Simultaneous determination of 15 phenylurea herbicides in rice and corn using HPLC with fluorescence detection combined with UV decomposition and post-column derivatization.

A method was developed for the simultaneous determination of 15 phenylurea herbicides (fenuron, tebuthiuron, metoxuron, monuron, chlortoluron, fluometuron, isoproturon, diuron, monolinuron, metobromuron, buturon, siduron, linuron, chlorbromuron, and neburon) in rice and corn samples by HPLC with fluorescence detection combined with UV decomposition and post-column derivatization. After extraction with acetonitrile and evaporation, the herbicides were redissolved in n-hexane and purified on a Florisil solid-phase extraction column. HPLC separation was carried out on a C18 column with water-acetonitrile gradient elution. UV decomposition was carried out under a 254-nm UV lamp. The method was evaluated in terms of the limits of detection and quantification. The linearity was satisfactory, with a correlation coefficient of >0.9980. Precision and recovery studies were evaluated at three concentration levels for each matrix. Good precision was obtained, with relative standard deviation in the range 1.5-9.6% for spiked rice samples and 0.9-9.9% for spiked corn samples. Recovery (n=6) ranged between 75.3% and 104.3% for rice and between 75.0% and 105.1% for corn. The intra-day precision (n=5) for the 15 herbicides in rice and corn samples spiked at an intermediate level was between 1.5% and 7.1%, and the inter-day precision over 10 days (n=10) was between 6.4% and 15.6%.

A sequence investigation on Wallerian degeneration after pontine infarction with diffusion tensor imaging / 中华神经科杂志

Objective To investigate the Wallerian degeneration of neural fiber tract in medulla and bilateral middle cerebellar peduncle following pontine infarction and to explore its impacts on neurological recovery.Methods Fourteen patients with a recent unilateral pontine infarct underwent the diffusion tensor imaging(DTI)and evaluations with the NIH stroke scale(NIHSS),the Fugl-Meyer motor scale(FM), ataxia rating scale(ARS)and the Barthel index(BI)at the first week(W1),the fourth(W4)and twelfth week(W12)respectively.Mean diffusivity(MD)and fractional anisotropy(FA)were measured at pons, medulla and middle cerebellar peduncle.Fourteenth age and gender matched volunteers underwent a DTI were studied as controls.Results Compared with the matched regions in controls,the FA values of infarct side medulla and bilateral middle cerebellar peduncle in patients significantly decreased at W1,W4 and W12(on the infarct side of medulla:W1:0.43?0.01;W4:0.37?0.02;W12:0.30?0.02;on the infarct side of middle cerebellar peduncle:W1:0.50?0.01;W4:0.43?0.02;W12:0.35?0.04;on the opposite side of middle cerebellar peduncle infarction:W1:0.54?0.02;W4:0.52?0.03;W12:0.47?0.04,t values are 1.92 to 28.56,P0.05 respectively).The absolute value of percent reduction of FA in infarct side medulla and bilateral middle cerebellar peduncle was correlated negatively to the absolute value of percent change of NIHSS and BI score(P