Analysis Of Liquid Samples Research Articles

Sub-nL thin-film differential scanning calorimetry chip for rapid thermal analysis of liquid samples.

Differential scanning calorimetry (DSC) is a popular thermal analysis technique. The miniaturization of DSC on chip as thin-film DSC (tfDSC) has been pioneered for the analysis of ultrathin polymer films at temperature scan rates and sensitivities far superior to those attainable with DSC instruments. The adoption of tfDSC chips for the analysis of liquid samples is, however, confronted with various issues including sample evaporation due to the lack of sealed enclosures. Although the subsequent integration of enclosures has been demonstrated in various designs, rarely did those designs exceed the scan rates of DSC instruments mainly because of their bulky features and requirement for exterior heating. Here, we present a tfDSC chip featuring sub-nL thin-film enclosures integrated with resistance temperature detectors (RTDs) and heaters. The chip attains an unprecedented sensitivity of 11 V W-1 and a rapid time constant of 600 ms owing to its low-addenda design and residual heat conduction (∼6 μW K-1). We present results on the phase transition of common liquid crystals which we leverage to calibrate the RTDs and characterize the thermal lag with scan rates up to 900 °C min-1. We then present results on the heat denaturation of lysozyme at various pH values, concentrations, and scan rates. The chip can provide excess heat capacity peaks and enthalpy change steps without much alteration induced by the thermal lag at elevated scan rates up to 100 °C min-1, which is an order of magnitude faster than those of many chip counterparts.

Laser induced breakdown spectroscopy: A robust technique for the detection of trace metals in water

Modernization and industrialization have resulted in the addition of significant micropollutants in the form of trace metals in the environment. Large amounts of wastewater containing traces of various metals are generated due to industrial output and pesticide usage, which can pollute surface as well as groundwater. Many metallic components, especially the heavy metal ones, are abundant, poisonous, difficult to degrade, and even their low concentrations can be toxic to natural health. Hence, it is essential to detect and remove these hazardous species in order to prevent water pollution. Traditional methods for detecting these metals in water such as inductively coupled plasma-optical emission spectroscopy (ICP-OES), atomic absorption spectroscopy (AAS), and inductively coupled plasma mass spectrometry (ICP-MS) are expensive, tedious, and these methods even cause secondary pollution. In contrast, Laser-induced breakdown spectroscopy (LIBS) is a quick and simple analytical technique for obtaining elemental information from materials without damaging them. LIBS can be applied to all types of samples, including solids, liquids, or gases. Although the collection of the signal for solid samples is easy, there are certain disadvantages or challenges associated with the analysis of liquid samples using LIBS. In this regard, there is a need toimprove the LIBS set-upto address the problems associated with LIBS in liquid. The present paper provides an insight into the various experimental methodologies and highlights the advantages of LIBS over other conventional techniques for the detection of trace heavy elements in water. This study will go a long way in establishing LIBS as a very convenient and reliable technique for the monitoring of trace elements in wastewater as well as drinking water, especially in the Indian context.

Soap film as a rapidly renewable and low-cost sensor for detecting ammonia in water and saliva

In this work, a novel, low-cost soap-film sensor for detecting ammonia in environmental water and saliva was developed. A 3D printed circular frame with two stainless steel electrodes was implemented as a carrier for a soap film. The soap film was manually generated by pulling the 3D printed frame from a mixture solution containing 20.7 g/L gelatin, 241.4 mL/L Glycerol, 34.5 mL/L Triton X-100 and 100 mM boric acid. The conductivity of the soap film was measured with a lab-made detector. For liquid sample analysis, sample and NaOH solution were mixed in a reagent bottle as the gas-diffusion vessel (GDV). The released ammonia from the reaction was then diffused into the headspace of the GDV and absorbed by the soap film. The conductivity increasing rate of the soap film was used for quantifying the ammonium concentration in sample. The analytical performance parameters were demonstrated, including a linear range of 0–500 μM, a relative standard deviation of 3.2 % (n = 10), and a limit of detection of 14 μM (0.2 mg N/L). This method showed a 90–110 % recovery rate for saliva and water samples. Compared to a reference indophenol blue method, the relative deviations of two method were less than 7.4 % (n = 33). The proposed method is easy to operate, and the device itself is compact and low cost. The soap-film sensor enables rapid renewal to avoid contamination.

Colorimetric Determination of 2-Chlorobenzylidene Malonitrile in Gases and Liquids

Here is described a new approach for the simple and rapid detection of 2-chlorobenzylidene malonitrile (CS riot control agent) based on the reaction with isatin (1H-indole-2,3-dione) and, alternatively, with ninhydrin (2,2-dihydroxy-1H-indene-1,3(2H)-dione), both in an environment of ammonium acetate, dimethyl sulfoxide, and dimethylformamide. The method was designed for the preparation of detection tubes for air analysis, test strips for the analysis of liquid samples, and for spectrophotometric determination. The use of ninhydrin appears to be more sensitive, but isatin provides higher stability and practical applicability.

Analysis of liquid samples by Low-Temperature Plasma Ionization Source-ion mobility spectrometry

In this study, liquid pharmaceutical samples are analyzed using an ion mobility spectrometer (IMS) with the Low-Temperature Plasma Ionization Source (LTPI) for the first time, overcoming limitations for this system due to intense interaction with IMS cell without sample pre-preparation. The direct sample introduction or newer methods that were presented in recent years in the LTP-MS are useful in mass spectroscopy, but these methods are incompetent in IMS. In new LTP-IMS, first, the sample is vaporized, then transferred to the ionization source by the carrier gas, and finally ionized. The new method has several salient characteristics as follows in comparison to the other similar devices. A new efficient way for sample entering which needs less amount of sample, does not waste it and ionizes liquid samples without any preparation or pre-extraction because the ionization source can vaporize, desorb, and ionize the samples simultaneously. In this work, the IMS cell, LTP, and sample introduction system must sync together, so they were redesigned to eliminate incompatibilities. Afterward, to achieve the best response, before evaluating the device, all parameters consist of gas flow, voltage, frequency, exhaust diameter of source, and IMS cell parameters were optimized. Then several pharmaceutical samples, including Papaverine, Codeine, Caffeine, and Diethylamine were analyzed to evaluate the qualitative and quantitative characteristics of the device. The samples were dissolved in methanol and detected in a few seconds, with a low detection limit of 41.75 ng for Codeine, 7.50 ng, and 8.25 ng for Caffeine and Papaverine, respectively.

Deep Eutectic Solvent-Enabled Plasmonic Nanocellulose Aerogel: On-Demand Three-Dimensional (3D) SERS Hotspot Based on Collapsing Mechanism.

Exceptional surface enhanced Raman scattering (SERS) can be achieved by on-demand mechanisms mediated by the formation of three-dimensional (3D) network supporting hotspots. Herein, a deep eutectic solvent (DES) is used to fabricate plasmonic aerogels as sustainable SERS substrates consisting of different gold nanoparticle (AuNP) heterostructures synthesized in the presence of cellulose nanocrystals (CNCs). This analytical approach is based on the AuNPs 3D arrangement within the CNC matrix, where the transient inter-CNCs interactions collapse after loading with the analyte aqueous solution, forming hotspots on demand. Theoretical calculations support the on-demand SERS mechanism, which consists of the hotspot formation by bringing the AuNPs closer upon activation with the liquid sample loading. To evaluate the plasmonic aerogel performance as a sensing platform, the organophosphorus pesticides edifenphos and parathion were tested in rice and tea extracts. Also, the detection of Methylene Blue in fish muscle extract resulted in a detection limit of 9.8 nM. The results demonstrate that the 3D plasmonic aerogel exhibits significantly higher SERS enhancement and sensitivity when compared to conventional 2D SERS substrates. The use of a green designer solvent, biobased ingredients, and the introduction of on-demand SERS-based sensing pave the way for further developments in the analysis of liquid samples within a sustainable framework.

Mid-IR dispersion spectroscopy – A new avenue for liquid phase analysis

Mid-IR dispersion spectroscopy is an attractive, novel approach to liquid phase analysis that extends the possibilities of traditional methods based on the detection of absorption via intensity attenuation. This technique detects inherent refractive index changes (phase shifts) induced by IR light interaction with absorbing matter. In contrast to classic absorption spectroscopy, it provides extended dynamic range, baseline-free detection, constant sensitivity, and inherent immunity to power fluctuation. In this paper, we provide a detailed experimental and theoretical characterization and verification of this method with special focus on broadband liquid sample analysis. For this purpose, we develop a compact benchtop dispersion spectroscopy setup based on an EC-QCL coupled to a Mach-Zehnder interferometer. Phase-locked interferometric detection enables to fully harness the advantages of the technique. By instrument operation in the quadrature point combined with balanced detection, the full immunity towards laser power fluctuations and the environmental noise can be achieved. On the example of ethanol (0.5–50% v/v) dissolved in water, it is experimentally demonstrated that changes of the refractive index function are linearly related to concentration also for strongly absorbing, highly concentrated samples beyond the validity of the Beer-Lambert law. Characterization of the sensitivity and noise behavior indicates that the optimum applicable pathlength for liquid analysis can be extended beyond the ones for absorption spectroscopy. Experimental demonstration of the advantages over classical absorption spectroscopy illuminates the potential of dispersion spectroscopy as upcoming robust and sensitive way of recording IR spectra of liquid samples.

Additively Manufactured Detection Module with Integrated Tuning Fork for Enhanced Photo-Acoustic Spectroscopy.

Starting from Quartz-Enhanced Photo-Acoustic Spectroscopy (QEPAS), we have explored the potential of a tightly linked method of gas/vapor sensing, from now on referred to as Tuning-Fork-Enhanced Photo-Acoustic Spectroscopy (TFEPAS). TFEPAS utilizes a non-piezoelectric metal or dielectric tuning fork to transduce the photoacoustic excitation and an optical interferometric readout to measure the amplitude of the tuning fork vibration. In particular, we have devised a solution based on Additive Manufacturing (AM) for the Absorption Detection Module (ADM). The novelty of our solution is that the ADM is entirely built monolithically by Micro-Metal Laser Sintering (MMLS) or other AM techniques to achieve easier and more cost-effective customization, extreme miniaturization of internal volumes, automatic alignment of the tuning fork with the acoustic micro-resonators, and operation at high temperature. This paper reports on preliminary experimental results achieved with ammonia at parts-per-million concentration in nitrogen to demonstrate the feasibility of the proposed solution. Prospectively, the proposed TFEPAS solution appears particularly suited for hyphenation to micro-Gas Chromatography and for the analysis of complex solid and liquid traces samples, including compounds with low volatility such as illicit drugs, explosives, and persistent chemical warfare agents.

Cu/Ag Nanoparticle-Based Surface-Enhanced Raman Scattering Substrates for Label-Free Bacterial Detection

Surface-enhanced Raman spectroscopy (SERS) is a promising analytical technique for fast and accurate disease detection due to its attractive features. However, realizing label-free direct detection is still challenging as most probes have extremely low Raman cross sections and little affinity to SERS substrates. Disappointingly, SERS spectra of most bacteria and other biological samples look similar as the differences in their molecular compositions are subtle and not detectable. Hence, the fabrication of highly enhancing plasmonic nanoparticles with excellent uniformity is demanded. Moreover, as SERS substrates are not reusable, cost-effective and simplistic fabrication methods are critical. Here, we report a facile approach to synthesizing Ag nanoparticle array on Cu-foil in less than 3 min, using only Cu-foil, silver nitrate, and hydroquinone. We employed the idea of galvanic replacement in combination with a seed-mediated particle-growth approach. The label-free bacterial detection has shown that our Cu/Ag nanoparticle substrate is superior to highly acclaimed Ag nanocubes. Creating strong second and third-generation SERS hot-spots through cooperative interaction of homo- (Ag–Ag) and heterogeneous (Ag–Cu) surfaces contributes mainly to the observed excellent enhancement. Interestingly, direct liquid bacteria sample analysis showed a 6-fold higher detection sensitivity than completely dried samples. We believe that our approach will offer remarkable advantages and change how SERS substrates are prepared and conducted in SERS-based bacterial detection.

Versatile, Cheap, Readily Modifiable Sample Delivery Method for Analysis of Air-/Moisture-Sensitive Samples Using Atmospheric Pressure Solids Analysis Probe Mass Spectrometry.

A cheap, versatile, readily modified, and reusable glass probe system enabling delivery of solid air-/moisture-sensitive samples for mass spectrometric (MS) analysis using an Atmospheric pressure Solids Analysis Probe (ASAP) is described. The simplicity of the design allows quick and easy ASAP MS analyses of sensitive solid and liquid samples without the need for any modifications to commercially available vertically loaded ASAP mass spectrometers. A comparison of ASAP mass spectra obtained for metal complexes under air and an inert atmosphere is given.

In-Situ and High-Throughput Determination of Antibiotics in Pork Using Electro-Filter Paper Spray Ionization Tandem Miniature Ion Trap Mass Spectrometry

In the recent years, the issue of antibiotic residues in food has become an important topic. Most current methods of detecting antibiotics are time-consuming, laborious, and cannot meet the requirements of field testing. In this study, electro-filter paper spray ionization was coupled with a portable linear ion trap mass spectrometer for the rapid determination of four antibiotics (norfloxacin, tetracycline, oxytetracycline, and chlortetracycline) in pork and milk samples. The experimental setup is not only structurally simple but enables analysis of both solid and liquid samples. The samples require only a simple pretreatment and the complete analysis of a sample requires less than 1 min. The linear range for the determination of the four antibiotic standards was from 1 to 100 mg/L (R 2≥0.960). The limits of detection (LOD) for the analytes were 0.100 mg/L, with recoveries from 72.4% to 11%. The relative standard deviations (RSDs) were between 2.70% and 16.5%. This study expands the capability for rapid field testing of antibiotics in meat using portable mass spectrometers, which is important for food safety, environmental protection, and criminal investigations.

Graphene thin film microextraction and nanoparticle enhancement for fast LIBS metal trace analysis in liquids

Several strategies have been effectively tested in the past to improve the Laser Induced Breakdown Spectroscopy (LIBS) signal for the analysis of liquid samples, involving peculiar experimental configurations, such as Double Pulse LIBS (DP-LIBS). Recently, sample treatment has proven to be a viable and simple way to enhance the performances of LIBS towards the analysis of solutions. Among the various strategies, the most promising and versatile appears to be Thin Film Microextraction (TFME) using carbon-based adsorbents.Another sample pre-treatment procedure, Nanoparticle-Enhanced LIBS (NELIBS), has gained significant interest due to its relative simplicity and effectiveness. This methodology uses a deposition of silver nanoparticles (AgNPs) on the sample to greatly increase the emission of the LIBS plasma.In this work, we investigate for the first time the possibility of combining TFME and NELIBS. We developed TFME supports by depositing an aqueous graphene nano-sheets (aq-GRA) prepared by Pulsed Laser Ablation in Liquid (PLAL) on a glass substrate. The preparation of the supports was optimized with regards to the substrate nature, deposition method, sorbent volume and drying method. Then, the TFME supports were tested for the extraction of Chromium from aqueous solution at different extraction times and analyte concentration. Subsequently, the TFME supports were treated with a deposition of silver nanoparticles (AgNP) to test the feasibility of the NELIBS approach.We observed an enhancement in the emission lines of Cr when the AgNPs were applied, as well as a lower estimated LOD value when compared to plain graphene TFME supports.

Three-Dimensional Dendritic Au-Ag Substrate for On-Site SERS Detection of Trace Molecules in Liquid Phase.

The development of a facile surface-enhanced Raman scattering (SERS) sensor for the on-site detection of trace molecules in liquid phase is a compelling need. In this paper, a three-dimensional (3D) dendritic Au–Ag nanostructure was constructed by a two-step electro displacement reaction in a capillary tube for the on-site liquid phase detection of trace molecules. The multiplasmon resonance mechanism of the dendritic Au–Ag structure was simulated using the finite-difference time domain (FDTD) method. It was confirmed that the highly branched 3D structure promoted the formation of high-density “hot spots” and interacted with the gold nanoparticles at the dendrite tip, gap, and surface to maximize the spatial electric field, which allowed for high signal intensification to be observed. More importantly, the unique structure of the capillary made it possible to achieve the on-site detection of trace molecules in liquids. Using Rhodamine 6G (R6G) solution as a model molecule, the 3D dendritic Au–Ag substrate exhibited a high detection sensitivity (10−13 mol/L). Furthermore, the developed sensor was applied to the detection of antibacterial agents, ciprofloxacin (CIP), with clear Raman characteristic peaks observed even at concentrations as low as 10−9 mol/L. The results demonstrated that the 3D dendritic Au–Ag sensor could successfully realize the rapid on-site SERS detection of trace molecules in liquids, providing a promising platform for ultrasensitive and on-site liquid sample analysis.

Atmospheric pressure thermal desorption chemical ionization mass spectrometry for ultra-sensitive explosive detection

Illegal explosives are a threat to aviation, transport sector, critical infrastructure and generally to public safety. Their detection requires extremely sensitive instruments with efficient workflows that allow large throughput of items. In this study, we built a trace explosives detection instrument that requires minimal sample treatment and reaches ultra-low picogram level detection limits for many common explosives. The instrument is based on thermal desorption of filters, which allows analysis of liquid and solid phase samples, and subsequent selective atmospheric pressure chemical ionization and detection with a mass spectrometer. We performed experiments to scope the optimal ionization chemistry for the system and selected Br− as the reagent ion, and measured the limit of detection for 14 different explosives that were generally in the picogram range. Finally, we demonstrate the usability of the system by sampling air to a filter from a storage room known to contain explosives, from which we detect four different explosives.

Rapid screening of illegal additives in functional food using atmospheric pressure solids analysis probe coupled to a portable mass spectrometer

Pharmaceutical drugs like Sildenafil are illegally added to functional food such as nutritional supplements and herbal remedies to deliver drugs without a regular prescription to consumers. Rapid screening of illegal additives is desirable for the public security department. The seized samples are often large in number and unknown in composition; methods are needed for qualitative screening of unknown samples. Here, a new approach is presented based on atmospheric pressure solids analysis probe (ASAP) coupled with single-quadrupole mass spectrometer to rapidly screen 42 common illegal additives in six categories of functional food. The ASAP-MS method could be applied to solid or liquid sample analysis with a very simple pre-treatment and no LC chromatographic separation, using a home-built library; the identification of suspicious additives could be obtained rapidly. More importantly, the approach is sensitive enough for complex matrix samples like coffee samples. 21 batches of seized unknown samples were tested by the ASAP-MS, and the positive results were confirmed by LC-MS/MS(QQQ), indicating that the ASAP-MS method is effective and reliable. The ASAP-MS with home-built library is a promising method for rapid screening of illegal additives in functional food, which could be widely used in the grassroots police station that lack professional laboratory environment.

Laser-induced breakdown spectroscopy for simultaneous determination of lighter lanthanides in actinide matrix in aqueous medium

Quantitative analysis of lanthanides (Ln's) in actinides matrix in aqueous medium using laser-induced breakdown spectroscopy (LIBS) is presented in this article. Mixture of lighter rare earth elements (REEs) such as La, Ce, Pr, Nd and Sm in U matrix is analysed. Results on identifying non-overlapping peaks, calibration plot, detection limit, deviation from the true values, and precision are discussed. The data obtained is compared with reported results for similar kind of systems. The method also describes the potential for determination of atom percentage fission of a nuclear fuel using LIBS. An in-housed designed sample cell is adopted for analysis of liquid sample which requires minimal quantity (<1 mL). Minimum sample quantity is advantageous for analysis of highly radioactive irradiated nuclear sample because of lesser radiation exposure to the analyst.

Development of time‐delay analysis method of inductance and capacitance for microfluidic circuit

AbstractIn this paper, we report the development of time‐delay analysis method of inductance and capacitance for microfluidic circuit. The sensor used in this method is composed of the sensing inductor (SI) and the sensing capacitor (SC) with a microfluidic circuit. This sensor measures inductance and capacitance in a time difference by delaying with microfluidic circuit. We confirmed that SI and SC have different responses to conductive and dielectric solution. This research is expected to be applied to the combined analysis of liquid samples.

Development of Time-Delay Analysis Method of Inductance and Capacitance for Microfluidic Circuit

In this paper, we report the development of time-delay analysis method of inductance and capacitance for microfluidic circuit. The sensor used in this method is composed of the sensing inductor (SI) and the sensing capacitor (SC) with a microfluidic circuit. This sensor measures inductance and capacitance in a time difference by delaying with microfluidic circuit. We confirmed that SI and SC have different responses to conductive and dielectric solution. This research is expected to be applied to the combined analysis of liquid samples.

Determination of trace elements in liquid samples with organic matrix by arc atomic emission spectrometry

Conditions for the analysis of liquid samples on a MFS-8 spectrometer upgraded with a MAES photodiode array by arc atomic emission spectrometry with dry residue technique are specified. It is shown that optimization of the electrode shape along with the method of calculating the intensity of the spectral line and time of the base exposure leads to the expansion of the operating range of calibration curves. The arc plasma parameters (temperature and electron density) are similar when the spectra of dry residues of aqueous solutions, saliva, blood serum, and dry wine are excited. This provides direct (without digestion) determination of trace elements in these samples with the detection limits at a level of μg/liter. When a sample of vegetable oil is deposited on the electrode, it is likely to be absorbed in depth and does not enter the arc plasma in full, which makes the direct analysis impossible. Nevertheless, the determination of trace elements in oils by the dry residue technique is possible after acid digestion of the sample.

Gold Nanoparticle-Decorated Porous Silica for Surface-Enhanced Raman Scattering-Based Detection of Trace Molecules in Liquid Phase

Development of a facile and cost-effective surface-enhanced Raman scattering (SERS) sensor with high sensitivity for the on-site rapid detection of trace molecules is a compelling need. Here we report how a capillary-based three-dimensional network porous silica material decorated with gold nanoparticles (3D-PSM@AuNPs) serves as an ideal platform for the rapid static liquid-phase detection of trace molecules. The SERS sensor is prepared by an in situ polymerization method to form a 3D continuous interconnected porous network in an ultraviolet transparent quartz capillary with a facile fabrication process. The unique porous network of the silica, which could provide a high specific surface area in a focus volume, endows the resultant material with a high density of SERS enhancement sites and a “hot-spot”, which has precisely guaranteed the detection sensitivity. More importantly, the unique structure of the capillary could also present an aid to reduce the energy loss of the laser via multiple reflections and thus effectively improve the utilization rate of the laser beam. Using 4-mercaptopyridine (4-MPY) in aqueous solution as a model molecule, the porous silica material exhibits a high detection sensitivity (10–11 M), excellent stability, and repeatability. Moreover, the obtained 3D-PSM@AuNP sensor is applied for the analysis of phosmet residues on orange peel and vegetables. The results demonstrate that this 3D-PSM@AuNP sensor can successfully realize Raman reporter-free and rapid on-site detection of trace molecules in liquids, which provides a promising platform in various fields of micro-volume liquid sample analysis, especially in liquid biopsy analysis.