Analytical Methods (v.11, #14)

Front cover (1837-1838).

Contents list (1839-1844).

In the analytical sciences regression methods have two main uses – in calibrations in instrumental analysis, and in testing for bias in method comparison studies. In first order (straight line) regression the true values of the intercept α and the slope β are independent of each other but their estimated values  and  are not independent. This can be appreciated visually by considering the straight lines joining all the individual pairs of points; those with a large slope will have a small intercept and vice versa, so the correlation between  and  is negative and possibly substantial. This correlation has important consequences when the estimated coefficients are used for significance testing in the interpretation of the regression line.

Point-of-care monitoring of intracellular glutathione and serum triglyceride levels using a versatile personal glucose meter by Jinqiong Xu; Xiujuan Qiao; Jingjing Zhang; Ni Cheng; Qinglin Sheng; Jianbin Zheng; Wei Cao; Tianli Yue; Yi Lu (1849-1856).
Portable, cost-effective and quantitative detection of various targets related to health at home and in the field has the potential to revolutionize medical diagnostics. Despite years of research, only a few detection methods are available to the public. The most successful example is the personal glucose meter (PGM). We report the use of the PGM to detect reduced glutathione and triglyceride, which are biomarkers for some diseases. The method is based on target-induced consumption or production of nicotinamide coenzymes that has a linear relationship with the response of the PGM, thus establishing a direct correlation between the target concentration and the amount of nicotinamide coenzymes measured using the PGM. The detection limits of glutathione and triglyceride were 0.08 mM and 0.17 mM, respectively. More importantly, the assays were also successfully used for the detection of glutathione and triglyceride in practical samples, such as human serum and cells. In both assays, it's just a simple mixture of enzyme solution, which is easy to operate and apply. Such a method can be generally applied to a wide range of other targets using the corresponding enzyme reaction included nicotinamide coenzymes.

A turn-on near-infrared fluorescent probe for detection of cysteine over glutathione and homocysteine in vivo by Qing He; Ruixi Li; Zhenwei Yuan; Habtamu Kassaye; Jinrong Zheng; Chen Wei; Fei Wang; Yuxin Yao; Lijuan Gui; Haiyan Chen (1857-1867).
Cysteine (Cys) has emerged as a significant sensing target in recent years. Although a lot of biothiol probes have been developed and applied to cellular imaging through thiol-induced disulfide cleavage or Michael addition reactions, relatively few probes assessing Cys with high selectivity over glutathione (GSH) and homocysteine (Hcy) with near-infrared (NIR) fluorescence are capable of in vivo fluorescence imaging in biological systems. Herein, a NIR fluorescent turn-on probe for Cys monitoring in vivo was designed and synthesized. This probe demonstrated a rapid, tremendously selective detection process for Cys with remarkable NIR fluorescence enhancement (Ex: 600 nm, Em: 712 nm, ∼20 fold). In addition, this probe could be utilized to quantitatively detect Cys with a detection limit of 82 nM over a wide linear range (0.01–160 μM), fast response time (5 min) and low toxicity. Moreover, it was further demonstrated that this NIR fluorescent probe could be applied to detect Cys in living cells including L02, A549 and MCF-7 cell lines and different mouse models (tumor-bearing mouse model, hepatitis model and inflammatory model), revealing that this probe possesses great promise for further biological applications.

Informatics analysis of capillary electropherograms of autologously doped and undoped blood by Shiladitya Chatterjee; Sean C. Chapman; George H. Major; Denis L. Eggett; Barry M. Lunt; Christopher R. Harrison; Matthew R. Linford (1868-1878).
An ‘Autologous Blood Transfusion’ (ABT) is the reinjection of blood previously taken from an athlete to increase its oxygen transport capabilities. Despite the World Anti-Doping Agency's ban on such practices, ABT abuse continues. Autologous blood doping (ABD) is challenging to detect because of the similarities between an individual's doped and undoped blood. Recently, Harrison et al. reported that high-speed capillary electrophoresis may identify ABD. In their work, first order derivatives of the electropherograms were used to identify doping. However, this method suffered from false negatives due to the subjective nature of the analysis. Here, we provide an informatics analysis of the data from this study, contrasting the results of traditional statistical methods and less traditional mathematical techniques. First, three well-known multivariate statistical tools: cluster analysis, principal component analysis (PCA), and partial least squares (PLS) are applied to develop calibrations and/or group electropherograms of undoped (0%) and doped (5% and 10%) blood samples. (These doping levels were chosen due to the low physiological effect of doping below 5%, with 10% corresponding to the approximate ‘gain’ derived from the transfusion of a single unit of blood into an adult.) Different preprocessing and variable selection methods were considered. Due to variation in the electropherograms and the limited sample size, these methods were inadequate. We next considered four less commonly used mathematical/informatics tools: pattern recognition entropy (PRE), the Euclidean distance between vectors, a peak fitting/integration method, and the second moment (SM). Each of these techniques showed some ability to differentiate between the 0, 5, and 10% doped samples. We then evaluated the prediction capabilities of inverse least squares (ILS) models based on these summary statistics. An ILS calibration based on PRE, the Euclidean distance, and peak fitting/integration proved more successful than the PLS model at predicting levels of blood doping from the corresponding electropherograms; the ILS model distinguished between doped (5% and 10%) and undoped (0%) blood. This methodology may be applicable to other challenging informatics problems like determining risk factors for genetically linked diseases, robust pattern finding in peak-like data such as ChIP-seq, or other genomic sequencing for understanding the 3D genome.

B,N-Co-doped graphene quantum dots as fluorescence sensor for detection of Hg2+ and F ions by Panxing Yang; Jie Su; Ruiwei Guo; Fanglian Yao; Caideng Yuan (1879-1883).
Herein, we develop a fluorescence sensing platform based on boron and nitrogen co-doped graphene quantum dots (B,N-GQDs), which are synthesized by a one-step bottom-up hydrothermal method. The prepared B,N-GQDs exhibit high-fluorescence quantum yield (75%) and long fluorescence lifetime (12.86 ns). In the B,N-GQDs–Hg2+ system, the fluorescence of B,N-GQDs is quenched with increasing Hg2+ concentration due to the affinity interaction between the surface functional groups of B,N-GQDs and Hg2+. Subsequently, the quenched fluorescence of the B,N-GQDs–Hg2+ system is gradually recovered with the addition of F ions due to their strong affinity with Hg2+. The linear ranges for the detection of Hg2+ and F ions are 0.2–2.6 μM and 0.25–7.0 mM, respectively, and the detection limits are 0.16 μM and 0.18 mM for Hg2+ and F ions, respectively, which are below the regulatory level of 0.25 μM and 0.526 mM in the Integrated Wastewater Discharge Standard. Therefore, B,N-GQDs provide a facile and effective approach for the detection of both Hg2+ and F ions with real-time monitoring and high-speed measuring.

Validation of alkaline oxidation as a pre-treatment method for elemental quantification in single-walled carbon nanotubes by Filipa R. F. Simoes; Nitin M. Batra; Abdul-Hamid Emwas; Pedro M. F. J. Costa (1884-1890).
Nanocarbons continue to stimulate the scientific community while their production has also started to reach the industrial scale. With the commercialization of products that are based on materials such as carbon nanotubes (CNTs), it has become imperative to implement reliable quality control protocols for the routine analysis of their chemical composition and structure. Herein, we propose alkaline oxidation (a.k.a., fusion) as a valuable approach to disintegrate the graphitic structure of carbon nanotubes. Using the certified reference material SWCNT-1, it was shown that fusion enables the subsequent determination of elemental concentrations (Ni, Co and Mo) by a routine analytical tool such as inductively coupled plasma optical emission spectroscopy (ICP-OES). Furthermore, the fusion residues were investigated, clarifying that the process does not result in the formation of non-intentional carbon compounds (e.g., carbides or carbonates) or lattice doping (e.g., B doping or Li intercalation).

Development of a simple, low-cost and rapid thin-layer chromatography method for the determination of individual volatile fatty acids by Fabien Robert-Peillard; Elodie Mattio; Aïnhoa Komino; Jean-Luc Boudenne; Bruno Coulomb (1891-1897).
In this paper, a new thin-layer chromatography (TLC) method for the determination of individual volatile fatty acids (VFAs) is presented. The experimental procedure is based on the derivatization of VFAs with activating agents and a naphthalene-based amine to form an amide derivative, followed by fast TLC separation of these VFA derivatives and visualization with phosphomolybdic acid at room temperature. Quantification is then performed by densitometric measurements using free software after taking TLC pictures in a home-made black box for homogeneous and reproducible lighting of the plates. Optimization of the experimental conditions enables fast determination (20 minutes for 3 samples) of VFAs with detection limits (1.5–2.5 mg L−1) and relative standard deviations (4.6–6.7%) satisfactory enough for our analytical purpose using low-cost instruments with easy to find materials and software. The protocol was then applied to real samples (aqueous extracts of sewage sludge composts) and the results were compared with gas chromatography analysis with good agreement between the two methods.

Electromembrane extraction (EME) and μ-dispersive liquid–liquid microextraction (μ-DLLME) have been applied in the simultaneous determination of biogenic amines (tyramine, histamine, putrescine and cadaverine) in canned fish samples. Gas chromatography-mass spectrometry (GC-MS) was employed as a powerful analytical technique. The affecting parameters in the extraction of biogenic amines from sample tissue were identified and optimized using response surface methodology (RSM) based on central composite design (CCD). The calibration curve of the proposed method was linear in the range of 1–1000 ng g−1 with the correlation coefficient (R2) higher than 0.9990. The relative standard deviations were between 5.2 and 7.7% (n = 6). The limits of detection were 0.03, 0.11, 0.06 and 0.29 ng g−1 for putrescine, tyramine, histamine and cadaverine, respectively. The relative recoveries in spiked samples at concentrations of 10, 50 and 100 ng g−1 were obtained between 82 and 99%. For real samples, putrescine with 57.36 ng g−1 had the highest concentration and tyramine with 2.64 ng g−1 had the lowest amount of BAs. ∑4BAs have been detected for each sample in the range 3.72–53.19 ng g−1. The enhanced sensitivity of the proposed method is significant due to the suitable removal of sample matrix interferences. High recovery, good enrichment factor, fast and low volume consumption of organic solvent are the other advantages of this technique. The results show that the proposed method is an accurate and reliable sample-pretreatment method for determining the amount of biogenic amines in various canned fish samples, which has the potential for application in determining BAs in other food samples.

Nanoceria-based reactive species scavenging activity of antioxidants using N,N-dimethyl-p-phenylenediamine (DMPD) probe by Gozde Kamer; Birsen Demirata; Reva Bayraktar; Dilek Ozyurt; Resat Apak (1908-1915).
The aim of this work was to develop a fast and low-cost method to measure the reactive species formed in an aqueous suspension utilizing nanoceria as a peroxidase-like catalyst. Nanoceria was produced with a green synthesis using Thymbra spicata L. (Zahter) extract in conjunction with {Ce(iii) + aqueous NH3} as a heterogeneous catalyst to generate reactive species (RS) from hydrogen peroxide. DMPD reagent was used as a colorimetric probe due to its absorbance increase at 515 nm accompanying a color change from transparent to red-violet in the presence of RS. The developed method was used to determine the percentage RS scavenging activity of synthetic antioxidant samples and herbal infusions with regard to their bleaching action on the DMPD radical cation. For validating the proposed method, the cupric reducing antioxidant capacity (CUPRAC) reactivity of the {nanoceria + H2O2} suspension before and after reaction with antioxidants was measured, and the difference between the CUPRAC absorbances was converted to RS scavenging, where the excess of H2O2 was decomposed with catalase. Both DMPD and CUPRAC methods showed a similar order of RS scavenging activities for a number of antioxidant compounds. As a result, it can be concluded that the combination of nanoceria, hydrogen peroxide and DMPD provided a fast detection system to investigate the RS scavenging antioxidant activity of food and plant samples, as confirmed by the CUPRAC assay.

Two coumarin-based compounds, 2-acetyl-3H-benzo[f]chromen-3-one (BCO) and (1E)-1-(1-(3-oxo-3H-benzo[f]-chromen-2-yl)ethylidene)thiosemicarbazide (BETC), were designed as excellent fluorescent probes for the detection of ClO in CH3OH : H2O (v/v = 1 : 1). The oxidizing reaction between the BCO & BETC probes and ClO induced an obvious fluorescence enhancement together with a color transformation from colorless to blue. The probes showed preferential selectivity towards ClO over various anions and metal ions. The detection limits of BCO and BETC were 154 nM and 32 nM, respectively. Interestingly, the tested reactive species, which include ˙OH, 1O2, and H2O2 do not interfere with the tests of ClO. Furthermore, cell imaging using HepG2 cells revealed that BCO & BETC could be applied as effective fluorescent probes for the detection of ClO in HepG2 cells.

A novel SERS sensor based on Fe3O4@mTiO2/P-ATP-TNT/Au@Ag magnetic nanoparticles (NPs) is reported for the first time to detect trace trinitrotoluene (TNT) explosive. Firstly, the mesoporous Fe3O4@mTiO2 magnetic NPs were synthesized and functionalized by P-ATP. Due to the increased surface area, the mesoporous TiO2 was conducive to P-ATP loading. Upon addition of TNT, the electronic resonance-active P-ATP-TNT complex formed through a charge transfer process from the electron-rich amino group of P-ATP to the electron-deficient aromatic ring of TNT. After that, introducing Au@Ag to Fe3O4@mTiO2/P-ATP-TNT NPs, the P-ATP-TNT complex largely enhanced the SERS signal in the presence of trace TNT. In addition, the SERS enhancement was also provided by Au@Ag and Fe3O4@mTiO2/P-ATP-TNT NPs plasmon resonance. The detection limit of TNT was as low as 10−12 M in deionized water, which was much lower than the maximum concentration of 88 nM allowed by the US Environmental Protection Agency (EPA). More importantly, Fe3O4@mTiO2/P-ATP-TNT/Au@Ag SERS substrate was further studied to detect TNT in real systems, such as lake water and liquor, using a portable-Raman spectrometer.

Recently, increasing attention has been paid for using commercial peracetic acid (PAA) solution as an efficient disinfectant or a strong oxidant in water treatment. Simultaneous determination of PAA and hydrogen peroxide (H2O2) is vital because PAA solution is commonly available as a mixed solution containing the peroxides PAA and H2O2. In this study, a simple, rapid and reliable spectrophotometric method for the simultaneous determination of PAA and H2O2 was developed. This method was based on the rapid oxidation of excess potassium iodide by PAA and H2O2 in the presence of ammonium molybdate to yield yellow-colored triiodide ions (I3) that could be quantitatively measured using an UV-Vis spectrophotometer. The absorption of generated I3 at 350 nm increased linearly (R2 > 0.999) with the concentrations of total peroxides and PAA in the range of 0–70 μM. The sensitivities were respectively measured to be as high as 2.596 × 104 M−1 cm−1 for total peroxides and 2.616 × 104 M−1 cm−1 for PAA, while the corresponding limits of detection were calculated to be as low as 0.19 μM and 0.18 μM. The concentration of the H2O2 coexisting in PAA solution was obtained by subtracting the concentration of PAA from the concentration of total peroxides. The concentrations of total peroxides, PAA and H2O2 in practical water samples measured with this proposed method were in good agreement with the values measured with the earlier reported spectrophotometric method using N,N-diethyl-p-phenylenediamine as the indicator. Therefore, this proposed spectrophotometric method could be considered as an alternative method for the simultaneous determination of PAA and H2O2 coexisting in PAA solution.

Quantification of capsaicinoids from chili peppers using 1H NMR without deuterated solvent by Thays Cardoso Valim; Danyelle Alves Cunha; Carla Santana Francisco; Wanderson Romão; Paulo Roberto Filgueiras; Reginaldo Bezerra dos Santos; Warley de Souza Borges; Raphael Conti; Valdemar Lacerda; Alvaro Cunha Neto (1939-1950).
Capsaicinoids are widely known for their pharmacological properties and are responsible for flavoring peppers through their pungent aroma. In turn, this pungency can be determined by quantifying the capsaicinoids present in peppers by means of chromatographic and spectroscopic techniques, or sensory analysis such as the Scoville scale. The present research presents a rapid and simple method for capsaicinoid quantification in commercial peppers by way of the relationship between analytes and an internal standard area resulting from 1H NMR analysis without the use of a deuterated solvent solution. Samples were diluted in a mixture of water and methanol, and then compared to a solution of maleic acid in deuterated water. For validation of the method, figures of merit such as selectivity, linearity, detection, and quantification limits, accuracy, precision, and robustness were obtained for capsaicin and dihydrocapsaicin. The presented method exhibits great linearity, with a correlation coefficient (R) of 0.9967, good accuracy for samples with concentration greater than 3 mg mL−1, with an error rate close to 3%, good robustness with minimal variation observed even one month after sample stored, good precision (<1%), and detection and quantification limits from 0.639 mg mL−1 to 2.633 mg mL−1, respectively. In order to evaluate the proposed method and apply it for pungency determination, analyses were performed in commercially acquired samples of Malagueta, Habanero, Bhut Jolokia, Trinidad Scorpion, and Carolina Reaper peppers to assign respective Scoville Heat Unit values.

Smart construction of an efficient enantioselective sensing device based on bioactive tripeptide by Qiumin Ye; Jihong Hu; Datong Wu; Baozhu Yang; Yongxin Tao; Yong Qin; Yong Kong (1951-1957).
Recognition of enantiomers using simple and smart devices remains a challenge in modern chemistry, and the development of advanced host materials is the key for the chiral recognition of guest enantiomers. Here, we report a novel enantioselective sensing device based on a bioactive tripeptide, glutathione (GSH). During the construction of the GSH-based enantioselective sensing device, the mercapto group (–SH) of GSH was effectively protected by α-cyclodextrin (α-CD) from being oxidized to disulfide bond (S–S). The α-CD/GSH showed an efficient recognition of tryptophan (Trp) enantiomers due to the intrinsic chiral microenvironment of GSH and the well-retained spatial configuration of GSH. The temperature sensitivity of the α-CD/GSH enantioselective sensing device is also discussed. Finally, the proposed α-CD/GSH was successfully applied in the analysis of the ratio of l- and d-Trp in non-racemic enantiomer mixtures.

Testing outside the laboratory environment, such as point of care testing, is a rapidly evolving area with advances in the integration of sample handling, measurement and sensing elements widely reported. Low cost, simple to use systems are important in this context because they provide a route to devices that can be used outside the laboratory and could be implemented in low resource settings where advanced diagnostic testing is often unavailable. Here, we present an open source highly simplified electrochemical platform, called SimpleStat, that has been programmed to perform differential pulse voltammetry and can be used to detect the presence of OXA-1 DNA sequences for oxacillin resistance. This DNA sensor can be used to specifically detect the presence of the OXA-1 gene, contrasted to the tetA gene which encodes for tetracycline resistance. These measurements were performed with both polycrystalline gold electrodes as a benchmark and electrodes integrated into the SimpleStat printed circuit.

Fast inline tobacco classification by near-infrared hyperspectral imaging and support vector machine-discriminant analysis by Marcelo C. A. Marcelo; Frederico L. F. Soares; Jorge A. Ardila; Jailson C. Dias; Ricardo Pedó; Samuel Kaiser; Oscar F. S. Pontes; Carlos E. Pulcinelli; Guilherme P. Sabin (1966-1975).
Classification systems are frequently used in tobacco Green Leaf Threshing (GLT) facilities to assess the chemical characteristics and quality of tobacco leaves. This classification is usually performed by a trained specialist who has to analyse and classify the leaf, in a short time, based on experience and visual information. However, this approach is not robust and may be biased due to its highly subjective nature. This work proposes the use of infrared hyperspectral imaging and chemometric tools for discriminant analysis. A fast and real-time method to classify flue-cured Virginia and air-cured Burley tobacco was developed by classifying the leaf based on three criteria: (a) stalk position, (b) leaf colour, and (c) leaf quality; this occurs within 5 seconds. The applicability of the method was evaluated by analysing standard tobacco leaf bundles using near-infrared imaging and Support Vector Machine-Discriminant Analysis (SVM-DA). The models classified the stalk position with a global prediction accuracy of 80.4% for flue-cured Virginia and 88.1% for air-cured Burley. The models for targeting leaf classification by colour presented a global prediction accuracy of 95.9% for flue-cured Virginia and 96.5% for air-cured Burley. For leaf quality, the prediction accuracy ranged from 61.5% to 100.0% for flue-cured Virginia and 78.8% to 100.0% for air-cured Burley. The system was implemented in a tobacco GLT facility for one year to cover an entire crop season and extended to include tobacco bales and leaf bundles. For the most complex classification parameter, leaf quality, flue-cured Virginia models presented a global accuracy of 50.2% to 71.6%. Considering the high complexity of the system and short period of analysis, the obtained accuracy was accepted as suitable when compared to traditional human classification.

A novel stainless steel needle electrode based on porous gold nanomaterials for the determination of copper in seawater by Haitao Han; Ying Li; Dawei Pan; Chenchen Wang; Fei Pan; Xiaoyan Ding (1976-1983).
This study describes the fabrication of a porous gold (P-Au) nanomaterial-functionalized stainless steel acupuncture needle electrode (ANE) with the help of polydopamine (PDA) nanospheres, which were partially sacrificed for the voltammetric determination of copper in seawater. The PDA nanospheres were covered on sensing part, i.e., the needle tip, by the self-polymerization method and employed as a reductant and adhesion agent for the growth of gold nanomaterials with a porous structure and improved stability. The gold nanomaterials with a porous structure were self-assembled and deposited on the ANE with the reduction of AuCl4 by PDA nanospheres, which were gradually sacrificed during this process. Moreover, there was no need to cover the protective layer additionally on the P-Au nanomaterial surface to prevent their peel off due to the strong adhesion capability of PDA. Owing to the excellent electrochemical properties of the P-Au nanomaterials and adhesion ability of the partially sacrificed PDA nanospheres, the modified ANE displayed remarkably improved performance and stability for the voltammetric determination of copper. Under optimal conditions, the linear range and detection limit of the modified ANE for copper ion determination are 0.7 nM to 1000 nM and 0.24 nM, respectively. Furthermore, the modified ANE has been successfully applied for the determination of copper in real seawater samples with satisfactory results.

Back cover (1985-1986).