Analytica Chimica Acta (v.626, #2)

Contents (iii-iv).

Comparison of N-alkyl acridine orange dyes as fluorescence probes for the determination of cardiolipin by P. Kaewsuya; J.D. Miller; N.D. Danielson; J. Sanjeevi; P.F. James (111-118).
The phospholipid (PL), cardiolipin (CL), is found almost exclusively in the inner membrane of mitochondria and loss of CL is considered as an important indication of cell apoptosis. Previously, 10-N-nonyl acridine orange (NAO) has been used as a fluorescent probe for the visualization of CL in mitochondrial cell membranes and in solution. In this work for the determination of CL, we have synthesized two new fluorescent probes, n-tetradecyl acridine orange (C14-AO), and n-octadecyl acridine orange (C18-AO) by reacting acridine orange with the corresponding n-alkyl bromide. Using excitation and emission wavelengths at about 500 and 525 nm and varying the percentage of methanol in water as the solvent, no interaction between CL and the fluorescent probes at 75% is noted but a proportional quenching of the fluorescence signal by CL is observed at 50% or less for C14-AO and 60% or less for C18-AO. Binding efficiency of these fluorescent probes to CL is compared using dye concentrations of 5, 10, and 20 μM. C18-AO shows a better sensitivity than C14-AO and NAO, respectively, but is less selective. For C14-AO, the detection limit and limit of quantitation are 0.07 and 0.21 μM, respectively, which are better than those previously reported for NAO. One anionic PL, phosphatidic acid, shows some quenching interference to both the C14 and C18 dyes but only at concentrations above the working range for sample analysis. The CL in mitochondrial membrane samples is determined by standard addition using C14-AO. The level of CL in the outer mitochondrial membrane compared to the inner membrane is significantly increased due to the addition of cadmium chloride into the cells causing cell apoptosis.
Keywords: Fluorescence; Cardiolipin; Phospholipids; Acridine orange alkyl derivatives;

Single-walled carbon nanotubes (SWNTs) have become one of the most intensely studied nanostructures because of their unique properties. The inherent physical properties of carbon nanotubes make them ideal supports for metal nanoparticles. The use of electrodeposition to modify SWNTs in order to facilitate applications in areas related to catalysis and sensing is presented in this manuscript. Preparation of raw SWNT material for electrochemical experiments involves various mild or oxidative pretreatments. In this review we focus on progress toward functionalization of SWNTs with metal nanoparticles using electrochemical methods and the applications of metal decorated carbon nanotubes in energy related applications.
Keywords: Single-walled carbon nanotube; Sensor; Aligned networks; Electrodeposition; Nanoparticle; Electrochemistry;

Does chemometrics enhance the performance of electroanalysis? by Yongnian Ni; Serge Kokot (130-146).
This review explores the question whether chemometrics methods enhance the performance of electroanalytical methods. Electroanalysis has long benefited from the well-established techniques such as potentiometric titrations, polarography and voltammetry, and the more novel ones such as electronic tongues and noses, which have enlarged the scope of applications. The electroanalytical methods have been improved with the application of chemometrics for simultaneous quantitative prediction of analytes or qualitative resolution of complex overlapping responses. Typical methods include partial least squares (PLS), artificial neural networks (ANNs), and multiple curve resolution methods (MCR-ALS, N-PLS and PARAFAC). This review aims to provide the practising analyst with a broad guide to electroanalytical applications supported by chemometrics. In this context, after a general consideration of the use of a number of electroanalytical techniques with the aid of chemometrics methods, several overviews follow with each one focusing on an important field of application such as food, pharmaceuticals, pesticides and the environment. The growth of chemometrics in conjunction with electronic tongue and nose sensors is highlighted, and this is followed by an overview of the use of chemometrics for the resolution of complicated profiles for qualitative identification of analytes, especially with the use of the MCR-ALS methodology. Finally, the performance of electroanalytical methods is compared with that of some spectrophotometric procedures on the basis of figures-of-merit. This showed that electroanalytical methods can perform as well as the spectrophotometric ones. PLS-1 appears to be the method of practical choice if the %relative prediction error of ∼±10% is acceptable.
Keywords: Electroanalysis; Chemometrics; Voltammetry; Potentiometry; Sensors;

Selective determination of acidic pharmaceuticals in wastewater using molecularly imprinted solid-phase extraction by Saioa Zorita; Brian Boyd; Stig Jönsson; Ecevit Yilmaz; Carin Svensson; Lennart Mathiasson; Staffan Bergström (147-154).
The determination of acidic pharmaceuticals, such as non-steroidal anti-inflammatory drugs NSAIDs and clofibric acid (metabolite of clofibrate), at low ng L−1 levels in wastewater requires highly selective and sensitive analytical procedures. The removal of matrix components during sample preparation results in significant benefits towards reducing the matrix effects during LC–MS analysis. Therefore this work describes a simple method to enrich and clean up NSAIDs and clofibric acid from sewage water using molecularly imprinted solid-phase extraction (MISPE). Final analysis was performed by liquid chromatography–tandem mass spectrometry. The performance of this method has been evaluated in fortified tap and sewage water in terms of recovery, precision, linearity, and method quantification limit. Recovery for all compounds ranged in all matrices between 84 and 116% with intra-day R.S.D. values below 11.5%. Matrix effect evaluation demonstrated that even complex sample matrixes, such as pond or sewage water did not showed significant ion suppression/enhancement compared to tap water. The performance of the method was further emphasized by the study of pond water, which receives treated water from a sewage treatment plant in south Sweden. Raw sewage and treated water were also tested. In those samples, all acidic pharmaceuticals were detected in concentration above method quantification limits ranging from 5.1 to 5153.0 ng L−1.
Keywords: Acidic pharmaceuticals; Sewage water; Molecularly imprinted polymers; Solid-phase extraction; Matrix effect;

A new, single-step extraction and purification method based on matrix solid-phase dispersion (MSPD) was developed to determine 17 polycyclic aromatic hydrocarbons (PAHs) in sewage sludge samples. The MSPD method consists of sample homogenisation, exhaustive extraction and clean-up by a single process. The different operational parameters of the method, such as the type of dispersant, type and amount of additives, clean-up co-sorbent and extractive solvent were evaluated. Reversed-phase (C18) and polymeric (Oasis HLB and Oasis MAX) materials, as well as normal phase sorbents (Florisil, silica, neutral alumina) and an inert support (sand) were tested to assess the sorbents effect on the yield and selectivity of the MSPD process. Analysis of extracts was performed by high performance liquid chromatography (HPLC) coupled with fluorescence detection.Quantification limits obtained for all of these considered compounds (between 0.0001 and 0.005 μg g−1 dry mass) were well below of the limits recommended in the EU. The extraction yields for the different compounds obtained by MSPD ranged from 76.3% to 103.6%. On the other hand, the extraction efficiency of the optimised method is compared with that achieved by microwave-assisted extraction and the method was applied to the analysis of real sewage sludge samples. A certified reference material (sewage sludge (BCR 088)) and a reference material (sewage sludge (RTC-CNS312-04)) were used to validate the proposed method.
Keywords: Polycyclic aromatic hydrocarbons; Matrix solid-phase dispersion; Sewage sludge analysis; Liquid chromatography;

A simple and efficient liquid-phase microextraction (LPME) in conjunction with gas chromatography-electron capture detector (GC-ECD) has been developed for extraction and determination of 11 organochlorine pesticides (OCPs) from water samples. In this technique a microdrop of 1-dodecanol containing pentachloronitrobenzene (internal standard) is delivered to the surface of an aqueous sample while being agitated by a stirring bar in the bulk of solution. Following completion of extraction, the sample vial was cooled by putting it into an ice bath for 5 min. Finally 2 μL of the drop was injected into the GC for analysis. Factors relevant to the extraction efficiency were studied and optimized. Under the optimized extraction conditions (extraction solvent: 1-dodecanol; extraction temperature: 65 °C; sodium chloride concentration: 0.25 M; microdrop and sample volumes: 8 μL and 20 mL respectively; the stirring rate: 750 rpm and the extraction time: 30 min), figures of merit of the proposed method were evaluated. The detection limits of the method were in the range of 7–19 ng L−1 and the RSD% for analysis of 2 μg L−1 of OCPs was below 7.2% (n  = 5). A good linearity (r 2  ≥ 0.993) and a relatively broad dynamic linear range (25–2000 ng L−1) were obtained. After 30 min of extraction, preconcentration factors were in the range of 708–1337 for different organochlorine pesticides and the relative errors ranged from −10.1 to 10.9%. Finally the proposed method was successfully utilized for preconcentration and determination of OCPs in different real samples.
Keywords: Liquid-phase microextraction; Organochlorine pesticides; Gas chromatography-electron capture detector; Solidified microdrop;

A novel and simple spectrophotometric method for the determination of Captopril with sodium 1,2-naphthoquinone-4-sulfonate is established in this paper. The detailed reaction mechanism is proposed and discussed. It is based on the fact that captopril can catalyze the reaction between sodium 1,2-naphthoquinone-4-sulfonate and hydroxyl ion to form 2-hydroxy-1,4-naphthoquinone in buffer solution of pH 13.00. Beer's law is obeyed in a range of 0.64–80 μg mL−1 at the maximal absorption wavelength of 442 nm. The equation of linear regression is A  = 0.05815 + 0.00589C (μg mL−1), with a linear regression correlation coefficient of 0.9981. The detection limit is 0.3 μg mL−1, R.S.D. is 0.77% and the recovery rate is in range of 96.0–103.8%. Furthermore, the method has been validated and successfully applied to the determination of captopril in pharmaceutical samples.
Keywords: Captopril; Sodium 1,2-naphthoquinone-4-sulfonate; Spectrophotometry; Catalytic reaction;

Tetracyclines (TCs) are widely used for prevention and control of infectious diseases and have a great activity against variety of Gram-positive and Gram-negative bacteria. Due to the widespread use of TCs in animal husbandry, it can lead to an increase the risk of TCs remaining in human food. To protect consumers, many countries have set acceptable tolerance levels for these drugs. Therefore, it is necessary to establish a suitable analytical technique with specificity, sensitivity and simplicity.The biotin–avidin mediated ELISA method was performed to determine TC residues in honey quantitatively. By using PBS-EDTA assay buffer at pH 7.2, a honey solution of TC standard was prepared and diluted. And no additional pre-treatment of sample was required in this method. The limit of detection and limit of quantitation of the optimized method were 3.98 × 10−10  M (0.19 μg L−1) and 7.94 × 10−10  M (0.38 μg L−1), respectively, and the dynamic range was from 1.52 μg L−1 to 152 μg L−1 of TC in honey. No cross-reactivity was observed with the structurally similar compounds, and mean percent recoveries of TC spiked in honey ranged from 95% to 101%. Compared to other methods, this method was superior in terms of detection limit, dynamic range, and % recovery with simple sample-preparation.
Keywords: Tetracycline; Antibiotics; Honey; Immunoassay;

Time-resolved luminescent lateral flow assay technology by Xuedong Song; Michael Knotts (186-192).
We here report a detection technology that integrates highly sensitive time-resolved luminescence technique into lateral flow assay platform to achieve excellent detection performance with low cost. We have developed very bright, surface-functionalized and mono-dispersed phosphorescent nanoparticles of long lifetime under ambient conditions. The phosphorescent nanoparticles have been used to conjugate with monoclonal antibody for C-reactive protein (CRP), an inflammatory biomarker. Lateral flow immunoassay devices have been developed using the conjugate for highly sensitive detection of CRP. The CRP assay can achieve a detection sensitivity of <0.2 ng mL−1 in serum with a linear response from 0.2 to 200 ng mL−1 CRP. We have also developed a low cost time-resolved luminescence reader for the lateral flow immunoassay (LFIA) devices. The reader does not use expensive band pass filter and still provide very low detection background and high detection sensitivity on solid substrates such as nitrocellulose membranes. The reader can detect less than 2.5 ng phosphorescent particles captured on a nitrocellulose membrane strip with more than three orders of magnitude linear detection dynamic range. The technology should find a number of applications, ranging from clinical diagnostics, detection of chemical and biological warfare agents, to food and environmental monitoring.
Keywords: Lateral flow immunoassay; Time-resolved luminescence; Fluorescence; Phosphorescence; Nanoparticle;

A single-drop liquid–liquid–liquid microextraction (LLLME) method coupled with high-performance liquid chromatography (HPLC) was developed for the determination of fentanyl in biological (plasma and urine) and wastewater samples. Fentanyl is a potent synthetic narcotic analgesic administered in the form of a transdermal patch for the management of chronic pain. Fentanyl was extracted from 0.01 M NaOH solution (donor phase) into a thin layer of organic phase (100 μL), then back-extracted into 5 μL of the acidic acceptor microdrop (1 × 10−3  M HClO4) immersed in the organic membrane from the tip of a 25-μL HPLC syringe. After the extraction, the microdrop was withdrawn into the syringe and injected directly into a HPLC system for analysis. The parameters influencing the extraction efficiency including the organic solvent and its volume, acceptor microdrop volume, composition of the donor and acceptor phases, stirring rate, temperature, salt addition and pre- and back-extraction times were investigated and optimized. At the most appropriate conditions (100 μL of n-octane, 3.6 mL of the donor phase maintained at 0.01 M NaOH, 5 μL of 1 × 10−3  M HClO4 as the acceptor microdrop, stirring rate of 1000 rpm for pre-extraction and 700 rpm for back-extraction, 30 °C, no salt addition, 30 min for pre-extraction and 20 min for back-extraction), an enrichment factor (EF) of 355 was obtained. The limit of detection (LOD) was 0.1 ng mL−1 (based on S/N = 3) and intra- and inter-day relative standard deviations less than 9% were obtained. The calibration graph was linear within the range of 0.5–1000 ng mL−1 with the correlation coefficient (r) of 0.9999. Finally, the feasibility of the proposed method was evaluated by extraction and determination of fentanyl in plasma, urine and wastewater samples and satisfactory results were obtained.
Keywords: Single-drop liquid–liquid–liquid microextraction; High-performance liquid chromatography; Fentanyl; Plasma; Urine; Water;

Gynostemma pentaphyllum (Thunb.) Makino, a traditional Chinese herb possessing antitumor and antioxidant activities, has been shown to contain several functional components like saponins and flavonoids. However, their identities remain uncertain. The objectives of this study were to develop an appropriate extraction, purification and HPLC–MS method to determine saponins and flavonoids in G. pentaphyllum. Both flavonoids and saponins were extracted with methanol, followed by purification with a C18 cartridge to elute the former with 50% methanol and the latter with 100% methanol. A total of 34 saponins were separated within 40 min by a Gemini C18 column and a gradient mobile phase of acetonitrile and 0.1% formic acid in water, in which 18 saponins were identified by LC–MS with ESI mode and Q-TOF (LC/MS/MS). Similarly, a total of eight flavonoids were separated within 45 min by the same column and a gradient solvent system of methanol and 0.1% formic acid in water, with identification being carried out by a post-column derivatization method and LC–MS with ESI mode. The amounts of flavonoids in G. pentaphyllum ranged from 170.7 to 2416.5 μg g−1, whereas saponins were from 491.0 to 89,888.9 μg g−1.
Keywords: Gynostemma pentaphyllum; Saponins; Flavonoids; HPLC–MS;