Analytical Methods (v.9, #35)

Inside front cover (5077-5077).

Front cover (5078-5078).

Contents list (5079-5085).

A ‘Periodic Table’ of mass spectrometry instrumentation and acronyms by Analytical Methods Committee AMCTB No. 81 (5086-5090).
The development and maturation of mass spectrometry (MS) technology has meant that MS users are no longer required to be experts in this field. With the increasing popularity of mass spectrometry (MS) with non-expert users, the Analytical Methods Committee (AMC) of the Royal Society of Chemistry has highlighted the need to generate a glossary of instrumentation terms that is accessible to users of this technology at all levels. In order to address a wide range of users it is also necessary to provide a context and explanation for the types of MS technology and their acronyms.

Spiegelmers as potential receptors for cTnI diagnostics by Zsuzsanna Szeitner; Anna Doleschall; Marina Varga; Katalin Keltai; Katalin Révész; Róbert E. Gyurcsányi; Tamás Mészáros (5091-5093).
We demonstrate the first application of a nuclease resistant aptamer, the so-called Spiegelmer, in a sandwich-type affinity assay by quantitative assessment of cardiac Troponin I (cTnI) in blood serum samples. To this end, we used a bead-based homogenous proximity assay (AlphaLISA) in which luminescence is generated by the Spiegelmer and antibody-modified donor and acceptor beads brought into proximity by their binding to cTnI.

Colorimetric sensor for highly sensitive and selective detection of copper ion by Qi Gao; Ling Ji; Qiaoning Wang; Kun Yin; Jinhua Li; Lingxin Chen (5094-5100).
The copper ion (Cu2+), as a type of essential element, plays important roles in various metabolic processes of organisms. However, an excessive intake of Cu2+ can induce a series of diseases, such as Alzheimer's disease, Menkes disease and Wilson's disease. Therefore, it is urgently needed to develop an analytical method to achieve a simple and sensitive detection of Cu2+. In this study, a colorimetric sensor for the detection of Cu2+ with a high sensitivity and selectivity has been developed. The design of the colorimetric sensor is based on the inhibiting effect of Cu2+ on the reaction of l-cysteine with our established probe Cy-NB. A significant color change could be directly observed by the naked eye as the concentration of Cu2+ increases. The as-prepared colorimetric sensor has a high sensitivity with a low detection limit of 8.6 nM, and a distinguishing recognition selectivity for Cu2+ over other possibly co-existent metal ions. Moreover, the sensor was successfully utilized for the analysis of tap water, seawater and biosamples, and high recoveries at two spiking levels of Cu2+ ranged from 102 to 114%. The results were consistent with those obtained by ICP-MS, indicating that the developed colorimetric sensor has great application potential as a simple highly sensitive and selective detection method for Cu2+.

As a novel injection preparation, propofol liposomes have extensive application prospects in clinical practice, and lipid components in them need to be quantified for quality control. In this study, a simple and accurate GC-FID method coupled with a methyl esterification pretreatment was developed for simultaneous determination of three main excipients (tricaprylin, TA; dipalmitoyl phosphatidylglycerol, DPPG; 2-dierucoyl-sn-glycero-3-phosphocholine, DEPC) in propofol liposomes with stearic acid used as the internal standard (IS). Response surface methodology was utilized for optimizing three factors of the methyl esterification reaction (the temperature, BF3 concentration and reaction time were optimized to be 75.0 °C, 14.5% and 6.5 min, respectively). Under optimum conditions, the average methyl esterification rate of the three analytes reached 96.43 ± 0.16% (n = 3). Moreover, multiple sample solutions could be simultaneously prepared, which would promote the efficiency and accuracy of quantitative analysis. Three calibration curves had good linear regression (r > 0.9999) within the tested ranges, the average recoveries ranged from 98.64% to 102.44% and the RSDs of the precision, repeatability, stability and recoveries were all below 1.53%. Finally, the validated method was successfully applied to the quantitative analysis of the three analytes in six batches of propofol liposomes.

A non-enzymatic ethanol sensor based on a nanostructured catalytic disposable electrode by Marta M. Pereira Silva Neves; M. Begoña González-García; Pablo Bobes-Limenes; Alejandro Pérez-Junquera; David Hernández-Santos; Francisco José Vidal-Iglesias; José Solla-Gullón; Pablo Fanjul-Bolado (5108-5114).
Herein, a simple and fast method for the electrocatalytic detection of ethanol using disposable nanostructured screen-printed carbon electrodes (SPCEs) is presented for the first time. Platinum nanoparticles (PtNPs), prepared in the presence of citrate and later purified and dispersed in ultrapure water, were employed in the modification of the SPCEs (SPCE-PtNPs). The synthetized nanoparticles and the catalytic nanostructured solid surface were characterized with transmission electron microscopy (TEM) and with scanning electron microscopy (SEM), respectively. Both systems were also characterized using voltammetric techniques. Finally, the PtNPs modified SPCEs were employed for the electro-oxidation of ethanol in an alkaline medium using portable instrumentation. The electrochemical results revealed that PtNPs can effectively enhance the electron transfer between the analyte of interest and the electrode. The content of ethanol was assayed in real samples (alcoholic beverages) revealing an accurate performance. Additionally, a stability study of the nanostructured surface was carried out. The results obtained corroborate the promising catalytic activity of PtNPs in ethanol detection using disposable, cost-effective and miniaturized sensing devices.

A novel three-dimensional DNA nanostructure used for thrombin detection by Huawei Shu; He Mei; Jinxin Gu; Yongbin Yang; Baoguang Chen; Ling Huang; Qun Wang; Xiaodong Chen; Dong Li; Jimin Gao (5115-5120).
In this paper, a label-free electrochemical aptasensor for the detection of thrombin with high sensitivity is proposed. A thrombin-binding capture probe (CP) was designed to form a thrombin/aptamer complex that could reduce the activity of ssDNA DNAzymes, to avoid the hydrolysis of the aptamer monolayers in the presence of thrombin. Furthermore, the presence of the CP enabled auxiliary DNA 1 (AD-1) to hybridize with auxiliary DNA 2 (AD-2) on the gold electrode (GE) and self-assemble into three-dimensional (3D) DNA networks. The electrochemical signal then originated from Ag NPs deposited in the DNA skeleton, owing to the high affinity between metal cations and DNA. Ag NPs deposited in the 3D DNA networks remarkably amplified the electrochemical signal, so as to significantly improve the sensitivity of the electrochemical aptasensor. The electrochemical aptasensor showed a linear range for thrombin detection from 0.0001 to 50 nM, with a detection limit (LOD) of 0.046 pM. Therefore, the proposed aptasensor for thrombin detection showed high sensitivity, good selectivity and excellent reproducibility, and could provide a promising sensing platform for the detection of thrombin in human serum.

A colorimetric assay for Hg2+ detection based on Hg2+-induced hybridization chain reactions by Li-Juan Wang; Li-Ping Jia; Rong-Na Ma; Wen-Li Jia; Huai-Sheng Wang (5121-5126).
A simple colorimetric sensing method for the detection of Hg2+ was developed by combining enzymatic catalysis with DNA-based hybridization chain reactions (HCRs). Firstly, thymine (T)-rich capture DNA (cDNA) was immobilized on a gold electrode via Au–S bonding. In the presence of Hg2+, thymine (T)-rich probe DNA (pDNA) hybridized with cDNA via T–Hg2+–T base pairs. Then the HCRs were realized using pDNA as an initiator and two biotin-labeled hairpin DNAs (H1 and H2) as fuel strands. Finally, numerous avidin-labeled horseradish peroxidase (HRP) enzymes were immobilized on long nicked ds-DNA strands, which can catalyze the H2O2-mediated oxidation of 3,3,5,5-tetramethylbenzidine dihydrochloride hydrate (TMB) to cause a dramatic color change. Under optimal conditions, the absorbance of TMB was linear with the logarithm of Hg2+ concentrations in the range of 1 fM to 1 pM, with a detection limit of 0.33 fM. This strategy exhibited good selectivity and high sensitivity, which might be a potential tool for the practical detection of Hg2+ in environmental monitoring.

In this work, headspace solid-phase microextraction (HS-SPME) coupled with ion mobility spectrometry (IMS) has been used as a simple and convenient method for acrylamide detection and quantification in heat treated food samples. IMS coupled with corona discharge (CD) ionization along with HS-SPME based on nanostructured polypyrrole (PPy) fiber has been successfully applied for the quantitative analysis of acrylamide in potato-based foods. The effect of various analytical parameters on the microextraction procedure like extraction temperature, extraction time, ionic strength and pH of the sample was also studied and optimized to obtain the best HS-SPME results. The HS-SPME-IMS method provided good repeatability (RSD ≤ 8%) and the calibration graph was linear in the range of 10–100 ng g−1 (R2 > 0.99) with a detection limit of 4 ng g−1. The proposed method was applied for the determination of acrylamide in potato-based foods, such as potato crisp and French fry samples. Validation of the analytical procedure was determined as the percentage of recovery and was confirmed by the add-found method in the potato-based food samples. The results obtained by the proposed method are in satisfactory agreement with the amounts added (92–96%). In conclusion, a direct relationship between temperature/time and acrylamide concentration in heat treated foods can be established.

A novel, effective and easy-to-operate method to enrich unsubstituted naphthalene and phenanthrene directly from crude oils was developed based on closed-system pyrolysis. The pyrolysis at 500 °C for 12 h was found to be sufficient for the enrichment of unsubstituted aromatics that were free of unresolved complex mixture (UCM) and poly-substituted aromatics. This allowed further accurate compound specific isotope analysis, and GC-IRMS data showed that the δ13C values of unsubstituted naphthalene and phenanthrene had no obvious fractionation during the enrichment process. This method provides an easy-to-operate pre-concentration technique for unsubstituted aromatics suitable for compound-specific isotope analysis (CSIA), laying the foundation for developing new oil–oil correlation indicators.

In this study, a polyoxometalate (POM) and graphene oxide (GO) were hydrothermally treated to form a novel three-dimensional (3D) macroporous hybrid 3D-mp-rGO–POM for nitrite sensing. Scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy and electrochemical methods were used to characterize the hybrid. The 3D porous rGO not only obviously enhances the conductivity and largely increases the active surface area, but also greatly facilitates the mass transport and efficiently decreases the leaching of the POM from the modified electrode. The synergistic interaction between the POM and 3D porous rGO endows 3D-mp-rGO–POM with a highly stable and efficient electrocatalytic activity towards the oxidation of nitrite. A nonenzymatic sensor for nitrite based on this hybrid shows two linear response ranges of 0.5 μM to 221 μM and 0.221 mM to 15.221 mM, with a detection limit of 0.2 μM (S/N = 3), which displays higher sensitivity, higher stability, a wider linear range and a lower detection limit than sensors based on POMs or 2D-rGO supported POM hybrids. Interference from H2O2 was effectively avoided by monitoring the oxidation current of nitrite instead of its reduction current. The 3D-mp-rGO–POM hybrid with facile preparation, high stability and good catalytic activity may have promising applications in catalysis, sensors, and so on.

Electrochemical enantiorecognition of tryptophan enantiomers based on a multi-walled carbon nanotube–hydroxyethyl chitosan composite film by Zhenliang Li; Zunli Mo; Ruibin Guo; Shujuan Meng; Ruijuan Wang; Huhu Gao; Xiaohui Niu (5149-5155).
A novel chiral electrochemical sensor based on hydroxyethyl chitosan (HECS) covalently binding with the carboxylic multi-walled carbon nanotubes (MWCNT–COOH) was fabricated for discrimination of tryptophan (Trp) enantiomers. HECS preferably combined with l-Trp than with d-Trp because of the favorability of host–guest interactions between HECS and Trp enantiomers. Thus, the recognition efficiency was remarkably improved after hydroxyethyl groups were grafted onto chitosan (CS); this might be attributed to the formation of hydrogen bonds between Trp enantiomers and HECS. In addition, the small stereo-hindrance effect could play an important role in enantioselective discrimination.

A novel calibration method was developed for the determination of macronutrients in suspension fertilizer samples by laser-induced breakdown spectroscopy (LIBS). The fertilizer samples were mixed with 10% m/v polyvinyl alcohol (PVA) and dried for approximately 2 h at 50 °C, resulting in a solid polymer film with the immobilized liquid sample. This study describes the use of LIBS and 12 normalization strategies to determine Cu, K, Mg, Mn and Zn as well as As, B, Ca, Cd, Cr, Fe, Na, P and Pb in suspension fertilizers by inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry (ICP-MS) analyses. LIBS equipment parameters were chosen following optimization with a Doehlert design. The results clearly demonstrate a good agreement between the LIBS predicted concentrations and the reference concentrations determined by ICP OES after microwave-assisted acid digestion (AOAC 2006.03 Official Method). Correlations of R2 = 0.9958, 0.9489, 0.9992, 0.9968 and 0.9809 for Cu, K, Mn, Mg and Zn, respectively, were obtained. Significant levels of potentially toxic elements such as 10 mg L−1 As, 4.0 mg L−1 Cd, 8.0 mg L−1 Cr and 20 mg L−1 Pb were detected after ICP-MS analysis. The results with low standard errors of prediction for LIBS (from 0.02 to 0.06%) indicate that this proposed suspension sample preparation procedure exhibits significant potential for the development and implementation of methods for determining essential nutrients in suspension fertilizers and other samples for which mineralization is difficult.

This study sought to develop a novel method for the trace analysis of N-nitrosodiethanolamine (NDELA) in shampoos inspired by a Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) extraction, followed by an RP-HPLC method with a water-rich mobile phase. To improve the extraction recovery of NDELA and clean-up efficiency of the shampoo matrix, effective parameters of the QuEChERS method including sample amount, sorbent type and amount, solvent type and amount, as well as salt amount were optimized. The obtained results showed that using primary secondary amine and C18 accompanied by silica as a polar sorbent led to a much cleaner chromatogram with a lower baseline drift without significant decrease in the extraction recovery of NDELA. Under optimum conditions, satisfactory extraction recovery of NDELA in shampoo (79 ± 3%) was achieved. The concentration range of the calibration curve was 5–500 ng mL−1 with a regression coefficient of 0.9993. Furthermore, the method's limits of detection (LODm) and quantification (LOQm) were 14 and 42 μg kg−1 respectively. The intra- and inter-day accuracy and precision of the proposed method yielded relative recoveries of 98–101% and a relative standard deviation of less than 5% respectively. Finally, the developed method was applied to determine the occurrence of NDELA in various shampoo samples, and the obtained results were confirmed using liquid chromatography coupled with triple quadrupole mass spectrometry.

Characterization of phenolic acids binding to thrombin using frontal affinity chromatography and molecular docking by Yu-Xiu Yang; Su-Ying Li; Qian Zhang; Hua Chen; Zhi-Ning Xia; Feng-Qing Yang (5174-5180).
As a serine protease, thrombin (THR) plays an important role in the coagulation cascade. In this study, a frontal affinity chromatography (FAC) method was developed for the characterization of interactions between immobilized thrombin and phenolic acids, which have potential thrombin inhibitory activity. First, a simple method to immobilize thrombin was developed, where an immobilized artificial membrane (IAM) chromatographic column was used as the carrier material for entrapping THR. Then the frontal analysis of five compounds was performed both on the THR-IAM column and argatroban-THR-IAM column. Finally, the dissociation constants were determined and the values are 2.46, 12.42, 44.93, 76.91 and 100.69 μmol L−1 for gallic acid, protocatechuic acid, ferulic acid, chlorogenic acid and sinapic acid, respectively. In addition, molecular docking was further applied to study the interaction between the compounds and thrombin, and the rank order of docking energy values is similar to that of the dissociation constants of the compounds determined by FAC. The results of the present study demonstrate that the interaction between the compounds and thrombin can be well characterized by FAC experiments along with molecular docking.

A coral 129I/127I measurement method using ICP-MS and AMS with carrier addition by Angel T. Bautista VII; Yasuto Miyake; Hiroyuki Matsuzaki; Fernando P. Siringan (5181-5188).
Iodine-129 in coral cores provides historical records of human nuclear activities, establishes or confirms coral age models, and traces environmental processes. At the time of this writing, the only published method (Biddulph et al., 2006) for measuring 129I/127(stable)I in corals required 10–30 g of sample, which can be too large for common practice. To reduce this sample size requirement, we modified the existing method in two aspects: (1) we used inductively coupled plasma mass spectrometry (ICP-MS) instead of an iodide selective electrode (ISE) for stable 127I measurement; and (2) we added 0.66 mg of a low-ratio (129I/127I = 1.5 × 10−14) iodine carrier instead of using a carrier-free method for target preparation for 129I measurement by accelerator mass spectrometry. For 127I measurement, we obtained the detection limit and limit of quantitation of 0.089 and 0.27 ppb, respectively, using a 133Cs internal standard, a 286× dilution factor, and drift correction. The average 127I concentration in corals was 4.5 ppm. For 129I/127I measurement, we determined the average anthropogenic (post-1950) and natural (pre-1950) ratios of 20 × 10−12 and 1.4 × 10−12, respectively, in our coral samples. In addition, the average relative standard deviations were 11.5% and 23% for anthropogenic- and natural-age coral samples, respectively. Our method successfully measured 129I/127I in 1–4 g of corals with accuracy and precision comparable to the existing method, which required 10–30 g of corals.

Ionic liquid based in situ solvent formation microextraction (IL-ISFME) followed by on-line phase separation coupled to cold vapor-atomic absorption spectrometry (CV-AAS) was introduced based on using a homemade in-line filter for phase separation. In this method, low cost and easy to access PTFE powder, as an industrial raw material, was used to fill a medical syringe and applied for the separation of hydrophobic ionic liquid containing analytes. The developed methodology is simple and eliminates the application of centrifugation in the phase separation step to overcome some limitations of emulsification techniques. In IL-ISFME an ion-pairing agent was added to a sample solution containing hydrophilic IL. In the following, the fine droplets of hydrophobic IL made by the promotion of a metathesis reaction were recovered via an in-line filter. To show the applicability of the proposed method, it was applied for the extraction and determination of mercury in seafood samples. The effects of some important parameters were investigated and optimized using a central composite design (CCD). Under the optimized conditions, the linearity of the method was obtained over a range of 2–200 μg L−1 with a determination coefficient (R2) higher than 0.996. The enrichment factor (EF) and absolute recovery (AR%) of the method achieved were 5.7 and 57.3%, respectively. The limits of detection (LOD) and quantification (LOQ) were found to be 0.6 and 2.0 μg L−1 respectively. The intra- and inter-day precisions expressed as relative standard deviations (RSD%, n = 3) were 4.8% and 7.6%, respectively. The relative recoveries (RR%) obtained were in the range of 80 to 90.5%, which correspond to the relative errors of −20% to −9.5%, respectively, confirming the achievement of satisfactory accuracies by the proposed procedure.

Simultaneous determination of chlorinated aromatic hydrocarbons in fly ashes discharged from industrial thermal processes by Yun Fan; Haijun Zhang; Dan Wang; Meihui Ren; Xueping Zhang; Longxing Wang; Jiping Chen (5198-5203).
Chlorinated aromatic hydrocarbons (CAHs) have received increasing attention because of their environmental persistence, bioaccumulation potential and high toxicity. In this study, an analytical methodology based on high-resolution gas chromatography/high-resolution mass spectrometry for the simultaneous determination of four typical kinds of CAHs including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), polychlorinated naphthalenes (PCNs) and chlorinated polycyclic aromatic hydrocarbons (ClPAHs) in fly ash was developed. Highly effective cleanup and separation procedures combined with optimum instrumental conditions provided a reliable method for the detection and quantification of CAHs. Meanwhile, the spike of 13C-labeled standards and deuterated phenanthrene achieved more accurate measurement. The method detection limits were determined to be in the ranges of 0.1–13.4 pg g−1 for tetra- to octa-CDD/F congeners, 0.04–11.1 pg g−1 for tri- to hepta-CB congeners, 0.2–48.5 pg g−1 for mono- to octa-CN congeners and 3.5–9.5 pg g−1 for mono- and di-chlorinated aromatic hydrocarbons. Good recoveries of CAHs (62–136%) were achieved, except for PCN-2 and PCN-6. The developed analytical methodology was validated and then used to determine the levels of CAHs in fly ashes collected from industrial thermal processes. All the target compounds were detected and the CAH congener concentrations showed a wide variation in different fly ashes.

The development of rapid and sensitive detection of foodborne pathogens could effectively prevent or reduce the outbreaks of foodborne diseases. Herein, a simple, rapid, and sensitive detection of E. coli O157:H7 was developed based on antimicrobial peptide functionalized magnetic nanoparticles (MNP–AMP) and urease-catalyzed signal amplification. In this study, MNP–AMP were fabricated to capture E. coli O157:H7 with a high efficiency via electrostatic and hydrophobic interactions. As the bacteria are captured by MNP–AMP, the binding sites for urease on the surface of MNP–AMP are blocked resulting in a large amount of urease in the supernatant after magnetic separation, which further induces the color change of the pH indicator by efficient catalytic hydrolysis of urea into ammonium. Due to the high capture affinity, efficient amplification strategy and simple manipulation, the proposed bioassay could detect E. coli O157:H7 as low as 12 cfu mL−1 within 30 min. Furthermore, this novel platform was successfully applied to detect E. coli O157:H7 in spiked apple juice and ground beef samples with a limit of detection of 84 and 233 cfu mL−1, respectively, indicating its potential application in real samples.

A rapid, accurate and precise normal phase high pressure liquid chromatographic method was developed and validated for the simultaneous determination of nine vitamin E forms comprised of α-tocomonoenol, α-, β-, γ-, and δ-tocopherols and α-, β-, γ-, and δ-tocotrienols in tocotrienol rich fractions (TRFs) derived from palm oil. The chromatographic separation of vitamin E was performed on a silica HPLC column thermostated at 40 °C using n-heptane and ethyl acetate as the mobile phase in a gradient elution mode. The calibration standard curves were linear over the concentration range from 0.1 to 1.0 mg mL−1 for all vitamin E forms with overall R2 > 0.9980. The percent relative standard deviation of the method repeatability was less than 2.0% and the recovery ranged between 90 and 110%. The instrument limit of detection and quantitation ranged from 0.04 to 0.05 mg mL−1 and from 0.11 to 0.18 mg mL−1 respectively. The separation was completed in 15 minutes with an additional 2 minutes for re-equilibration. In conclusion, a method has been successfully developed and validated for the simultaneous analysis of nine vitamin E forms in palm oil which is suitable for routine quality control of all vitamin E forms in palm TRFs at different compositions.

The human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) pandemic continues to adversely affect human health and life. Although several classes of HIV treatment drugs (antiretrovirals, ARVs) are available, there is a continuing need for new drug modalities, due to inferior drug safety profiles and development of virus resistance. A potential novel class of ARVs are the maturation inhibitors (MIs), which inhibit the ultimate step of HIV-1 protease cleavage during final virus assembly, resulting in immature virus particles incapable of productively infecting other cells. To support ongoing studies on MIs that focus on the biochemical process at the mechanistic level, a liquid chromatography-mass spectrometric (LC-MS) based in vitro assay was developed to quantitatively characterize the HIV-1 protease driven rate of cleavage of HIV-1 virus-like particles (VLPs, fully assembled immature HIV-1 Gag polyprotein), thereby affording kinetic cleavage profiles. Utilizing surrogate analyte methodology on proteinaceous analytes and high resolution accurate mass analysis allowed for the multidimensional design of experiments affording quality data on variables such as Gag (VLP) polymorphic variants, structure–activity-relationship (SAR) of MIs, reagent concentrations, and sampling times. The unique approach of data normalization to an assay internal proteolytic analyte as a control standard eliminated the need for external stable isotope labeled analytes but nevertheless resulted in precise bioanalytical assay data utilized in comparative MIs inhibitory studies.

Back cover (5227-5228).