This paper reviews the primary literature reporting the use of ionic liquids (ILs) in optical sensing technologies. The optical chemical sensors that have been developed with the assistance of ILs are classified according to the type of resultant material. Key aspects of applying ILs in such sensors are revealed and discussed. They include using ILs as solvents for the synthesis of sensor matrix materials; additives in polymer matrices; matrix materials; modifiers of the surfaces; and multifunctional sensor components. The operational principles, design, texture, and analytical characteristics of the offered sensors for determining CO2, O2, metal ions, CN−, and various organic compounds are critically discussed. The key advantages and disadvantages of using ILs in optical sensing technologies are defined. Finally, the applicability of the described materials for chemical analysis is evaluated, and possibilities for their further modernization are outlined.
A highly sensitive and selective fluorescence method of quantitative detection for mercury in soil was developed using non-labeled molecular beacon (MB), single-stranded nucleic acid (ssDNA) and fluorescent dye Hoechst 33258. In this analytical method, the loop of MB was designed to be a sequence that was complementary to the ssDNA with multiple T-T mismatches, the stem of MB was completely designed as C-G base pairs, and both ends of the MB are not modified by any fluorophore and quencher. In the absence of Hg2+, the interaction between Hoechst 33258 and the MB was very weak, and the fluorescence signal of Hoechst 33258 was very low. In the presence of Hg2+, the MB and ssDNA with multiple T-T mismatches formed a double-stranded nucleic acid (dsDNA) via the T-Hg2+-T coordination structure which provided binding sites for Hoechst 33258. Then Hoechst 33258 binded to A-T base pairs of dsDNA, and the fluorescence intensity of Hoechst 33258 was significantly enhanced. Thus, a highly sensitive fluorescence quantitative detection method for Hg2+ can be realized. In this strategy, the optimal determination conditions for Hg2+ were a buffer solution pH of 8.2, an incubated temperature of 50°C, an incubated time of 5 min and NaCl of 60 mmol L−1. Under the optimum conditions, the fluorescence intensity of Hoechst 33258 exhibited a good linear dependence on the concentration of Hg2+ in the range of 5 × 10−9 – 400 × 10−9 mol L−1. The fitted regression equation was ΔI = 2.1084C – 8.9587 with a correlation coefficient of 0.9943 (R2), and the detection limit of this method was 3 × 10−9 mol L−1 (3σ). The proposed method had a high selection; the common substances in soil such as Ca2+, Mg2+, Mn2+, Fe3+, Cu2+, Pb2+, Al3+, K+, Na+, Ni2+, Cd2+, Cr3+, SiO32−, Cl−, PO43−, NH4+ and S2− had no interference to the detection of mercury. The proposed method had a high accuracy, and it was applied to detect mercury of ten different types of soil; the recoveries were 97.65 – 103.22%. In addition, the proposed method had a low background emission, fast detection speed and low detection cost.
Glutathione is an important antioxidant found in body fluids and tissues, which inhibit damage to essential cellular constituents caused by reactive oxygen species. The analysis of glutathione levels in biological systems is important in early clinical diagnosis. A novel, cost-effective synthetic strategy has been developed for the fluorescent probe ethylenediamine passivated carbon dots. Tissue paper was chosen as the carbon source for this “green one pot” synthesis. Glutathione could induce quenching of the fluorescence intensity of ethylenediamine passivated carbon dots through surface interactions, resulting from their aggregation. Based on this, a novel fluorescence sensor was fabricated for the determination of Glutathione in body fluids. A linear calibration graph was obtained in the range of 6.0 × 10−7 to 5.0 × 10−8 M with a detection limit of 1.74 × 10−9 M. The developed sensor was successfully used for the determination of glutathione in artificial saliva samples.
Two sensors for paracetamol were obtained on the basis of a GC electrode modified with poly(3,4-ethylenedioxythiophene) (PEDOT). The first sensor was a GC electrode modified with a conductive composite layer of PEDOT doped with poly(4-lithium styrenesulfonic acid) (PSSLi), and the second one was a GC electrode modified by a composite of PEDOT doped with PSSLi and multiwall carbon nanotubes (MWCNT). A conductive PEDOT polymer film was used as an electron mediator with a rich electron cloud. Both sensors were developed for the determination of paracetamol (ACOP) in the presence of interference compounds. Differential pulse voltammetry (DPV) and adsorptive stripping differential pulse voltammetry (AdsDPV) were applied as analytical methods. The modified electrodes were successfully employed for the determination of ACOP in a pharmaceutical formulation.
A sensitive non-derivatization method for the determination of the highly polar compound 3-aminopiperidine was developed using a mixed-mode column combined with a charged aerosol detector (CAD). Chromatographic conditions, including the type of detector, separation mode, and mobile phase composition, were optimized to achieve high sensitivity towards and sufficient retention of 3-aminopiperidine. Compared to the precolumn derivatization UV method, the current method showed higher recovery and greater simplicify. High sensitivity (LOQ <2.73 μg mL−1) and good precision (RSD of peak area <2%) were also observed in the current method. Furthermore, the parameters such as buffer solution and column bleed that affected the sensitivity of the CAD were investigated. Finally, the current method was applied for the determination of 3-aminopiperidine in linagliptin samples. This is a new non-derivative for the determination of 3-aminopiperidine, and constitutes a novel application of the CAD for the quantitative analysis of highly polar basic compounds.
In order to evaluate the antioxidant capacity/activity of β-carotene (BC) in aqueous media, we investigated the inclusion complexes of BC with methyl-β-cyclodextrin (Me-β-CD), 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and 2-hydroxyethyl-β-cyclodextrin (HE-β-CD) that enhance water solubility and chemical stability. The inclusion complexes (monitored by FTIR) exhibited higher solubility than free BC, and phase solubility studies showed a linear increase in the solubility with the Me-β-CD concentration. Cupric ion-reducing antioxidant capacity (CUPRAC), ABTS-persulfate, peroxyl and hydroxyl radical scavenging assays were applied. CD-complexed β-carotene exhibited less effective antioxidative and radical scavenging than free BC dissolved in acetone. β-Carotene showed the highest antioxidant capacity in the presence of HE-β-CD, and the lowest with Me-β-CD, probably due to the deeper and more hydrophobic cavity of the latter. We believe that this is the first report on devising simple spectrophotometric methods for the wholistic assessment of antioxidant activity/capacity, hydroxyl and peroxyl radical scavenging activity of β-carotene in aqueous solution with CDs.
An N-butyl-N′-(4-mercaptobutyl)-4,4′-bipyridinium (4BMBP) was modified on a gold electrode to improve the electrochemical control of the bacterial luciferase (BL) luminescence system. The 4BMBP-modified gold electrode (4BMBP/Au) was able to prevent the adsorption of BL on the electrode surface, and enhanced the electrochemical regeneration rate of the reduced flavin mononucleotide (FMNH2), which is one of the substrates of the BL luminescence reaction. By using the 4BMBP/Au, the luminescence intensity increased by about 27% compared to that of a bare gold electrode (bare Au). Moreover, the modified electrode improved the time required for analysis because the modified layer prevented BL adsorption. Even without a refreshing procedure for each measurement, a constant luminescence intensity could be observed, and the analysis time was reduced to half (about 10 min) for one sample. The 4BMBP/Au is not only useful to control of the BL luminescence system, but also for electrochemical measurements in the presence of proteins.
A low-pressure separation procedure of α-tocopherol and γ-oryzanol was developed based on a sequential injection chromatography (SIC) system coupled with an ultra-short (5 mm) C-18 monolithic column, as a lower cost and more compact alternative to the HPLC system. A green sample preparation, dilution with a small amount of hexane followed by liquid–liquid extraction with 80% ethanol, was proposed. Very good separation resolution (Rs = 3.26), a satisfactory separation time (10 min) and a total run time including column equilibration (16 min) were achieved. The linear working range was found to be 0.4 – 40 μg with R2 being more than 0.99. The detection limits of both analytes were 0.28 μg with the repeatability within 5% RSD (n = 7). Quantitative analyses of the two analytes in vegetable oil and nutrition supplement samples, using the proposed SIC method, agree well with the results from HPLC.
In this study, a sensitive colorimetric method for the detection of copper ion (Cu2+) was developed based on controlling the peroxidase-like activity of (gold core)@(ultrathin platinum shell) nanocatalysts (Au@Pt-NCs). It was found that D-penicillamine can effectively inhibit the activity of Au@Pt-NCs. After being incubated with Cu2+, D-penicillamine lost inhibition toward the catalytic ability of Au@Pt-NCs. Based on the above interaction, a colorimetric detection of Cu2+ was develop by measuring the colorimetric signal variation of the H2O2-3,3′,5,5′-tetramethylbenzidine (TMB) reaction. This method exhibited high sensitivity and selectivity toward Cu2+ over a panel of other metal ions. The detection limit of this method was 3.7 nM and the linear range was 20 – 300 nM. Moreover, 20 nM Cu2+ can be distinguished directly by the naked eye. Furthermore, this method was applied to the analysis of water samples with good accuracy. These results demonstrated the excellent application potential of the method.
An ultrasensitive label-free impedimetric immunosensor is constructed by modifying a 3-mercaptoproponic acid (MPA) monolayer on highly rough gold nanostructure (AuNS)-electrodeposited screen printed carbon electrodes (SPCEs) for the detection of small molecular weight drugs (SMWDs), such as salbutamol (SAL). The SPCEs preoxidized in a 0.1 M H2SO4 solution (called po-SPCEH2SO4) are electrodeposited with the AuNS to increase the roughness factor to 23.64 ± 1.76, larger than the AuNS/po-SPCENaOH or the AuNS/po-SPCEPBS. Furthermore, the MPA modified layer as a link for the anti-SAL immobilization to give the immunosensors an impedimetric signal-to-noise ratio larger than the 11-mercapto-undecanoic acid- and 16-mercaptohexadecanoic acid-modified layer, due to the lower interfacial impedance of the MPA monolayer. The MPA/AuNS/po-SPCEH2SO4-based immunosensors have a wide linear range of 1 fg mL−1 to 1 ng mL−1 and a limit of detection of 0.6 fg mL−1. Moreover, the immunosensors can practically quantify the SAL concentrations in 1000 times-diluted serum samples with good recovery.
In this study, key factors affecting the chromatographic separation of Cd from plants, such as the resin column, digestion and purification procedures, were experimentally investigated. A technique for separating Cd from plant samples based on single ion-exchange chromatography has been developed, which is suitable for the high-precision analysis of Cd isotopes by multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The robustness of the technique was assessed by replicate analyses of Cd standard solutions and plant samples. The Cd yields of the whole separation process were higher than 95%, and the 114/110Cd values of three Cd second standard solutions (Münster Cd, Spex Cd, Spex-1 Cd solutions) relative to the NIST SRM 3108 were measured accurately, which enabled the comparisons of Cd isotope results obtained in other laboratories. Hence, stable Cd isotope analyses represent a powerful tool for fingerprinting specific Cd sources and/or examining biogeochemical reactions in ecological and environmental systems.
This paper describes the fundamental process of laser ablation occurring in a laser-induced plasma. The sampling process in laser-induced breakdown plasma spectrometry is very complicated and thus has not been fully understood. Our study focused on a relationship between the composition of ablation amounts and the bulk composition, when Fe-based binary alloys were employed as test samples. For this purpose, the ablation amounts of constituent elements in the alloys were determined by ICP-OES, through a method in which ablated deposits by laser irradiation were collected on a glass plate and then dissolved in an acid solution. In Fe-Ni binary alloys, the Ni content in the ablated deposits was almost the same as the bulk composition, which implied that Ni and Fe atoms evaporated along with the chemical composition of the samples; however, in Fe-Cr binary alloys, the Cr content in the ablated deposits was half of the bulk composition, probably because Cr atoms were difficult to be released from the sample surface. X-ray photoelectron spectra of ablated Fe-Cr alloy samples indicated that the resultant surface layer after laser irradiation comprised a thin oxide layer, consisting of Cr2O3 and FeO, and a relatively thick oxide layer beneath the outermost surface oxide, of which the composition was a complex of Cr2O3, Fe and FeO. The reason for this is that the dissociation energy of Cr2O3 is obviously higher than that of FeO, and thus Cr2O3 decomposed with more difficulty and thus left preferentially in a surface oxide layer of the Fe-Cr alloys. As a result, the Cr2O3 layer could suppress the ablation of Cr.
It is desirable to be able to monitor the intake or release of the components at different organs of aquatic plants in real time and in-situ. Here, we report a novel optical detection system that allows for real-time in-situ simultaneous monitoring of the dissolved oxygen and material movements at a vicinity of micrometers from the aquatic plant surface. A blue semiconductor diode-laser was used as the light source of both the probe beam and excitation light for fluorescence. The laser light reflected by a dichroic mirror was focused to a vicinity of the plant/water interface in a culture dish by an objective lens. The distance between the focused laser beam and the plant surface was adjusted by an X-Y-Z micro-stage. Deflection of the probe beam was detected by a position sensor, and fluorescence from the vicinity was monitored by a PMT. A commercial fluorescent DO sensor, which simultaneously monitored temperature, was immersed into the culture dish at about 1 cm away from the aquatic plants. A white-light LED was used to illuminate the aquatic plants in the dish in photosynthesis process. A Ru-complex (tris (2,2′-bipyridyl)ruthenium(II) chloride) was used as a fluorescent probe, and Egeria densa Planch. was used as a model aquatic plant. The DO-quenched fluorescence and material movement-induced deflection signals are compared at different distances from the aquatic plant surface. The results show that the optical detection system can monitor DO and the material movements at a vicinity of the aquatic plants not only much more sensitively, but also much more closely to real time than analytical methods that monitor concentration changes at a bulk solution.
The analytical method for ultra-trace metal impurities at μg kg−1 level in high-purity Cd was examined by inductively coupled plasma mass spectrometry (ICP-MS) combined with matrix separation by Bio-Rad AG MP-1M anion exchange resin. After the separation of Cd, the metal impurities such as Li, In, Cr, Mn, Fe, Co, Ni, Cu, Ga, Sr, Ba and Pb were measured by an ICP-quadrupole mass spectrometer (ICP-QMS) and ICP-sector field mass spectrometer (ICP-SFMS). From the comparison of measured results, it was evaluated that the analytical sensitivity by ICP-SFMS was 10 times higher than ICP-QMS. In addition, ICP-SFMS could obtain determined values of Li and Fe that could not be determined by ICP-QMS. These results suggest the ICP-SFMS combined with matrix separation by anion exchange resin could be utilized for the determination of ultra-trace metal impurities in high-purity materials for the assessment of the purity of the materials.
A simple and rapid ultra-fast liquid chromatography–ultraviolet spectrophotometry (UFLC-UV) method combined with modified 2-nitrophenylhydrazine (2-NPH) derivatization was developed for determining phytanic acid (Phy) in rat serum. Serum Phy and heptadecanoic acid (the internal standard) were derivatized by 2-NPH at ambient temperature for 20 min and extracted in n-hexane. After extracting derivatized Phy (D-Phy) and derivatized IS from the reaction mixture, the extracts were separated with a YMC-Pack C8 column (150 × 3.0 mm i.d., S-3 μm) using an isocratic mobile phase comprised of acetonitrile:H2O (90:10; pH 4.4) at 0.5 mL/min. The detection wavelength was 228 nm. Linearity was observed over 1 – 20 μg/mL (r = 0.9997). The intra- and inter-day reproducibilities of D-Phy measurements were ≤13.0%. To our knowledge, this is the first report of the quantitative and qualitative measurement of serum Phy using 2-NPH derivatization and UFLC-UV. This method can be performed rapidly under mild conditions.
We describe a procedure to determine concentrations of amino acid standard solutions by quantitative NMR spectroscopy using an internal standard. The measurement samples were prepared by solvent exchange to remove any intense solvent signal in the 1H NMR spectra. The method was demonstrated on valine aqueous solutions of different concentrations. The accuracy of the measured concentrations that fell well within the range of the expanded uncertainty is also discussed. All of the results are in good agreement with the preparation values. We believe that this approach should be useful to determine the concentrations of standard solutions whose solute components are difficult to weigh because of extremely small amount or hygroscopicity.
Fundamental studies on isotope ratio measurement of Cl were carried out using inductively coupled plasma triple-quad mass spectrometry (ICP-MS/MS) and the analytical performance obtained was compared to that obtained by ICP sector field mass spectrometer (ICP-SFMS). Though the polyatomic ion interferences of 16O18O1H and 36Ar1H with respect to 35Cl and 37Cl, respectively, made a negative effect on the accuracy and the precision for isotope ratio measurements of Cl, the ICP-SFMS could eliminate these interferences by medium mass resolution mode (m/Δm = 4000) and achieved the isotope ratio measurements with 0.2 – 0.5% of relative standard deviation (RSD) at the concentrations of Cl from 1 to 10 mg kg−1. In the case of ICP-MS/MS, both the single-MS mode without collision reaction gas and the MS/MS mode with collision reaction gases such as oxygen (O2) and hydrogen (H2) were examined and compared their analytical sensitivities as well as the precisions of isotope ratio measurement of Cl. The precisions of Cl isotope ratio measurements were 3 – 14% of RSD at the concentrations of Cl from 5 to 100 mg kg−1, when single-MS mode was carried out, even though the similar isotope ratios of 35Cl/37Cl could be obtained. In the case of O2 gas for MS/MS mode with mass-shift method, precisions of 0.3 – 2% of RSD were obtained at the concentration range of 1 – 100 mg kg−1. In the case of H2 gas, similar sensitivities as those obtained by ICP-SFMS and the precisions of 0.2 – 0.5% of RSD at the concentration range of 1 – 10 mg kg−1 were obtained. From these results, it was evaluated that the ICP-MS/MS in MS/MS mode with collision reaction gas could be used for Cl isotope ratio measurements for such studies as stable isotope tracers, isotope abundance measurements in nuclear chemistry and accurate determinations by isotope dilution mass spectrometry.
CdTe quantum dots capped with glutathione (GSH) and thioglycolic acid (TGA) were synthesized and the interaction between QDs and tetracationic Fe complex was investigated. Based on the specific interaction between Ag+ and cytosine bases (C), we designed a label-free DNA sensor for the detection of Ag+ in aqueous solution. Furthermore, tetracationic Fe complex with a higher positive charge is demonstrated to improve the sensitivity of the sensor. A detection limit of 3.3 nmol dm−3 was obtained, which was lower than in previous reports. This sensor also exhibits promising potential for real sample analysis.
In this study, a highly accurate, fast and practical separation/enrichment technique is described to determine the Pb in tap water samples by graphite furnace atomic absorption spectrometry. For this purpose, at first, Pb was collected on montmorillonite by batch technique, the supernatant was decanted and the solid phase was slurried in a mixture of 0.1% Triton X-114 and 0.1 mol L−1 HNO3 then directly introduced into graphite furnace without elution. Since the elution step was not applied, the method was simpler and faster compared to conventional techniques. The risks of elution step on the precision and recovery were eliminated. Up to 50-fold enrichment could be obtained by this method. The limit of detection (3δ, N = 10) and characteristic concentration of the method for Pb were 0.46 and 1.13 μg L−1, respectively. In addition, the Pb in water samples (tap and river) collected from different regions of Turkey were determined.
Here, we developed a multichannel dialysis microchip having three sets of dialysis systems, which consisted of three independent circulation channels with a common micropump. Each dialysis system was composed of a pneumatic micropump (heart), dialysis unit (renal corpuscle), and cell culture chamber (drug target) as well as circulation and dialysate channels to mimic the circulation system. Small molecules were successfully separated in parallel from macromolecules at the dialysis components. Anticancer tests using this microchip showed results that considered both serum protein-binding nature and drug activity. In the anticancer bioassay, the multichannel chip showed similar reproducible and reliable results as those of the single-channel system but with higher throughput.
Laser ionization time-of-flight mass spectrometry (LI-TOFMS) was applied to the direct measurement of a silane coupling agent in slurries. In the present study, a slurry with dispersed TiO2 nanoparticles treated with phenyltriethoxysilane (PTES) was prepared. As a result, the peaks for PTES could be observed from the slurry sample containing unreacted PTES, and no peaks were observed from the slurry sample where unreacted PTES was removed by washing. This method can be used to directly analyze surface coating agents, such as PTES in slurries, and would be useful for obtaining a direct understanding of the characteristics of slurries.
The role of an external force on chemical equilibria is an important subject in mechanobiochemistry. The effect of an electromagnetophoretic force for the stretching of cysteamine molecules was examined by using SERS spectrometry. Polystyrene particles modified with cysteamine were bound to silver nanoparticles adsorbed on the wall of a silica capillary cell. Under a constant magnetic field, when an electric current was applied to the conductive medium in the capillary, the shift of SERS bands and the increase of the trans/gauche ratio of cysteamine were observed, suggesting a molecular conformation change of cysteamine due to the stretching force.
A certified reference material (CRM), NMIJ CRM 7203-a, was developed for the elemental analysis of tap water. At least two independent analytical methods were applied to characterize the certified value of each element. The elements certified in the present CRM were as follows: Al, As, B, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb, Rb, Sb, Se, Sr, and Zn. The certified value for each element was given as the (property value ± expanded uncertainty), with a coverage factor of 2 for the expanded uncertainty. The expanded uncertainties were estimated while considering the contribution of the analytical methods, the method-to-method variance, the sample homogeneity, the long-term stability, and the concentrations of the standard solutions for calibration. The concentration of Hg (0.39 μg kg−1) was given as the information value, since loss of Hg was observed when the sample was stored at room temperature and exposed to light. The certified values of selected elements were confirmed by a co-analysis carried out independently by the NMIJ (Japan) and the KRISS (Korea).
Edited and published by : The Japan Society for Analytical Chemistry Produced and listed by : Sobun Print Co., Ltd. (Vol.25 No.6-) Chuo Printing Co., Ltd. (Vol.14-Vol.18, Vol.20-Vol.25 No. 5) The Japan Society for Analytical Chemistry (Vol.19)