Uncertainties in the oxygen isotopic composition of barium sulfate induced by coprecipitation of nitrate

Coprecipitation of nitrate and sulfate by barium has probably resulted in significant error in numerous studies dealing with the oxygen isotopic composition of natural sulfates using chemical/thermal conversion of BaSO(4) and analysis by isotope ratio mass spectrometry. In solutions where NO(3) (-)/SO(4) (2-) molar ratios are above 2 the amount of nitrate coprecipitated with BaSO(4) reaches a maximum of approximately 7% and decreases roughly linearly as the molar ratio decreases. The fraction of coprecipitated nitrate appears to increase with decreasing pH and is also affected by the nature of the cations in the precipitating solution. The size of the oxygen isotope artifact in sulfate depends both on the amount of coprecipitated nitrate and the delta(18)O and Delta(17)O values of the nitrate, both of which can be highly variable. The oxygen isotopic composition of sulfate extracted from atmospheric aerosols or rain waters are probably severely biased because photochemical nitrate is usually also present and it is highly enriched in (18)O (delta(18)O approximately 50-90 per thousand) and has a large mass-independent isotopic composition (Delta(17)O approximately 20-32 per thousand). The sulfate delta(18)O error can be 2-5 per thousand with Delta(17)O artifacts reaching as high as 4.0 per thousand. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Flow injection spectrophotometry coupled with a crushed barium sulfate reactor column for the determination of sulfate ion in water samples

A new type of a reactor column, a crushed BaSO₄ reactor column used for the flow injection spectrophotometric determination of sulfate ion using the exchange reaction of sulfate ion and barium-dimethylsulfonazo III is proposed. The column is very simple and economical. It can be continuously used for 8 h before washing with water for repeated usage of at least 1 month. The procedure is sensitive. Application to various water samples was demonstrated.     

An electrolytic device for preparation of hydrogen and oxygen from water for isotopic analysis

An electrolytic device for decomposition of water has been developed which readily gives hydrogen and oxygen for isotopic measurement with a mass spectrometer. A 20-mul sample can be decomposed quantitatively in 10 min with good reproducibility. The results produced are comparable with those obtained by reduction with uranium.     

An unusual isotopic fractionation of boron in synthetic calcium carbonate precipitated from seawater and saline water

Inorganic calcium carbonate precipitation from natural seawater and saline water at various pH values was carried out experimentally. The results show the clear positive relationships between boron concentration and δ11B of inorganic calcium carbonate with the pH of natural seawater and saline water. However, the variations of boron isotopic fractionation between inorganic calcite and seawater/saline water with pH are inconsistent with the hypothesis that B(OH)4- is the dominant spe-cies incorporated into the biogenic calcite structure. The isotopic fractionation factors α between synthetic calcium carbonate precipitate and parent solutions increase systematically as pH increases, from 0.9884 at pH 7.60 to 1.0072 at pH 8.60 for seawater and from 0.9826 at pH 7.60 to 1.0178 at pH 8.75 for saline water. An unusual boron isotopic fractionation factor of larger than 1 in synthetic calcium carbonate precipitated from seawater/saline water at higher pH is observed, which implies that a substantial amount of the isotopically heavier B(OH)3 species must be incorporated preferentially into synthetic inorganic carbonate. The results propose that the incorporation of B(OH)3 is attributed to the formation of Mg(OH)2 at higher pH of calcifying microenvironment during the synthetic calcium carbonate precipitation. The preliminary experiment of Mg(OH)2 precipitated from artificial seawater shows that heavier 11B is enriched in Mg(OH)2 precipitation, which suggests that isotopically heavier B(OH)3 species incorporated preferentially into Mg(OH)2 precipitation. This result cannot be applied to explain the boron isotopic fractionation of marine bio-carbonate because of the possibility that the unusual environment in this study appears in formation of marine bio-carbonate is infinitesimal. We, however, must pay more attention to this phenomenon observed in this study, which accidentally appears in especially natural environment.     

An installation for the preparation of foraminifera micro samples for the isotopic analysis of carbon and oxygen

A technical modification of the traditional method of decomposition of carbonates in phosphoric acid was proposed for the determination of δ¹³C and δ¹⁸O in organogenic carbonate samples weighing 10–30 μg with an accuracy of 0.05%. The extraction of CO₂ was carried out under a vacuum at 95°C in 105% phosphoric acid. The isotopic composition of CO₂ was measured by CG-IRMS. The used feed-motion of samples to the reactor provides a consecutive delivery of the samples from the sample holders to the acid. This sample feeding method prevents the contamination of the acid with impurities from the surface of the sample, obviates the necessity of removing the sample holders from the acid, and allows the use of the same acid for performing a very large numbers of analyses. The accuracy and reproducibility of the δ¹³C and δ¹⁸O values was estimated by measuring international standards and comparing with the δ¹³C and δ¹⁸O values for organogenic carbonate samples obtained by the proposed method of analysis at a microgram level and the traditional method at a milligram level. The proposed technology was successfully used to study the isotopic composition of oxygen and carbon in the plankton and benthos foraminifers in order to reconstruct the Okhotsk Sea palaeotemperatures.     

Effect of surfactants on the determination of nitrite and nitrate in water samples

Summary The effect of four surfactants on the determination of nitrite and nitrate has been examined. The method which has been tested for nitrite is based on the formation of an azodye. The results show that cationic and non-ionic surfactants do not interfere with the determination of nitrite while anionic surfactants cause significant interferences, which could be eliminated by treating the water samples with a cationic surfactant.Two methods have been tested for the determination of nitrate in the presence of surfactants. One method is based on the nitration of salicyclic acid, while the other is based on the reduction of nitrate to nitrite. Results for the first method show that the non-ionic surfactant Triton-X causes significant interferences. Cationic and anionic surfactants do not interfere, when their concentration is relatively low. For higher concentrations an increasing interference is observed. Results for the second method show effects similar to those obtained for nitrite.

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Wirkung oberflächenaktiver Substanzen auf die Bestimmung von Nitrit und Nitrat in Wasserproben

     

Improved method for isotopic and quantitative analysis of dissolved inorganic carbon in natural water samples

We present here an improved and reliable method for measuring the concentration of dissolved inorganic carbon (DIC) and its isotope composition (delta(13)C(DIC)) in natural water samples. Our apparatus, a gas chromatograph coupled to an isotope ratio mass spectrometer (GCIRMS), runs in a quasi-automated mode and is able to analyze about 50 water samples per day. The whole procedure (sample preparation, CO(2(g))-CO(2(aq)) equilibration time and GCIRMS analysis) requires 2 days. It consists of injecting an aliquot of water into a H(3)PO(4)-loaded and He-flushed 12 mL glass tube. The H(3)PO(4) reacts with the water and converts the DIC into aqueous and gaseous CO(2). After a CO(2(g))-CO(2(aq)) equilibration time of between 15 and 24 h, a portion of the headspace gas (mainly CO(2)+He) is introduced into the GCIRMS, to measure the carbon isotope ratio of the released CO(2(g)), from which the delta(13)C(DIC) is determined via a calibration procedure. For standard solutions with DIC concentrations ranging from 1 to 25 mmol . L(-1) and solution volume of 1 mL (high DIC concentration samples) or 5 mL (low DIC concentration samples), delta(13)C(DIC) values are determined with a precision (1sigma) better than 0.1 per thousand. Compared with previously published headspace equilibration methods, the major improvement presented here is the development of a calibration procedure which takes the carbon isotope fractionation associated with the CO(2(g))-CO(2(aq)) partition into account: the set of standard solutions and samples has to be prepared and analyzed with the same 'gas/liquid' and 'H(3)PO(4)/water' volume ratios. A set of natural water samples (lake, river and hydrothermal springs) was analyzed to demonstrate the utility of this new method.     

Determination of chloride, sulfate and nitrate in groundwater samples by ion chromatography

Groundwater is a significant source of water for both domestic and agricultural use in some regions of the Maracaibo lake basin in Venezuela. Chemically suppressed ion chromatography with a Dionex Model 2000i/sp, lonpac AS11, ASRS-I system was used for the analysis of major inorganic anions in groundwater samples. About 50 samples of groundwater, taken over several months in three different locations, were analyzed after filtration and sometimes dilution. In all the samples, the separation between the peaks of chloride, nitrate and sulfate showed good resolution (symmetrical peaks, not broadened), even when the chloride concentration was as high as 850 mg l(-1) and reproducibility (RSD) was -2%. No other peaks (i.e. fluoride, nitrite and phosphate) were observed at selected experimental conditions. With the chosen parameters, the method is well-suited for the routine determination of these anions in groundwater samples, giving results in less than 10 min (including column clean-up). With an appropriate combination of detector output ranges (300 and 1,000 microS), only one set of calibration solutions was needed for all samples. In the Sierra Maestra location, the groundwater samples, were significantly different in total anion levels. Mean total chloride plus sulfate concentrations (approximately 525 mg l(-1)) were about 100 times higher than in the other sites. Some water quality implications of these groundwater samples are also discussed.     

不同次级结构的硫酸钡多晶体制备研究

以过氧化钡(Ba O2)晶体为母体钡源,利用溶液中碱性条件下过氧化氢电离控制Ba O2分解速度,结合过量SO42-制备了具有Ba O2宏观形貌的Ba SO4多晶体,该多晶体由条形结构单元组成。进一步通过不同聚合物添加剂调节次级结构单元的形貌,在溶液中引入聚苯乙烯磺酸钠制备了由球形次级结构单元组成的Ba SO4多晶体;而在不同浓度的聚丙烯酸添加剂作用下,可制得由纳米颗粒和纳米棒状结构单元组成的Ba SO4多晶体。制备的多晶体材料为具有母体材料统一宏观形貌的大颗粒,其次级结构可通过聚合物添加剂调控,为合成具有特定形貌的功能晶体材料提供了一个新的途径。     

Morphology of silver electrolytically precipitated from acetonitrile solutions of silver nitrate

The electrochemical deposition of silver was investigated from 0.01–0.1 M acetonitrile solutions of Ag NO₃ by stationary and pulse current. An effect of the main parameters of the pulse current (duration and pause of pulse), concentrations of silver ions, time of electrolysis, and nature of support was considered on form and size of structural particles of deposit.     

The role of the cation in the oxygen isotopic exchange in crystalline sulfate salt hydrates

The oxygen isotopic exchange during dehydration and decomposition of five sulfate salt hydrates (CoSO₄·6H₂O, NiSO₄·7H₂O, ZnSO₄·7H₂O, CaSO₄·2H₂O, Li₂SO₄·H₂O) was studied in detail by temperature programmed desorption mass spectrometry (TPD-MS) in a supersonic molecular beam (SMB) inlet mode. Crystals of the ¹⁸O-enriched salts were grown and the detailed desorption steps of the various gaseous products released during dehydration and decomposition of these compounds were recorded. The desorption patterns confirmed the known characteristic stepwise dehydration of these salts, where regardless of the crystalline structure and composition, in all the salts (excluding the Li and Ca sulfates) a major group of n ? 1 loosely bounded water of crystallization molecules (out of total of n molecules in the fully hydrated form) are released at adjacent temperatures in a typical low temperature range (<200 °C), while the last, most strongly bounded water molecule, consistently desorbs at relatively higher temperatures (240 < T < 440 °C). Interestingly, it is established that the oxygen isotopic exchange occurs exclusively between that latter, most strongly bound water molecule, and the salt anion. Remarkably, the results point out that the exchange process is mostly of solid-solid nature. Finally, the results point out that the probability of the isotopic exchange increases with the increment in the desorption temperature of the last dehydration step, i.e. with the bond strength in the monohydrate, between the last water molecule of crystallization and the cation.     

Soapless emulsion polymerization of methyl methacrylate in water in the presence of barium sulfate

To investigate the kinetics of soapless emulsion polymerization in the presence of a solid phase, polymerization experiments were carried out for the methyl methacrylate? K₂S₂O₈? H₂O system using barium sulfate powder, which is assumed to be chemically inert. Reaction conditions were varied with respect to the ranges of initiator concentration, monomer concentration, agitation speed, and quantity of powder. Experimental results showed that the polymerization rate is greatly affected by the addition of powder. It is concluded that the physical circumstances of the polymerization are changed considerably with the addition of the powder. A conceptual model for the mechanism of the polymerization was proposed to explain the effects of the experimental variables.     

Multiparametric automated system for sulfate,nitrite and nitrate monitoring in drinking water and wastewater based on sequential injection analysis

An automated monitoring system for sulfate, nitrite and nitrate based on sequential injection analysis (SIA) was developed. For nitrite determination the modified Griess-Ilosvay method was used, whereas nitrate was previously reduced to nitrite using a cadmium column followed by nitrite determination. A turbidimetric method was carried out in order to determine sulfate. The results showed that the proposed SIA monitoring system constitutes an effective approach for nitrite, nitrate and sulfate determination since it is able to determine levels required by international agencies that regulate these parameters in water. Detection limits of 0.0207 mg N L^? 1, 0.0022 mg N L^? 1 and 3 mg SO₄^2? L^? 1 were obtained for nitrate, nitrite and sulfate, respectively. The developed method offers also typical characteristics of the multicommutated systems, as portability, low reagents consumption and the subsequently minimization of waste generation. The proposed system was successfully applied to drinking water and wastewater samples and validated with a certified river water sample (ION-96.3, LGC Standards).     

New metallochromic indicator for barium: Determination of sulfate in water and soil extracts

A new metallochromic indicator for barium, Orthanilic NM, is synthesized and proposed. The color reaction of Orthanilic NM with barium ions is compared with the reactions of carboxyarsenazo and other orthanilic group reagents, such as Orthanilic K, nitchromazo, etc. The quantitative characteristics of the reactions are determined. It is shown that Orthanilic NM can be used for the titrimetric (down to 20 mg/L) and photometric (down to 0.2 mg/L) determinations of sulfate. Substantial amounts of conventional anions, alkali, alkaline-earth, and nonferrous metals do not interfere with the titrimetric determination (at pH 2.5). For the photometric determination, a 1:1 Ba²⁺-Orthanilic NM complex is used at pH 2. In these conditions, sulfite and phosphate do not interfere with the determination either. Procedures are developed for the determination of sulfate in various types of water and soil extracts. Examples of their practical application are given.     

生物样品中亚硝酸根和硝酸根分析研究进展EI北大核心CSCD

亚硝酸根和硝酸根以盐的形式广泛存在于生活中,其测定一直是各领域的研究热点。在法医毒物分析领域,亚硝酸盐中毒案件频发,少量亚硝酸盐即可引起中毒或死亡,案件现场体内外检材中其含量测定可为案件提供证据。亚硝酸盐不稳定易氧化,小体积生物样品中亚硝酸盐和硝酸盐的测定仍是一个挑战。本文对生物样品中亚硝酸盐和硝酸盐的测定方法进行了综述,方法分为光谱法和色谱法两大类,重点综述了色谱法中准确度较高的气相色谱-质谱(GC-MS)技术,以便为2种物质的检测和相关科学研究提供参考。