Analysis of Polar Thermally Labile Pesticides using Different Solid-Phase Extraction (SPE) Materials with GC and HPLC Techniques

Abstract

In the present study, an efficient method for extraction, separation and determination of a limited number (30) of polar pesticides in aqueous matrices has been developed. Pesticides were extracted with high recoveries (usually >85%) from 1 L water samples, using the solid-phase extraction (SPE) technique. Affinities to different SPE materials (C-18 and XAD resins) have been studied for all pesticides. Special attention has been paid to the following 5 pesticides (which have classified by the EC as compounds which are particularly difficult to analyse): benazolia, bromofenoxim, ethofumesate, fenamiphos and phenmediphain. Thermally labile compounds have been determined with high pressure liquid chromatography (HPLC) and UV detection in comparison to TSP-LC-MS. Absolute limits of detection (LODs) for the HPLC technique are usually below 1 ng at 220 nm. Thermospray LC-MS determination shows usually limits of detection of 1-10 ng (SCAN) and 60-800 pg (SIM). All pesticides, which are amenable to GC have been detected in a comparative study with the following detectors: flame ionization detector (FID), nitrogen-phosphorus detector (NPD), electron capture detector (ECD) and atomic emission detector (AED). Element-specific detection of various functional groups of these pesticides has been achieved using GC-AED. Thus, while the FID has the lowest specificity, the AED is the most specific detector. LODs are usually < 300 pg (FID < 20 pg, NPD < 1 pg, ECD < 1 pg, AED < 300 pg). Spiked river water samples (from the River Leine and River Weser in Lower Saxony, Germany) have been used to test the employed method. With the spiked surface water samples recoveries were usually >80%.     

Study on the nanoscale current of ZnO film by photoassisted peak force tunnel atomic force: A novel technique for UV detection

ZnO film-based ultraviolet (UV) detector was fabricated by photoassisted peak force tunnel atomic force (PFTUNA) on fluorine tin oxide (FTO) substrate. The PFTUNA current in dark and in UV light was ~0.1 and 2.0 nA, respectively. The UV sensitivity (photocurrent/dark current) is more than 20. The response time and the recovery time are ~0.12 and 0.32 s, respectively. The UV sensing mechanism is that the holes will transport to the ZnO surface to capture the adsorbed oxygen ions to weaken the depletion layer under UV illumination. The PFTUNA current between the tip and the ZnO film is consistent with the Richardson–Schottky (RS) thermionic emission model.     

基于黑体标定的红外图像非均匀性校正系统设计

为提高某中波红外探测器的图像质量,设计了基于FPGA的红外图像实时处理系统,系统能够完成实时的非均匀性校正与盲元补偿处理。介绍了目前常用的非均匀性校正、盲元识别和补偿算法,并结合实际工程需求采用多点法进行非均匀性校正以及8点平均法进行盲元补偿。在仿真实验成功的基础上,基于FPGA平台构建了硬件平台。系统可以实现系数自定义更新,可以手动或自动完成非均匀性较正系数计算,以及实现盲元列表的自动更新操作。利用某国产中波红外探测器对处理系统进行了测试试验,实验结果表明:校正后图像非均匀性0.3%,盲元率0.001%。系统工作稳定、可靠,图像处理满足实时性和精度要求。     

A waveguide high-pass filter system for measuring the spectrum of pulsed terahertz sources

We propose a system for measuring spectra of terahertz (THz) pulses, including single pulses, which is based on high-pass filters (HPFs). The system consists of channels for measuring amplitudes of pulses (initial pulses and those transmitted via HPFs with different cutoff frequencies) and an algorithm for processing of the obtained data. The pulse spectrum is restored by using the iteration method or the amplitude–frequency method. The iteration method of spectrum restoration is applicable in the range of THz pulse durations from 10⁻⁹ s to 10⁻⁷ s. The amplitude–frequency method is applicable to THz pulses with durations exceeding 10⁻⁸ s. The system for measuring of THz pulse spectra was simulated by using the characteristics of specially developed waveguide HPFs. The relative simulation error of determining the central frequency by the amplitude–frequency method is equal to 2 · 10⁻⁶ for THz pulse durations of 10⁻⁵ s and longer.     

Towards a microchannel‐based X‐ray detector with two‐dimensional spatial and time resolution and high dynamic range

X‐ray detectors that combine two‐dimensional spatial resolution with a high time resolution are needed in numerous applications of synchrotron radiation. Most detectors with this combination of capabilities are based on semiconductor technology and are therefore limited in size. Furthermore, the time resolution is often realised through rapid time‐gating of the acquisition, followed by a slower readout. Here, a detector technology is realised based on relatively inexpensive microchannel plates that uses GHz waveform sampling for a millimeter‐scale spatial resolution and better than 100 ps time resolution. The technology is capable of continuous streaming of time‐ and location‐tagged events at rates greater than 10⁷ events per cm². Time‐gating can be used for improved dynamic range.     

1/f Noise QWIPs and nBn detectors

The low-frequency noise is a ubiquitous phenomenon and the spectral power density of this fluctuation process is inversely proportional to the frequency of the signal. We have measured the 1/f noise of a 640 × 512 pixel quantum well infrared photodetector (QWIP) focal plane array (FPA) with 6.2 μm peak wavelength. Our experimental observations show that this QWIP FPA’s 1/f noise corner frequency is about 0.1 mHz. With this kind of low frequency stability, QWIPs could unveil a new class of infrared applications that have never been imagined before. Furthermore, we present the results from a similar 1/f noise measurement of bulk InAsSb absorber (lattice matched to GaSb substrate) nBn detector array with 4.0 μm cutoff wavelength.     

Fabrication of type-II InAs/GaSb superlattice long-wavelength infrared focal plane arrays

In this paper, we present an InAs/GaSb type-II superlattice (SL) with the M-structure for the fabrication of a long-wavelength (10 μm range) infrared (LWIR) focal plane arrays (FPA), which are grown by molecular beam epitaxy (MBE). The M-structure is named for the shape of the band alignment while the AlSb layer is inserted into the GaSb layer of InAs/GaSb SL. A 320 × 256 LWIR FPA has been fabricated with low surface leakage and high R₀A product of FPA pixels by using anodic sulfide and SiO₂ physical passivation. Experiment results show that the devices passivated with anodic sulfide obviously have higher R₀A than the un-sulphurized one. The 50% cutoff wavelength of the LWIR FPA is 9.1 μm, and the R₀A is 224 Ω cm² with the average detectivity of 2.3 × 10¹⁰ cm Hz^1/2 W⁻¹.     

利用多像素光子计数器的光学串话效应提高光子探测效率

通过分析多像素光子计数器(MPPC)的工作原理和其光学串话(OC)效应的特点,提出在使用MPPC输出雪崩信号的幅度或电荷量作为光子计数的参量时,利用MPPC的OC效应能提高MPPC的光子探测效率的观点,并从理论上分析了OC效应对光子探测效率的影响。理论分析结果显示,在这两种光子计数模式下,利用OC效应能明显提高MPPC的光子探测效率。利用本文模型计算得出当MPPC的雪崩单元数M为1 600个,忽略OC效应时的光子探测效率等于30%,光学串话概率等于50%,以及单脉冲入射光子数均值为10时,包含OC效应影响的等效光子探测效率可提高50%,达45%左右。该结果对MPPC在天体物理、粒子物理、荧光光谱探测等弱光探测场合的应用有一定指导意义。     

8×8APD阵列激光三维成像接收机研制

为了实现对目标的无扫描阵列激光三维成像并研究系统参数对三维成像距离分辨率的影响,研制了8×8 pixel激光三维成像接收机。接收机采用线性模式APD阵列,设计了模拟信号放大、阈值处理将回波光信号转换为数字信号后,利用FPGA设计实现64通道高精度阵列计时系统,实现了对目标的无扫描实时三维成像功能。首先对设计完成的三维成像接收机组成及成像原理进行了介绍,对三维成像接收机中APD探测器阵列信号的模拟处理和数字处理流程和实现方式进行了说明。随后分别对三维成像的核心FPGA计时系统及探测器整体进行了电子学测试和实验测试。测试结果表明,FPGA计时子系统的时间分辨率优于140 ps,三维成像系统整体距离分辨率在0.2 m左右。最后对分辨率的误差进行了分析,结果表明,激光回波强度波动是影响此接收机距离分辨率的最主要因素。