Sensitive determination of captopril by flow injection analysis with chemiluminescence detection based on the enhancement of the luminol reaction

This work reports a novel flow injection (FI) method for the determination of captopril, 1-[(2S)-3-mercapto-2-methylpropionyl]-l-proline (CPL), based on the enhancement CPL affords on the chemiluminescence (CL) reaction between luminol and hydrogen peroxide. For this purpose alkaline luminol and hydrogen peroxide solutions were mixed online, the sample containing CPL was injected into an aqueous carrier stream, mixed with the luminol-hydrogen peroxide stream and pumped into a glass flow cell positioned in front of a photomultiplier tube (PMT). The increase in the CL intensity was recorded in the form of FI peaks, the height of which was related to the CPL mass concentration in the sample. Different chemical and instrumental parameters affecting the CL response were investigated. Under the selected conditions, the log-log calibration curve was linear in the range 5-5000 μg l⁻¹ of CPL, the limit of detection was 2 μg l⁻¹ (at the 3σ level), the R.S.D., s_r was 3.1% at the 100 μg l⁻¹ level (n=8) and the sampling rate was 180 injections h⁻¹. The method was applied to the determination of CPL in pharmaceutical formulations with recoveries in the range 100±3%.     

A new method for the HPLC determination of gamma-hydroxybutyric acid (GHB) following derivatization with a coumarin analogue and fluorescence detection: application in the analysis of biological fluids

A new method of the determination of gamma-hydroxybutyric acid (GHB) in human biological fluids cerebrospinal fluid (CSF) and saliva after off-line derivatization is described. The proposed method was based on the reaction of 4-bromomethyl-7-methoxy coumarin (Br-MMC) with GHB in the presence of dibenzo-18-crown-6-ether (acting as reaction catalyst) to produce a fluorescent derivative. The formed derivative was monitored fluorimetrically at lambda(ext.)=330 nm and lambda(em.)=390 nm. The effect of derivatization parameters such as the concentration of Br-MMC, reaction time and the temperature was investigated in order to achieve the maximum method's sensitivity. The separation was achieved by use of a C(18) analytical column (Kromasil 250 mm x 4 mm i.d., 5 microm) while the injected sample volume was set to 25 microL. A binary gradient elution program of methanol versus phosphate buffer (40 mM, pH 3) was selected for the quantitative analysis of GHB. The method showed satisfactory linearity (R(2)=0.9979) in a linear range from 2.4 x 10(-6) to 7.2 x 10(-5) M. Ultrafiltration method was employed for the pre-treatment of the cerebrospinal fluid (CSF) prior to the analysis of GHB. The limit of detection (LOD) of the method was 3 x 10(-7) M in saliva and 2 x 10(-7) M in CSF samples, respectively, while the limit of quantitation (LOQ) was 1 x 10(-6) M for both specimens. The proposed protocol offers sensitivity comparing with the existing HPLC analytical methods or the CE indirect UV methods and can function as an attractive alternative to be used in clinical and toxicological analysis.     

Distant energy transfer for artificial human implants

The powering of human implants via inductive coupling has been an object of interest for the past two decades. This paper discusses some of the issues concerning a distant energy link used for supplying artificial human implants, operating at the frequency of 13.56 MHz. A procedure for the design of an energy-receiving coil is given for general applications. A design procedure is also developed, with focus on coils used for supplying human implants. The correctness of the analysis of this later design procedure has been verified by experimental results. Measurements with a human tissue simulant also show little deviation from the predictions.     

Daptomycin determination by liquid chromatography–mass spectrometry in peritoneal fluid, blood plasma, and urine of clinical patients receiving peritoneal dialysis treatment

A 13-min LC–MS method was developed for the determination of daptomycin, a new potent antibiotic, in peritoneal fluid, blood plasma, and urine of patients receiving renal replacement therapy. Chromatography was performed on a C₁₈ column and detection was performed by a single-quadrupole mass spectrometer coupled to LC via an electrospray interface (ESI). The column effluent was also monitored at 370 nm using a photodiode-array detector. The developed method provided a linear dynamic range for concentrations from 0.5 μg mL⁻¹ to 100 μg mL⁻¹. Method precision and accuracy were found to be satisfactory for clinical application, thus the method was successfully used for the analysis of daptomycin in pharmacokinetic studies. The drug was preventively administered against Gram-positive infections to 19 clinical patients undergoing peritoneal dialysis. Peritoneal fluid, blood plasma, and urine samples were collected at 13 time points over a period of 48 h. Clinical samples were analysed following simple sample-preparation procedures and daptomycin was unambiguously detected and quantified.     

Three-Dimensional Calculations of the Flow Field around a Turbine Blade with Film Cooling Injection near the Leading Edge

Injection of coolant air from a showerhead injection system at the leading edge of a high pressure turbine blade is investigated using a fully implicit three-dimensional finite-volume method on multi-block grids. For various blowing rates, the calculation results for the velocity and pressure fields and turbulence intensity are compared with available experimental data. The present method yields excellent agreement with the experiments for the isentropic Mach number distributions on the blade surface. The standardk–ε turbulence model with wall functions is already capable of capturing the major details of the flow field including the injection-induced secondary-flow vortices, particularly so on the suction side. On the pressure side, however, the lateral jet spreading is under-predicted somewhat together with an exaggeration of the near-wall sink-flow vortices. On this side with convex walls, where turbulence anisotropy is appreciable according to the experiments, overall better predictions were obtained with the anisotropy correction of Bergeles et al. [23] promoting the Reynolds stress in the lateral direction. The correction has no beneficial effect on the suction side with concave walls where the turbulence anisotropy was observed to be much smaller. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the least-squares performance of a novel efficient center estimation method for clustering-based MLSE equalization

Recently, a novel maximum-likelihood sequence estimation (MLSE) equalizer was reported that avoids the explicit estimation of the channel impulse response. Instead, it is based on the fact that the (noise-free) channel outputs, needed by the Viterbi algorithm, coincide with the points around which the received (noisy) samples are clustered and can thus be estimated directly with the aid of a supervised clustering method. Moreover, this is achieved in a computationally efficient manner that exploits the channel linearity and the symmetries underlying the transmitted signal constellation. The resulting computational savings over the conventional MLSE equalization scheme are significant even in the case of relatively short channels where MLSE equalization is practically applicable. It was demonstrated, via simulations, that the performance of this algorithm is close to that using a least-squares (LS) channel estimator, although its computational complexity is even lower than that of the least-mean squares (LMS)-trained MLSE equalizer. This paper investigates the relationship of the center estimation (CE) part of the proposed equalizer with the LS method. It is proved that, when using LS with the training sequence employed by CE, the two methods lead to the same solution. However, when LS is trained with random data, it outperforms CE, with the performance difference being proportional to the channel length. A modified CE method, called MCE, is thus developed, that attains the performance of LS with perfectly random data, while still being much simpler computationally than classical LS estimation. Through the results of this paper, CE is confirmed as a methodology that combines high performance, simplicity, and low computational cost, as required in a practical equalization task. An alternative, algebraic viewpoint on the CE method is also provided.     

Application of the maximum entropy spectrum analysis technique to signals with spectral peaks of finite width

The Maximum Entropy Spectral Analysis technique is applied to signals with spectral peaks of finite width. The Burg and Least Squares algorithms are used and in each case the performance is compared to that of a conventional Fourier method.     

On the resolution properties of an adaptive algorithm for maximum entropy spectrum analysis

The resolution properties of the adaptive mean squares algorithm when used for maximum entropy spectrum estimation are compared with those of Burg's algorithm and the standard periodogram method using the FFT algorithm.     

Headspace solid-phase microextraction for the gas chromatographic analysis of organophosphorus insecticides in vegetables

Residues of organophosphorus insecticides (diazinon, methyl parathion, fenitrothion, malathion, and parathion) were determined in 13 different vegetable matrixes by headspace solid-phase microextraction performed with a polydimethyl-siloxane fiber (100 microm). Determination was carried out by gas chromatography with a nitrogen-phosphorus detector. Limits of detection and quantification were < 0.005 and 0.017 mg/kg, respectively; thus, the limits of maximum residue levels (MRLs) required by European regulations can be verified without difficulty. Pesticide residues were found in 38% of the 125 fresh commercial samples (imported and domestic) that were analyzed. Residues of methyl parathion and parathion, which were withdrawn in Greece in 2003, were detected in 36.8 and 4% of all samples, respectively. The MRLs were exceeded overall by 1%.     

Semi-blind maximum-likelihood joint channel/data estimation for correlated channels in multiuser MIMO networks

The aim of this paper is to investigate receiver techniques for maximum likelihood (ML) joint channel/data estimation in flat fading multiple-input multiple-output (MIMO) channels, that are both (i) data efficient and (ii) computationally attractive. The performance of iterative least squares (LS) for channel estimation combined with sphere decoding (SD) for data detection is examined for block fading channels, demonstrating the data efficiency provided by the semi-blind approach. The case of continuous fading channels is addressed with the aid of recursive least squares (RLS). The observed relative robustness of the ML solution to channel variations is exploited in deriving a block QR-based RLS-SD scheme, which allows significant complexity savings with little or no performance loss. The effects on the algorithms’ performance of the existence of spatially correlated fading and line-of-sight paths are also studied. For the multi-user MIMO scenario, the gains from exploiting temporal/spatial interference color are assessed. The optimal training sequence for ML channel estimation in the presence of co-channel interference (CCI) is also derived and shown to result in better channel estimation/faster convergence. The reported simulation results demonstrate the effectiveness, in terms of both data efficiency and performance gain, of the investigated schemes under realistic fading conditions.