Multiresidue analysis of pesticides with hydrolyzable functionality in cooked vegetables by liquid chromatography tandem mass spectrometry

It would be preferable for pesticide residues substituted by hydrolyzable functionality to be analyzed after cooking because their structures are apt to degrade during boiling and/or heating. A liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method for the quantitative determination of 44 pesticide residues with hydrolyzable functional group in five typical vegetable widely consumed in Republic of Korea is described. The sample clean‐up was carried out according to the method of Food Code No. 83 established by the Korea Food and Drug Administration (KFDA). Zorbox XDB‐C₁₈ column was selected for the analysis because of the best peak separation. The LC mobile phase consisted of water and 5 mm methanolic ammonium formate, which resulted in a peak shape with good symmetry at each run. Tandem mass spectroscopic (MS/MS) experiments were performed in ESI positive mode and the multiple reaction monitoring modes. A conventional matrix effect was modified to more comprehensive form 100γ_ij (%). A high matrix effect (相似文献   

Positive Toeplitz operators between the pluriharmonic Bergman spaces

We study Toeplitz operators between the pluriharmonic Bergman spaces for positive symbols on the ball. We give characterizations of bounded and compact Toeplitz operators taking a pluriharmonic Bergman space b ^p into another b ^q for 1 < p, q < ∞ in terms of certain Carleson and vanishing Carleson measures. This research was supported by KOSEF (R01-2003-000-10243-0) and Korea University Grant.     

Some connections between an operator and its Helton class

In this paper we show that the nilpotent perturbation of operators in the Helton class of p-hyponormal operators has scalar extensions. As a corollary we get that the nilpotent perturbation of each operator in the Helton class of p-hyponormal operators has a nontrivial invariant subspace if its spectrum has nonempty interior in the plane.     

HPLC determination of irbesartan in human plasma: its application to pharmacokinetic studies

A simple and rapid HPLC method using fluorescence detection was developed for determination of irbesartan in human plasma. Sample preparation was accomplished through a simple deproteinization procedure with 0.4 mL of acetonitrile containing 800 ng/mL of losartan (internal standard), and to a 0.1 mL plasma sample. Chromatographic separation was performed on a Zorbax Xclipse XDB C₁₈ column (150 × 4.6 mm, i.d., 5 µm) at 40°C. An isocratic mobile phase, acetonitrile:0.1% formic acid (37:63, v/v), was run at a flow‐rate of 1.0 mL/min, and the column eluent was monitored using a fluorescence detector set at excitation and emission wavelengths of 250 and 370 nm, respectively. The retention times of irbesartan and losartan were 4.4 and 5.9 min, respectively. This assay was linear over a concentration range of 10–5000 ng/mL with a lower limit of quantification of 10 ng/mL. The coefficient of variation for this assay precision was less than 8.48%, and the accuracy exceeded 94.4%. The mean relative recoveries of irbesartan and losartan were 98.4 and 99.1%, respectively. This method was successfully applied for pharmacokinetic study after oral administration of irbesartan (300 mg) to 23 Korean healthy male volunteers. Copyright © 2009 John Wiley & Sons, Ltd.     

Teaching Algebraic Expressions to Young Students: The Three‐day Journey of “a+ 2”

This classroom scholarship report is based on the teaching experience using Davydov's mathematics curriculum, which was developed in the former Soviet Union. While “from arithmetic to algebra” is the normally accepted instructional sequence in school mathematics, Davydov's curriculum is laid out “from algebra to arithmetic,” focusing on algebraic thinking from the very beginning of the elementary grades. The purpose of this report is not to provide a definitive conclusion about which curriculum or sequence is better nor to address which instructional strategy is right in all circumstances. Rather, it is to explore how primary grade students develop their own conceptual understanding while confronting difficulties met within a specific context. This report provides actual classroom episodes from working with a group of first graders and describes dynamic interactions between the teacher and children while they discuss the use of algebraic expressions and understand the meaning behind them.     

Full automatic synthesis of [<Superscript>18</Superscript>F]THK-5351 for tau protein PET imaging in Alzheimer’s disease patients: 1 year experience

[¹⁸F]THK-5351, a new candidate for tau protein imaging, is based on an aryl quinoline structure. We report the full automatic synthesis using disposable cassettes under pH controlled [¹⁸F]fluorination. After the trapping of 88.5 ± 21.9 GBq of [¹⁸F]fluoride, it was eluted with potassium methansulfonate (KOMs) (pH 7.8)/K₂₂₂. After drying, 3 mg of the precursor was added to 1 mL DMSO and subjected to [¹⁸F]fluorination at 110 °C for 10 min. After hydrolysis, the final product was purified by HPLC. The overall radiochemical yield was 31.9 ± 11.1% (n = 22), satisfying all quality control criteria. It was stable for up to 6 h with high radiochemical purity as 99.8 ± 0.5%.     

Sensitivity enhancement of CE and CE-MS for the analysis of peptides by a dynamic pH junction

An analytical method of CE-MS and CE with an online preconcentration technique induced by a dynamic pH junction, addition of organic solvent and large volume injection was developed for sensitive determination of peptides in biological samples. Leucine enkephalin, methionine enkephalin, dynorphin A, β-endorphin and angiotensin II were used as model peptides. The optimal online preconcentration conditions were obtained at a sample matrix consisting of 100?mM borate buffer (pH 10.0) with 50% v/v acetonitrile and a BGE containing 1?M formic acid at pH 2.0, along with a 25-cm injection length. Under the optimized conditions, a 4.0×10(3)-1.1×10(4)-fold increase in peak intensity was achieved without degrading the peak shape. This online preconcentration method was applied to analyze the intracellular angiotensin II within the peptides extracted from HL1 cells and approximately increase of 1×10(4)-fold sensitivity was achieved compared to normal condition. Thus, the developed method could be applied to the analysis of various peptides for peptidomics study in biological samples.     

TRPC3 cation channel plays an important role in proliferation and differentiation of skeletal muscle myoblasts

During membrane depolarization associated with skeletal excitation-contraction (EC) coupling, dihydropyridine receptor [DHPR, a L-type Ca²⁺ channel in the transverse (t)-tubule membrane] undergoes conformational changes that are transmitted to ryanodine receptor 1 [RyR1, an internal Ca²⁺-release channel in the sarcoplasmic reticulum (SR) membrane] causing Ca²⁺ release from the SR. Canonical-type transient receptor potential cation channel 3 (TRPC3), an extracellular Ca²⁺-entry channel in the t-tubule and plasma membrane, is required for full-gain of skeletal EC coupling. To examine additional role(s) for TRPC3 in skeletal muscle other than mediation of EC coupling, in the present study, we created a stable myoblast line with reduced TRPC3 expression and without α1_SDHPR (MDG/TRPC3 KD myoblast) by knock-down of TRPC3 in α1_SDHPR-null muscular dysgenic (MDG) myoblasts using retrovirus-delivered small interference RNAs in order to eliminate any DHPR-associated EC coupling-related events. Unlike wild-type or α1_SDHPR-null MDG myoblasts, MDG/TRPC3 KD myoblasts exhibited dramatic changes in cellular morphology (e.g., unusual expansion of both cell volume and the plasma membrane, and multi-nuclei) and failed to differentiate into myotubes possibly due to increased Ca²⁺ content in the SR. These results suggest that TRPC3 plays an important role in the maintenance of skeletal muscle myoblasts and myotubes.