Tip Micro Research Articles

Fabrication and application of aminated metal–organic cages doped monolithic column for pipette tip micro solid-phase extraction of eight phenolic compounds in milk

A Zr-based metal–organic tetrahedron (ZrT-1-NH2) doped monolithic column was sythesized and applied for pipette tip micro solid-phase extraction (PT-μSPE) of 8 phenolic compounds. Scanning electron microscopy, energy dispersive spectrometry, Fourier transform infrared spectroscopy, thermogravimetric analysis and N2 adsorption and desorption experiment were employed to characterize the morphology, composition, structure and thermal stability of the monolithic column. The experimental results showed that the monolithic column had good stability and excellent adsorption selectivity for phenolic compounds. The adsorption mechanism was speculated to be π-π stacking and H-bond interaction based on ESP maps. After the extraction conditions were optimized, a PT-μSPE-high performance liquid chromatography-ultraviolet detector (HPLC-UV) method was established for the detection of 8 phenolic compounds in milk. The PT-μSPE-HPLC-UV method has wide linearities (0.3–1000 μg L−1) (R2 > 0.997), low limits of detection (0.1–0.3 μg L−1), satisfactory recoveries (80.5–113.6 %) and high precision (RSDs < 6.7 %). Thus, the ZrT-1-NH2 doped monolithic column is an ideal medium for the separation and determinaton of phenolic compounds in milk.

Evaluating lesion integrity with diamond temp system

Abstract Background Pulmonary vein (PV) isolation by temperature-controlled (TC) radiofrequency ablation (RFA) is regaining popularity due to tissue-temperature feedback from thermocouples attached at the distal tip. The Diamond Temp (DT) ablation catheter system is uniquely able to monitor real time tissue temp during RFAs. The DT catheter tip has a 1.1 mm split tip electrode, allowing precise bipolar pacing during RFA. Loss of capture (LOC) with High output pacing (HOP) has been considered a surrogate to assess lesion transmurality [1]. This study evaluated the utility of DT catheter distal pacing to achieve durable lesions. Standard guidelines for TC ablation recommend achieving target tissue-temperature of 60ºC to produce durable lesions. The purpose of this study was to assess whether LOC is achieved at target tissue-temperature of 60ºC. Objective Pacing during ablation from distal tip micro electrode of the DT catheter and observing the time it takes for LOC at different segments around pulmonary veins. First pass isolation (FPI) percentage was also collected. Methods While target enrollment for this prospective study is 50 patients, these preliminary findings are based on analysis of the first 15 patients enrolled, all of whom had symptomatic, drug-refractory paroxysmal AF. Point-by-point RF lesions were delivered around ipsilateral PVs, divided into 4 segments: superior, inferior, anterior, and posterior. Ablation was performed in a TC mode with max temp setting of 60°C and max power of 50 watts. HOP was performed prior to start of ablation and discontinued once LOC was observed. Time taken to LOC around all 4 segments of PVs were recorded. Intracardiac echocardiography (ICE) was used to guide contact and monitor lesion formation. Results Overall mean time to LOC was 3.32 sec. Anterior sites exceeded this mean. Inferior, superior, and posterior sites generally had shorter times. 92.53% of locations achieved LOC within 2-5 sec of ablation. The right anterior PV had the longest time at 3.73 sec, exceeding the overall mean of 3.32 sec. All patient achieved FPI. Conclusion Reaching target therapeutic temp of 60°C alone may not be sufficient to achieve LOC around PVs. Ablation duration of 4 sec led to LOC in 92.53% of lesions. Certain anatomical regions like anterior locations required prolonged ablation time. Tissue thickness on ICE correlated directly with time required to LOC. This analysis shows that TC ablation with DT is effective; however, a therapeutic stable temperature of 60°C for at least 4 sec may be needed to achieve durable lesions around PVs. Tissue thickness on ICE and stability of temperature appear to be independent variables affecting duration prior to LOC.

Melamine sponges incorporated azo-linked porous organic polymer as adsorbent for extraction and determination of six B vitamins using pipette tip micro solid-phase extraction

A novel azo-linked porous organic polymer (AL-POP) was synthesized from caffeic acid and benzidine via an azo-coupling reaction and characterized by FTIR, SEM-EDS, BET, TGA, XRD and zeta potential analysis. AL-POPs were incorporated into melamine sponges and used for pipette tip micro solid-phase extraction (PT-MSPE) of six types of B vitamins (including thiamine, riboflavin, nicotinamide, pyridoxine, folic acid, and cyanocobalamin). After extraction, the samples were analyzed using high performance liquid chromatography-diode array detection (HPLC-DAD) system. The effect of AL-POP composition on the extraction efficiency (EE) of vitamins was investigated and benzidine to caffeic acid mol ratio of 1.5, 3.35 mmol of NaNO2, and reaction time of 8 h were selected as optimum conditions. The efficiency of the extraction process was improved by optimizing various parameters such as the amount of sorbent, pH and ionic strength of the sample, sample volume, number of sorption and desorption cycles, type of wash solvent, and type and volume of eluent solvent. Linearity (R2≥0.9987), Limit of detection (LOD) (11.88–18.97 ng/mL), limit of quantification (LOQ) (39.62–63.23 ng/mL), and enrichment factor (EF) (1.27–4.31) were obtained using calibration curves plotted under optimum conditions. Recovery values of these six B vitamins in the spiked multivitamin syrup samples varied from 80.01% to 108.35%, with a relative standard deviation (RSD) below 5.44%. Eventually, the optimized method was successfully used to extract and quantify the B vitamins in multivitamin syrup and non-alcoholic beer.

Fabrication of a Molecularly Imprinted Polymer Adsorbent for Pipette Tip Micro Solid-phase Extraction of Levofloxacin from Aqueous Samples Prior to its Spectrophotometric Determination

Aims: The main goal of this research was to find a simple, selective, sensitive and rapid protocol for the detection of traces of levofloxacin (Lev) in seawater, pills, urine, and human plasma samples by using a novel sorbent made of molecularly imprinted polymer (MIP) for its pipette-tip micro-solid phase extraction (PT-μSPE), followed by spectrophotometry. Parameters affecting the method were evaluated employing one-variable-at-a-time, Box-Behnken design (BBD) and central composite design (CCD) techniques, and results were compared together. Background: Lev, the active L-isomer isolated from racemic of loxacin, is a fluoroquinolone (FQ) antibiotic that is widely in use for curing infectious diseases due to its high activity against a large spectrum of both Gram-positive and Gram-negative bacteria. If it enters the environment, such as seawater, due to low degradation, it can remain there for the long term. Besides water, since Lev cannot be metabolized completely in the body, a selective and sensitive protocol for the analysis of Lev in biological fluids is necessary for physiological pharmacokinetics and clinical diagnosis. Objective: The objective was to find a fast, accurate and sensitive method for the determination of Lev in different sample matrices. This method should be very economical as well. Methods: This technique is based on using molecularly imprinted polymer adsorbent for pipette tip micro solid-phase extraction of Lev prior to its spectrophotometric detection. Results: The limit of detection of the developed protocol was 0.1 μg L-1, and its linear range was 1.0- 1,000.0 μg L-1 (R2=0.9934). The total time of analysis, including microextraction, was less than 10 min and for the analysis, a sample volume of 14 mL was adequate. 2.0 mg of the sorbent was sufficient for the extraction, and the sorbent could be reused for 4 times without loss in its extraction performance. For the spiked real samples at three levels, recoveries were in the range of 97.4% to 99.5%, with relative standard deviations better than 4.7%. Conclusion: The proposed protocol has advantages, including the simplicity of sorbent preparation and operation, consumption of a low amount of solvent and sorbent, which is in consistency with green chemistry, and high enrichment factor. In addition, it can be applied in samples with different matrices, has low analysis time (10 min), and uses inexpensive instruments.

Electrospun poly(ST-Co-AC)/Co-ZIF-67@Chitosan composite nanofibers as a sorbent with superior reusability for pesticide residues analysis in food samples

Pollution caused by pesticides have attracted huge attention, and it is of a great significance to develop sensitive methods for trace monitoring these analytes in complicated matrices. Herein, the composite of styrene acrylonitrile copolymer p(St-Co-AC)/zeolitic based metal–organic frameworks (Co-ZIF-67)/Chitosan (CS) electrospun nanofibers was fabricated by using an electrospinning approach. The resultant composite nanofibers were characterized to apply as a novel adsorbent for pipette tip micro solid-phase extraction (PT- μSPE) of four pesticides prior to GC-FID analysis. Incorporating Co-ZIF-67@Chitosan into p(ST-Co-AC) results in increasing the porosity features and surface area of the nanofibers. The effect of different main parameters on extraction efficiency was evaluated. Under the optimal conditions, linearity ranges were 1.5–2000.0 ng mL−1 for ethofumasate, 2.0–2000.0 ng mL−1 for ametryn and propazine, and 3.0–2000.0 ng mL−1 for tribenuron-methyl (R2 = 0.9951–0.9997). The LODs (according to S/N = 3) were calculated in the range of 0.5 to 1.0 ng mL−1.The relative standard deviations (RSDs) were obtained between 5.1 % – 6.1 % (intra-day, n = 5) and 5.6 %–6.4 % (inter-day, n = 3) for three sequential days. The developed method was investigated in food samples including apple, tomato, honey, and milk, and achieved recoveries (88.1–95.2 %) indicated that the fabricated sorbent could be a promising composite for the pre-concentration of pesticides in various matrices.

Amylodextrin Hydrogel as a Green Sorbent for Pipette Tip Micro Solid Phase Extraction Followed by Ion Mobility Spectrometry for Analysis of Triazole Fungicides in Environmental Water Samples

Amylodextrin Hydrogel as a Green Sorbent for Pipette Tip Micro Solid Phase Extraction Followed by Ion Mobility Spectrometry for Analysis of Triazole Fungicides in Environmental Water Samples

A green hybrid microextraction for sensitive determination of bisphenol A in aqueous samples using three different sorbents: Analytical and computational studies

A green hybrid of pipette tip micro solid phase extraction (PT-µSPE) and supported liquid extraction (SLE) was tailored and applied for sensitive determination of bisphenol A (BPA) in water and thermal paper samples using three different sorbents namely chitin, chitosan and cellulose acetate. Self-ensembled in lab, three respective hybrid podiums were setup for three sorbents with PT-µSPE platform using basic SLE principle on it. Coupled with HPLC-UV detection, the three set ups were compared for their respective performances to determine the BPA in water in terms of detection limit, recovery, precision and repeatability values. Under optimized conditions, chitin and cellulose acetate demonstrated comparable performances whereas chitosan showed better performance with detection limit up to pg/mL (0.008 ng/mL), high recovery (>90%), good precision (RSD % 3.8–7.4) and repeatability values (RSD % 2.02–3.04). In addition, computational simulations were performed to have insights on the possible sorbent-analyte interactions for all three sorbents. The method in general termed as sorbent supported pipette tip micro liquid extraction (SSPT-µLE) is a rapid, technically innovated, easily operated, cheap, green and highly efficient method for trace determination of BPA in water samples with successful applications to thermal papers also. Overall a novel and innovative analytical approach is introduced for sample preparation and established for trace determination of BPA in water and thermal paper using three different sorbents. Furthermore, the approach should also allow easy expansion to other emerging contaminants in water and other aqueous matrices including biological, pharmaceutical and environmental samples.

Effect of cold working on crack growth rate of environmentally assisted cracking of 316L SS

Environmentally assisted cracking (EAC) is a main failure mode of key structural materials of nuclear power pressure vessels and pipelines in service. The key structural materials of nuclear power will undergo plastic deformation due to cold working during manufacturing, assembly and welding, and cold working will affect the EAC crack growth rate. In order to understand effect of cold working on crack growth rate of EAC, a combination of theory, experiment and finite element simulation is used. There are experiments to obtain the mechanical properties of 316L stainless steel at different degrees of cold working, and the creep characteristics of 316L stainless steel at low temperature and high stress were obtained by experiment. Based on experiment and theoretical analysis, creep rate of crack tip is used to replace strain rate of crack tip in Ford-Andresen model, and effect of cold working on crack growth rate of EAC is analyzed with hardening at crack tip and without hardening at crack tip. The results show that cold working accelerates crack growth rate of EAC, and the hardening of crack tip micro zone restrains crack growth rate of EAC, causing the “hysteresis” phenomenon in the EAC crack growth process. It is more reasonable to use creep rate of crack tip instead of strain rate of crack tip to calculate crack growth rate of EAC.

A new asymptotic crack tip model to predict failure processes

A two dimensional finite element asymptotic crack tip model (ABAQUS® code) to simulate crack tip opening displacement (CTOD) and damage in ductile materials has been developed. Pure Mode I is considered with asymptotic displacements applied on the outer boundary of the finite element mesh constructed using plane strain solid and cohesive elements. CTOD profiles and damage variation along cohesive element path are clearly observed. Evolution of CTOD for various ratios of solid/cohesive Young´s Modulus are also presented. The evolution of damage was based on a power law fracture criterion. In an effort to extend isotropic hardening plasticity theory to small scales, the research was focused on room-temperature crack growth in polycrystalline Aluminium alloys. In a future work, stress enhancement will be considered in a framework of cohesive zone modeling and strain gradient plasticity based on the micromechanics of dislocations. An asymptotic crack tip micro structured mesh will be also accounted into the finite element analysis.

A novel hybrid micro extraction for the sensitive determination of 17β-estradiol in water samples.

A novel and green hybrid of pipette tip micro solid-phase extraction (PT-μSPE) and supported liquid extraction (SLE) was tailored and established for efficient and sensitive determination of 17β-estradiol (E2) in water samples. The hybrid design used chitin as a solid phase in PT-μSPE and applies the SLE principle on it for micro extraction. The analytical setup was termed as chitin-supported pipette tip-micro liquid extraction (CPT-μLE). E2 is a highly active environmental endocrine disruptor, widely spread in the water environment, and thus it is relevant to develop a novel and noble method for its monitoring at trace concentrations in water. The detection and quantification of E2 were performed via HPLC-UV. Under the optimal conditions, E2 showed excellent linearity in the lower scale range of 0.02-20 ng mL-1, and the correlation coefficient (R2) value was 0.9958. The limit of quantitation (LOQ) and limit of detection (LOD) were 0.01 ng mL-1 and 0.008 ng mL-1, respectively, with inter-day and intra-day precision in the range of 3.2-5.1% and 3.6-4.8%, respectively. The method was successfully applied for the sensitive determination of E2 in real water samples. Overall, the method is simple, rapid, technically innovative, cost-effective, highly sensitive, environment friendly, and highly efficient. Furthermore, this method should allow easy expansion to pharmaceutical and biological samples. Finally, this novel hybrid analytical approach proposes a new direction in sample pre-treatment advancements and should act as a reference for other noble analytical advancements in the trace analysis of various emerging contaminants in environmental and biological matrices.

Highly Sensitive Determination of Bisphenol A in Bottled Water Samples by HPLC after Its Extraction by a Novel Th-MOF Pipette-Tip Micro-SPE.

In this study, a novel thorium metal organic framework was synthesized, characterized and used as a sorbent for very efficient pipette tip micro solid-phase extraction of bisphenol A in bottled drinking water samples using high-performance liquid chromatography as detecting instrument. Parameters which influence extraction efficiency such as pH, sample volume, amount of sorbent, type and volume of eluent, number of aspirating and dispensing cycles for extraction and elution, and volume of the sample solution were studied and optimized. A linear calibration curve was obtained in the range of 0.002-0.456ngmL-1 (r2=0.996) with a detection limit of 0.0010ngmL-1. Repeatability of batch-to-batch extraction was better than 5.0% and a reproducibility of 3.2% for real samples obtained.

Percutaneous soft tissue release performed using a blunt cannula in rabbits with chronic collagenase-induced Achilles tendinopathy

BackgroundThis study investigated the effects of percutaneous soft tissue release (PSTR) performed using a blunt cannula on (1) the inflammatory cells-count, (2) expressions of calcitonin gene-related peptide (CGRP) and (3) substance P (SP) in rabbits with chronic phase of collagenase-induced Achilles tendinopathy. MethodsThirty-two adult male New Zealand rabbits were randomly divided into four groups: (1) collagenase and PSTR treatment; (2) collagenase and sham-operated PSTR treatment; (3) vehicle-only injection and PSTR treatment; and (4) vehicle-only injection and sham-operated PSTR treatment. Achilles tendon of adult male rabbits was injected with 10μl of collagenase under ultrasonography localization. After 30 days, PSTR was performed using an 18G beauty cosmetic blunt tip micro cannula needle to release the soft tissue and paratenon above the inflamed Achilles tendon. The treated tendons and spinal cords of L5-S2 were harvested 5days after treatment for histological assessment and immunohistochemical analysis. ResultsHistopathological examination revealed that PSTR achieved significant reduction in hypercellularity with pronounced infiltration of immune cells at the site of paratenon in tendons injected with collagenase compared with sham operation (p<0.05). Immunohistochemical analysis also showed marked decrease in expression of CGRP in tendon and SP in dorsal horns after PSTR (p<0.05). ConclusionsThis study showed positive effects in an animal model of chronic tendinopathy, and can be considered a treatment option, but that further research is necessary to determine its role in clinical practice.

Application of Nanofiber-packed SPE for Determination of Urinary 1-Hydroxypyrene Level Using HPLC.

It is always desirable to achieve maximum sample clean-up, extraction, and pre-concentration with the minimum possible organic solvent. The miniaturization of sample preparation devices was successfully demonstrated by packing 10 mg of 11 electrospun polymer nanofibers into pipette tip micro column and mini disc cartridges for efficient pre-concentration of 1-hydroxypyrene in urine samples. 1-hydroxypyrene is an extensively studied biomarker of the largest class of chemical carcinogens. Excretory 1-hydroxypyrene was monitored with HPLC/fluorescence detector. Important parameters influencing the percentage recovery such as fiber diameter, fiber packing amount, eluent, fiber packing format, eluent volume, surface area, porosity, and breakthrough parameters were thoroughly studied and optimized. Under optimized condition, there was a near perfect linearity of response in the range of 1–1000 μg/L with a coefficient of determination (r2) between 0.9992 and 0.9999 and precision (% RSD) ≤7.64% (n = 6) for all the analysis (10, 25, and 50 μg/L). The Limit of detection (LOD) was between 0.022 and 0.15 μg/L. When compared to the batch studies, both disc packed nanofiber sorbents and pipette tip packed sorbents exhibited evident dominance based on their efficiencies. The experimental results showed comparable absolute recoveries for the mini disc packed fibers (84% for Nylon 6) and micro columns (80% for Nylon 6), although the disc displayed slightly higher recoveries possibly due to the exposure of the analyte to a larger reacting surface. The results also showed highly comparative extraction efficiencies between the nanofibers and conventional C-18 SPE sorbent. Nevertheless, miniaturized SPE devices simplified sample preparation, reducing back pressure, time of the analysis with acceptable reliability, selectivity, detection levels, and environmental friendliness, hence promoting green chemistry.

Alliage d’aluminium à haute résistance 2024-T351. Comportement plastique et élastoplastique en bout de fissure

Crack closure occurs as a consequence of crack tip plasticity. For a fattigue crack partially or entirely closed, ductile materials always result in a plastic strain at the crack tip even under small amplitude loading. Many theoretical and experimental studies have been carried out to evaluate the size and shape of the plastic zone in particular for large scale yielding. However in the case of confined plasticity, i.e. under small scale yielding conditions where the size of the affected zone is very small, the researchers are faced with some difficulties to evaluate the plastic and elastoplastic behavior near in the crack tip.In this study, it is shown that a correlation of the results obtained by two different measurment techniques can help one to determine the evaluation of strains in the strongly deformed regions in the viscinity of the crack tip. For distances greater than 500 µm from the crack tip micro strain gages have been used to measure the strain rate evaluation for a high strength aluminum alloy, 2024 T351, tested under constant ΔK loading conditions. For smaller distances, an interferometric method is used to determine the size of the deformed zones and the deformation rate evolution. Some of the obtained results are comparred with a finite element estimation by Anquez of the deformation profiles near the crack tip.