular detergent and by sampling pyrolysis products of Kraton 1107. When the LVIS was used with a gas Chromatograph equipped with mass-selective (MSD) and light-pipe Fourier-transform infrared (FT-IR) [IRD] spectrometers, it was possible to achieve identification limits by IRD approaching 1 ppb v/v when analyzing one liter of headspace, and ca. 100 ppb when analyzing 100 μl of a liquid sample. Identification limits with the MSD were lower.

A simple large volume injection system with a solid-phase sample loop for packed column supercritical fluid chromatography

The design and use of an easy-to-build large-volume injection system for packed column supercritical fluid chromatography (SFC) are reported. Two 6-port injection valves are used. After introduction of a liquid sample via the sample loop of one of the valves, nitrogen is used to transport the sample to a solid-phase extraction disk which is placed in a pressure tight fitting. The sample solvent evaporates into the nitrogen stream leaving the analytes on the solid-phase material. After a certain evaporation time the mobile phase of the SFC is directed to the solid phase, introducing the solvent-free sample into the SFC. It is possible to introduce liquid sample volumes of PAH- and PCB-solutions of up to 100 μl without loss of chromatographic resolution. The relative standard deviations of peak areas are in the range of 4–9%.