Interrogation of a large-capacity densely spaced fiber Bragg grating array using chaos-based incoherent-optical frequency domain reflectometry.

An interrogation technique for large-capacity densely spaced fiber Bragg grating (FBG) arrays is demonstrated using incoherent optical frequency domain reflectometry (I-OFDR). A distributed-feedback laser diode under chaotic oscillation, modulated by a frequency-swept microwave, is adopted as the optical source. The reflected sensing signals are converted into electrical signals and subsequently mixed with the original microwave. Fast Fourier transform is applied to the generated beat signal to obtain the position of individual FBGs, while thermal tuning of the lasing wavelength leads to the demodulation of wavelength. By using the chaotic source, interference among the reflected sensing signals is reduced, leading to a significantly improved spatial resolution of 10 cm, with a multiplexing capacity of 3640 and wavelength demodulation accuracy of 15 pm.

High-Density Distributed Crack Tip Sensing System Using Dense Ultra-Short FBG Sensors.

Crack generation starts at the crack tip, which bears the highest stress concentration. Under further stress, the crack propagates and leads to severe structural damage. To avoid such damage, the identification of the crack tips, and monitoring of the surrounding stress and strain fields, are very important. In this work, the location of, and strain distribution monitoring around, the crack tip are achieved using a dense ultra-short (DUS) fiber Bragg grating (FBG) array together with an improved optical frequency domain reflectometry (OFDR) interrogator. The adjacent grating interference correlation algorithm helps overcome the limitation on the demodulation precision, which is imposed by the inherently broad reflection spectra of individual ultra-short gratings. High spatial resolution measurement of the strain profile around the crack tip is performed at different levels of induced strain. Furthermore, the vertical-crossed layout is adopted to avoid the omission of cracks, which usually occurs in the case of the one direction layout. We achieve 1 mm spatial resolution and 7.5 m detection distance. Location of a single crack, multiple cracks, and an oblique crack was realized experimentally by locating the crack tips. The experimental results are consistent with the theoretical analysis, verifying the feasibility of the DUS-FBG system for high-density distributed crack tip sensing.

Large-scale multiplexing of a FBG array with randomly varied characteristic parameters for distributed sensing.

Large-scale multiplexing of a fiber Bragg grating (FBG) array with randomly varied characteristic parameters (RVCPs) is proposed. The center wavelength of each FBG and the grating spacing between adjacent FBGs are randomly varied within a controlled range. Due to the low reflectivity (<-45 dB) and RVCPs of the FBGs, the sensing array presents low spectral-shadowing crosstalk and multiple-reflection crosstalk, implying high FBG multiplexing capacity. The numerical and experimental results show that the RVCP-FBG array significantly improves the signal-to-noise ratio and demodulation accuracy of the distributed sensing system. Large-scale multiplexing of 10,000 FBGs along a 10 m long fiber is achieved.

Fast and selective extraction of nicotine from human plasma based on magnetic strong cation exchange resin followed by liquid chromatography-tandem mass spectrometry.

In the study, a fast and selective method based on magnetic separation has been developed for the extraction of nicotine from human plasma using magnetic strong cation exchange (MSCX) resins as adsorbent. MSCX resins were prepared using hydrophobic Fe(3)O(4) magnetite as magnetically susceptible component, styrene and acrylic acid as polymeric matrix components, and acetyl sulfonate as the sulfonation agent. The extraction procedure was carried out in a single step by stirring the mixture of diluted plasma sample and MSCX resins in the vortex for 5 min. Then, the resins with adsorbed nicotine were separated from the sample matrix by applying an appropriate magnetic field. Main factors affecting the extraction of nicotine such as the amount of MSCX resins, pH value of the extraction solvent, extraction time, and washing and eluting conditions were optimized. The nicotine eluted from the resins was determined by liquid chromatography-tandem mass spectrometry. The calibration curve obtained by analyzing matrix-matched standards shows excellent linear relationship (r (2) = 0.9998) in the concentration range of 10-2,500 ng mL(-1). The limit of detection and quantification obtained are 2.9 and 9.7 ng mL(-1), respectively. The relative standard deviations of intra- and inter-day obtained are in the range of 1.9-6.9% and 2.5-7.8% with the recoveries ranging from 78.7% to 99.1%. The proposed method was successfully applied to determine nicotine in human plasma phlebotomized from ten male smokers. Nicotine was detectable with the contents ranging from 44.4 to 221.9 ng mL(-1) in five samples.

Determination of roxithromycin from human plasma samples based on magnetic surface molecularly imprinted polymers followed by liquid chromatography-tandem mass spectromer.

In this paper, a simple and reproducible method for the determination of roxithromycin in human plasma samples is proposed. The surface magnetic molecularly imprinted polymers (MMIPs) were utilized as sorbent. Roxithromycin was used as imprinted compound. The experimental results showed that the MMIPs had high affinity and selectivity toward roxithromycin. The extraction process was carried out in a single step by mixing the extraction solvent, MMIPs and human plasma samples by vortex. When the extraction process was completed, the MMIPs adsorbed the analyte were separated from the sample matrix by an external magnet due to the magnetism. The analyte eluted from the MMIPs was analysed by liquid chromatography-tandem mass spectrometry. Some main factors affecting the extraction of roxithromycin such as the amount of MMIPs, extraction solvent, extraction time, washing and elution conditions were optimized in this study. The calibration curve obtained by analyzing matrix-matched standards showed excellent linear relationship (r(2)=0.9997) in the concentration range of 10-1000ngmL(-1). The limit of detection and quantification obtained were 3.8 and 9.8ngmL(-1), respectively. The relative standard deviations of intra- and inter-day obtained were in the range of 3.9 %-5.5 % and 2.9 %-4.6 % with the recoveries ranging from 86.5 % to 91.5 %.