Analytical Methods (v.9, #12)

Front cover (1827-1828).

Contents list (1829-1834).

Serial microbubble imaging technology (sMBI) for rapid screening of hydrogen-evolution materials used in photocatalytic water-splitting reactions by Jiarui Zhang; Jianchao Lee; Liping Wang; Yunyun Zheng; Wenxiao Wang; Jiabo Guo; Jinhong Gao (1835-1838).
In this study, a serial microbubble imaging technology (sMBI) is proposed as a new high-throughput technology (HTE) detection method for rapid screening of hydrogen-evolution catalytic materials. The mechanism for the screening is based on capturing the variation in the growth of microbubbles in a system involving thousands of catalysts to evaluate numerous reactions. As an example of the process, three catalysts with high catalytic activity were rapidly selected from 1260 candidates.

A diagnostic test for cocaine and benzoylecgonine in urine and oral fluid using portable mass spectrometry by Mahado Ismail; Mark Baumert; Derek Stevenson; John Watts; Roger Webb; Catia Costa; Fiona Robinson; Melanie Bailey (1839-1847).
Surface mass spectrometry methods can be difficult to use effectively with low cost, portable mass spectrometers. This is because commercially available portable (single quadrupole) mass spectrometers lack the mass resolution to confidently differentiate between analyte and background signals. Additionally, current surface analysis methods provide no facility for chromatographic separation and therefore are vulnerable to ion suppression. Here we present a new analytical method where analytes are extracted from a sample using a solvent flushed across the surface under high pressure, separated using a chromatography column and then analysed using a portable mass spectrometer. The use of chromatography reduces ion suppression effects and this, used in combination with in-source fragmentation, increases selectivity, thereby allowing high sensitivity to be achieved with a portable and affordable quadrupole mass spectrometer. We demonstrate the efficacy of the method for the quantitative detection of cocaine and benzoylecgonine in urine and oral fluid. The method gives relative standard deviations below 15% (with one exception), and R2 values above 0.998. The limits of detection for these analytes in oral fluid and urine are <30 ng ml−1, which are comparable to the cut-offs currently used in drug testing, making the technique a possible candidate for roadside or clinic-based drug testing.

Reactive aldehyde species are important byproducts of lipid peroxidation and oxidative stress due to their role in the secondary damage caused by traumatic events such as epileptic seizures and brain injury. In this study, a liquid chromatography/fluorescence method was developed to determine 4-hydroxynonenal, acrolein, and malondialdehyde in urine samples. These analytes react with dansylhydrazine to produce fluorescent dansyl derivatives with experimentally determined excitation and emission wavelengths of 250 and 550 nm, respectively, which were dependent on the organic composition of the mobile phase. Using a solid-phase extraction pre-concentration method prior to LC-FL resulted in limits of detection ranging from 6 nM to 200 nM for the three compounds. This method was then demonstrated for the detection of the compounds in urine samples. The method was then applied to the analysis of rat urine samples obtained following a chemically induced seizure. A statistically significant increase in acrolein concentration was observed. There was no change in 4-hydroxynonenal concentration, and the results for malondialdehyde were inconclusive. The method will be applied in the future to monitor lipid oxidation in different brain regions using microdialysis sampling during epileptic seizures.

A method of binary mixed solvent-based solvent demulsification dispersive liquid-liquid microextraction coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS) was developed for the determination of polycyclic aromatic hydrocarbons (PAHs) in water samples. A binary mixed solvent of methylene chloride and n-hexane (v/v = 1 : 1) which has a lower density than water was used as the extraction solvent, obtaining satisfactory extraction efficiencies for PAHs, and also allowing convenient operation. Acetonitrile as the dispersive solvent was injected into the water sample solution to form an emulsion. The extraction can be completed in 5 min and ethanol was used as the demulsification solvent to bring about successful phase separation without centrifugation. Coupled with GC-MS/MS analysis, the method was simple, sensitive, accurate and suitable for batch analysis of PAHs in water samples. Good linearity was obtained within the linear range for 16 PAH compounds, with determination coefficients from 0.9980 to 0.9998. This method can be used to effectively evaluate the situation of PAH pollution in water intended for human consumption and environmental water, the method detection limits (MDLs) of which were 2.1 to 13.6 ng L−1 and only 20 mL of water samples were used for analysis. The proposed method was applied to determine PAHs in actual water samples including tap water, and the upper, middle and lower reaches of the Jinjiang river in Chengdu city. Meanwhile, spiked samples and procedural blanks were used for quality control measurements according to ISO/TS 13530-2009 to guarantee the accuracy of this method. The average spiked recoveries of PAHs were in the range of 85.0–104% with RSDs in the range of 5.8–10.9%. Naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, fluoranthene and pyrene were predominantly measured, and PAH pollution was found at the total concentrations of 0.162–0.206 μg L−1 in the Jinjiang river of Chengdu city of P. R. China. Considering their toxicity, attention should be paid to water pollution by PAHs and necessary monitoring should be done.

Characterization of bacteria causing acute otitis media using Raman microspectroscopy by O. D. Ayala; C. A. Wakeman; I. J. Pence; C. M. O'Brien; J. A. Werkhaven; E. P. Skaar; A. Mahadevan-Jansen (1864-1871).
Otitis media (OM) is a prevalent disease that is the most frequent cause of acute physician visits and prescription of antibiotics for children. Current methods to diagnose OM and differentiate between the two main types of OM, acute otitis media (AOM) and otitis media with effusion (OME), rely on interpreting symptoms that may overlap between them. Since AOM requires antibiotic treatment and OME does not, there is a clinical need to distinguish between AOM and OME to determine whether antibiotic treatment is necessary and guide future prescriptions. We used an optical spectroscopy technique, Raman spectroscopy (RS), to identify and characterize the biochemical features of the three main pathogens that cause AOM in vitro. A Renishaw inVia confocal Raman microscope at 785 nm was used to spectrally investigate the Raman signatures of Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae. Biochemical features or biomarkers important for classification of each bacterial species were identified and yielded a 97% accuracy of discrimination. To test the effectiveness of Raman-based bacterial classification in a clinical sample, human middle ear effusion (MEE) from patients affected by recurrent AOM was collected, cultured, and measured using RS. The probability of bacterial involvement from each of the three main bacteria that cause AOM was determined from the clinical MEE samples. These results suggest the potential of utilizing RS to aid in accurately diagnosing AOM and providing physicians with bacterial identification to guide treatment.

A novel fluorescent probe HPQB based on ESIPT and AIE was developed for the detection of H2O2 and glucose. HPQB was found with large Stokes shift (167 nm) characters. Probe HPQB exhibited high selectivity and excellent sensitivity for H2O2 and glucose. Moreover, HPQB was also employed as a fluorescent probe for imaging H2O2 in nasopharyngeal carcinoma (NPC) cells.

The use of sequential injection analysis (SIA) for key nutrient determination in water has been previously described using a copperised cadmium column to attain nitrate reduction to nitrite prior to determination, yielding hazardous waste. Here, a greener alternative is proposed for nitrate reduction using a UV lamp, aiming to avoid the use of cadmium. This method was based on the colorimetric Griess reaction for nitrite determination, after the UV reduction of nitrate. The reduction was performed inline during the determination of nitrite, minimizing both effluent production and the overall determination rate. Its application to natural waters, namely river water, proved to be effective as the results were comparable to those obtained with the reference procedure. Furthermore, certified reference samples were analysed, and an average of 3% relative deviation was observed. A limit of detection of 5.30 μM was achieved, enabling the nitrate determination in the dynamic range of 25–500 μM with a determination rate of 24 h−1, and with a recovery percentage rate around 100%.

In this work, a SAR micromixer with F-shape mixing units is analyzed by simulation and experimentation. The results prove that the mixing performance of SAR micromixers with F-shape mixing units has a huge advantage over that of T micromixers. A satisfactory mixing efficiency can be achieved by splitting-recombination and chaotic advection mechanisms. The results indicate that when the Reynolds number increases from 0.5 to 15, the mixing efficiency of the two micromixers decreases. And at Re = 15, the lowest mixing efficiency of the SAR micromixer is 54%. When the Reynolds number increases from 15 to 50, the mixing efficiency of the SAR micromixer reaches about 90%. When the Reynolds number exceeds 50, the mixing efficiency of both micromixers begins to decrease. And the mixing performance of the SAR micromixer with F-shape mixing units is superior to that of the T micromixer.

A sensitive and selective red fluorescent probe for imaging of cysteine in living cells and animals by Xuezhen Song; Baoli Dong; Xiuqi Kong; Chao Wang; Nan Zhang; Weiying Lin (1891-1896).
Cysteine (Cys) is one of the important semi-essential amino acids, which often participates in many enzymatic reactions and has lots of biological functions. Herein, we present a sensitive and selective red fluorescent probe (RCys) for detecting Cys in living cells and animals. RCys utilized a rhodamine derivative as the fluorescent platform, and employed acrylate as the response site for Cys. When RCys responded to Cys, a significant turn-on red fluorescence at 638 nm was observed. RCys displayed obvious fluorescence response to Cys in a short time, and exhibited favorable selectivity to Cys over other thiols including GSH and Hcy. The biological applications demonstrated that RCys can be applied for the imaging of Cys in living cells and animals.

Adulterations and geographical origins are two essential quality factors of foods and herbs. In this work, the authentication of a traditional Chinese herb, Gastrodia elata BI. (GE), against artificial frauds and fine classification of geographical origins, was performed using near-infrared (NIR) spectroscopy and chemometrics. Class models of representative and authentic GE samples collected from different geographical origins were developed using one-class partial least squares (OCPLS) for untargeted detection of 4 common exogenous adulterants, including taro starch, sweet potato starch, potato starch and Polygonatum sibiricum powder. Fine classification of GE samples from 14 geographical origins was performed using a new large-class-number classification strategy, interval-combination one-versus-one partial least squares discriminant analysis (IC-OVO-PLSDA). Different data preprocessing methods were investigated to improve the classification accuracy of models. As a result, OCPLS with second-order derivative (D2) spectra could detect 1.0% (w/w) or higher levels of 4 different adulterants and obtain a sensitivity of 0.9107. For fine classification of geographical origins, a total classification accuracy of 0.9250 was achieved by IC-OVO-PLSDA with standard normal variate (SNV) spectra. The study demonstrates the potential of using NIR combined with chemometrics for the authentication of pure GE against multiple adulterants and fine classification of geographical origins.

Self-supported Co3O4 nanoneedle arrays decorated with PPy via chemical vapor phase polymerization for high-performance detection of trace Pb2+ by Wenjing Wang; Chao Wang; Peng Dou; Lifang Zhang; Jiao Zheng; Zhenzhen Cao; Xinhua Xu (1905-1911).
Highly ordered three-dimensional (3D) polypyrrole (PPy) coated cobalt oxide (Co3O4) nanoneedle arrays (NAs) anchored on Cu foams (Co3O4 NAs@PPy) are fabricated for electrochemical sensors to detect trace lead ions (Pb2+). The 3D hybrid Co3O4 NAs@PPy is synthesized via a hydrothermal method followed by a chemical vapor phase polymerization process. Free-standing Co3O4 NAs@PPy can be directly utilized as a 3D electrochemical working electrode without being decorated onto a working electrode like Au and glassy carbon electrodes. In the mean time, the simultaneous incorporation of PPy, Co3O4 and Cu foams creates a platform with significantly improved electrochemical properties and excellent sensitivity for a large specific surface area, eminent adsorption capacity and high conductivity. Square wave anodic stripping voltammetry (SWASV) is carried out to observe the electrochemical behavior of the Co3O4 NAs@PPy electrode. Under the optimum conditions, a linear range between the currents and the concentrations of Pb2+ from 0.024 to 0.48 μM with a high sensitivity of 85.5 μA μM−1 was obtained. The limit of detection can reach 0.58 nM. The results confirmed that the modified electrode is a good candidate for Pb2+ detection sensors with excellent reproducibility, stability and lower detection limit. In addition, the developed method was successfully applied to determine Pb2+ in real water samples with satisfactory results.

Phthalate esters (PAEs) are a group of endocrine disrupters that have been detected in many beverages. A simple and rapid sample pretreatment procedure based on dispersive liquid–liquid microextraction (DLLME) was performed to simultaneously extract 15 PAEs from non-alcoholic and alcoholic beverages. The extracts were analyzed using gas chromatography-mass spectrometry (GC-MS). To optimize the extraction efficiency for the 15 PAEs, various parameters, including the type and volume of extractants and dispersants, effect of salts, and extraction time were studied. Under optimum conditions, the limits of detection (LODs) and the limits of quantification (LOQs) for the 15 PAEs ranged from 0.003–0.57 ng mL−1 and 0.010–1.861 ng mL−1, respectively. Good linearity (0.9908 ≤r2≤ 0.9999) and extraction recoveries (72.6–115.5%) in the range of 0.002–0.5 μg mL−1 were obtained for all selected analytes. The relative standard deviation (RSD%) for the analysis of 0.02 μg mL−1 of the selected PAEs was 0.16–8.59% (n = 3). An optimized DLLME-GS-MS method was applied to detect the 15 PAEs in different beverage products, and the results demonstrated that the DLLME-GC-MS method was effective for the simultaneous analysis of 15 phthalates in beverages. The results suggest that more attention should be given to possible PAE contamination in commercial beverage products.

Determination of the superoxide radical anion (O2˙) with high sensitivity and selectivity is a challenge for evaluating the role of O2˙ in physiological and pathological processes. Herein, a novel gold nanodot (Au ND) biosensor for detecting O2˙ was developed, which was prepared with d(+)-mannose as the reducing agent and 2-mercaptobenzothiazole as the stabilizing agent via a facile, one-pot and rapid sonochemical approach. The as-prepared Au NDs possess a small size (∼1.9 ± 0.1 nm), and exhibit intense orange fluorescence emission and good water-dispersibility. Interestingly, the Au NDs would react with the superoxide radical anion (O2˙) which results in quenching of the fluorescence. A good linearity between the fluorescence intensity and O2˙ within the range from 0.6 to 78 μM is found, with a detection limit of 0.445 μM. In addition, the Au NDs exhibited good biocompatibility and low cytotoxicity to HepG2 cells in the MTT assay. Due to their superior advantages of low-toxicity, excellent stability and satisfactory fluorescence, the as-prepared Au NDs have been successfully used in cell imaging. As a result, the present Au ND sensor is successfully used for bioimaging and monitoring of O2˙ changes, and is quite promising for biological applications.

Increasing flame ionization detector (FID) sensitivity using post-column oxidation–methanation by Charles S. Spanjers; Connor A. Beach; Andrew J. Jones; Paul J. Dauenhauer (1928-1934).
The flame ionization detector (FID) is a robust tool in gas chromatography (GC) due to its sensitivity and linear response in the detection of common organic compounds. However, FID response to oxygenated or highly functionalized organic molecules is low, or in some cases non-existent, making it difficult or impossible to detect and quantify some organic compounds. In this work, the combination of a GC/FID system with a catalytic microreactor, which performs post-column combustion–methanation to convert organic compounds to methane, is shown to be an effective approach for quantifying low-response organic compounds. Molecules that were previously undetectable by conventional FID, including carbon monoxide and carbon dioxide, respond with the same high response of methane in the FID. Low-response molecules, including formaldehyde, formic acid, formamide, and ten other oxygenates also demonstrated enhanced detector response equivalent to that of methane in the FID. The linear response of the FID to these molecules and the equivalent sensitivity to methane indicate that accurate quantification is possible without the usual calibration-corrections (e.g., response factors or correction factors) to the FID response.

Effect of sample temperature, pH, and matrix on the percentage protein binding of protein-bound uraemic toxins by Olivier Deltombe; Annemieke Dhondt; Wim Van Biesen; Griet Glorieux; Sunny Eloot (1935-1940).
While studying and trying to optimise dialysis clearances of protein-bound uraemic toxins (PBUTs), the percentage protein binding (% PB) may be an important parameter and can be calculated from measured free and total concentrations. Since different parameters may alter this % PB, we investigated whether the ultrafiltration temperature, sample pH, and sample matrix (i.e. serum or plasma) affects the % PB of PBUTs. Pre-dialysis serum and plasma samples were obtained from 10 stable haemodialysis patients. Ultrafiltration was performed at 37 °C for fresh samples and at 4 °C, room temperature, and 37 °C for thawed samples (all n = 10). Total and free serum/plasma concentrations of hippuric acid, indole-3-acetic acid, indoxyl sulphate, and p-cresylsulphate were simultaneously measured by high-performance liquid chromatography with ultraviolet and fluorescence detection. No differences in % PB were found between fresh and thawed samples at 37 °C or between serum and plasma samples prepared at the same temperatures. However, in both serum and plasma samples, the free concentration increased with increasing ultrafiltration temperatures and resulted in a decrease in % PB from 4 °C to 37 °C. In conclusion, the % PB of PBUTs can be determined in both thawed serum and plasma samples and ultrafiltration should be performed at 37 °C.

Validation of pretreatment of filter samples for airborne plutonium monitoring: a feasibility study by Dongmei Li; Longbo Liu; Hangbing Tang; Mei Li; Guoqing Zhou (1941-1947).
Airborne plutonium monitoring is a significant component of radioecology, environmental surveys and early warning. However, plutonium loss in pretreatment of filter samples can still be easily neglected, while suitable certified reference materials are currently unavailable. The feasibility of preparation of filter samplers was studied with regard to validation of pretreatment such as dry ashing. Utilising an in-house device, Pu-bearing soils are dispersed to aerosol by using a Venturi tube disperser, with the aerosol deposited into filter media to produce filter samples. During this process, the soil particles should be of the same distribution in the filter samples as in the real samples, hence the reliability of validation will be enhanced. This method was validated by the experimental results, where the relative uncertainties of the 239Pu content in soils with inhomogeneity are below 2%, while the soils can be transferred quantitatively with a device possessing (98.2 ± 2.0)% efficiency. An ashing process for the filter samples at 600 °C for 6 h was then applied to the filter samples. The measured 239Pu content in soil in the filter samples is consistent with uncertainties regarding the 239Pu content in the soil only.

Rapid determination of boron in oilfield water using a microfluidic instrument by Cedric F. A. Floquet; Thomas Lindvig; Vincent J. Sieben; Bruce A. MacKay; Farshid Mostowfi (1948-1955).
We developed and validated an interference free microfluidic instrument for rapid determination of boron concentration in produced water using the carminic acid assay. Interferences from other species are eliminated by controlling crucial aspects of the kinetics and thermodynamics of the assay. The use of a microfluidic mixer improves the reaction kinetics by reducing the diffusion time. The high surface-to-volume characteristic of microchannels efficiently dissipates the heat generated by the exothermic reaction of the carminic acid with water. We incorporate a 6.5 bar back pressure element, which offsets the onset of calcium sulfate precipitation and hydrochloric acid outgassing that often disturb optical measurement for the assay when performed at atmospheric pressure. The analyzer has a measurement rate of 1 sample per min, a precision of 5%, a limit of detection of 0.16 mg L−1 at 615 nm, and a measurement range of 0–420 mg L−1. The instrument accurately measured ten water samples that were representative of fluids encountered in the oilfield when compared to ICP-MS measurements. The fast measurement rate of the instrument enables near real-time decision of the fate of produced water in the oilfield.

In the present study, a simple and highly sensitive electrochemical method was developed for the determination of hydrogen peroxide (H2O2) through a Ni–Al/layered double hydroxide/Ag nanoparticle composite modified carbon-paste electrode (Ni–Al/LDH/Ag NPs/CPE) as a renewable electrode in 0.1 M phosphate buffer solution (PBS, pH = 7.0). Scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) were performed for the characterization of the Ni–Al/LDH/Ag NP composite. The electrocatalytic activity of the Ni–Al/LDH/Ag NPs/CPE for H2O2 reduction was studied by cyclic voltammetry and chronoamperometric (at an applied potential of −0.9 V) methods. The prepared renewable modified electrode as a H2O2 sensor shows good electrocatalytic activity, fast response time, good stability and reproducibility. The present sensor also displays a linear range from 10 μM to 10 mM concentration of H2O2 with a detection limit of 6 μM (S/N = 3) and sensitivity of 1.863 μA mM−1 cm−2. This sensor was employed successfully for the determination of H2O2 in real samples by the chronoamperometric method, which indicates its applicability in practical analysis.

Back cover (1965-1966).