Just Published:Sensors & Actuators A: Physical

A new issue of this journal has just been published. To see abstracts of the papers it contains (with links through to the full papers) click here:

Sensors & Actuators A: Physical
http://rss.sciencedirect.com/publication/science/5282

Selected papers from the latest issue:

An improved sensitivity normalization technique of PGC demodulation with low minimum phase detection sensitivity using laser modulation to generate carrier signal

31 December 2012, 09:28:22

1 March 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 191

The phase carrier signal of the PGC demodulation in fiber optic interferometric sensors (FOIS) may be generated by using laser current modulation to achieve all-fiber structures in long-distance and outdoor applications. An optical intensity modulation with carrier frequency induced from the laser modulation will cause the instability and distortion in the PGC demodulation output. Additionally, since the optical intensity attenuation of the FOIS will degrade the PGC demodulation output, proper sensitivity compensation on the PGC demodulator is necessary for the field applications. In this paper, we propose an improved technique by using a balanced photoreceiver in the FOIS to attain significant improvements in the instability and distortion of the PGC demodulation output. Moreover, we choose a small phase scrambler signal amplitude of 1rad to achieve improved the minimum phase detection sensitivity (MPDS) as well as sensitivity normalization because the improvement of the MPDS is very important to the advanced FOIS. The experimental results show that the improved values of the best MPDS are 5.7dB (for DFB laser diode) and 4.3dB (for EP1550 laser diode), respectively, by using the improved technique. From the sensitivity normalization experiment results, the relative error is shown to be less than 0.5% when the optical intensity attentuation is no more than 15dB. It verifies the effectiveness of the sensitivity normalization technique proposed in our improved PGC demodulation system.

Demonstration of an optically actuated ferrule-top device for pressure and humidity sensing

31 December 2012, 09:28:22

1 February 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 190

Ferrule-top micro mechanical sensors are an alternative platform for point measurements in critical environments, where standard micro-electro-mechanical systems are prone to failure. To fully benefit from the all-optical character of this design, it is important to demonstrate that the mechanical pieces fabricated on top of the ferruled fiber can be actuated with light. In this paper we propose a convenient, all-optical actuation scheme that can be applied without any additional modification of the sensor design. The scheme relies on the photo thermal effect, which is proven to be sufficient both for inducing significant static bending and for exciting the sensor to resonance. We also demonstrate that this mechanism can be successfully used to implement ferrule-top resonant sensors for humidity and pressure measurements.

Highlights

► We demonstrate an all-optical actuation scheme for ferrule-top sensors. ► The new approach does not require any modification of sensors design. ► The method is sufficient for static and dynamic excitation. ► We present an all-optical gravimetric humidity and pressure sensor.

Novel optical fiber humidity sensor based on a no-core fiber structure

31 December 2012, 09:28:22

1 February 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 190

A novel and simple optical fiber structure with a section of no-core fiber for measuring relative humidity (RH) is presented. Moisture-sensitive materials HEC/PVDF are used to form the hydrogel coating on the no-core fiber by dip impregnation method. Under different humidity conditions, the humidity induced refractive index changes on the outside coating of no-core fiber will lead to the variations of the optical output power. The different lengths of no-core fiber are tested at the two wavelengths of 1310nm and 1550nm, respectively. The results show that the structure with 2cm no-core fiber has a higher RH sensitivity of 0.196dB/%RH at 1310nm and a better linearly response when the RH is lower than 75%. Furthermore, the optical output powers are measured with the rise and drop of RH, and the four times repetition are also recorded, which all demonstrate the good stability and repeatability of our proposed structure.

Resonance frequency of locally heated cantilever beams

31 December 2012, 09:28:22

1 February 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 190

This paper investigates the temperature dependence of the resonance frequency for locally heated cantilever beams and proposes a solution to minimize it. In the first part of the paper a theoretical study, supported by simulations, is carried out in order to determine the temperature distribution on locally heated cantilever beams. The theoretical results are supported by measurements performed with an IR camera. Knowing the temperature distribution on the cantilever beams, the frequency shifts due to the temperature gradient on the beams is calculated. A comparison between three locally heated cantilever beams made of Si, SiO2 and SiN shows that SiN is the best choice in order to minimize the temperature dependence of the resonance frequency. Measurements on a SiN cantilever paddle show that its resonance frequency is constant with heater temperature for temperature up to 590 K. The device exhibits a temperature dependence of the resonance frequency of about 20ppm/K, for heater temperature from 590K to 920K.

Measurement of thermal elongation induced strain of a composite material using a polarization maintaining photonic crystal fiber sensor

31 December 2012, 09:28:22

1 February 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 190

A measurement scheme to measure a composite material's thermal elongation induced strain using a buffer stripped Polarization Maintaining Photonic Crystal Fiber (PM-PCF) sensor is investigated in this paper. A composite material sample with an embedded PM-PCF based polarimetric fiber sensor is fabricated and characterized. It is found that the buffer stripped PM-PCF polarimetric sensor which is temperature insensitive in free space, shows significant phase change when embedded in the composite material due the thermal elongation of the composite material. The temperature induced phase change of buffer stripped PM-PCF polarimetric sensors embedded in carbon-epoxy, E glass-epoxy, E glass-unsaturated polyester resin composite material samples is measured and the results are used to determine the thermal elongation induced strain over a temperature range from 0°C to 65°C. The experimentally measured thermal elongation induced strain of the same samples are found to be 3.648×10⁻⁵ ɛ/°C, 1.52×10⁻⁵ ɛ/°C, and 2.42×10⁻⁵ ɛ/°C. The Coefficient of Thermal Expansion (CTE) estimated theoretically using composite laminate theory shows good agreement with that derived using the PM-PCF sensor. The present investigation offers a simple non destructive method to determine thermal elongation induced strain in composite structures. It is shown that the method allows the measurement of thermal expansion for those composite materials having negligible residual strain and moisture expansion.

A review of nanometer resolution position sensors: Operation and performance

31 December 2012, 09:28:22

1 February 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 190

Position sensors with nanometer resolution are a key component of many precision imaging and fabrication machines. Since the sensor characteristics can define the linearity, resolution and speed of the machine, the sensor performance is a foremost consideration. The first goal of this article is to define concise performance metrics and to provide exact and approximate expressions for error sources including non-linearity, drift and noise. The second goal is to review current position sensor technologies and to compare their performance. The sensors considered include: resistive, piezoelectric and piezoresistive strain sensors; capacitive sensors; electrothermal sensors; eddy current sensors; linear variable displacement transformers; interferometers; and linear encoders.

Transparent force sensing arrays with low power consumption using liquid crystal arrays

31 December 2012, 09:28:22

1 February 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 190

A transparent force sensing array with low power consumption is developed from a 3×3 liquid crystal (LC) array. As force is applied to the LC array, the force-dependent capacitance curve of a sensor pixel under a higher voltage will shift to larger capacitance. Accordingly, the force range of the LC array can be divided into many sub-ranges at one of the capacitance values. The number of the input voltage is equal to that of the output capacitance in each of the sub-ranges, and the voltage-to-capacitance number is small (large) in the high (low)-force sub-range. The sensing array measures force in terms of the voltage-to-capacitance number. The transparent force sensing array shows potential as a touch panel, while it is immune to the need of rectifying the nonlinear relation between the applied force and the output capacitance using complex algorithm via high-end microcontrollers.

Preparation of semiconductor ZnO powders by sol–gel method: Humidity sensors

31 December 2012, 09:28:22

1 February 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 190

Undoped and Sn-doped ZnO nanopowder samples were prepared by the sol–gel method. The crystalline structure and surface morphology of the samples were analyzed by X-ray diffraction and atomic force microscopy. X-ray diffraction results indicate that the samples exhibit a hexagonal crystal structure. Electrical properties of the samples were measured by two probe method. The activation energies of the ZnO samples for low and high temperatures regions were determined. The optical band gaps of the samples were determined by optical absorption method. It was found that the samples have a direct transition optical band gap and the optical band gap values of the ZnO samples were changed with Sn doping. Quartz crystalline microbalance (QCM) technique was employed to investigate sensor features of the ZnO samples. The humidity sensor properties of undoped and Sn-doped ZnO samples based on quartz crystalline microbalance sensors were investigated. The obtained results indicate that the undoped and Sn-doped ZnO nanopowder samples can be used for humidity sensor applications.

ZnO nanowires–polyimide nanocomposite piezoresistive strain sensor

31 December 2012, 09:28:22

1 February 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 190

In this paper, we report a significant piezoresistive effect found in ZnO nanowires–polyimide nanocomposite. ZnO nanowires were synthesized through a simple hydrothermal route and subsequently mixed with polyimide matrix to form ZnO nanowires–polyimide nanocomposite. Electrical properties of the nanocomposite films, such as electrical conductivity, relative dielectric permittivity, impedance spectrum and electrical I–V curve, change with weight ratio of ZnO nanowires were characterized. Electrical measurement results indicated that the percolation threshold of the nanocomposite is about 15% weight ratio of ZnO nanowires. Piezoresistive effect of the nanocomposite was investigated and large gauge factor was observed for this nanocomposite. Strain sensors based on the nanocomposite thin films using interdigital electrodes were fabricated and used to measure the static and dynamic strain in a cantilever beam and the results were validated by theoretical calculation and measurements by other technique. With excellent flexibility, simple fabrication process, and large piezoresistive gauge factor, this novel ZnO nanocomposite can be used for strain sensors in many mechanical, civil, aerospace, and medical applications.

Worm like zinc oxide nanostructures as efficient LPG sensors

31 December 2012, 09:28:22

1 February 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 190

Multi-layered films of zinc oxide (ZnO), prepared using sol–gel spin-coating method, were used to study the response on exposure to liquefied petroleum gas (LPG). The X-ray diffraction (XRD) pattern of the thin films showed preferred orientation of the crystallites along the c-axis. Surface morphology studies using scanning electron microscopy (SEM) reveal a wrinkled surface with a worm like appearance for the film thickness varying from 85nm to 419nm. The films of different thickness were exposed to LPG and sensing characteristics were recorded using electrical methods. The ZnO thin films showed good sensitivity toward LPG at optimum temperature of 200°C with sensitivity strongly depending on the number of layers deposited. The sensing characteristics were further correlated with the microstructure of the thin films investigated using atomic force microscopy (AFM).

Model 150 Dynacalibrator® Calibration Gas Generator

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CO2/O2 Controller Ideal for Hypoxia and Hyperoxia Live-Cell Imaging Experiments

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A Harvard Apparatus Company
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Fax: 203-776-1278
E-mail: pr@warneronline.com
Web: www.warnerinstruments.com

Just Published: Spectrochimica Acta Part B: Atomic Spectroscopy

A new issue of this journal has just been published. To see abstracts of the papers it contains (with links through to the full papers) click here:

Spectrochimica Acta Part B: Atomic Spectroscopy
http://rss.sciencedirect.com/publication/science/5287

Selected papers from the latest issue:

A dried urine spot test to simultaneously monitor Mo and Ti levels using solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry

24 December 2012, 09:33:37

Available online 21 December 2012
Publication year: 2012
Source:Spectrochimica Acta Part B: Atomic Spectroscopy

Home-based collection protocols for clinical specimens are actively pursued as a means of improving life quality of patients that require frequent controls, such as patients with metallic prosthesis, for whom monitoring the evolution of Mo and Ti in biological fluids may play a decisive role to detect prosthesis mal-functioning. The collection of biological fluids on clinical filter papers provides a simple way to implement these protocols. This work explores the potential of solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry for the simultaneous and direct determination of Mo and Ti in urine, after its deposition onto clinical filter paper, giving rise to a dried urine spot. The approach used for depositing the sample was found crucial to develop a quantitative method, since the filter paper acts as a chromatographic support and produces a differential distribution of the target analytes. Furthermore, the high spreading of urine onto a filter paper results in a small amount of urine per surface unit, and thus, ultimately, in lack of sensitivity. In order to circumvent these problems, the use of an alternative approach based on the use of pre-cut 17x19 mm filter paper pieces onto which larger amounts of sample (500 μL) can be retained by single deposition was proposed and evaluated. In this way, an approximately 12-fold increase in sensitivity and a more homogeneous distribution of the target analytes were obtained, permitting the development of a quantification strategy based on the use of matrix-matched urine samples of known analyte concentrations, which were subjected to the same procedure as the samples. Accuracy of this method, which provides LODs of 1.5μgL^-1 for Mo and 6.5μgL^-1 for Ti, was demonstrated after analysis of urine reference materials. Overall, the performance of the method developed is promising, being likely suitable for determination of other analytes in dried urine spots.

Highlights

► deposition of urine on clinical filters is a simple way to implement home-base collection procedures to monitor patient's evolution ► solid sampling HR CS GFAAS is investigated for the direct determination of Mo and Ti, used as biomarkers to detect prosthesis malfunctioning, in urine dried spots; ► the way in which the sample is deposited in the filter is key to ensure sufficient sensitivity and to avoid chromatographic effects; ► use of matrix-matched urine standards for calibration is proposed, permitting achieving accurate results and LODs of a few μgL^-1;

Hydride generation - in-atomizer collection of Pb in a quartz trap-and-atomizer device for atomic absorption spectrometry – an interference study

24 December 2012, 09:33:37

Available online 21 December 2012
Publication year: 2012
Source:Spectrochimica Acta Part B: Atomic Spectroscopy

Interferences of selected hydride forming elements (As, Sb, Bi, Se and Sn) on lead determination by hydride generation atomic absorption spectrometry were extensively studied in both on-line atomization and preconcentration (collection) modes. The commonly used on-line atomization mode was found free of significant interferences, whereas strong interference from Bi was observed when employing the preconcentration mode with plumbane collection in a quartz trap-and atomizer device. Interference of Bi seems to take place in the preconcentration step. Interference of Bi in the collection mode cannot be reduced by increased hydrogen radical amount in the trap and/or the atomizer.

Highlights

► Interference study on Pb determination by in-atomizer trapping was performed for the first time. ► Bi was found as a severe interferent in the preconcentration mode (Pb:Bi ratio 1:100). ► No interference was found in the on-line atomization (no preconcentration). ► Bi interference occurs during preconcentration.

Atomic and Molecular Emissions in Laser-Induced Breakdown Spectroscopy

24 December 2012, 09:33:37

Available online 20 December 2012
Publication year: 2012
Source:Spectrochimica Acta Part B: Atomic Spectroscopy

This article summarizes measurements and analysis of hydrogen Balmer series atomic lines following laser-induced optical breakdown. Electron number density on the order of 1 × 10²⁵ m⁻³ can be measured using H α Stark width and shift in the analysis of breakdown plasma in 1 to 1.3 × 10⁵ Pa, gaseous hydrogen. The H β line can be utilized for electron number density up to 7 × 10²³ m⁻³. The historic significance is elaborated of accurate H β measurements. Electron excitation temperature is inferred utilizing Boltzmann plot techniques that include H γ atomic lines and further members of the Balmer series. Laser ablation of aluminium is discussed in view of limits of application of the Balmer series. H β and H γ lines show presence of molecular carbon in a 2.7 and 6.5 × 10⁵ Pa, expanding methane flow. Diagnostic of such diatomic emission spectra is discussed as well. Laser-induced breakdown spectroscopy historically embraces elemental analysis, or atomic spectroscopy, and to a lesser extent molecular spectroscopy. Yet occurrence of superposition spectra in the plasma decay due to recombination or due to onset of chemical reactions necessitates consideration of both atomic and molecular emissions following laser-induced optical breakdown. Molecular excitation temperature is determined using so-called modified Boltzmann plots and fitting of spectra from selected molecular transitions. The primary interest is micro-plasma characterization during the first few micro-seconds following optical breakdown, including shadowgraph visualizations.

Graphical abstract

Highlights

► Electron density measurements in plasma using H-alpha and H-beta lines; ► Analysis of recorded data using accepted theories; ► Limitations of hydrogen Balmer series in study of laser-induced optical breakdown; ► Analysis of atomic and molecular superposition spectra; ► Computed atomic profiles and diatomic molecular spectra using line-strength-files.

Elemental analysis by surface-enhanced Laser-Induced Breakdown Spectroscopy combined with liquid–liquid microextraction

24 December 2012, 09:33:37

Available online 7 December 2012
Publication year: 2012
Source:Spectrochimica Acta Part B: Atomic Spectroscopy

In this work, the possibility of using Laser-Induced Breakdown Spectrometry (LIBS) combined with liquid–liquid microextraction techniques is evaluated as a simple and fast method for trace elemental analysis. Two different strategies for LIBS analysis of manganese contained in microdroplets of extraction solvent (Triton X-114) are studied: (i) analysis by direct laser irradiation of microdroplets; and (ii) analysis by laser irradiation of microdroplets dried on metallic substrates (surface-enhanced LIBS — SENLIBS). Experiments were carried out using synthetic samples with different concentrations of manganese in a 10% w/w Triton X-114 matrix. The analysis by direct laser irradiation of microdroplets showed low precision, sensitivity and poor linearity across the concentration range evaluated (R² <0.95). On the other hand, the SENLIBS method of analysis improved the sensitivity, the precision and the linearity of the calibration curve with respect to the direct analysis of microdroplets. In comparison with experimental results obtained by direct analysis, SENLIBS also allowed several replicate measurements to be carried out in a single microdroplet. The limit of detection obtained was 6μgg⁻¹ of Mn.

Highlights

► LIBS combined with microextraction procedures for trace analysis is proposed. ► The proposed combination depends on LIBS ability to analyze sample microvolumes. ► A surface-enhanced LIBS methodology for microdroplet analysis was evaluated. ► Results indicate this combination to be promising for trace analysis in liquids.

Calculation of elemental columnar density from self-absorbed lines in Laser-Induced Breakdown Spectroscopy: A resource for quantitative analysis

24 December 2012, 09:33:37

Available online 7 December 2012
Publication year: 2012
Source:Spectrochimica Acta Part B: Atomic Spectroscopy

The presence of self-absorption of emission lines is usually an undesired effect in Laser Induced Breakdown Spectroscopy because it introduces non linear effects in the growth of line intensity versus the concentration of the emitting species. Several methods have been proposed in recent years for identifying and quantifying self-absorption in the emission spectra. After this diagnostic stage, the lines affected by self-absorption are usually disregarded; otherwise, appropriate corrective factors are applied to their intensity before the utilization for analytical purposes. Changing the point of view, this paper remarks as self-absorption can provide useful information for analyzing the composition of laser-induced plasmas and for their characterization. Whenever the extent of self-absorption is quantified, in fact, the optical depth of the line can be rapidly calculated; then, for plasmas in local thermodynamic equilibrium conditions, the columnar density of the emitting species can be derived. Assuming the plasma homogeneity, the concentration ratio between different elements can be obtained. Moreover, in particular cases, the columnar densities can be used to calculate the plasma temperature and the absolute number densities of plasma species. Some applications of the method are reported in the paper and potentialities and limitations are discussed.

Highlights

► A method for LIBS plasma characterization based on self absorption is presented. ► It allows to calculate absolute columnar number densities of plasma species. ► It allows also to calculate plasma temperature and analytical composition. ► The method does not rely on the spectral calibration of the detection apparatus.

Chemical speciation of chlorine in atmospheric aerosol samples by high-resolution proton induced X-ray emission spectroscopy

24 December 2012, 09:33:37

Available online 5 December 2012
Publication year: 2012
Source:Spectrochimica Acta Part B: Atomic Spectroscopy

Chlorine is a main elemental component of atmospheric particulate matter (APM). The knowledge of the chemical form of chlorine is of primary importance for source apportionment and for estimation of health effects of APM. In this work the applicability of high-resolution wavelength dispersive proton induced X-ray emission (PIXE) spectroscopy for chemical speciation of chlorine in fine fraction atmospheric aerosols is studied. A Johansson-type crystal spectrometer with energy resolution below the natural linewidth of Cl K lines was used to record the high-resolution Kα and Kβ proton induced spectra of several reference Cl compounds and two atmospheric aerosol samples, which were collected for conventional PIXE analysis. The Kα spectra which refers to the oxidation state, showed very minor differences due to the high electronegativity of Cl. However, the Kβ spectra exhibited pronounced chemical effects which were significant enough to perform chemical speciation. The major chlorine component in two fine fraction aerosol samples collected during a 2010 winter campaign in Budapest was clearly identified as NaCl by comparing the high-resolution Cl Kβ spectra from the aerosol samples with the corresponding reference spectra. This work demonstrates the feasibility of high-resolution PIXE method for chemical speciation of Cl in aerosols.

Highlights

► Chemical specation of Cl in aerosol samples by high resolution PIXE spectroscopy. ► Fine structure of Kα and Kβ lines of reference compounds and APM samples was given. ► Kα spectra were well aligned with each other confirming the same Cl oxidation state. ► Pronounced chemical effects were observed in the Kβ spectra. ► We showed that chemical speciation of Cl was possible on thin aerosol samples.

USB POTENTIOSTAT

BVT Technologies has launched the USB POTENTIOSTAT which opens new field of electrochemical devices. The device is compatible with AC1 sensors with integrated microreactor. The device contains the amperommetry, cyclic voltammetry and puls amperommetry. It is convenient for fast screening electrochemical measurement via USB.

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Advanced Cooling for Flow Chemistry

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Just Published: Journal of Pharmaceutical and Biomedical Analysis

A new issue of this journal has just been published. To see abstracts of the papers it contains (with links through to the full papers) click here:

Journal of Pharmaceutical and Biomedical Analysis
http://rss.sciencedirect.com/publication/science/5266

Selected papers from the latest issue:

Application of an efficient strategy for discovery and purification of bioactive compounds from Chinese herbal medicines, a case study on the Puerariae thomsonii Flos

18 December 2012, 07:00:59

5 March 2013
Publication year: 2013
Source:Journal of Pharmaceutical and Biomedical Analysis, Volume 75

In this study, an efficient strategy based on bioassay-guided fractionation, high-performance liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry (HPLC-ESI-Q/TOF-MS) and high-speed counter-current chromatography (HSCCC) was established to screen and purify bioactive compounds from Chinese herbal medicines (CHMs). This screening system was efficient and successfully applied to reveal anti-prostate cancer candidates from Puerariae thomsonii Flos. As a result, an active fraction with strong in vitro anti-prostate cancer activity was obtained, and the main compounds in the fraction were purified by HSCCC, giving 82mg of tectoridin, 36mg of tectorigenin-7-O-[β-d-xylopyranosyl-(1→6)-β-d-glucopyranoside and 64mg of tectorigenin. Among them, tectorigenin, possessing the highest anti-prostate cancer activity with IC50 value of 0.08μM, has priority to be lead compound. The results of this work demonstrated that the developed method was efficient and could be employed for the rapid screening, identification and purification of active components from CHMs.

Graphical abstract

Highlights

► An efficient strategy based on bioassay-guided fractionation, HPLC-ESI-Q/TOF-MS and HSCCC was established to screen and purify bioactive compounds from CHMs. ► The screening system succeeded in discovering anti-prostate cancer candidates from Puerariae thomsonii Flos. ► Tectoridin, tectorigenin-7-O-[β-d-xylopyranosyl-(1→6)-β-d-glucopyranoside and tectorigenin were prepared from Puerariae thomsonii Flos by HSCCC for the first time. ► Tectorigenin possessed potent inhibition effect on growth of RM-1 prostate cancer cells with IC50 value of 0.08μM.

Assay at low ppm level of dimethyl sulfate in starting materials for API synthesis using derivatization in ionic liquid media and LC–MS

18 December 2012, 07:00:59

5 March 2013
Publication year: 2013
Source:Journal of Pharmaceutical and Biomedical Analysis, Volume 75

Dimethyl sulfate (DMS) is frequently used in pharmaceutical manufacturing processes as an alkylating agent. Trace levels of DMS in drug substances should be carefully monitored since the compound can become an impurity which is genotoxic in nature. Derivatization of DMS with dibenzazepine leads to formation of the N-methyl derivative, which can be retained on a reversed phase column and subsequently separated from other potential impurities. Such derivatization occurs relatively slowly. However, it can be substantially speed up if ionic liquids are used as reaction media. In this paper we report the use of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (IL1) and 1-butyl-4-methylpyridinium tetrafluoroborate (IL2) as reaction media for the derivatization of DMS with dibenzazepine. It was determined that the stoichiometry between the substrate and DMS may be 1:1 or 2:1, in relation with the nature of the reaction media. An (+)ESI-MS/MS approach was used for quantitation of the derivatized product. Alternatively, DMS derivatization may be carried out with pyridine in acetonitrile (ACN). The N-methylpyridinium derivative was separated by hydrophilic interaction liquid chromatography (HILIC) and detected through (+)ESI-MS (in the SIM mode). In both cases, a limit of quantitation (LOQ) of 0.05μg/ml DMS was achievable, with a linearity range up to 10μg/ml. Both analytical alternatives were applied to assay DMS in 4-(2-methoxyethyl)phenol, which is used as a starting material in the synthesis of metoprolol.

Graphical abstract

Highlights

► LC/MS–MS analysis at sub-ppm level of dimethyl sulfate in starting materials for APIs is proposed. ► Derivatization of DMS with dibenzazepine or pyridine was achieved. ► Derivatization kinetics was studied in acetonitrile and ionic liquids (pseudo-first-order). ► Derivatization with dibenzazepine in ionic liquids is much faster than in acetonitrile. ► RPLC (for N-methyl-dibenzazepine) and HILIC (for N-methyl-pyridine) separation modes were used.

The development of a method to quantify encapsulated and free prednisolone phosphate in liposomal formulations

18 December 2012, 07:00:59

5 March 2013
Publication year: 2013
Source:Journal of Pharmaceutical and Biomedical Analysis, Volume 75

This paper presents the development of a new method for the simple and reliable quantification of the free drug amount in liposomal preparations of prednisolone phosphate (PP). In this method the free drug is distinguished from the encapsulated drug by means of hydrolysis of the free PP into prednisolone (P) by alkaline phosphatase (AP). During method development reaction progress curves were recorded to determine the required AP concentration and the corresponding incubation time to achieve hydrolysis of all free PP. Reaction progress curves also showed that small changes in the amount of weighted AP and the incubation periods used do not cause a change in outcome. Further, several organic solvents were tested as precipitation solvent and the use of tetrahydrofuran (THF) yielded clean chromatograms, rapid AP deactivation and complete liposome rupture avoiding under- and overestimations of the encapsulated and free drug concentrations. Method accuracy was evaluated during a cross-validation involving dialysis. Intra- and interday precision were evaluated by determining the standard deviation (SD) and relative standard deviation (RSD) after applying the new method on one day (n =4) and on different days (n =3). The accuracy of the developed method is comparable to the accuracy determined by dialysis, while clearly the method using AP is more precise. In conclusion, comprehensive method development yielded an accurate and precise method, which can replace traditional methods like dialysis and solid phase extraction (SPE). With little effort the method can be upgraded and become part of the liposome certification prior to human use. The overall principle behind the method offers possibilities for many drug carrier systems.

Highlights

► A method for the quantification of the free drug amount in liposomal preparations of prednisolone phosphate was developed. ► The free drug is distinguished from the encapsulated drug by means of enzymatic hydrolysis. ► In this way difficulties accompanying traditional separation techniques were circumvented. ► Thismethod is reliable, accessible, inexpensive,fast and suitable for small sample volumes and a large number of samples. ► The principle behind this method offers also possibilities for the free drug determination of many drug carrier systems.

A separation strategy combining three HPLC modes and polysaccharide-based chiral stationary phases

18 December 2012, 07:00:59

5 March 2013
Publication year: 2013
Source:Journal of Pharmaceutical and Biomedical Analysis, Volume 75

Nine polysaccharide-based chiral stationary phases (CSPs) were used to define a separation strategy that combines normal-phase (NP), reversed-phase (RP) and polar organic solvent chromatography (POSC) modes. After limiting ourselves to two CSPs per mode, in total, five CSPs, Chiralpak AD (NP), Chiralcel OD (RP and POSC), Lux Cellulose-1 (NP), Lux Cellulose-2 (POSC) and Lux Cellulose-3 (RP), showed the broadest enantioselectivity and most complementarity. Six sequences of the three modes were considered to decide which sequence is the most successful for screening a set of 56 pharmaceutical compounds. Starting the strategy with the NP mode, followed by RP and finally POSC was found preferable from both the number of cumulative separations and of baseline separations. Two approaches were considered for strategy fine tuning using an additional set of eight racemic mixtures. In both approaches, seven of the eight compounds were baseline resolved, on one of the examined columns at either screening or optimization conditions of a mode. One approach was finally preferred because of its lower workload.

Highlights

► 56 compounds and nine CSPs were used to update strategies in three common HPLC modes. ► An HPLC chiral method development strategy that combines NPLC, RPLC and POSC modes was defined. ► Success rate: all compounds were separated with the updated strategy in less experiments. ► The updated strategy was fine tuned.

A microflow chemiluminescence sensor for indirect determination of dibutyl phthalate by hydrolyzing based on biological recognition materials

18 December 2012, 07:00:59

5 March 2013
Publication year: 2013
Source:Journal of Pharmaceutical and Biomedical Analysis, Volume 75

A microflow chemiluminescence (CL) sensor for determination of dibutyl phthalate (DBP) based on magnetic molecularly imprinted polymer (MMIP) as recognition element was fabricated. Briefly, a hydrophilic molecularly imprinted polymer layer was produced at the surface of Fe3O4@SiO2 magnetic nanoparticles (MNPs) via combination of molecular imprinting and reversible stimuli responsive hydrogel. In this protocol, the initial step involved co-precipitation of Fe²⁺ and Fe³⁺ in an ammonia solution. Silica was then coated on the Fe3O4 nanoparticles using a sol–gel method to obtain silica shell magnetic nanoparticles. The MMIP was synthesized using methacrylic acid (MAA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as cross-linker and 2, 2-azobisisobutyronitrile (AIBN) as initiator in chloroform. Then the synthesized MMIP and magnetic non-molecular imprinted polymers (MNIP) were employed as recognition by packing into lab-made straight shape tubes, connected in CL analyzer for establishing the novel sensor with a single channel syringe pump. And a mixer for hydrolyzing of DBP was followed. Based on this experiment principle, DBP was determined indirectly. And the MMIP showed satisfactory recognition capacity to DBP, resulting to the wide linear range of 3.84×10⁻⁸ to 2.08×10⁻⁵ M and the low detection limit of 2.09×10⁻⁹ M (3σ) for DBP. The relative standard deviation (RSD) for DBP (3.20×10⁻⁶ M) was 1.40% (n =11). Besides improving sensitivity and selectivity, the sensor was reusable. The proposed DBP–MMIP–CL sensor has been successfully applied to determine DBP in drink samples.

Graphical abstract

Highlights

► Fe3O4@SiO2 was used as support for easier to control. ► Microscale Syringe Pump was used for saving reagent. ► A mixer for hydrolyzing was used for chemiluminescence.

Dispersive liquid–liquid microextraction combined with ultra-high performance liquid chromatography for the simultaneous determination of 25 sulfonamide and quinolone antibiotics in water samples

18 December 2012, 07:00:59

5 March 2013
Publication year: 2013
Source:Journal of Pharmaceutical and Biomedical Analysis, Volume 75

In this work, a dispersive liquid–liquid microextraction (DLLME) procedure combined with ultra-high performance liquid chromatography with diode-array detection was developed to determine 25 antibiotics in mineral and run-off waters. Optimum DLLME conditions (5mL of water at pH=7.6, 20% (w/v) NaCl, 685μL of CHCl3 as extractant solvent, and 1250μL of ACN as disperser solvent) allowed the repeatable, accurate and selective determination of 11 sulfonamides (sulfanilamide, sulfacetamide, sulfadiazine, sulfathiazole, sulfadimidin, sulfamethoxypyridazine, sulfadoxine, sulfamethoxazole, sulfisoxazole, sulfadimethoxine and sulfaquinoxaline) and 14 quinolones (pipemidic acid, marbofloxacin, fleroxacin, levofloxacin, pefloxacin, ciprofloxacin, lomefloxacin, danofloxacin, enrofloxacin, sarafloxacin, difloxacin, moxifloxacin, oxolinic acid and flumequine). The method was validated by means of the obtention of calibration curves of the whole method as well as a recovery study at two levels of concentration. The LODs of the method were in the range 0.35–10.5μg/L with recoveries between 78% and 117%.

Graphical abstract

Highlights

► A DLLME–UHPLC-DAD method was developed to determine antibiotics in water. ► A total of 25 compounds (11 sulfonamides and 14 quinolones) was analyzed. ► Relative recoveries values of the method were between 74% and 117%. ► The procedure is simple, fast and reliable to determine the selected antibiotics.

Proteomics-based identification of plasma biomarkers in oral squamous cell carcinoma

18 December 2012, 07:00:59

5 March 2013
Publication year: 2013
Source:Journal of Pharmaceutical and Biomedical Analysis, Volume 75

Oral squamous cell carcinoma (OSCC) is an aggressive cancer and its occurrence is closely related to betel nut chewing in Taiwan. However, there are few prognostic and diagnostic biomarkers for this disease especially for its association with betel nut chewing. Recent progresses in quantitative proteomics have offered opportunities to discover plasma proteins as biomarkers for tracking the progression and for understanding the molecular mechanisms of OSCC. In present study, plasma samples from OSCC patients with at least 5-year history of betel nut chewing and healthy donors were analyzed by fluorescence 2D-DIGE-based proteomic analysis. Totally, 38 proteins have been firmly identified representing 13 unique gene products. These proteins mainly function in inflammatory responses (such as fibrinogen gamma chain) and transport (Apolipoprotein A–I). Additionally, the current quantitative proteomic approach has identified numerous OSCC biomarkers including fibrinogen (alpha/beta/gamma) chain, haptoglobin, leucine-rich alpha-2-glycoprotein and ribosomal protein S6 kinase alpha-3 (RSK2) which have not been reported and may be associated with the progression and development of the disease. In summary, this study reports a comprehensive patient-based proteomic approach for the identification of potential plasma biomarkers in OSCC. The potential of utilizing these markers for screening and treating OSCC warrants further investigations.

Graphical abstract

Highlights

► Oral squamous cell carcinoma (OSCC) is an aggressive cancer closely related to betel nut chewing. ► Quantitative proteomics have offered opportunities to discover plasma OSCC protein biomarkers. ► This study identified numerous unreported OSCC markers such as RSK2. ► The utilization of these markers for screening and treating OSCC warrants further investigations.

Pre-column derivatization combined with UHPLC–MS/MS for rapid and sensitive quantification of bakuchiol in rat plasma

18 December 2012, 07:00:59

5 March 2013
Publication year: 2013
Source:Journal of Pharmaceutical and Biomedical Analysis, Volume 75

Psoralea corylifolia L. (Fabaceae) is a traditional Chinese medicine with many beneficial effects in medical therapies. Bakuchiol was the main active ingredient of Psoralea corylifolia L. In this study, a novel method of pre-column derivatization with dansyl chloride followed by analysis of ultra high-performance liquid chromatographic–tandem mass spectrometry (UHPLC–MS/MS) was established and validated for quantification of bakuchiol in rat plasma. The linearity of this approach was confirmed to be within the concentration range of 0.5–1000ng/mL and the lower limit of quantification was at 0.5ng/mL. The total analysis time was 1.5min for each pretreated sample. Also, the precision, accuracy, stability, recovery and matrix effect of this method were proved to meet the requirements for bioanalysis. The intravenous and oral pharmacokinetic profiles of bakuchiol were obtained by utilizing this approach. The oral bioavailability of bakuchiol in rats (3.2%) was identified.

Graphical abstract

Highlights

A novel method of pre-column derivatization with dansyl chloride followed by analysis of ultra high-performance liquid chromatographic–tandem mass spectrometry (UHPLC–MS/MS) was established and validated for quantification of bakuchiol in rat plasma. The intravenous and oral pharmacokinetic profiles of bakuchiol were obtained by utilizing the established method.

► An UHPLC–MS/MS method with pre-column derivatization was built for bakuchiol. ► The method demonstrated high sensitivity, wide linear range and short runtime. ► The method was used to explore the pharmacokinetic profile of bakuchiol in rats. ► The oral bioavailability of bakuchiol (3.2%) was reported for the first time.

Development of generic immunoassay for the detection of a series of aminoglycosides with 6′-OH group for the treatment of genetic diseases in biological samples

18 December 2012, 07:00:59

5 March 2013
Publication year: 2013
Source:Journal of Pharmaceutical and Biomedical Analysis, Volume 75

Over the last two decades, a growing number of scientific evidences highlighted the potential therapeutic value of several structures of aminoglycoside antibiotics (including gentamicin and G418) for the treatment of various genetic diseases caused by nonsense mutations. These findings resulted in a fast evolvement of synthetic derivatives of aminoglycosides which were shown to be more target specific and less toxic than the clinically used antibiotics. The emerging progress in drug design and development has necessitated the urge to develop a fast, easy and accurate procedure for the determination of these potential therapeutic agents in various biologically derived matrices. Here we describe the preparation of a generic polyclonal antibody that was used for the development of homologous and heterologous immunoassays for the detection of a wide range of natural and synthetic aminoglycoside derivatives, highlighted today as potential therapeutic agents for the treatment of various genetic diseases. A common two-ring scaffold, NB82, present in the majority of compounds exhibiting potent biological activity, was used as a generic immunization hapten for the immunization of two rabbits. By using a series of chemical steps, NB82 was selectively conjugated via the N-1 position through glutaric acid linker to a carrier protein. Sensitivity (I 50) values for the recognition of three representative compounds NB82, NB84 and NB124 were determined to be 10±3ngmL⁻¹, 0.5±0.04μgmL⁻¹ and 1±0.12μgmL⁻¹, respectively. Limits of detection were determined to be 1±0.3ngmL⁻¹ for NB82, 20±7ngmL⁻¹ for NB84 and 15±8ngmL⁻¹ for NB124. The developed assays were further exploited for the in vivo monitoring of the therapeutic compounds in mice serum. Serum experimentations exhibited similar detection limits as observed for the PBS calibration experiments, demonstrating no interference with assays sensitivity, with rather high recovery ratios ranging from 92 to 107% in whole blood samples.

Graphical abstract

Highlights

► A broad-specific ELISA for the detection of aminoglycosides with 6′-OH was developed. ► These 6′-OH aminoglycosides are best candidates for the treatment of genetic diseases. ► A two-ring scaffold was selectively conjugated to a carrier protein at N-1 position. ► A generic antibody allowed highly sensitive monitoring of therapeutic agents in vivo. ► The assay will aid in further development of therapeutic compounds in clinic.

Structural characterization of minor metabolites and pharmacokinetics of ganoderic acid C2 in rat plasma by HPLC coupled with electrospray ionization tandem mass spectrometry

18 December 2012, 07:00:59

5 March 2013
Publication year: 2013
Source:Journal of Pharmaceutical and Biomedical Analysis, Volume 75

The metabolites and pharmacokinetics of ganoderic acid C2 (GAC2), a bioactive triterpenoid in Ganoderma lucidum in rat plasma were investigated by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC–ESI-MS/MS). Totally, ten minor phase I metabolites of GAC2 were characterized after oral administration of GAC2, on the basis of their mass fragmentation pathways or direct comparison with authentic compounds by high-performance liquid chromatography coupled with diode array detection and electrospray ion trap tandem mass spectrometry (HPLC–DAD–ESI-MS ⁿ ), and liquid chromatography coupled with electrospray ionization hybrid ion trap and time-of-flight mass spectrometry (LC–ESI-IT-TOF/MS) methods. Moreover, a rapid and specific method for quantification of GAC2 in rat plasma after oral administration was developed by using a liquid–liquid extraction procedure and HPLC–ESI-MS/MS analysis. It is the first time to report the metabolites and pharmacokinetics of GAC2.

Graphical abstract

Highlights

Proposed metabolic pathways of ganoderic acid C2 (M0) in rats.

► Ten minor phase I metabolites were characterized. ► A rapid quantification method was developed by LC–MS/MS. ► The metabolites and pharmacokinetic of GAC2 were reported firstly.