Lab-on-fiber: laser-induced micro-cavity for a relative humidity measurement.

The lab-on-fiber design philosophy is the foundation for creating high-performance integrated fiber sensors. Hence, this Letter proposes an ultra-compact Fabry-Perot interferometer (FPI) based on a laser-induced micro-cavity (LIMC-FPI) on a fiber end for measuring relative humidity. To our knowledge, this novel approach, named the fiber-end photopolymerization (FEP) technique, is applied to create a micro-cavity. Specifically, a pair of humidity-sensitive polymer pillars and a resin end cap obtained by FEP are integrated to generate the cavity. As the ambient humidity changes, the pillars lengthen or shorten, resulting in the spectral evolution of the LIMC-FPI. A typical humidity sensitivity of 0.18 nm/%RH is obtained experimentally. For monitoring the human breathing process, the LIMC-FPI is responsive in the breathing frequency range of 0.2 to 0.5 Hz, allowing a response and recovery time of less than 0.388 s and 1.171 s, respectively. This work introduces a fresh and cost-effective approach for developing lab-on-fiber concept-based sensors.

Highly-sensitive temperature sensor based on photopolymerized-waveguide embedded Mach-Zehnder interferometer.

Biology, medicine, and chemistry all rely heavily on highly sensitive optical fiber temperature sensors. To the best of our knowledge, this research introduces a unique design framework for high-performance fiber temperature sensors that helps eliminate the all-fiber interferometers' sensitivity bottleneck. A section of photopolymerized waveguide is embedded in a typical Mach-Zehnder interferomenter framework with multimode fiber-single mode fiber-multimode fiber (MSM) structure. The thermal-optical coefficient (TOC) of the photopolymerized waveguide core, which is created via the fiber-end lithography technique, differs dramatically from that of the resin cladding. Due to the considerable TOC difference, the phase difference between the interfering beams significantly increases as the temperature changes. The fundamental variables affecting temperature sensitivity are conceptually explored and experimentally verified. The suggested device achieves a typical temperature sensitivity of 1.15 nm/ ∘C in the range of 30-100 ∘C, which is about 10 times as high as that of the all-fiber MSM sensors. The suggested designing framework offers a fresh thought for creating high-performing fiber optic temperature sensors.

Exoskeleton type long-period fiber grating for cross-talk-resistance single-parameter measurement.

This paper proposes a new, to the best of our knowledge, design framework of long-period fiber grating (LPFG) sensors resistant to multi-parameter cross talk. A section of hollow quartz capillary (HQC), which acts as an exoskeleton, is periodically merged with a single-mode fiber (SMF) by the arc-discharge method. The mechanical stress in the SMF is released while the thermal stress is enhanced after a high-temperature fusion process. Under the influence of the elastic-optical effect, the refractive index of the core is periodically modulated along the axial direction to form an exoskeleton long-period fiber grating (Es-LPFG). The unique exoskeleton structure not only induces mode coupling but also enables the proposed device to resist cross talk among the strain, ambient refractive index, and vector bending. The temperature is able to be measured independently with a sensitivity of 74 pm/ ∘C. The novel Es-LPFG is promising in single-parameter sensing, mode-locked lasers, and frequency-locked gain flattening.

Targeted and nontargeted screening and identification of 50 antihypertensive adulterants in dietary supplements and herbal medicines using quadrupole-orbitrap high resolution mass spectrometry with compound database.

In the present work, a novel database of drug compounds and a rapid screening method based on ultra-high performance liquid chromatography coupled to high resolution orbitrap mass spectrometry were developed and applied in the screening and identification of targeted and nontargeted antihypertensive adulterants in dietary supplements and herbal medicines. The established screening database includes retention time, exact mass, fragments, isotopic pattern, and MS2 spectra library of the target compounds and thus provides automated search and identification of the targets with a single injection. The nontargeted compounds in the samples are identified through the full MS scan and MS2 data by using the Chemspider database and the data analysis in XCalibur, MassFrontier and TraceFinder software. In addition, this method possesses excellent quantitative capacity. The novel approach was applied to 65 batches of samples that are claimed as "all-natural" products having the antihypertensive function, among which nine batches were found to be positive. Multiple targeted and nontargeted antihypertensive adulterants were detected at levels ranging from 2.8 to 27.9 mg/g. The novel database and screening method demonstrated herein will be promising and powerful tools for rapid screening of antihypertensive adulterants in dietary supplements and herbal medicines.

[Determination of N-nitrosodimethylamine in metformin hydrochloride and its preparations by high performance liquid chromatography-tandem mass spectrometry].

A method was established for the determination of N-nitrosodimethylamine (NDMA) in metformin hydrochloride active pharmaceutical ingredient (API) and preparation samples by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Water was used as the extraction solvent for the metformin hydrochloride API and preparation samples. The samples were analyzed by HPLC-MS/MS after vortex mixing, constant temperature shaking, high speed centrifugation and microfiltration. An ACE EXCEL 3 C18-AR column (150 mm×4.6 mm, 3 µm) was used for chromatographic separation. The mobile phases were water and methanol both containing 0.1% formic acid with gradient elution. The flow rate, column temperature, and autosampler temperature were set as 0.8 mL/min, 40℃, and 10℃, respectively. The valve switching technique was used to protect the mass spectrometer, while six-way valve switching was adopted to allow the mobile phase with a retention time of 2.85-7.00 min to enter the mass spectrometer and the mobile phase with other retention times to enter the waste liquid. For the mass spectrometer, an atmospheric pressure chemical ionization (APCI) ion source was used in positive ion MRM scanning mode. The other conditions were as follows:atomizer flow, 3 L/min; heater flow, 10 L/min, interface temperature, 300℃; desolvation line (DL) temperature, 250℃; heating block temperature, 400℃; and dryer flow, 10 L/min. The quantitative transition of NDMA was m/z 75.0→43.1 with a collision energy of-17.0 eV, while the qualitative transition was m/z 75.0→58.2 with a collision energy of-16.0 eV. The external standard method was utilized for quantitative analysis. The established method was validated in detail by investigating the specificity, linear range, limit of detection, limit of quantification, recovery, precision, and stability. This method showed good specificity, since the solvents and excipients did not interfere with the determination of NDMA. A good linear relationship was observed the NDMA peak area and the mass concentrations in the range of 1.00-100.00 ng/mL with an excellent correlation coefficient (r>0.9999). The limit of detection and limit of quantification in solution were 0.20 ng/mL and 1.00 ng/mL, respectively. The recoveries of NDMA at low, medium, and high spiked levels ranged from 94.55% to 114.67%, and the RSDs ranged from 4.73% to 13.46%, indicating good accuracy and precision for the quantification of NDMA. Stability tests showed that NDMA was stable when placed in the autosampler for 0, 8, 24 h, since the RSD of the peak area was as low as 2.08%. The validated method was then applied to the determination of NDMA in metformin hydrochloride raw materials and preparations (tablets, capsules or enteric tablets). The detected amount of NDMA in the API did not exceed the limit in 113 batches of samples, but NDMA was detected and exceeded the limit in eight batches of preparations. This method is sensitive, accurate, and easy to operate, and it can be used for the determination of NDMA in metformin hydrochloride raw materials and preparation samples.

Antifungal bis[bibenzyls] from the Chinese liverwort Marchantia polymorpha L.

Bioassay-guided separation of the antifungal constituents of the Chinese liverwort Marchantia polymorpha L. (Marchantiaceae) led to the isolation of seven bis[bibenzyl]-type macrocycles. On the basis of NMR and MS analyses, the three new compounds plagiochin E (1), 13,13'-O-isoproylidenericcardin D (4), and riccardin H (7) were identified, together with four known compounds: marchantin E (2), neomarchantin A (3), marchantin A (5), and marchantin B (6). Their antifungal activities against Candida albicans were determined by TLC bioautography.