Final Sample Solution Research Articles

Method Validation for Simultaneous Quantification of Some High-risk Pesticides in Surface Water Samples by SPE-LC-MS/MS

ABSTRACT In this paper, a solid phase extraction procedure was developed for the simultaneous extraction of 22 multiclass high-risk pesticides, containing a variety of chemical groups (organophosphate, neonicotinoid, sulfonylurea, strobilurin, triazole, triazine, and acetanilide), from surface water samples. The target analytes extracted on the HLB SPE cartridge, and then eluted with acetonitrile with 5% (v/v) formic acid. The final sample solution was analysed by high-performance liquid chromatography-tandem quadrupole mass spectrometry (HPLC–MS/MS) system. Under optimum conditions, good linearity was obtained for the target pesticides with correlation coefficient greater than 0.99. The limit of quantitation (LOQ) for the 22 pesticides was 0.1 ng/mL. The absolute recoveries of the pesticides from spiked water samples ranged from 70.0% to 121.5%. Relative standard deviations (RSD) for five replicate determinations were below 14.7%. The proposed method has been successfully applied to detect the presence of multiclass pesticides in environmental water samples.

Determination of Organophosphorus Pesticides Using Solid-Phase Extraction Followed by Gas Chromatography-Mass Spectrometry.

In this study, a method was developed for determination of three organophosphorus pesticides (OPPs) using graphene aerogel solid-phase extraction (SPE) combined with gas chromatography-mass spectrometry (GC-MS). The experimental results showed that the target analytes could be extracted on packed SPE cartridges and then eluted with tetrahydrofuran. The final sample solution was analyzed by GC-MS, which demonstrated good linearity between 0.5 and 500μgL-1 with a correlation coefficient (r) of 0.9991-0.9998. The limits of detection (S/N=3) and the limits of quantification (S/N=10) for the three OPPs ranged from 0.38 to 0.82μgL-1 and 1.32 to 2.75μgL-1, respectively. The accuracy of the proposed method was evaluated by measuring the recovery of the spiked samples, which ranged from 91.2 to 103.7%, with relative standard deviations of 2.1-7.2%. This method was successfully applied for the determination of the target analytes in water samples taken from tap, wetlands and canal water.

Low-sulphate water sample preparation for LSC detection of 35S avoiding sulphate precipitation

Information about groundwater residence times is essential for evaluating appropriate groundwater abstraction rates and aquifer vulnerabilities and hence for sustainable groundwater management in general. Naturally occurring radionuclides are suitable tools for related investigations. While the applicability of several long-lived radionuclides for the investigation of long-term processes has been demonstrated frequently, residence times of less than one year are only scarcely discussed in the literature. That is due to the rather small number of applicable radionuclides that show adequately short half-lives. A promising approach for investigating sub-yearly residence times applies radioactive sulphur. 35S is continuously produced in the upper atmosphere from where it is transferred with the rain to the groundwater. As soon as the water enters the subsurface its 35S activity concentration decreases with an 87.4 day half-life. This makes 35S suitable for investigating sub-yearly groundwater residence times. However, the low 35S activities in natural waters require sulphate pre-concentration for 35S detection by means of liquid scintillation counting (LSC). That is usually done by sulphate extraction from large water samples with an anion-exchange resin (Amberlite IRA400, Cl-form), elution from the resin with NaCl, and precipitation as BaSO4. Our study aimed at optimizing the standard sample preparation procedure by avoiding the laborious precipitation step. We suggest (i) sulphate extraction using the exchange resin Amberlite IRA67 (OH-form), (ii) elution with ammonium hydroxide, (iii) evaporation of the eluate and (iv) dissolving the resulting dry precipitate in 2 ml H2O. In contrast to the standard approach our method results in a final sample solution of low ionic strength, which allows applying the water miscible scintillation cocktail Hionic-Fluor®. Since Hionic-Fluor accepts only aqueous solutions of low ionic strength the approach is applicable for waters with high 35S/32SO42− ratios, i.e., low total sulphate sample loads (e.g. rainwater).

Quantification of lignin oxidation products as vegetation biomarkers in speleothems and cave drip water

Abstract. Here we present a sensitive method to analyze lignin oxidation products (LOPs) in speleothems and cave drip water to provide a new tool for paleo-vegetation reconstruction. Speleothems are valuable climate archives. However, compared to other terrestrial climate archives, such as lake sediments, speleothems contain very little organic matter. Therefore, very few studies on organic biomarkers in speleothems are available. Our new sensitive method allows us to use LOPs as vegetation biomarkers in speleothems. Our method consists of acid digestion of the speleothem sample followed by solid-phase extraction (SPE) of the organic matter. The extracted polymeric lignin is degraded in a microwave-assisted alkaline CuO oxidation step to yield monomeric LOPs. The LOPs are extracted via SPE and finally analyzed via ultrahigh-performance liquid chromatography (UHPLC) coupled to electrospray ionization (ESI) and high-resolution Orbitrap mass spectrometry (HRMS). The method was applied to stalagmite samples with a sample size of 3–5 g and cave drip water samples with a sample size of 100–200 mL from the Herbstlabyrinth-Advent Cave in Germany. In addition, fresh plant samples, soil water, and powdered lignin samples were analyzed for comparison. The concentration of the sum of eight LOPs (Σ8) was in the range of 20–84 ng g−1 for the stalagmite samples and 230–440 ng L−1 for the cave drip water samples. The limits of quantification for the individual LOPs ranged from 0.3–8.2 ng per sample or 1.5–41.0 ng mL−1 of the final sample solution. Our method represents a new and powerful analytical tool for paleo-vegetation studies and has great potential to identify the pathways of lignin incorporation into speleothems.

Uncertainty of Trypsin Inhibitor Activity Measurement of Legume Crops Using Microtiter Plate Method

Trypsin inhibitors could limit utilization of legumes in human nutrition, but they could also have beneficial health effects. The objective of this study was to measure trypsin inhibitor activity (TIA) of different legumes using microtiter plate method and to identify factors that contribute to uncertainty of TIA measurement. TIA measurements were performed on seeds of faba bean, pea, common vetch, soybean, and common bean cultivars. The significant effect of legume crop on TIA measurement uncertainty was confirmed with P = 0.045. Certain sources of measurement uncertainty were related with the content of trypsin inhibitors (Tis) in legume seeds. In respect to that, significant effect of level of sample dilution (P ˂ 0.001) was confirmed. Significant influence of the repeated absorbance measurement of sample reaction mixture on uncertainty of TIA measurement was identified (P ˂ 0.001), and it took 60% of overall TIA measurement uncertainty for soybean cultivars. TIA of soybean cultivars exceeded 90 TUI/mg. Repeated absorbance measurement of positive control reaction mixture took 70% of TIA measurement uncertainty of cultivars with TIA lesser than 4.5 TUI/mg. Graduated cylinder used for preparation of the final sample solutions took the range from 45 to 90% of overall TIA measurement uncertainty of the cultivars whose TIA were in the middle of previously mentioned. The uncertainty of TIA measurement of legume crops was not studied before; thus, this study pointed out that acquiring insight into factors contributing to uncertainty of TIA measurement could give directions for improvement of TIA testing if microtiter plate method is used.

Graphene based solid phase extraction combined with ultra high performance liquid chromatography–tandem mass spectrometry for carbamate pesticides analysis in environmental water samples

In this paper, graphene, a new sorbent material, was synthesized and used for solid-phase extraction (SPE) of the six carbamate pesticides (pirimicarb, baygon, carbaryl, isoprocarb, baycarb and diethofencarb) in environmental water samples. The target analytes can be extracted on the graphene-packed SPE cartridge, and then eluted with acetone. The eluate was collected and dried by high purity nitrogen gas at room temperature. 1mL of 20% (v/v) acetonitrile aqueous solution was used to redissolve the residue. The final sample solution was analyzed by ultra performance liquid chromatography-tandem quadrupole mass spectrometry (UPLC–MS/MS) system. Under optimum conditions, good linearity was obtained for the carbamates with correlation coefficient in the range of 0.9992–0.9998. The limits of detection (S/N=3) for the six carbamate pesticides were in the range of 0.5–6.9ngL−1. Relative standard deviations (RSD) for five replicate determinations were below 5.54%. RSD values for cartridge-to-cartridge precision (n=7) were in the range of 1.27–8.13%. After proper regeneration, the graphene-packed SPE cartridge could be re-used over 100 times for standard solution without significant loss of performance. The enrichment factors for the target analytes were in the range of 34.2–51.7. The established method has been successfully applied to the determination of carbamate pesticide residues in environmental water samples such as river water, well water and lake water.

Synchronous derivative fluorimetric determination of boron in Uranium fuel samples

We report a sensitive and selective method for determination of boron in uranium samples by spectrofluorimetry in synchronous derivative mode. This method is based on the complexation of non-fluorescent boron with fluorescent chromotropic acid to form fluorescent boron–chromotrope complex. The spectrum of native fluorescence of chromotropic acid seriously overlaps with that of the complex and hence, synchronous derivative mode was employed in which physical separation of excess ligand and complex is not necessary. With the optimized experimental and instrumental conditions, limit of detection obtained is 2ngmL−1. The linear concentration range is 5–100ngmL−1 with regression coefficient better than 0.997. The precision is better than 5% at 10ngmL−1 level and 3% at 50ngmL−1 level (n=9). Fluorescence quenching by residual matrix elements in the final sample solution is corrected by slope-ratio method. The method is validated with reference materials and successfully applied to the uranium nuclear fuels with the accuracy of ±10%. The proposed method reduces sample size requirement; thereby reducing load of uranium recovery from analytical waste in case of enriched uranium based samples.

A Method of Measurement of 239Pu, 240Pu, 241Pu in High U Content Marine Sediments by Sector Field ICP–MS and Its Application to Fukushima Sediment Samples

An accurate and precise analytical method is highly needed for the determination of Pu isotopes in marine sediments for the long-term marine environment monitoring that is being done since the Fukushima Dai-ichi Nuclear Power Plant accident. The elimination of uranium from the sediment samples needs to be carefully checked. We established an analytical method based on anion-exchange chromatography and SF-ICP-MS in this work. A uranium decontamination factor of 2 × 10(6) was achieved, and the U concentrations in the final sample solutions were typically below 4 pg mL(-1), thus no extra correction of (238)U interferences from the Pu spectra was needed. The method was suitable for the analysis of (241)Pu in marine sediments using large sample amounts (>10 g). We validated the method by measuring marine sediment reference materials and our results agreed well with the certified and the literature values. Surface sediments and one sediment core sample collected after the nuclear accident were analyzed. The characterization of (241)Pu/(239)Pu atom ratios in the surface sediments and the vertical distribution of Pu isotopes showed that there was no detectable Pu contamination from the nuclear accident in the marine sediments collected 30 km off the plant site.

Novel sample preparation method for surfactant containing suppositories: Effect of micelle formation on drug recovery

Rectal drug delivery is currently at the focus of attention. Surfactants promote drug release from the suppository bases and enhance the formulation properties. The aim of our work was to develop a sample preparation method for HPLC analysis for a suppository base containing 95% hard fat, 2.5% Tween 20 and 2.5% Tween 60. A conventional sample preparation method did not provide successful results as the recovery of the drug failed to fulfil the validation criterion 95–105%. This was caused by the non-ionic surfactants in the suppository base incorporating some of the drug, preventing its release. As guidance for the formulation from an analytical aspect, we suggest a well defined surfactant content based on the turbidimetric determination of the CMC (critical micelle formation concentration) in the applied methanol–water solvent. Our CMC data correlate well with the results of previous studies. As regards the sample preparation procedure, a study was performed of the effects of ionic strength and pH on the drug recovery with the avoidance of degradation of the drug during the procedure. Aminophenazone and paracetamol were used as model drugs. The optimum conditions for drug release from the molten suppository base were found to be 100mM NaCl, 20–40mM NaOH and a 30min ultrasonic treatment of the final sample solution. As these conditions could cause the degradation of the drugs in the solution, this was followed by NMR spectroscopy, and the results indicated that degradation did not take place. The determined CMCs were 0.08mM for Tween 20, 0.06mM for Tween 60 and 0.04mM for a combined Tween 20, Tween 60 system.

Rapid coprecipitation-separation and flame atomic absorption spectrometric determination of lead and cadmium in water with cobalt (II) and ammonium pyrrolidine dithiocarbamate

A coprecipitation technique which does not require complete collection of the precipitate was proposed for the determination of trace lead and cadmium in water with flame atomic absorption spectrometry (FAAS) after preconcentration of lead and cadmium by using cobalt (II) and ammonium pyrrolidine dithiocarbamate (Co-APDC) as coprecipitant and known amount of cobalt as an internal standard. Since lead, cadmium and cobalt were well distributed in the homogeneous precipitate, the concentration ratio of lead to cobalt, and cadmium to cobalt remained unchanged in any part of the precipitate. The amount of lead and cadmium in the original sample solution can be calculated respectively from the ratio of the absorbance values of lead and cadmium to cobalt in the final sample solution that is measured by FAAS and the known amount of the lead and cadmium in the standard series solutions. The optimum pH range for quantitative coprecipitation of lead and cadmium is from 3.0 to 4.5. The 16 diverse ions tested gave no significant interferences in the lead and cadmium determination. Under optimised conditions, lead ranging from 0 to 40 µg and cadmium ranging from 0 to 8 µg were quantitatively coprecipitated with Co-APDC from 100 mL sample solution (pH ∼ 3.5). This coprecipitation technique coupled with FAAS was applied to the determination of lead and cadmium in water samples with satisfactory results (recoveries in the range of 94.0–108%, relative standard deviations <6.0%).

Polyatomic interferences in plutonium determination in the femtogram range by double-focusing sector-field ICP-MS

The determination of very low concentrations of plutonium, in the femtogram per millilitre range, in environmental samples using ICP-MS can be interfered by polyatomic species containing heavy elements, from hafnium to bismuth. Mass-to-charge ratios of these polyatomic species are very close to the ones of the plutonium isotopes and cannot be separated from them in the low resolution mode currently used for trace analysis. In this paper, we present an evaluation of the extent and impact of these interferences on the background at masses of plutonium isotopes 239Pu and 240Pu, based on measurement of environmental samples for three years using a double-focusing sector-field ICP-MS. We demonstrate that these molecular interferences, especially the ones involving lead, mercury, and iridium through species PbO2+, ArHg+, IrO3+, must be considered as the additional background induced by these interferences (on average for all interferences respectively ∼1.2 and ∼1.9 counts s−1 at 239 and 240 atomic mass units) is often higher than the instrumental background measured with deionised water acidified at 2% by ultra-pure grade HNO3 (∼0.4 counts s−1), and are generally of the same order as other usual sources of background for low-level plutonium analysis by ICP-MS, i.e.242Pu tracer isotopic impurities, 238U hydrides and peak tail. Thus, if not corrected, these polyatomic interferences may lead to false detection of femtogram amounts of plutonium or overestimation of results. The extents of formation of the main polyatomic species are highly variable from one analysis to the other, over one or two orders of magnitude, depending on instrumental settings. Chemical purification procedures are very efficient in eliminating the greater part of heavy elements present in the initial samples. However, these procedures also bring heavy elements into the final sample solutions through contamination by the atmosphere, glassware and reagents.

Determination of trace elements in biological samples treated with formic acid by inductively coupled plasma mass spectrometry using a microconcentric nebulizer

A simple and fast method for the determination of As, Ba, Cd, Co, Cu, Fe, Ga, Mn, Mo, Ni, Pb, Rb, Se, Sr, Tl, U, V and Zn in biological samples by inductively coupled plasma mass spectrometry (ICP-MS), after sample solubilization with formic acid and introduction by a microconcentric nebulizer, is proposed. The sample is mixed with formic acid, kept at 90 °C for one hour and then diluted with nitric acid aqueous solution to a 50% v/v formic acid and 1% v/v nitric acid final concentrations. The final sample solution flow rate for introduction into the plasma was 30 μL min −1. The optimized and adopted nebulizer gas flow rate was 0.7 L min −1 and RF power was 800 W. These conditions are very different than those normally used when a conventional nebulizer is employed. Rodhium was used as internal standard. External calibration against aqueous standard solutions, without formic acid, could be used for quantification, except for As, Se and Zn. However, external calibration with 50% formic acid allows the determination of all analytes with high accuracy and it is recommended. The detection limits were between 0.0005 (Tl) and 0.22 mg kg −1 (Fe) and the precision expressed by the relative standard deviations (RSD) were between 0.2% (Sr) and 3.5% (Ga). Accuracy was validated by the analysis of four certified reference biological materials of animal tissues, comparing the results by linear regressions and by the t-test at a 95% confidence level. The recommended procedure avoids plasma instability and carbon deposit on the cones.

Fast Cleanup Method for the Analysis of Sudan IIV and Para Red in Various Foods and Paprika Color (Oleoresin) by High-Performance Liquid Chromatography/Diode Array Detection: Focus on Removal of Fat and Oil as Fatty Acid Methyl Esters Prepared by Transesterification of Acylglycerols

A fast and effective cleanup method was developed for the analysis of Sudan I, II, III, IV, and Para Red (Sudan dyes) in various foods and paprika color (oleoresin) by high-performance liquid chromatography (LC) with a diode array detector (DAD). Removal of fat or oil in fatty sample was a critical point for reducing the volume of the final sample solution in order to obtain a sufficient level of the analytes. Separation of fat or oil from the dyes with a silica gel solid-phase extraction (SPE) column seemed unfeasible, because elution profiles of oil, fat, and the dyes were similar. Finally, fat and oil were separated from the dyes by elution from the SPE column with n-hexane, not as intact compounds but as fatty acid methyl esters prepared by direct transesterification of acylglycerols in fat and oil, leaving the dyes on the column. The dyes were eluted with n-hexane-diethyl ether (9 + 1). Gradient elution with water and tetrahydrofuran was used for separation on a C18 column by LC. Measurement of spectral of 0.5 microg/g of Sudan dyes in foods and 1 microg/g in paprika color (oleoresin) with the DAD was achieved.

Estimation of uncertainty for the determination of mercury in food by CVAAS

This paper is aimed at reporting a full validation of a Cold Vapour Atomic Absorption Spectrometry (CVAAS) method for mercury determination in fishery products. Method precision, trueness, limit of detection and limit of quantification are evaluated. The uncertainty of measurement is estimated following the bottom-up approach in conjunction with the validation data as suggested for complex analysis. The precision is evaluated using a pooled relative standard deviation and the recovery is added to the measurement uncertainty budget. Uncertainties of weight of sample, dilution factor, calibration, work solution and analyte amount are also assessed. The most relevant uncertainty sources result those associated to amount of mercury determined in the final sample solution, to method precision and to recovery. The relative contributions have different weights according to the analyst decision regarding recovery correction of results. In conclusion, the adopted CVAAS method fully complies with EU requirements.

알긴산칼슘 비드 상 흡착에 의한 흔적량 구리(II)와 납(II)의 동시 농축 및 정량

Department of Chemical Engineering, Samcheok National University, Samcheok, Gangwon 245-711, Korea(Received October 11, 2004) . Cu(II) Pb(II) . Ca(II) . pH, Ca(II) , , , . Cu(II) Pb(II) Ca(II) pH 5.0 , . , . , 1.0 mol/L . Na(I), K(I) Mg(II) Pb(II) Cu(II) . 2 90.4~104.3% Cu(II) Pb(II) . : , , , (II), (II)ABSTRACT. The preconcentration and determination of trace Cu(II) and Pb(II) on calcium alginate beads in aqueous solu-tion were studied. A calcium alginate beads were prepared by adding an alginic acid to sample solution contained Ca(II). Somefollowing conditions were optimized: the pH of sample solution, amount of alginic acid, and stirring time for effective adsorp-tion; the type and concentration of acid, and sonication time in an ultrasonic vibrator for the perfect de-sorption. A sample solu-tion was prepared with Cu(II) and Pb(II) in DI water. And Ca(II) and ethanol was added into the sample solution. The pH ofthe final sample solution was controlled with buffer solution. The alginic acid were dispersed in the sample solution by a mag-netic stirrer. This mixture was stored in room temperature for 30 min to form a calcium alginate. After the beads were filteredand washed on a membrane filter, the analytes were redissolved from the beads by an ultrasonic vibration of 10 minutes in 1.0MHNO

Application of internal standardization to rapid coprecipitation technique using lanthanum phosphate for flame atomic absorption spectrometric determination of iron and lead.

By applying an internal standardization, we could use a rapid coprecipitation technique using lanthanum phosphate as a coprecipitant for preconcentration of iron(III) and lead in their flame atomic absorption spectrometric determination. Indium as an internal standard was added to the initial sample solution together with lanthanum and phosphoric acid; the coprecipitation of iron(III) and lead was then carried out at pH about 3. After measuring the atomic absorbances of iron, lead, and indium in the final sample solution, we determined the contents of iron(III) and lead in the original sample solution by using the internal standardization with indium. In this method, complete collection of the precipitate was not required after the coprecipitation of iron(III), lead, and indium, because the ratio of the recovery of iron(III) or lead to that of indium was almost constant regardless of the recovery of the precipitate. This method was simple and rapid, and was available for the determination of 2-300 micrograms L-1 of iron(III) and 5-400 micrograms L-1 of lead in some water samples.

Flame atomic absorption spectrometric determination of lead in waste water and effluent after preconcentration using a rapid coprecipitation technique with gallium phosphate.

A determination method for lead in waste water and effluent was studied using flame atomic absorption spectrometry after preconcentration of lead by the rapid coprecipitation technique with gallium phosphate. Lead ranging from 0.5 to 50 microg was quantitatively coprecipitated with gallium phosphate from 100-150 mL sample solution (pH approximately 5). The presence of gallium phosphate did not affect the atomic absorbance of lead. Since the concentration of gallium in the final sample solution is also measurable by flame atomic absorption spectrometry at 250.0 nm without further dilution, the rapid coprecipitation technique, which does not require complete collection of the precipitate, becomes possible using a known amount of gallium and measuring the concentrations of both lead and gallium in the final sample solution by flame atomic absorption spectrometry. The 32 diverse ions tested gave no significant interferences in the lead determination. The method proposed here is rapid and has good reproducibility.

Feasibility of using beryllium as internal reference to reduce non-spectroscopic carbon species matrix effect in the inductively coupled plasma–mass spectrometry (ICP-MS) determination of boron in biological samples

The mechanism by which carbon matrix species cause non-spectroscopic matrix interference on boron (B) and beryllium (Be) during the determination of B in biological samples is investigated. The study indicates that, unlike other matrix species such as Ca and Na that cause non-spectroscopic matrix interference only through space charge effect, carbon species manifest non-spectroscopic interference by two mechanisms. The minor non-spectroscopic interference of carbon is through space charge effect. However, the major non-spectroscopic effect of carbon is by a charge transfer mechanism from C +-species to B and Be atoms in the central channel of the plasma discharge. The large difference in the magnitude of the carbon charge transfer non-spectroscopic matrix interference between Be and B makes Be unsuitable as an internal reference for B in solutions containing more than 1500 μg/ml dissolved organic carbon (DOC). This DOC content is approximately half the DOC usually present in the final sample solution for B determination in biological samples. However, Be still acts as a perfect internal reference to B in solution containing matrix elements that exert their non-spectroscopic interference effect through space charge mechanism (such as Na, K, Ca, etc.).

Effects of co-culture with bovine uterine or oviductal epithelial cells on development of Korean Native Cattle oocytes fertilized in vitro

Geologic reservoirs containing gas hydrate occur beneath permafrost environments and within marine continental slope sediments, representing a potentially vast natural gas source. Numerical simulators provide scientists and engineers with tools for understanding how production efficiency depends on the numerous, interdependent (coupled) processes associated with potential production strategies for these gas hydrate reservoirs. Confidence in the modeling and forecasting abilities of these gas hydrate reservoir simulators (GHRSs) grows with successful comparisons against laboratory and field test results, but such results are rare, particularly in natural settings. The hydrate community recognized another approach to building confidence in the GHRS: comparing simulation results between independently developed and executed computer codes on structured problems specifically tailored to the interdependent processes relevant for gas hydrate-bearing systems. The United States Department of Energy, National Energy Technology Laboratory, (DOE/NETL), sponsored the first international gas hydrate code comparison study, IGHCCS1, in the early 2000s. IGHCCS1 focused on coupled thermal and hydrologic processes associated with producing gas hydrates from geologic reservoirs via depressurization and thermal stimulation. Subsequently, GHRSs have advanced to model more complex production technologies and incorporate geomechanical processes into the existing framework of coupled thermal and hydrologic modeling.This paper contributes to the validation of these recent GHRS developments by providing results from a second GHRS code comparison study, IGHCCS2, also sponsored by DOE/NETL. IGHCCS2 includes participants from an international collection of universities, research institutes, industry, national laboratories, and national geologic surveys. Study participants developed a series of five benchmark problems principally involving gas hydrate processes with geomechanical components. The five problems range from simple geometries with analytical solutions to a representation of the world's first offshore production test of methane hydrates, which was conducted with the depressurization method off the coast of Japan. To identify strengths and limitations in the various GHRSs, study participants submitted solutions for the benchmark problems and discussed differing results via teleconferences. The GHRSs evolved over the course of IGHCCS2 as researchers modified their simulators to reflect new insights, lessons learned, and suggested performance enhancements. The five benchmark problems, final sample solutions, and lessons learned that are presented here document the study outcomes and serve as a reference guide for developing and testing gas hydrate reservoir simulators.

Differential Pulse Polarographic Determination of Lead Using a Rapid Coprecipitation Technique with Indium Hydroxide

An analytical method involving lead in water was studied using differential pulse polarography (DPP) after being concentrated by the rapid coprecipitation technique with indium hydroxide. Indium hydroxide coprecipitates quantitatively 1-1500μg of lead from up to 1000cm3 of sample solution at a pH of about 9. The presence of indium does not affect the polarogram of lead. Since the concentration of indium is also measurable by DPP, the rapid coprecipitation technique, which does not require a complete collection of the collector precipitate, becomes possible using a known amount of indium and measuring the concentrations of both lead and indium in the final sample solution by DPP. The calibration curve is linear over the 0.04-60μg cm-3 range of lead. Of the 39 diverse ions tested, tin(IV) and selenium(IV) interfered with the determination. The effect of tin(IV), however, could be eliminated by the addition of phosphoric acid. The proposed method is rapid and applicable to the determination of lead in water samples.