Simple and sensitive determination of low-molecular-mass aromatic aldehydes in swimming pool water by LC-diode array detector

This work reports the development of a simple method for the quantitative determination of aromatic and aliphatic low-molecular-mass aldehydes (LMMAs) as disinfection by-products (DBPs) in indoor swimming pool waters after chlorination with a simplified SPE sample treatment. The method is based on the continuous in situ derivatization/preconcentration of the aldehydes with 2,4-dinitrophenylhydrazine (DNPH) on a Lichrolut EN column in the presence of β-CD. After elution, the 2,4-dinitrophenylhydrazine derivatives were separated on an RP-C(18) analytical column using gradient of ACN-water at 60-80%. The optimized sample treatment described here allowed the direct analysis of large volumes of water in order to improve the sensitivity of the method; LODs in the 60-120 ng/L range were achieved for aromatic LMMAs by using a volume of 50 mL of water, precision being 7.5% or better at a concentration level of 5 μg/L. These results indicate that the ensuing method is a useful choice for the determination of LMMAs in water samples that provides better results than reported LC alternatives in terms of the LOD (except for MS/MS detection), sample requirements for analysis and cost.     

Extraction of ketamine from urine using a miniature silica monolithic cartridge followed by quantification with liquid chromatography tandem mass spectrometry (LC-MS/MS)

The high surface area monolith with reactive hydroxyl group on its surface enables it to function as a miniature solid‐phase extraction (SPE) cartridge in size of 1 cm in diameter and 0.5 cm in length. The prepared silica monolith was characterized by Brunauer–Emmett–Teller method, scanning electron microscopy, X‐ray diffraction and Fourier transform infrared (FTIR) spectroscopy. Ketamine was selected as model analyte to validate the extraction efficiency of the prepared cartridge. The extracted ketamine from urine sample was quantitated by liquid chromatography tandem mass spectrometry (LC‐MS/MS) using positive electrospray ionization. The limit of detection and quantification for ketamine was found to be 0.5 and 1.6 ng/mL, respectively. The analysis exhibited linearity in the range of 10–500 ng/mL with coefficient of correlation >0.99. The recovery was found to be in the range of 89–107% with relative standard deviation (RSD) less than 10%. The prepared cartridge was found robust in extracting ketamine efficiently and repeatedly without any significant deterioration in its performance. Moreover, the batch‐to‐batch variations in the performance of the prepared cartridges in terms of % ion suppression of the extracts and recoveries of samples were small, suggesting the consistency in the properties of the monolith.     

Retention behaviors of natural products in reversed-phase liquid chromatography using mobile phase comprising methanol, acetonitrile and water

The three-component mobile phase, methanol-acetonitrile-water, has been frequently used for the separation of natural products in complicated herbal extracts by reversed-phase liquid chromatography, especially when two-component solvent systems do not work. However, the rational for optimization of this three-solvent system is not clear, so far. In this study, the retention behavior of different types of natural products in RP-LC with a methanol-acetonitrile-water elution system was studied. A total of 27 compounds from four classes, including steroids, flavonoids, phenolic acids, and triterpene saponins were analyzed by high-performance liquid chromatography coupled with mass spectrometry or ultraviolet detectors. It was interesting to find that prolonged retention times and improved separation capabilities were obtained when the acetonitrile-to-methanol ratio was 3-16%. This rule applied to all four classes of natural products under different instrumental conditions, and could be valuable for the separation of natural products in complicated samples.     

Some <Emphasis Type="Italic">I</Emphasis>-convergent sequence spaces defined by Orlicz functions

In this article we introduce the sequence spaces cI(M),c0I(M),mI(M) and m0I(M) using the Orlicz function M.We study some of the properties like solid,symmetric,sequence algebra,etc and prove some inclusion relations.     

Factors that affect quantification of diode array data in comprehensive two-dimensional liquid chromatography using chemometric data analysis

There has been a tremendous increase in research on comprehensive two dimensional LC (LC×LC); however, to date, the central analytical issue, quantification, has received only minimal attention. It is vital to the further development of LC×LC that a greater understanding of the specific factors affecting peak quantification in LC×LC be attained. This work focuses on the following factors: data complexity, retention time shifting, dynamic range issues, chromatographic and spectral peak overlap and difficulties related to background signal removal. The above mentioned factors that affect peak quantification are investigated using fourteen replicate analyses of a urine sample, representing the effects of such factors when analyzing samples in complex matrices. We demonstrate that quantification of LC×LC data is improved following implementation of chemometric techniques that minimized the deleterious effects on quantification due to chromatographically overlapped peaks, retention time shifting and background signal interference. The chemometrically resolved data shows a 2.5-fold increase in precision of quantification over the quantification of the raw data. It is also demonstrated that the method quantifies sixteen peaks that were not visually evident prior to chemometric analysis. The purpose of this paper is to determine the impact of these issues on the effectiveness of LC×LC as a technique for the quantitative analysis of complex samples.     

基于FFT校频的分段匹配滤波器性能分析

为了对动态PN码捕获中使用的分段匹配滤波器的设计进行指导,在建立其数学模型的基础上,分析了分段数、FFT点数与载波频偏对滤波器性能的影响。结果表明,增加分段数可以减小载波频偏对相关峰的影响;增加FFT点数可以提高频偏校正的精度;在环境噪声为高斯白噪声情况下,存在最佳的分段数和FFT点数组合,可以用最小运算量达到最佳捕获效果。     

Dual‐Transmission‐Line Microstrip Equiripple Lowpass Filter with Sharp Roll‐Off

A novel application of a dual‐transmission line is proposed to design a lowpass filter (LPF). The proposed structure uses only transmission line elements to produce an equiripple LPF response with sharp roll‐off. Design equations are derived using a lossless transmission line model. Controlling the electrical lengths, three transmission‐zeros are realized in the stopband to obtain a sharp roll‐off rate and wide stopband bandwidth. A single unit microstrip LPF with a 3‐dB cut‐off frequency at 1.0 GHz having a roll‐off of 135 dB/GHz along with a stopband bandwidth of 69.5% is designed for validation.     

三相不控整流器输入LC滤波器的研究

鉴于单相供电的局限性以及三相供电的优越性,目前大功率变频空调领域主要采用三相无源功率因数校正方案。在考虑校正效果以及成本、体积、重量、效率、输出电压等因素情况下,提出并分析了不控整流器采用单级LC滤波器时关键问题,包括混合谐波源等效原理、谐波电流滤波原理、输出直流电压提升原理、整流桥最佳输入线电压波形,并对搭建的最大输...     

一种并联有源电力滤波器的复合控制方法研究

在采用并联有源电力滤波器来消除电网谐波时,由于其滤波器的检测精度、指令电流计算延时等原因,一般的控制方法很难达到理想的滤波效果。因此,本文提出了基于常规PI控制和重复控制的复合控制方法,能使系统获得很好的静态性能和动态性能。仿真实验表明,这种控制方法实现相对比较简单,在响应速度和控制精度上都具有一定的优势,且能有效地对...