Analytical Methods (v.10, #12)

Front cover (1393-1394).

Contents list (1395-1398).

In this paper three variants of the electrophoretic method for the determination of thioamides, quinoline derivatives are given: aqueous capillary electrophoresis, micellar electrokinetic capillary chromatography and non-aqueous electrophoresis. CE has some advantages over other approaches: rapid and effective separation, relatively a simple set of tools, and a minimum amount of a sample, and the analysis time is usually short. Non-aqueous capillary electrophoresis (NACE) is an alternative technique to aqueous CE. NACE has been applied for separating some molecules under special circumstances, i.e. when analytes and electrolytes are insoluble or partially soluble in water. Micellar chromatography makes it possible to separate both ionogenic and uncharged components of the sample, due to the introduction of a surfactant into the lead electrolyte. Thus this paper reports successful separation of a mixture of compounds quinoline-2-thione (I) and 8-mercaptoquinoline hydrochloride (II) and the quantitative determination of compounds I–II by capillary zone electrophoresis (CZE) was optimized. CZE provides the sensitive and reproducible estimation of analyte concentration in the range from 0.8–161.2 μg ml−1 for quinoline-2-thione in aqueous medium and 2.19–219.2 μg ml−1 for 8-mercaptoquinoline hydrochloride in non-aqueous medium. The detection limit was 0.4 μg ml−1 for quinoline-2-thione and 1.5 μg ml−1 for 8-mercaptoquinoline hydrochloride respectively.

Herein we propose a rational design to construct peroxidase mimetics in response to S1 nuclease by employing guanine-rich oligonucleotides and Cu2+ ions. The enzymatic activities of DNA–Cu(ii) are highly dependent upon the binding stoichiometry between Cu2+ and DNA. In the H2O2-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine, the catalytic activity of Cu2+ can be accelerated approximately 88 times in the presence of AG3(T2AG3)3, whereas it shows slight enhancement in the presence of a mononucleotide (GMP). The coordination of Cu2+ with DNA structures greatly strengthens its ability to generate reactive oxygen species. The most intriguing finding in this study is that DNA–Cu(ii) complexes lose their enzymatic activities after the cleavage of DNA scaffolds by S1 nuclease. A colorimetric method was established for selectively evaluating the S1 nuclease activity with a limit of detection of 4.7 × 10−3 U mL−1, only by using label-free oligonucleotides and copper ions without complicated synthesis and apparatus. This facile method can also be applicable for quantitative analysis in biological fluids.

Sex determination from fingermarks using fluorescent in situ hybridization by Annemieke van Dam; Angela van Weert; Kim Falkena; Chantal Weymans; Ate D. Kloosterman; Saskia A. G. Lambrechts; Ton G. van Leeuwen; Maurice C. G. Aalders (1413-1419).
When fingermarks are not suited for automated fingerprint identification, caused by for instance, poor development or when no match can be found in the fingerprint database, the chemical composition can be used to extract additional information about the donor of the fingermark. DNA potentially allows identification, however, the recoverable amount of DNA present in fingermarks is often too low to allow successful DNA-profiling. Therefore, in this research we focus on a method of in situ analysis of the available nucleated cells in fingermarks without prior DNA sampling and extraction and target specific DNA sequences in these cells to reveal potential additional donor profile information. To prove the principle, we determine the sex of the fingermark donor by targeting specific sequences on the X and Y chromosome using fluorescent in situ hybridization. Successful determination of the donor's sex based on the presence of male or female cells in the fingermark depositions is demonstrated. Powder dusting and lifting the fingermarks with gelatine lifters does not influence fluorescent in situ hybridization as male and female nucleated cells can be established reliably in fingermark residues. We show that both biometric information and donor characteristics can be obtained from fingermarks including both the morphological and the chemical properties of the fingermark.

Designed multifunctional ionic liquids–magnetic graphene nanocomposites as the adsorbent of MSPE for the determination of preservatives by Shurui Cao; Yaling Chen; Lei Zhang; Cunxian Xi; Xianliang Li; Bobin Tang; Guomin Wang; Zhiqiong Chen (1420-1430).
A new structural design for fabricating four types of ionic liquids was successfully adapted, which was based on changing the anion of 1-vinyl-3-octylimidazolium bromide (VOIm+Br) with benzene sulfonic acid (BenSO3), 2-naphthalene sulfonic acid (NapSO3), 1-anthraquinonesulfonic acid (AQSO3) and 1,2-naphthoquinone-4-sulfonic acid (NQSO3). Then, designed ionic liquids were directly modified on the surface of magnetic graphene oxide reduced nanoparticles (Fe3O4@SiO2@G) and used as a novel magnetic adsorbent for the determination of preservatives in vegetables via ultra-high performance liquid chromatography-triple quadrupole/linear ion trap mass spectrometry (UPLC-MS/MS). In this study, the specific adsorption capacity of the four types of functional ionic liquid–magnetic graphene adsorbents was investigated. The adsorption abilities of the as-prepared novel magnetic adsorbents towards 34 preservatives were investigated. The adsorbent comprising functional ionic liquid 1-vinyl-3-octylimidazole-2-naphthalene sulfonate (VOIm+NapSO3) combined with Fe3O4@SiO2@G adsorbent had better adsorption capacity than the other adsorbents due to the following factors: the structure of the ionic liquid with two benzene rings could produce an appropriate intensity of π–π conjugation; lower steric hindrance enabled the facile combination with preservatives; the imidazole ring and the hydroxyl groups provided the possibility of formative hydrogen bonding. The detailed chemical and microstructural features of the hybrid nanomaterials were studied via SEM, VSM, FTIR and XPS analyses. Under the optimal conditions, the satisfactory detection limits (LOD) of this method were in the range of 0.01–0.15 μg L−1. This study reveals the potential of the VOIm+NapSO3 attached Fe3O4@SiO2@G nanomaterial composite as a novel adsorbent for pretreatment applications.

In recent years, an increasing number of stimulant drugs and new psychoactive substances (NPSs) have caused concern in scientific communities and therefore innovative methods to extract compounds from complex biological samples are required. This work is aimed at developing and validating a clean, convenient and straightforward extraction procedure with microliter amounts of organic solvent using Solid Phase Micro-Extraction tips (SPME tips) and analysis using Gas Chromatography-Mass Spectrometry (GC-MS) in human urine samples. Another aim is to evaluate three different types of SPME fibre tips C18, C18-SCX (mixed mode) and PDMS-DVB. The quantification method examined the different classes of stimulant compounds included Amphetamine-Type Stimulants (ATSs) (amphetamine, methamphetamine, para-methoxyamphetamine (PMA), and (±)-3,4-methylenedioxymethamphetamine (MDMA)) and synthetic cathinones (mephedrone, buphedrine (buphedrone ephedrine metabolite), 4-methylephedrine (mephedrone metabolite), and pentylone). The method was developed with respect to several areas of the experimental design including pH, ionic strength, addition of salts, vial dimensions, analytes and derivatisation, type of solvents, solvent volume, extraction and desorption time, agitation speeds in the extraction and desorption steps and matrix volume. The optimised method was validated for eight compounds using the SPME PDMS/DVB fibre tips with satisfactory linearity and selectivity ranging between 50 and 2000 ng mL−1, and limits of detection (LODs) and low limits of quantification (LLOQs) ranging between (5–25) and (25–100) ng mL−1 respectively. Within-run and between-run accuracy and precision were <15%. The method was applied to real human urine samples indicating its suitability for common stimulant drugs and provided clean chromatograms with no interfering peaks. The assessment of green analytical chemistry for the method used was discussed and compared with Solid Phase Extraction (SPE). According to the results obtained we recommend the method for use in routine laboratories carrying out drug/forensic analysis for confirmation tests of the studied compounds.

The proposed work introduces an electrochemical sensor based on an Fe3O4/Ag nanocomposite for highly sensitive and selective electrochemical determination of dicyclomine hydrochloride (DcCl) using adsorptive stripping square wave voltammetry (AdSSWV). A nanocomposite of silver decorated Fe3O4 nanocubes has been synthesized using a facile sonochemical method. The prepared nanocomposite was characterized using various characterization techniques. The impact of various parameters such as pH, scan rate, accumulation potential and accumulation time on peak current was studied employing different techniques including differential pulse voltammetry (DPV), cyclic voltammetry (CV) and AdSSWV. Under the optimized conditions, the peak current is found to be linearly proportional to the DcCl concentration in a wide linear working range from 2.0 × 10−7 to 8.0 × 10−4 M with a limit of detection (LOD) and a limit of quantification (LOQ) of 4.8 × 10−9 M and 1.6 × 10−8 M, respectively. The fabricated sensor exhibited high sensitivity and selectivity along with good stability and reproducibility, and therefore the proposed method can serve as an excellent platform for the determination of DcCl at the nanomolar level with adequate recovery in pharmaceutical as well as biological samples.

A study of the chemical stability of the antiepileptic drug ethosuximide (ESX) under certain ICH-recommended stress conditions was conducted for the first time. A stability-indicating HPLC method was applied using a mobile phase containing 0.05 M sodium dihydrogen phosphate and methanol (90 : 10 v/v) at pH 3.5 and a Promosil C18 column for separation of ESX from its potential degradation products with UV detection at 210 nm. The method validity was confirmed showing a linearity range of 2.0–30.0 μg mL−1 with a lower limit of detection of 0.14 μg mL−1. The results of the developed method showed good agreement with those obtained by the USP official method. The stability of ESX was investigated by subjecting it to some stress conditions of the ICH guideline such as acidic, alkaline and oxidative conditions. The drug was liable to degradation under these conditions yielding specific degradation products. The validated stability-indicating HPLC method efficiently separated the drug from all of the formed degradation products proving its suitability for purity and stability testing.

Chemometrics-assisted liquid chromatography-full scan mass spectrometry for simultaneous determination of multi-class estrogens in infant milk powder by Xiao-Dong Sun; Hai-Long Wu; Zhi Liu; Li-Xia Xie; Yong Hu; Huan Fang; Tong Wang; Rong Xiao; Yu-Jie Ding; Ru-Qin Yu (1459-1471).
In the present study, a smart analytical strategy that combines liquid chromatography-full scan mass spectrometry with the second-order calibration method based on the alternating trilinear decomposition (ATLD) algorithm was developed for the simultaneous determination of seven estrogens in infant milk powders. The seven estrogens were rapidly eluted out within 7.0 min under a simple gradient condition and then, they were detected by mass spectrometry operated in the full scan mode. With the aid of the prominent “second-order advantage” of the algorithm, specific qualitative and quantitative information about the target analytes could be extracted from the complex system even in the presence of considerable peak overlaps, baseline drifts and unknown interferences. The proposed strategy avoided time-consuming and laborious sample pretreatment procedures, resulting in minimal loss of analytes, which improved the analytical accuracy. Average recoveries of the seven estrogens in two spiked infant milk powder samples were in the range of 91.2–104.2% with the relative standard deviations (RSDs) lower than 5.0% (with the exception for 17α-estradiol), and the limits of detection (LOD) ranged from 0.07 to 2.49 ng mL−1. Besides, to further confirm the feasibility and reliability of the proposed method, the same batch of samples was analyzed using the LC-MS/MS method, and the statistical tests showed that no significant difference existed between the two methods, which fully indicated that the proposed strategy could provide satisfactory prediction results in real infant milk powder samples as well as other actual chemical systems.

Development of a novel voltammetric sensor for the determination of quercetin on an electrochemically pretreated carbon-paste electrode by Konstantin Pliuta; Alexander Chebotarev; Anastasiya Koicheva; Kateryna Bevziuk; Denys Snigur (1472-1479).
In this work, a simple, cheap and sensitive sensor for quercetin voltammetric determination was developed. Quercetin is a flavonoid that is widely distributed in plants. The antioxidant, anti-cancer, antibacterial and anti-inflammatory activities of quercetin make it an important biologically active substance. Therefore, the development of new methods for its rapid and inexpensive determination is an urgent task. The presence of a large number of hydroxyl groups in quercetin makes its accumulation possible due to hydrogen bonding. Using the electrochemical activation of a carbon-paste electrode, a sensor with great ability for quercetin adsorption has been developed. Using the proposed sensor, the electrochemical behavior of quercetin has been investigated. The adsorption nature of the current was established. After pre-accumulation on the sensor, quercetin is oxidized reversibly. Using SWVs under optimal conditions (electrochemical pretreatment of the CPE was carried out in 1 M NaOH solution at 1.5 V for 120 seconds; quercetin adsorption at 0 mV for 300 s from Britton–Robinson buffer solution with pH 3 and a sweep rate of 200 mV s−1, an amplitude of 50 mV, and a frequency of 30 Hz), it is possible to determine quercetin in the concentration range of 0.06–2 μM, with the LOD and LOQ equal to 1.6 × 10−3μM and 5.2 × 10−3μM, respectively, and a sensitivity of 19.9 μA μM−1. The developed sensor was satisfactorily used for the determination of quercetin in pharmaceuticals and extracts of green and black tea with a RSD of 3.5%.

Preparation of artificial antibodies and development of an antibody-based indirect ELISA for the detection of ancient wool by Bing Wang; Jincui Gu; Qiushi You; Boyi Chen; Hailing Zheng; Yang Zhou; Zhiwen Hu (1480-1487).
The use of wool from sheep is widespread in ancient and historic textiles. The detection of ancient wool can provide meaningful information for both archaeologists and academics. However, the efficacy of conventional methods is likely to be limited in the detection of ancient samples with severe degradation or contamination. This is also one of the main challenges in archaeological sites. In this study, a novel immunological approach was proposed to overcome this difficulty. Two diagnostic antibodies, the anti-K (keratin) antibody and the anti-P (peptide) antibody, were carefully designed and prepared through the immunization of animals with a complete antigen (keratin) and the conjugation product of hapten (diagnostic peptide) with a carrier protein, respectively. Next, an indirect enzyme-linked immunosorbent assay (ELISA) was established under the optimal binding concentration of the coating antigens and the antibodies. The results indicated that the antibody-based immunological method exhibited high sensitivity, specificity and reliability. The limit of detection in the ELISA for the anti-K and anti-P antibodies was 81.39 ng mL−1 and 6.81 ng mL−1, respectively. The ELISA revealed a lower cross-reactivity (less than 0.01%) for the two antibodies with interference antigens. The recoveries of the two antibodies from standard soil samples were in the range of 80% to 100%, with a relative standard deviation (RSD) of lower than 9%. The coefficients of variation for the anti-K antibody and anti-P antibody were in the range of 3.27% to 12.40% and 9.48% to 10.31%, respectively. Moreover, both the anti-K and anti-P antibodies can positively identify ancient wool samples, even for wool traces in soil, verifying the validity and practicability of the immunological method in the detection of ancient wool.

Back cover (1489-1490).