High-precision laser spectroscopy D/H and 18O/16O measurements of microliter natural water samples

Newly available gas analyzers based on off-axis integrated cavity output spectroscopy (OA-ICOS) lasers have been advocated as an alternative to conventional isotope-ratio mass spectrometers (IRMS) for the stable isotopic analysis of water samples. In the case of H2O, OA-ICOS is attractive because it has comparatively low capital and maintenance costs, the instrument is small and field laboratory portable, and provides simultaneous D/H and 16O/18O ratio measurements directly on H2O molecules with no conversion of H2O to H2, CO, or H2/CO2-water equilibration required. Here we present a detailed assessment of the performance of a liquid-water isotope analyzer, including instrument precision, estimates of sample memory and sample mass effects, and instrumental drift. We provide a recommended analysis procedure to achieve optimum results using OA-ICOS. Our results show that, by using a systematic sample analysis and data normalization procedure routine, measurement accuracies of +/-0.8 per thousand for deltaD and +/-0.1 per thousand delta18O are achievable on nanoliter water samples. This is equivalent or better than current IRMS-based methods and at a comparable sample throughput rate.     

Extraction technique for the determination of oxygen-18 in water using preevacuated glass vials

The need for a rapid, inexpensive technique for routine 18O/16O extraction from water has arisen recently through applications in the medical sciences and in hydrology. The traditional experimental technique for determining the oxygen isotope composition of water, the CO2-H2O equilibration method, is tedious, time consuming, and involves the use of custom-made glass apparatus. Furthermore, because of potential memory effects from one sample to the next, the glassware needs to be thoroughly cleaned between runs. A few attempts have been made to improve upon the method. Attempts to analyze water directly in the source of the mass spectrometer produced large memory effects and questionable results. Commercially available apparatus for automated extraction of 18O/16O from water is generally prohibitively expensive and often is designed to interface only with the manufacturer's own mass spectrometer. The method described in this paper utilizes inexpensive, off-the-shelf, preevacuated, glass vials. Preevacuated vials have been used by others for the isotopic analysis of breath CO2 and are well tested. The vials can be purchased in bulk from scientific apparatus suppliers at a relatively low cost. These are coupled with a simplified extraction line consisting of a stainless steel syringe needle and a glass cold trap. Vials are filled with CO2 and H2O and shaken in a constant-temperature water bath for at least 90 min. Since the vials are discarded after use, no cleaning is necessary, essentially eliminating any memory effect. Reproducibility is generally better than +/- 0.05%. The only reagents required are gaseous CO2 for equilibration, a dry ice/alcohol mixture for trapping water, and liquid nitrogen for transferring the CO2.     

Development and validation of a technique for the determination of 226Ra and 228Ra by liquid scintillation in liquid samples

Radium isotopes are dispersed in the environment according to their physicochemical characteristics. Considering their long half-lives and radiological effects, (226)Ra and (228)Ra are very important issues in radiological protection. In Brazil, radium isotopes represent an exposure problem both in nuclear fuel cycle installations and in high natural radiation background areas. The experimental part of this work includes the development of a technique for the determination of (226)Ra and (228)Ra by liquid scintillation with potential application in biological samples. Radium was concentrated and then separated from other constituents of the sample by co-precipitation/precipitation with Ba(Ra)SO(4). The precipitate was filtered and weighted to calculate the chemical yield. The filter containing the precipitate of Ba(Ra)SO(4) was transferred to a scintillation vial. Two methods were used to prepare the sources. The first one consisted of the addition of water (8 ml), Instagel XF (8 ml) and UltimaGold (4 ml) in the vial containing the filter and the precipitate, forming a gel suspension. In the second method, the precipitate was dissolved with 0.2 M ethylene-diamine-tetra-acetic-acid solution (9 ml) and 11 ml of scintillation solution (Optiphase Hisafe 3) was added to the vial, forming an aqueous and an organic phase. The solutions obtained were counted in a low background scintillation spectrometry system (Quantulus) suitable for the detection and identification of both alpha and beta particles for the determination of (226)Ra and (228)Ra. The activity values of (226)Ra and (228)Ra calculated by the two methods are in good agreement with the reference values, indicating that both methods are suitable for the determination of (226)Ra and (228)Ra.     

固相萃取-高效液相色谱-串联质谱测定水中5种大环内酯类抗生素

建立固相萃取(SPE)、高效液相色谱-串联质谱(HPLC-MS/MS)同时测定水中5种大环内酯类抗生素(罗红霉素、克拉霉素、阿奇霉素、螺旋霉素和泰乐菌素)的分析方法。水样中的抗生素通过Oasis HLB固相萃取小柱富集后,以C18反相色谱柱为分析柱,甲醇和0.1%甲酸水溶液为流动相,采用HPLC-MS/MS进行定量分析,检测方式为多反应监测模式(MRM),内标法定量。5种大环内酯类抗生素的回收率在64.8%~90.8%之间,仪器检出限为0.012~0.085μg/L,定量限为0.041~0.285μg/L。将建立的方法用于检测某化学工业园区周边地表水中5种目标分析物的残留,均未检测到泰乐菌素,其余4种抗生素均有不同程度检出,检出浓度在ng/L水平。     

超声辅助-乳化液液微萃取-气相色谱法测定水体中7种苯系物

采用正己烷为萃取剂,乙腈为乳化剂,建立超声辅助-乳化液液微萃取-气相色谱法(USA-ELLME-GC)检测水中甲苯、乙苯、对二甲苯、间二甲苯、邻二甲苯、1,3,5-三甲苯,1,2,4-三甲苯的分析方法。当萃取剂正己烷为150μL,乳化剂乙腈为400μL,超声时间为12 min时,50 m L水溶液中苯系物被成功萃取到正己烷中,富集倍数达到333倍。色谱条件为:DB-5MS(30 m×0.25 mm,0.25μm)毛细管柱,进样口温度220℃,检测器(FID)温度250℃,程序升温(初始45℃保持3 min,3°C/min升温至70℃,再以30℃/min升至200℃保持2 min),氢气流量10m L/min,尾吹气流量30 m L/min,分流比30∶1。在优化的萃取和色谱条件下,7种苯系物在0.08~1.00 mg/L浓度范围内与峰面积呈线性关系,相关系数均0.9980,方法检出限为0.005~0.01 mg/L,质量浓度均为0.10 mg/L的苯系物的7次前处理及测定结果相对标准偏差RSD为1.5%~4.7%。建立的方法应用于学校内湖水和实验室废水中7种苯系物的测定,平均回收率为86.5%~110.4%,测定结果满足分析化学痕量分析要求。     

Multiclass determination of sunscreen chemicals in water samples by liquid chromatography-tandem mass spectrometry

A novel analytical method based on solid-phase extraction (SPE) and liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) for the determination of UV sunscreen agents in the water environment is presented. After a thorough investigation of SPE and LC-MS/MS conditions, it permits the enrichment and determination of nine of these compounds in a single methodology, including three very polar sulfonates (e.g., 2-phenylbenzimidazole-5-sulfonic acid, PBSA) and six other less polar compounds (e.g., benzophenone-3, BP-3; octocrylene, OC,...). Other important matters of concern in the determination of UV filters at trace levels in water, i.e., adsorption on glassware and blank contamination problems, have also been discussed and minimized. This methodology affords detection limits between 7 and 46 ng L-1 and SPE recoveries in the range 63-102% from different real water matrixes, except for butylmethoxydibenzoylmethane (BM-DBM), which was not determinable in wastewater samples due to adsorption problems. The application of the method allowed reporting the levels of benzophenone-4 (BP-4) in environmental water samples for the first time, where it was identified as one of the most important in concentration among the UV filters studied, particularly in wastewater (237-1481 ng L-1).     

Simultaneous determination of the (2)h/(1)h, (17)o/(16)o, and (18)o/(16)o isotope abundance ratios in water by means of laser spectrometry

We demonstrate the first successful application of infrared laser spectrometry to the accurate, simultaneous determination of the relative (2)H/(1)H, (17)O/(16)O, and (18)O/(16)O isotope abundance ratios in water. The method uses a narrow line width color center laser to record the direct absorption spectrum of low-pressure gas-phase water samples (presently 10 μL of liquid) in the 3-μm spectral region. It thus avoids the laborious chemical preparations of the sample that are required in the case of the conventional isotope ratio mass spectrometer measurement. The precision of the spectroscopic technique is shown to be 0.7‰ for δ(2)H and 0.5‰ for δ(17)O and δ(18)O (δ represents the relative deviation of a sample's isotope abundance ratio with respect to that of a calibration material), while the calibrated accuracy amounts to about 3 and 1‰, respectively, for water with an isotopic composition in the range of the Standard Light Antarctic Precipitation and Vienna Standard Mean Ocean Water international standards.     

Method for the analysis of delta18O in water

A new method has been developed for the oxygen isotopic analysis of water utilizing the exchange of oxygen atoms with nitrite followed by conversion of nitrite to nitrous oxide by hydrazoic acid. This method is analogous to that employing carbon dioxide equilibration in that the analyte is added as a reagent to the water sample and exchanges oxygen isotopes with the water. In this procedure, however, the equilibration is more rapid and less sensitive to changes in ambient temperature, as the exchange is terminated by conversion of nitrite to nitrous oxide prior to analysis. The nitrous oxide is then analyzed using an on-line purge and trap system coupled to an isotope ratio mass spectrometer. This method makes use of previously established methods for nitrite isotopic analysis and commercially available equipment. It has high throughput, relatively low standard deviation (0.1 per thousand or better), and small sample size (down to 100 microL), is simple, and is applicable to both fresh- and seawater samples.     

A simple cleanup method for the isolation of nitrate from natural water samples for O isotope analysis.

The analysis of O-isotopic composition of nitrate has many potential applications in studies of environmental processes. O-isotope nitrate analysis requires samples free of other oxygen-containing compounds. More than 100% of non-NO3- oxygen relative to NO3- oxygen can still be found in forest soil water samples after cleanup if improper cleanup strategies, e.g., adsorption onto activated carbon, are used. Such non-NO3- oxygen compounds will bias O-isotopic data. Therefore, an efficient cleanup method was developed to isolate nitrate from natural water samples. In a multistep cleanup procedure using adsorption onto water-insoluble poly(vinylpyrrolidone), removal of almost all other oxygen-containing compounds, such as fulvic acids, and isolation of nitrate was achieved. The method supplied samples free of non-NO3- oxygen which can be directly combusted to CO2 for subsequent O-isotope analysis.     

Multiresidue determination of ultratrace levels of fluoroquinolone antimicrobials in drinking and aquaculture water samples by automated online molecularly imprinted solid phase extraction and liquid chromatography

The present work describes the development of a sensitive and highly selective innovative method for the simultaneous detection of six fluoroquinolone (FQ) antimicrobials (enrofloxacin, ciprofloxacin, norfloxacin, levofloxacin, danofloxacin, and sarafloxacin) in water samples. This detection is based on online solid phase extraction, coupled to liquid chromatography (LC), using for the first time tailor-made molecularly imprinted microspherical polymer particles prepared via precipitation polymerization. Various parameters affecting the extraction efficiency of the polymer have been optimized to reduce nonspecific interactions and to achieve selective uptake of the antibiotics from real samples. The method shows good recoveries ranging between 62% and 102% (V = 25 mL) for the different FQs tested and excellent interday and intraday precision with relative standard deviation (RSD) values between 2-5% and 2-6%, respectively. The detection limits were between 1-11 ng L(-1) (drinking water) and 1-12 ng L(-1) (fish farm water) when 25 mL samples were processed. The polymer showed selectivity for FQs containing a piperazine moiety whereas no retention was found for other antibiotics or nonrelated compounds. The method has been applied to the analysis of trace amounts of the FQs tested in drinking and fish farm water samples with excellent recoveries (>91%) and good precision (RSDs <5%).     

催化电位法测定环境水样中痕量亚硝酸根的研究

研究了以亚硝酸根对溴酸钾氧化碘化钾的催化作用,用碘离子选择电极跟踪测定催化体系的电位。实验表明,在适宜的条件下,该指示反应为拟一级反应;电位差与亚硝酸讯浓度在测定条件下呈线性关系,其检出限为3.0×10~(-5)mg/mL。该法用于环境水样的测定,其结果良好。     

Accurate determination of solid and liquid dispersions from spectra channeled with the Fabry-Perot interferometer

The band spacing of the fringes of equal chromatic order of a thin Fabry-Perot interferometer is compared when this interferometer contains air, a solid, or a liquid. This comparison enables the dispersion of the group velocity of light in these media to be known accurately to 2.4 parts in one thousand. The Sellmeier dispersion function is used to deduce the refractive indices with the same degree of accuracy. The order-transformation method is used to find the exact order values from the roughly known optical thickness. The exact order values for air and the sample are used to find the refractive index accurately to approximately 3 x 10(-5). A least-squares fitting of the accurate experimental data to the Sellmeier dispersion function enables the coefficients of the latter to be more precisely defined for solids such as glass and mica and for liquids such as glycerin and distilled water. The atomic parameters such as the density of states and the absorption wavelengths in the ultraviolet region of the spectrum for the given samples are deduced from the more precisely found Sellmeier coefficients.     

Isotope 18O/16O ratio measurements of water vapor by use of the 950-nm wavelength region with cavity ring-down and photoacoustic spectroscopic techniques

Two optical methods, cavity ring-down spectroscopy and photoacoustic spectroscopy, are applied to the measurement of the isotope ratio 18O/16O in water-vapor samples with a Nd3+:YAG pumped-dye laser. The combination band of (2v1 + v3) in the 960-nm region of water molecules is investigated for two standard water samples, the Vienna Standard Mean Ocean Water and the Standard Light Antarctic Precipitation. The results demonstrate that the two methods have the potential of compact systems for in-situ measurements of H2O isotope ratio in the environment.     

Coupled-column liquid chromatography applied to the trace-level determination of triazine herbicides and some of their metabolites in water samples

In the present work, a study is reported of the potential of coupled-column liquid chromatography (LC) applied to the determination of triazine residues in environmental water samples. For this purpose, two different techniques have been compared: on-line trace enrichment followed by LC (SPE-LC) and coupled-column liquid chromatography (LC-LC). First, a completely automated liquid chromatographic method based on on-line trace enrichment in a prepacked precolumn and using diode array detection has been developed for the simultaneous trace-level determination of six triazine herbicides (simazine, cyanazine, atrazine, terbumeton, terbuthylazine, and terbutryn) and the main atrazine metabolites (desisopropylatrazine, desethylatrazine, and hydroxyatrazine). After preconcentration parameters were optimized by testing two different sorbents (C18 and PRP-1) in three cartridges with different dimensions, a sample volume of 100 mL was selected in order to achieve maximal solute preconcentration. Detection limits lower than 0.1 microgram.L-1 were obtained even for the most polar analyte (desisopropylatrazine), which presented recoveries of around 30%. The method was validated by means of recovery experiments in groundwater and surface water samples spiked with the analytes at different levels (0.2-2 micrograms.L-1). Afterward, the procedure was successfully applied in a program for monitoring of triazine residues in surface water carried out in a wet area of Castellón, Spain. Different triazine herbicides such as simazine, terbumeton, terbuthylazine, and terbutryn were identified and quantified. The identity of these compounds was confirmed by their absorption UV spectra and by GC/MS analysis. Finally, two rapid, sensitive, and selective procedures, previously developed in our laboratory for the trace-level determination of triazine compounds, both based on LC-LC, were compared with the former procedure. The SPE-LC approach showed a considerable improvement in the global sensitivity at the expense of a decrease in selectivity as well as in sample throughput.     

Optical emission from laser-induced breakdown plasma of solid and liquid samples in the presence of a magnetic field

The optical properties of laser-induced plasma generated firm solid (Al alloy) and liquid (Mn, Cr, Mg, or Ti solutions) samples expanded across an external, steady magnetic field have been studied by atomic-emission spectroscopy. Various line emissions obtained from the constituents of the Al alloy and of the aqueous solution show an enhancement in intensity in the presence of an approximately 5-kG magnetic field. The enhancement of the signal was nearly a factor of 2 for the minor constituents of the solid samples and a factor of 1.5 for the elements in liquid phase. Temporal evolution of the emission from the solid sample showed maximum enhancement in emission intensity at 3-10-micros time delay after plasma formation in the laser energy range 10-50 mJ. However, for the liquid sample the maximum signal was for a gate delay of 3-25 micros the energy range 50-200 mJ. This enhancement in the emission intensity was found to be due to an increase in effective density of the plasma as a result of magnetic confinement when the plasma cooled after expansion. This enhanced emission was due to an increase in the rate of radiative recombination in the plasma.     

Use of laser spectroscopy to measure the 13C/12C and 18O/16O compositions of carbonate minerals

The stable carbon and oxygen isotope compositions of carbonate minerals are utilized throughout the earth and environmental sciences for various purposes. Here, we demonstrate the first application of a prototype instrument, based on off-axis integrated cavity output laser spectroscopy, to measure the carbon and oxygen isotope composition of CO(2) gas evolved from the acidification of carbonate minerals. The carbon and oxygen isotope ratios were recorded from absorption spectra of (12)C(16)O(16)O, (13)C(16)O(16)O, and (12)C(16)O(18)O in the near-infrared wavelength region. The instrument was calibrated using CaCO(3) minerals with known δ(13)C(VPDB) and δ(18)O(VSMOW) values, which had been previously calibrated by isotope ratio mass spectrometry relative to the international isotopic standards NBS 18 and NBS 19. Individual analyses are demonstrated to have internal precision (1 SE) of better than 0.15‰ for δ(13)C and 0.6‰ for δ(18)O. Analysis of four carbonate standards of known isotopic composition over 2 months, determined using the original instrumental calibration, indicates that analyses are accurate to better than 0.5‰ for both δ(13)C and δ(18)O without application of standard-sample-standard corrections.