A modified simplex method for multifactor optimization of selectivity in gas chromatography

A computer-assisted advanced simplex method is presented for the simultaneous optimization of multifactor ( stationary phase loading, carrier gas flow rate and column temperature ) for separation of ten compounds in gas chromatography. A three factors factorial design was used. The method was based on a special polynomial established from fifteen preliminary runs, using resolution as the selection criterion, with connection to a general simplex method. Excellent agreement is found between the predicted data and the experimental results, and most of experiments required in the general simplex method can be omitted.     

Simultaneous optimization by neuro-genetic approach for analysis of plant materials by laser induced breakdown spectroscopy

A simultaneous optimization strategy based on a neuro-genetic approach is proposed for selection of laser induced breakdown spectroscopy operational conditions for the simultaneous determination of macro-nutrients (Ca, Mg and P), micro-nutrients (B, Cu, Fe, Mn and Zn), Al and Si in plant samples. A laser induced breakdown spectroscopy system equipped with a 10 Hz Q-switched Nd:YAG laser (12 ns, 532 nm, 140 mJ) and an Echelle spectrometer with intensified coupled-charge device was used. Integration time gate, delay time, amplification gain and number of pulses were optimized. Pellets of spinach leaves (NIST 1570a) were employed as laboratory samples. In order to find a model that could correlate laser induced breakdown spectroscopy operational conditions with compromised high peak areas of all elements simultaneously, a Bayesian Regularized Artificial Neural Network approach was employed. Subsequently, a genetic algorithm was applied to find optimal conditions for the neural network model, in an approach called neuro-genetic. A single laser induced breakdown spectroscopy working condition that maximizes peak areas of all elements simultaneously, was obtained with the following optimized parameters: 9.0 µs integration time gate, 1.1 µs delay time, 225 (a.u.) amplification gain and 30 accumulated laser pulses. The proposed approach is a useful and a suitable tool for the optimization process of such a complex analytical problem.     

The study of electron beam flue gas treatment for coal-fired thermal plant in Japan

The fundamental research work with simulated coal-fired flue gas was performed in JAERI to get basic data for electron beam treatment of flue gas from thermal power plants in Japan. The standard condition of the experiments was set to be the same as that of next large scale pilot test in Nagoya. The concentrations of NO_x and SO_x were 225 ppm and 800 ppm, respectively. The temperature of the system was 65°C. The effect of multiple irradiation was observed for NO_x removal. The target SO_x and NO_x removals (94% and 80%, respectively) with low NH₃ leakage (less than 10 ppm) were achieved at 9 kGy irradiation with 0.9 NH₃ stoichiometry during 7 hours continuous operation. The facility for the pilot plant (12,000 Nm³/hr) has just built at the site of Shin-Nagoya power plant of Chubu Electric Power Company and will be started in full operation in November 1992.     

Computer-aided design and optimization of an on-line gas chromatographic procedure for the analysis of purgeable compounds in waste water

This report describes the application of a computer-aided column design and optimization program to the analysis of purgeable compounds in waste water. Series-coupled columns with dissimilar phases can be “selectivity-tuned” to provide the maximum separation factors, thus facilitating the most rapid analysis. A computer program calculates the column lengths and operating conditions which are required to provide the desired resolution at a specified flow rate.     

Multivariate optimization of a headspace solid‐phase microextraction method followed by gas chromatography with mass spectrometry for the determination of terpenes in Nicotiana langsdorffii

A simple and sensitive procedure based on headspace solid‐phase microextraction and gas chromatography with mass spectrometry was developed for the determination of five terpenes (α‐pinene, limonene, linalool, α‐terpineol, and geraniol) in the leaves of Nicotiana langsdorffii. The microextraction conditions (extraction temperature, equilibration time, and extraction time) were optimized by means of a Doehlert design. The experimental design showed that, for α‐pinene and limonene, a low temperature and a long extraction time were needed for optimal extraction, while linalool, α‐terpineol, and geraniol required a high temperature and a long extraction time. The chosen compromise conditions were temperature 60°C, equilibration time 15 min and extraction time 50 min. The main analytical figures of the optimized method were evaluated; LODs ranged from 0.07 ng/g (α‐pinene) to 8.0 ng/g (geraniol), while intraday and interday repeatability were in the range 10–17% and 9–13%, respectively. Finally, the procedure was applied to in vitro wild‐type and transgenic specimens of N. langsdorffii subjected to abiotic stresses (chemical and heat stress). With the exception of geraniol (75–374 ng/g), low concentration levels of terpenes were measured (ng/g level or lower); some interesting variations in terpene concentration induced by abiotic stress were observed.     

An efficient cleanup method coupled with gas chromatography and mass spectrometry for multi‐pesticides residue analysis in complex plant matrices

We aimed to develop an efficient cleanup method for multi‐pesticides residue analysis in complex plant matrices, shallot, ginger, garlic, onion, leek, and celery. Column chromatography was used as the cleanup method and fabricated with florisil and graphitized carbon black as the adsorbents. The amount of the graphitized carbon black adsorbent and the choice of the elution solvent were systematically investigated for exploring the best combination. The target pesticides covered organochlorine, pyrethroid, and organophosphorus pesticides, and were 38 in total. The method validation and comparison were performed to verify its feasibility and advantages in operation convenience and purification efficiency. The method limit of quantitation varied from 0.01 to 0.03 mg/kg, which depends on the pesticides and the sample matrices. The recoveries of the pesticides ranged from 60.5 to 128% (RSD ≤ 19.0%) at the spiked concentration level of 0.01 (or 0.03) mg/kg and 62.9 to 130% (RSD ≤ 13.0%) at 0.1 mg/kg. Compared with the commercial cleanup solid‐phase extraction cartridges, the present adsorbent combination displayed better purification effect and shorter sample pretreatment time, demonstrating potential application prospect in the complex matrix sample analysis.     

Optical biosensor for pharmaceuticals, antibiotics, hormones, endocrine disrupting chemicals and pesticides in water: Assay optimization process for estrone as example

Certain contaminants at trace concentrations in surface waters can have dramatic effects on the hormonal system of organisms in the aquatic environment. Therefore, immunoanalytical methods at a very low limit of detection (LOD) and a low limit of quantification (LOQ) are becoming more and more important for environmental analysis and especially for monitoring drinking water quality. Environmental monitoring of antibiotics, hormones, endocrine disrupting chemicals, and pesticides in real water samples (e.g. surface, ground or drinking water) with difficult matrices places high demands on chemical analysis. Biosensors have suitable characteristics such as efficiency in allowing very fast, sensitive, and cost-effective detection. Here we describe an assay optimization process with a fully automated immunoassay for estrone which resulted in a LOD below 0.20 ng L⁻¹ and a LOQ below 1.40 ng L⁻¹. In contrast to common analytical methods such as GC-MS or HPLC-MS, the biosensor used requires no sample pre-treatment and pre-concentration. The very low validation parameters for estrone are the result of the continuous optimization of the immunoassay. The basis of our sensitive assay is the antibody with a high affinity constant towards estrone. During the optimization process, we reduced the amount of antibody per sample and improved the chip surface modification. Finally, this proceeding led to a calibration routine with an amount of antibody of only 3.0 ng per sample (sample volume: 1.0 mL). The reduction of the amount of antibody per sample results in better validation parameters (LOD, LOQ, and IC₅₀), but this reduction leads to the current device-related limitation of the River Analyser (RIANA).For some endocrine disrupting compounds, no effect levels (NOELs) in the lower nanogram per liter range are reported. This defines the challenge, which analytical methods have to compete with and our RIANA instrument with its improved sensitivity for the detection of a single hormone in the lower nanogram per liter range is a powerful tool in aquatic analytics in addition to the common analytical methods.     

Development of multi‐response optimization and quadratic calibration curve for determination of ten pesticides in complex sample matrices using QuEChERS dispersive liquid–liquid microextraction followed by gas chromatography

In this study, QuEChERS combined with dispersive liquid‐liquid microextraction is developed for extraction of ten pesticides in complex sample matrices of water and milk. In this regard, effective factors of proposed extraction technique combined with gas chromatography with flame ionization detector were designed, modeled, and optimized using central composite design, multiple linear regression, and Nelder–Mead simplex optimization. Later, univariate calibration model for ten pesticides was developed in concentration range of 0.5–100 ng/mL. Surprisingly, quadratic calibration behavior was observed for some of the pesticides. In this regard, Mandel's test was used for evaluating linearity and types of calibration equation. Finally, four pesticides followed linear calibration curve with sensitivity (0.23–0.66 mL/ng), analytical sensitivity (0.20–0.32), regression coefficient (0.988–0.995), limit of detection (0.39–1.83 ng/mL), and limit of quantitation (1.30–6.10 ng/mL) and six of them followed quadratic calibration curve with sensitivity (0.18–0.93 mL/ng), analytical sensitivity (0.25–0.86), regression coefficient (0.944–0.999), limit of detection (0.59–1.92 ng/mL), and limit of quantitation (1.96–6.40 ng/mL). The calculated limits of detection were below the maximum residue limits according to European Union pesticides database of European Commission. Finally, the proposed analytical method was used for determination of ten pesticides in water and milk samples.     

紫草油有效成分的高效液相色谱测定法及其在超临界流体萃取制备紫草油中的应用

紫草提取制备成的紫草油能够预防及治疗婴儿尿布疹、皮肤溃烂、湿疹等多种皮肤疾患,临床应用非常广泛,超临界流体萃取是紫草有效成分提取的优选方法.该文建立了紫草油有效成分的高效液相色谱(HPLC)测定方法,并以紫草油所含的有效成分含量为评价指标,采用三因素三水平正交试验法对紫草超临界流体萃取制备过程中的几个重要因素(萃取压力...