The Effect of Bottle Fill Rate and Pour Technique on the Recovery of Volatile Organics

This field study was conducted to examine whether the method or the flow rate (fill rate) used to fill a sample vial affects recovery of volatile organics (VOCs). To our knowledge, there have not been any systematic studies that have examined this issue. For this field study, three fill rates (50 mL/min, 250 mL/min, and ~1 L/min) and three filling methods (top‐pour, side‐pour, and bottom‐fill) were used to fill sample vials. We found that the bottom‐fill method, with the tubing submerged in the sample as it fills, yielded the greatest recovery (i.e., highest concentrations) of VOCs. Little improvement was observed by pouring down the side of a vial vs. simply pouring straight down from the top. We also found that filling the vials at the fastest fill rate (~1 L/min) yielded higher recovery than the slowest fill rate (50 mL/min) using all three filling methods. These results are counter to prevailing guidance and conventional wisdom that slower filling is preferable to faster filling and that pouring down the side of a sample vial is the best practice for VOC sampling. However, because we were unable to randomize the order the samples were collected with respect to fill rate, we recommend a follow‐on study be conducted that will allow us to confirm our findings and better determine which fill rates minimize losses of VOCs     

Determination of Copper in Water Samples after Solid‐phase Extraction Using Dimethylglyoxime‐modified Silica

This work describes the modification of silica gel with dimethylglyoxime, in order to prepare an effective sorbent for the preconcentration and determination of copper. The sorption capacity of dimethylglyoxime‐modified silica‐gel (DMGMS) was 71.37 mg g^–1 and the optimum pH for the quantitative recovery of copper was found to be 5.0. The optimum flow rate, sorbent amount, and sample volume were 1 mL min^–1, 300 mg, and 50 mL, respectively. 10 mL of 0.1 mol L^–1 HCl was the most suitable eluent. The detection limit of copper was 6.0 ng mL^–1. The recommended method, for the determination of copper, is simple and reliable, without any notable matrix effect and can be successfully applied to environmental water samples. Copper recovery in the range from 99–100% was obtained from seawater and thermal spring water using this method. The method was applied to standard reference materials, NIST‐1515 (apple leaves) and NIST‐1643e (simulated fresh water), for the determination of copper and the results were in good agreement with certified values.     

Preconcentration of trace multi-elements in water samples using Dowex 50W-x8 and Chelex-100 resins prior to their determination using inductively coupled plasma atomic emission spectrometry (ICP-OES)

This work presents a solid phase extraction (SPE) method for simultaneous preconcentration of trace elements in water samples prior to their ICP-OES determination. Dowex 50W-x8 and Chelex-100 resins were used as SPE sorbent materials for preconcentration of trace Cd, Co, Cr, Cu, Fe, Ni, Pb and Zn. The optimum sample pH, eluent concentration and sample flow rates were found to 6, 3.0 mol L⁻¹ and 3.0 mL min⁻¹, respectively. In terms of multi-element preconcentration capabilities, Dowex 50W-x8 appeared to be a better sorbent. The recoveries for all the tested analytes were >95%. However, Chelex-100 showed a better performance in terms of recovery (>95%) towards Cu, Fe and Zn. Under optimized conditions using Dowex 50W-x8, the relative standard deviations for different metals were <3%. The limits of detection and limits of quantification ranged from 0.01–0.39 μg L⁻¹ and 0.05–0.1.3 μg L⁻¹, respectively. The accuracy of the preconcentration method was confirmed by spike recovery test and the analysis of certified reference materials. The SPE method was applied for preconcentration of the analyte ions in tap water, bottled water and wastewater samples.     

Selective Separation/Preconcentration of Silver Ion in Water by Multiwalled Carbon Nanotubes Microcolumn as a Sorbent

The present paper proposes the application of multiwalled carbon nanotubes (MWCNTs) as a solid adsorbent for selective separation/preconcentration of silver(I) in water samples prior to flame atomic absorption spectrometry. The procedure is based on the solid phase extraction of Ag(I)–2‐mercaptobenzothiazole chelate on MWCNTs. The elution step is carried out with 5 mL of 2 mol L^?1 HNO₃ in acetone solution at a flow rate of 1.0 mL min^?1. The influences of the various analytical parameters including pH of the solution, eluent type, sample volume, flow rates of eluent, matrix ions were investigated for optimization of the presented procedure. Tests of addition/recovery for analyte ion in real samples were performed with satisfactory results. Preconcentration factor and limit of detection for Ag(I) were 160 and 0.21 µg L^?1, respectively. The synthesized MWCNT exhibited excellent stability in eluent solution and its adsorption capacity was 5.4 mg of silver per gram of sorbent. The proposed method was successfully applied to trace silver determination in a variety of environmental water samples.     

Online Preconcentration and Determination of Trace Levels Cadmium in Water Samples Using Flow Injection Systems Coupled with Flame AAS

A rapid and sensitive method for the determination of trace levels cadmium in water samples by flame atomic absorption spectrometry was developed. It is based on the online sorption of Cd(II) ions on a microcolumn packed with HCl treated bamboo charcoal. In a pH range of 5.0–7.5, Cd(II) ions were effectively retained on the microcolumn, which exhibited fast kinetics, permitting the use of high sample flow rates up to at least 12.8 mL/min without the loss of retention efficiency. The retained Cd(II) ions were quantitatively eluted with HCl (2.0 mol/L) for an online determination. With a preconcentration time of 80 s at a sample loading flow rate of 8.6 mL/min, a sensitivity enhancement factor of 63 was obtained compared with the slope of the linear portion of the calibration curves before and after preconcentration. The calibration graph using the preconcentration system for cadmium was linear with a correlation coefficient of 0.9997, at levels from 1–40 ng/mL. The precision (RSD) for 11 replicate measurements were 3.2% for the determination of 5 ng/mL Cd(II) and 1.8% for 20 ng/mL Cd(II), respectively, and the detection limit (3s) was 0.36 ng/mL. The accuracy was assessed through the determination of a certified reference material, and also through recovery experiments.     

Problems and Solutions in Pesticide Analysis Using Solid‐phase Extraction (SPE) and Gas Chromatography Ion‐trap Mass Spectrometry Detection (GC‐MS)

In the present study an analytical method was tested for the determination of selected pesticides and metabolites using solid‐phase extraction (SPE) and gas chromatography ion‐trap mass spectrometry (GC‐MS). The extraction efficiency of C18, Isolut ENV+, and Lichrolut EN for SPE was compared for trifluralin, fenitrothion, endosulfan, propargite, 2,4‐D, 3‐methyl‐4‐nitrophenol, 2‐(4‐tert‐butylphenoxy)cyclohexanol, endosulfan sulfate, and 2,4‐dichlorophenol. Isolut ENV+ and C18 showed good results as sorbents and acetone as an elution solvent for SPE for the selected pesticides. Recoveries varied between 36% and 176% with a relative standard deviation of 2...18%. Because of coextracts from the SPE materials, recovery values higher than 100% were obtained for fenitrothion, endosulfan sulfate, and 2,4‐D with C18 as well as for endosulfan sulfate and 3‐methyl‐4‐nitrophenol with Isolut ENV+. A standard addition method was used to verify the occurrence of coextracts in the sample after SPE.     

Effect of organic matter source and salinity on dissolved organic matter isolation via ultrafiltration and solid phase extraction

In this study, samples were taken from three contrasting freshwater sources and amended with salt in order to determine the influence of salinity and dissolved organic matter (DOM) composition on DOM recovery via ultrafiltration and solid phase extraction (SPE) with C₁₈ disks. Salt addition caused variable recovery of DOM when using C₁₈ SPE, and ultraviolet–visible spectroscopic characterization of the extracted material showed spectral responses that varied among sample sources. In contrast, increasing sample salinity from 0 to 30 ppt consistently caused a 15–25% reduction in the amount of high molecular weight DOM isolated by ultrafiltration for both dissolved organic carbon (DOC) and chromophoric DOM (CDOM), regardless of DOM composition. We hypothesize that a change in conformation (such as coiling or disaggregation) of DOM molecules occurs in the presence of salt, allowing them to pass through the ultrafiltration membrane and thereby decreasing the DOM retained by ultrafiltration. These results are important because they demonstrate that changes in salinity can influence DOM recovery in estuaries. Interpretation of DOM characteristics along estuarine gradients needs to account for potential artifacts introduced by sample isolation techniques.     

Hollow fiber liquid-phase microextraction as clean-up step for the determination of organophosphorus pesticides residues in fish tissue by gas chromatography coupled with mass spectrometry

Hollow fiber liquid-phase microextraction (HF-LPME) technique was used as a clean-up procedure for the determination of organophosphorus pesticides (OPPs) in fish tissue. In this study, eight OPPs were first extracted with acetone from fish sample, the organic extract after rotatory evaporation was then redissolved with water-methanol (95:5, v/v) solution, followed by polyvinylidene difluoride (PVDF) HF-LPME. Experimental HF-LPME and other sample preparation conditions were carefully investigated and optimized. Under the optimum conditions, good linearity were observed in the range of 20-500 ng/g, limits of detections (LODs) were in the range of 2.1-4.5 ng/g. The repeatability and recovery of the method also showed satisfactory results. Compared with traditional sample preparation method for the determination of OPPs in fish tissue, the method developed in this study eliminated the solid phase extraction (SPE) step, simplified the sample preparation procedure and lowered the cost of analysis.     

Selective Preconcentration of Trace Amounts of Cu(II) With Surface‐Imprinted Multiwalled Carbon Nanotubes

In this study, a new sorbent is synthesized using surface imprinting technique. Cu(II)‐imprinted multiwalled carbon nanotube sorbent (Cu(II)‐IMWCNT) is used as the solid phase in the solid‐phase extraction method. After the preconcentration procedure, Cu(II) ions are determined by high‐resolution continuum source atomic absorption spectrometry. A total of 0.1 mol L^?1 ethylenediaminetetraacetic acid (EDTA) is used to remove Cu(II) ions from the sorbent surface. The optimum experimental conditions for effective preconcentration of Cu(II), parameters such as pH, eluent type and concentration, flow rate, sample volume, sorbent capacity, and selectivity are investigated. The synthesized solid phase is characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The maximum adsorption capacities of Cu(II)‐IMWCNT and non‐imprinted solid phases are 270.3 and 14.3 mg g^?1 at pH 5, respectively. Under optimum experimental conditions for Cu(II) ions, the limit of detection is 0.07 μg L^?1 and preconcentration factor is 40. In addition, it is determined to be reusable without significant decrease in recovery values up to 100 adsorption–desorption cycles. Cu(II)‐IMWCNT have a high stability. To check the accuracy of the developed method, certified reference materials, and water samples are analyzed with satisfactory analytical results.     

Making the Most of Field-Measurable Ground Water Quality Parameters

The primary ground water quality parameters temperature, pH, Eh, electrical conductivity, and dissolved oxygen must be measured in the field, though not necessarily in situ, to avoid errors caused by contamination such as aeration. These measurements, when made during the purging of a well, can be used to verify aquifer-representativeness of a sample, detect abnormalities within an aquifer, check laboratory measurements to detect sample deterioration, and prompt further monitoring actions.
Electronic sensors are available for reliable field measurement of the primary parameters. Measurements should be made continuously in an in-line flow cell that is sealed from the atmosphere. Flow can be provided by a bladder pump dedicated to a single well. Samples for laboratory analysis should be collected when the values of the primary parameters do not vary more than 10 percent per casing volume pumped.     

Low‐Flow Hydraulic Conductivity Tests at Wells that Cross the Water Table

Wells with screens and sand packs that cross the water table represent a challenging problem for determining hydraulic conductivity by slug testing due to sand pack drainage and resaturation. Sand pack drainage results in a multisegmented recovery curve. One must then subjectively pick a portion of the curve to analyze. Sand pack drainage also results in a change in the effective radius of the well which requires a guess at the porosity or specific yield in analyzing the test. In the study of Robbins et al. (2009) , a method was introduced to obtain hydraulic conductivity in monitoring wells using the steady‐state drawdown and flow rate obtained during low‐flow sampling. The method was tested in this study in wells whose screens cross the water table and shown to avoid sand pack drainage problems that complicate analyzing slug tests. In applying the method to low‐flow sampling, only a single pair of steady‐state flow rate and drawdown are needed; hence, to derive meaningful results, an accurate determination of these parameters is required.     

Estimating the Sampling Uncertainty for the Analysis of Solid Refused Fuel

Uncertainty assessment of the parameters used for the reporting in the emissions trading system (ETS) to characterize fuels includes not only the processes in a laboratory but has to be expanded for inclusion of sampling and sample preparation. Analysis of variance was used to allocate the contributing uncertainties to the steps described. Apart from some specific results for sampling methods, it was observed that the uncertainty of sampling was in the same order of magnitude than the analytical and the sample preparation error. Several measures to enhance quality assurance in sampling and sample preparation could be derived from specific results. The results were used in the European Monitoring and Reporting Regulation, which set out the requirements for ETS. Sampling and sample preparation have to be included in uncertainty assessment as well as sampling procedures and sampling plans (including quality assurance) have to be agreed upon by the laboratories, carrying out the analytics of those samples.     

螺旋CT灌注成像在肾上腺增生的诊断价值

目的：研究多层螺旋CT灌注成像在肾上腺增生的诊断价值。方法：对23例正常肾上腺和18例经临床证实的肾上腺增生进行16层螺旋CT灌注成像研究,利用CT灌注软件计算灌注参数,包括相对血流量（RBF）、平均通过时间（MTT）和表面通透性（PS）,参数间比较采用t检验。结果：正常肾上腺的RBF、MTT和PS分别为0.63±0.22mL/100g/min、70.65±12.31s和0.72±0.13mL/100g/min,肾上腺增生RBF、MTT和PS分别为0.45±0.19mL/100g/min、118.39±19.98s和0.49±0.21mL/100g/min。正常肾上腺的RBF、PS均大于肾上腺增生,肾上腺增生的MTT大于正常肾上腺,其差异有统计学意义（t值分别为15.91、20.03和9.96,P〈0.05）。结论：肾上腺多层螺旋CT灌注成像是可行的肾上腺功能成像检查,它反映了肾上腺微循环的血流灌注状况,为肾上腺增生的诊断提供有用的信息。     

Simultaneous Analysis of Natural Free Estrogens and Their Conjugates in Wastewater by GC‐MS

A solid‐phase extraction (SPE)‐gas chromatography (GC)‐mass spectrometry (MS) analytical method was developed for the simultaneous analysis of natural free estrogens and their conjugates in wastewater samples. Natural free estrogens and their conjugates in wastewater were successfully separated by the oasis hydrophilic‐lipophilic balance solid phase extraction (Oasis HLB SPE) method, and the conjugates were initially enzyme hydrolyzed by β‐glucuronidase or arylsulfatase from Helix pomatia prior to derivatization. N‐methyl‐N‐(tert‐butyldimethylsilyl)trifluoroacetamide (MTBSTFA) plus 1% tert‐butyldimetheylchlorosilane (TBDMCS) was chosen as the derivatization reagent, and the most appropriate conditions of derivatization were determined to be at 95°C for 90 min. The recovery ratios of nine target chemicals were determined by spiking them in 1 L of ultra‐purified water or the influent of a wastewater treatment plant (WWTP). The recovery ratios of six out of nine for the analytes ranged from 73.3–114.9% with relative standard deviations (RSD) from 1.6–19.9%. The established method was successfully applied to environmental wastewater samples which were collected from one municipal wastewater treatment plant (WWTP) in Osaka, Japan, for the determination of natural free estrogens and their conjugates. In the influent sample, E1, E2, E1‐3S, E3‐3S, and E1‐3G were detected at concentrations of 16.6, 9.6, 8.2, 21.9, and 3.2 ng L^–1, respectively. However, only E1 was detected at a high concentration of 44 ng L^–1 in the effluent sample, suggesting that it is the dominant natural free estrogen in the effluent.     

The Effect of Oxygen on Anaerobic Color Removal of Azo Dye in a Sequencing Batch Reactor

In this study, various amounts of oxygen were added to the anaerobic phase of an anaerobic‐aerobic sequencing batch reactor (SBR) receiving azo dye remazol brilliant violet 5R to mimic the input of oxygen into the anaerobic zones of biological textile wastewater treatment plants. The effect of oxygen on the anaerobic biodegradative capability of the mixed microbial culture for remazol brilliant violet 5R was investigated. To investigate the effect of oxygen on anaerobic azo dye biodegradation, the anaerobic phase of the SBR cultures were exposed to a very low limited amount of oxygen for various air flow rates. Initially, an air flow rate of 20 mL/min was applied, further on the air flow rate in the anaerobic phase was increased up to 40 mL/min. System performance was determined by monitoring chemical oxygen demand, color removal rate, activities of anaerobic (azo reductase) and aerobic enzymes (catechol 2,3‐dioxygenase, catechol 1,2‐dioxygenase). The results of percentage COD reduction at each stage were similar for all runs, giving an overall reduction of 96%. Anaerobic color removal efficiency and azo reductase activity of anaerobic microorganisms were adversely affected by the addition of oxygen. Color removal efficiencies of the anaerobic phases decreased from 80% down to 42 and 38% for the limited oxygen conditions of 20 mL/min and 40 mL/min, respectively. It was observed that the activity of catechol 2,3‐dioxygenase and catechol 1,2‐dioxygenase, involved in breakage of aromatic rings, increased after they are exposed to oxygen limited conditions compared to fully anaerobic conditions. It was also observed that catechol 1,2‐dioxygenase enzyme activity increased by increasing the oxygen level on oxygen limited conditions in the anaerobic zone.     

Biosorption of Cadmium(II) Ions by Citrus Peels in a Packed Bed Column: Effect of Process Parameters and Comparison of Different Breakthrough Curve Models

The efficiency of low cost citrus peels as biosorbents for removal of cadmium ions from aqueous solution was investigated in a fixed bed column, a process that could be applied to treat industrial wastewaters similar to commonly used ion exchange columns. Effluent concentration versus time profiles (i.e., breakthrough curves) were experimentally determined in a laboratory‐scale packed bed column for varying operational parameters such as flow rate (2, 9, and 15.5 mL/min), influent cadmium concentration (5, 10, and 15 mg/L), and bed height (24, 48, and 72 cm) at pH 5.5. Column operation was most efficient for empty bed contact times of at least 10 min, which were apparently necessary for mass transfer. While the sorption capacity was largely unaffected by operational variables, the Thomas (Th) rate constant increased with the flow rate, and slightly decreased with increasing column length. Three widely used semi‐mechanistic models (Th, Bohart–Adams, and Yoon–Nelson) were shown to be equivalent and the generalized model was compared with a two‐parameter empirical model (dose‐response). The latter was found to be able to better simulate the breakthrough curve in the region of breakthrough and saturation.     

Assessing Arkansas Ground Water for Pesticides: Methodology and Findings

During 1985 to 1987, 119 wells, Springs and municipal drinking water supplies throughout Arkansas were monitored for the presence of pesticides. Pesticides selected for analysis included acifluorfen, alachlor, aldicarb, atrazine, benomyl, cyanazine, cypermethrin, 2,4-D, dichlorprop, diuron, fenvalerate, fluometuron, hexazinone, linuron, metolachlor, permethrin, picloram, and propanil. Not every sample was analyzed for every pesticide. Overall, results indicated that the 18 herbicides, fungicides, and insecticides were not present in the ground water samples studied. (Note: Detectable concentrations of three herbicides – alachlor, atrazine, and metolachlor – were found in one irrigation well, at 5.5,5.8, and 6.9 μg/L, respectively. However, since previous and subsequent sampling failed to detect these compounds, their presence is attributed to a localized spill or handling error rather than agricultural application.)     

Use of a single-bowl continuous-flow centrifuge for dewatering suspended sediments: Effect on sediment physical and chemical characteristics

The use of a single-bowl continuous-flow centrifuge (CFC, Sharples-Pennwalt Model AS-12) for dewatering suspended sediment from large volumes of river water is evaluated. Sediment-recovery efficiency of 86-91 per cent is comparable to that of other types of CFC units. The recovery efficiency is limited by the particle-size distribution of the feed water and by the limiting particle diameter that is retained in the centrifuge bowl. The limiting particle diameter, using the parameters for this study (bowl radius = 10.5cm; bowl length = 71.1 cm; rotational velocity = 16000 r min^?1; flow rate = 2 L min^?1, and an assumed hydrated particle density = 1.7 gm cm^?3), is 370 nm. There seems to be no particle-size fractionation within the centrifuge bowl—the median particle size was the same at the top as at the bottom. Particle electrophoretic mobility plays some role in fractionation of particles within the centrifuge. The mobility ranged from ?1.19 to ?2.01 × 10^?8 m² V^?1 s^?1, which is typical of clays coated with organic matter, the charge of which is partially neutralized by divalent cations and iron. Contamination by trace metals and organics is minimized by coating all surfaces that come in contact with the sample with either FEP or PFA Teflon and using a removable FEP Teflon liner in the centrifuge bowl. Because of the physical and chemical factors affecting particle fractionation within the centrifuge, care must be exercised in interpreting the environmental consequences of particles collected by continuous-flow centrifugation.     

华东地区具有短期预测意义的特殊显著性地震事件识别

依据华东地区中强地震前的地震活动特点,初步提出“特殊显著性地震事件”SPE的概念及其可能的识别方法.具有前兆指示意义的SPE可划分为三类,三类SPE分别表达了主震前中小地震与主震之间的时空位置关系.I类SPE距主震时、空距离均较近,在一定程度上与“直接前震”具有相似之处;II类SPE距主震时间较近、而空间距离可能较远,但与主震之间有一定的构造联系,具有时间上的“信号地震”的意义.Ⅲ类必须首先通过地震活动性方法对可能的SPE进行筛选,之后通过比较其与之前在同一位置发生的一系列中小地震的地震波参数之间的差异,在一定程度上进一步确认其短期预测意义.华东6次中强地震震例的研究结果表明,当可能的SPE的单台波速比小于此前该区域长时期的均值、归一化尾波持续时间大于此前该区域长时期的均值以及振幅衰减系数与此前该区域长时期均值之差大于长时期均值的30％时,可进一步认定其短期前兆意义.     

Sampling Trace-Level Organic Solutes with Polymeric Tubing Part 2. Dynamic Studies

This is the second part of a study conducted to determine whether polymeric sampling tubing can affect organic analyte concentrations during a sampling event. In this part of the study, we looked for sorption and desorption of tricholoroethylene (TCE) and leaching of organic constituents in water pumped through five types of polymeric tubing. The materials tested were a rigid fluoropolymer, a flexible fluoropolymer, low-density polyethylene (LDPE), and two plasticized polypropylene tubings. The effects of tubing length and flow rate were examined.
The least sorptive tubings, both initially and at equilibrium, were the fluoropolymers. However, in some instances the LDPE tubing had little effect on TCE concentrations. This was when a slow flow rate was used to sample relatively shallow wells (50 feet [15 m] or less) or when a faster flow rate (1 L/min) was used to sample wells that are less than 500 feet (152 m). Further testing is recommended using more sorptive analytes.
Using high performance liquid chromatography (HPLC), we were unable to detect any constituents leaching from any of the tubings used in these studies, even when a slow flow rate was used. However, desorption of sorbed analytes is a concern for all the tubings tested, including the rigid fluoropolymer.