Assuring the quality of data in the pesticide residue laboratory

Abstract

The importance of quality control procedures to the collection of pesticide residue data is discussed. The equipment requirements of an adequate, safe pesticide residue laboratory are presented. Equipment maintenance, personnel training, and preservation of samples is also reviewed. Appropriate objectives for an intra‐laboratory quality control program are outlined.     

顶空固相微萃取-气相色谱质谱法测定水体中的苯甲醚

建立了顶空固相微萃取-气相色谱质谱法定性定量检测水中苯甲醚的分析方法。对影响检测结果的因素如萃取头的选择、萃取时间等进行了优化。经过条件优化，方法在1～1 000 μg/L 范围内线性良好，线性相关系数＞0.999，实际水样加标质量浓度分别为10，60，300 μg/L时，加标回收率为85%～120%，相对标准偏差（RSD）为3.95%～6.72%。全扫描模式下，苯甲醚的检出限为0.3 μg/L。实验结果表明，该方法快速、简便、灵敏度高，方法精密度和准确度均能满足水中微量及痕量苯甲醚检测的要求。     

Development and validation of a thermally regulated atmospheric simulation chamber (THALAMOS): A versatile tool to simulate atmospheric processes

Atmospheric simulation chambers, are unique tools for investigating atmospheric processes in the gas and heterogeneous phases. They can provide a controlled yet realistic environment that simulates atmospheric conditions. In the current study, a Teflon atmospheric simulation chamber of 600 L, named THALAMOS (thermally regulated atmospheric simulation chamber) has been developed and cross-validated. THALAMOS can be operated over the temperature range 233 to 373 K under both static and flow conditions. It is equipped with state of the art instrumentation (selective ion flow tube mass spectrometry (SIFT-MS), long path Fourier transform infrared spectroscopy (FTIR), gas chromatography-mass spectrometry (GC-MS), various analyzers) for the in-line monitoring of both reactants and products. THALAMOS was validated by measuring the rate coefficients of well documented reactions, i.e. the reaction of ethanol with OH radicals and the reaction of dichloromethane with Cl atoms, in a wide temperature range. Two different detection techniques were used in parallel, FTIR and SIFT-MS, to internally cross-validate the obtained results. The measured rate coefficients are in excellent agreement, both between each other and with the literature recommended values. Furthermore, the gas phase oxidation of toluene by Cl atoms (kinetics and product yields) was studied in the temperature range of 253 to 333 K. To the best of our knowledge, THALAMOS is a unique facility on national level and among a few smog chambers internationally that can be operated in such a wide temperature range providing the scientific community with a versatile tool to simulate both outdoor and indoor physicochemical processes.     

Scaling parameters for vented gas and dust explosions

Results of experiments or calculations for vented explosions are usually presented by expressing a term containing the peak (reduced) pressure as a function of a vent parameter. In gas explosions, the reactivity of the system has been typically characterized through an effective burning velocity, u_f. In the case of dust explosions, a normalized peak rate of pressure rise, K(=V^1/3(dp/dt)_max), has been used instead. Depending on the chosen approach, comparisons between systems with the same “reactivity” take different meanings. In fact, correlation formulas resulting from these two approaches imply different scaling between important system parameters. In the case of a constant-u_f system, and for sufficiently large vent areas, the reduced pressure, Δp_r, is approximately proportional to the square of the peak unvented pressure, Δp_m. On the other hand, correlations developed for constant-K systems imply proportionality of Δp_r with Δp_m raised to a power between −5/3 and −1, with the exact value depending on the assumptions made on the shape of the pressure profile. While the ultimate resolution of the details of the scaling may require recourse to experiments, this theoretical analysis offers a tool for the planning of such experiments and for the interpretation of their results. The paper provides a discussion of these scaling issues with the help of predictions from an isothermal model of vented explosions.     

Accuracy improvement in evaluation of gas explosion overpressures in congestions with safety gaps

This paper reports a comparison of simulations and published data from experiments carried out by TNO Prins Maurits Laboratory on geometric configurations that involved safety gaps of various separation distances. The Computational Fluid Dynamics (CFD) based software – FLACS is utilized to conduct the numerical simulations. In the majority of cases, good agreement is found between the simulated results and those obtained by experiment in both the donor and acceptor modules. However, a large discrepancy in the overpressures in the acceptor module is seen when the size of the separation gap approaches one or two times of the module size. A Data-dump technique is used in this study to reset the turbulence length scale for these cases with different separation distances, five sets of explosion scenarios are then numerically simulated and the overpressures are compared with experimentally measured explosion overpressures. The overall results indicate that the software with the Data-dump technique is still an extremely effective tool when it comes to the evaluation of gas explosion overpressures in areas with large separation gaps.     

Experimental study on the suppression of gas explosion using the gas–solid suppressant of CO2/ABC powder

Gas explosion is the leading accident in underground coal mining in China. Using the self-improved 20 L spherical experimental system, the impacts of 8% CO₂, ABC powder at various concentrations and mixture of them on the suppression of mine gas explosion were investigated. The results indicate that cooperative synergism exists between ABC powder and CO₂. Their combination has a better effect than each of the two components acting alone, especially for the gas of larger concentration. When 0.25 g/L ABC powder was mixed with 8% CO₂, the explosion limits were reduced by about 55%, the time to reach the peak explosion pressure was prolonged 3.56 times on average. Meanwhile, the maximum explosion pressure declined on an average of 59.4% and the maximum explosion overpressure rising rate decreased on an average of 91.1%. A combination of 0.20 g/L ABC powder and 8% CO₂ completely suppressed 11% gas explosion. The explosion suppression mechanism of CO₂ and ABC powder were probed theoretically. CO₂ plays a key part in the whole explosion processes, and it can effectively suppress the forward reaction between gas and oxygen. While it is during the middle-later period of explosion processes that ABC powder plays a critical role. The particles decomposed from heated ABC powder such as nitrogen and phosphor will react with free radicals rapidly. Besides, atoms as N, P are capable of participating in chain reaction and reacting with active groups, significantly suppressing the gas explosion.     

水、氮控制对短花针茅草原气体交换的影响

随着对气候变化日趋关注,人们对生态系统气体交换及其主要影响因素进行了大量研究。短花针茅草原作为荒漠草原的典型代表,是亚洲特有的一种草原类型,是最干旱的草原类型,生态环境异常严酷,系统极度脆弱,稳定性差,在自然和人为干扰下极易退化。以短花针茅（Stipa breviflora）草原为研究对象,通过控制降雨量以及氮素添加对生态系统气体交换进行监测,研究气体交换对降雨量和氮素添加的响应过程,揭示降雨量和氮素添加对生态系统气体交换的影响作用。该文在2012年自然条件下,采用自动CO2通量系统（Li-6400, Li-COR, Lincoln, NE, USA）野外测定短花针茅（Stipa breviflora）草原生态系统气体交换数据,比较研究了增雨施肥（WN）、增雨不施肥（W）、减雨施肥（RN）、减雨不施肥（R）、单独施肥（N）、自然状况（CK）条件下2012年气体交换变化规律。结果表明：整个生长季生态系统净 CO2交换（NEE）、总的生态系统生产力（GEP）、生态系统呼吸值（ER）都呈先升高后降低的趋势,并在生长旺盛期（8月）达到最大值。NEE在N、W处理下有升高,其他处理都降低。ER在N、WN处理下都有升高,其他处理都降低。GEP在W、N、WN处理下都有升高,其他处理都降低。NEE、ER、GEP都是在N处理中达到最大值。     

The propagation speed of the cracks in coal body containing gas

The destabilization of coal body containing gas that is caused by the quick propagation of the cracks in coal body containing gas and the high pressure gas, which result into coal and gas outburst. Thus, according to the theory of brittleness rupture mechanics the propagation speed calculation formula of the cracks in coal body containing gas is derived under constant stress and the mechanism of the cracks propagation is analyzed. The propagation speed of the cracks in coal body containing gas is calculated by the experimental work. The research results show that gas pressure make the cracks propagation easier, which is consistent with the analysis result of the propagation speed calculation of the cracks. As well as the propagation speed of the cracks increase with the augment of gas pressure.     

Rapid regional outburst elimination technology in soft coal seam with soft roof and soft floor

In order to solve the problems in outburst elimination of coal seams with outburst potential, methods of field testing, theoretical analysis and numerical simulation are employed in this study. It is found that the horizontal stress concentration surrounding coal unloading boreholes is the primary cause of the coal and gas blowouts in the process of the coal unloading and permeability improvement with high-pressure water jet. The results indicate that low borehole density and inefficient drainage are the main reasons for the occurrence of high outburst indices in the effeteness validation of regional measures to control outbursts. Based on numerical modeling results and onsite parameter testing, reasonable parameters such as borehole density are determined, and hydraulic fracturing is applied to improve coal seam permeability and relieve stress levels so as to eliminate regional outburst potential. The effect is significant in the field application, coal and gas blowout during the coal unloading period with high-pressure water jet is reduced dramatically, and the roadway development rate is increased by 48%. It is demonstrated that the gas drainage combined with the hydraulic fracturing, coal unloading with high-pressure water jet is a practical and effective technique for rapid elimination of coal and gas outburst potential in roadway development.     

Experimental study on leak detection and location for gas pipeline based on acoustic method

The leak of gas pipelines can be detected and located by the acoustic method. The technologies of recognizing and extracting wave characteristics are summarized in details in this paper, which is to distinguish leaking and disturbing signals from time and frequency domain. A high-pressure and long distance leak test loop is designed and established by similarity analysis with field transmission pipelines. The acoustic signals collected by sensors are de-noised by wavelet transform to eliminate the background noises, and time-frequency analysis is used to analyze the characteristics of frequency domain. The conclusion can be drawn that most acoustic signals are concentrated on the ranges of 0-100 Hz. The acoustic signal recognition and extraction methods are verified and compared with others and it proves that the disturbing signals can be efficiently removed by the analysis of time and frequency domain, while the new characteristics of the accumulative value difference, mean value difference and peak value difference of signals in adjacent intervals can detect the leak effectively and decrease the false alarm rate significantly. The formula for leak location is modified with consideration of the influences of temperature and pressure. The positioning accuracy can be significantly improved with relative error between 0.01% and 1.37%.