Reduction of mercury(II) by tropical river humic substances (Rio Negro)-Part II. Influence of structural features (molecular size, aromaticity, phenolic groups, organically bound sulfur)

The influence of structural features of tropical river humic substances (HS) on their capability to reduce mercury(II) in aqueous solutions was studied. The HS investigated were conventionally isolated from Rio Negro water-Amazonas State/Brazil by means of the collector XAD 8. In addition, the isolated HS were on-line fractionated by tangential-flow multistage ultrafiltration (nominal molecular-weight cut-offs: 100, 50, 30, 10, 5 kDa) and characterized by potentiometry and UV/VIS spectroscopy. The reduction of Hg(II) ions to elemental Hg by size-fractions of Rio Negro HS was assessed by cold-vapor AAS (CVAAS). UV/VIS spectrometry revealed that the fractions of high molecular-size (F₁>100 kDa and F₂: 50-100 kDa) have a higher aromaticity compared to the fractions of small molecular-size (F₅: 5-10 kDa, F₆: <5 kDa). In contrast, the potentiometric study showed different concentration of functional groups in the studied HS fractions. The reduction of Hg(II) by aquatic HS fractions at pH 5 proceeded in two steps (I, II) of slow first order kinetics (t_1/2 of I: 160 min, t_1/2 of II: 300 min) weakly influenced by the molecular-size, in contrast to the differing degree of Hg(II) reduction (F₅>F₂>>F₁>F₃>F₄>>F₆). Accordingly, Hg(II) ions were preferably reduced by HS molecules having a relatively high ratio of phenolic/carboxylic groups and a small concentration of sulfur. From these results a complex ‘competition’ between reduction and complexation of mercury(II) by aquatic HS occurring in tropical rivers such as the Rio Negro can be suggested.     

Occurrence,fate and determination of tobacco (nicotine) and alcohol (ethanol) residues in waste- and environmental waters

This review includes one hundred and two peer reviewed papers that focus on metabolic residues of the two most used licit drugs globally, nicotine (nicotine, cotinine, trans-3’-hydroxycotinine – HCOT) and alcohol (ethyl sulphate and ethyl glucuronide), in waste- and environmental waters. Sampling strategies and analytical methods are also summarised and discussed. Although grab sampling is the most widely applied method for collecting environmental samples (74% cases), wastewater samples are typically composite samples collected automatically at the wastewater treatment plants (66% cases). Sample preparation and analysis usually include solid-phase extraction (SPE) followed by reverse-phased liquid chromatography with tandem mass spectrometry detection (RP-LC-MS/MS) for nicotine residues. In contrast, alcohol residues are commonly determined via direct injection onto the LC-MS/MS using an ion-pair reagent to improve retention, leaving room for method improvement, e.g., introducing a suitable extraction procedure to achieve lower detection limits and quantification. In comparison to alcohol residues, more studies look into nicotine residues (85% of the studies). Concentration ranges for nicotine, cotinine, HCOT and ethyl sulphate were < 424,000, < 42,300, 50–52,000 and 500–33,000 ng/L in wastewater influents and 15–32,000, < 18,000, 15–1,552 and < 500 ng/L in effluents, while nicotine (12.6–947 ng/L) and cotinine (17–62 ng/L) were detected in reclaimed waters. Among environmental waters, the highest concentrations of nicotine residues were measured in surface waters (nicotine: < 9,340 ng/L, cotinine: < 6,582 ng/L and HCOT: 14–777 ng/L), while their concentrations in groundwater and drinking water were generally in the low ng/L range. This review also reveals the discrepancy between the number of studies in developed countries (90%) compared to developing countries and the need for more studies in the former, where most wastewater flows untreated into the environment.     

Occurrence of pharmaceutical metabolites and transformation products in the aquatic environment of the Mediterranean area

The presence of pharmaceutically active substances (PhACs) in aquatic ecosystems is of great concern due to their constant occurrence in different water systems and potential negative effects on the quality of water and living organisms. After consumption, PhACs are excreted as the parent compound, and/or as free or conjugated metabolites, which might finally arrive to surface and ground waters after their incomplete removal (and possible degradation) in the wastewater treatment plants (WWTP). A large amount of data about parent PhACs in water has been reported in the literature in the last decade; however, there is a lack of information about the presence of their metabolites and transformation/degradation products (TPs). Recent publications report that PhACs found in water are only the “top of the iceberg” in relation to the environmental impact associated to the consumption of PhACs. From a scientific-technological point of view, the overall study of PhACs is a challenge and requires to advance with respect to current knowledge and analytical capacities, considering several key aspects, such as the reliable identification and quantification of the compounds, the improvement of the removal efficiency by the WWTPs, the study of their behaviour in the environment (e.g. persistence and biodegradability), and the environmental risk assessment, considering not only the parent PhACs but also their transformation/metabolism products. In this work, it is intended to delve into this problem, presenting a detailed overview on metabolites and TPs of PhACs in environmental waters from the Mediterranean area. Analytical and environmental problems associated to the determination of these compounds are briefly commented, ending the paper with the main conclusions and expected future trends in relation to this field.     

Ultrasound‐assisted extraction and solid‐phase extraction as a cleanup procedure for organochlorinated pesticides and polychlorinated biphenyls determination in aquatic samples by gas chromatography with electron capture detection

The feasibility of developing a quick, easy, efficient procedure for the simultaneous determination of organochlorinated pesticides and polychlorinated biphenyls in aquatic samples using gas chromatography with electron capture detection based on solid‐phase extraction was investigated. The extraction solvent (n‐hexane/acetone, cyclohexane/ethyl acetate, n‐hexane/dichloromethane, n‐hexane) for ultrasound‐assisted solid–liquid extraction and solid‐phase extraction columns (florisil, neutral alumina, acidic alumina, aminopropyl trimethoxy silane, propyl ethylenediamine, aminopropyl trimethoxy silane/propyl ethylenediamine, graphitized carbon black and silica) for cleanup procedure were optimized. The gas chromatography with electron capture detection method was validated in terms of linearity, sensitivity, reproducibility, and recovery. Mean recoveries ranged from 75 to 115% with relative standard deviations <13%. Quantification limits were 0.20–0.40 ng/g for organochlorinated pesticides and polychlorinated biphenyls. The satisfactory data demonstrated the good reproducibility of the method with relative standard deviations lower than 13%. In comparison to other related methods, this method requires less time and solvent and allows for rapid isolation of the target analytes with high selectivity. This method therefore allows for the screening of numerous samples and can also be used for routine analyses.     

ESI-MS analyses of lake dissolved organic matter in light of supramolecular assembly

A high-performance size-exclusion chromatography (SEC) system was coupled on-line to an electrospray ionization (ESI) interface to detect gas-phase ions by an API 365 LC/MS/MS triple quadrupole analyzer. The SEC fractions of a strongly coloured freshwater solution containing dissolved organic matter-humic substances (DOM-HS) were screened both by UV₂₅₄ and by ESI mass spectrometry (ESI-MS) in the full-scan mode within the m/z range of 100–2,900 amu in negative and positive polarities. The ESI-MS spectra were also collected by direct infusion of the DOM-HS solution in both polarities. ESI-MS spectra did not primarily favour low mass compounds, and negative and positive total ion chromatograms were parallel to the SEC elution profile obtained by UV₂₅₄ detection from DOM-HS solution. The UV₂₅₄ detection overestimated the SEC portion of higher size/mass solutes and underestimated that of solutes of smaller sizes/masses as compared with the total ion chromatogram intensities in negative or positive polarities. The change of mass-weighted and number-weighted average sizes/masses (M _w and M _n) of different SEC fractions was fairly small, in contrast to UV₂₅₄ detection, with increasing elution volume. A reasonable explanation for the great differences between M _w and M _n values, obtained by UV₂₅₄ and ESI-MS detections for eight different SEC fractions, seems to be a supramolecular-type association of relatively small components through weak dispersive forces. M _n values obtained by vapour-pressure osmometry for different SEC fractions were to some extent analogous with those of negative and positive ESI-MS. The shapes obtained by either negative or positive polarities and calculated M _w and M _n values indicated a close structural similarity between each SEC fraction. Positive ion and negative ion spectra of different humic fractions represented quite similar components, and there was no evidence for noteworthy occurrence of multiply charged ions being able to lower mass distributions of negative ion spectra. The effect of nitrogen on the mass spectra seemed to be unimportant, and the weak ions observed at even m/z values correspond most likely to the ¹³C counterparts of the more abundant ¹²C odd ions. No uncontrolled ESI fragmentation was observable and humic solutes seemed to be quite heat-resistant. Direct infusion of the untreated DOM-HS solution and statistical calculation verified that the SEC-separated different fractions really represent distinct entities of the original DOM-HS mixture. ESI-MS results support the opinion that the structural composition of humic solutes in their original combined mixture resembles supramolecular-type associations of smaller molecular size entities possessing similar structural functionalities.     

高效液相色谱法同时检测水产品中螺旋霉素与泰乐菌素药物残留

建立了同时检测水产品中螺旋霉素与泰乐菌素药物残留的分析方法。在碱性条件下采用乙酸乙酯提取,提取液挥干后溶于酸性缓冲液中,经正己烷去脂、HLB SPE小柱净化后,采用高效液相色谱进行分析。采用Meck Purospher STAR RP18色谱柱(250 mm×4.6 mm,5μm)及乙腈和pH 2.5磷酸缓冲溶液的混合液作梯度淋洗进行分离。分别在232 nm及287 nm对螺旋霉素及泰乐菌素进行紫外检测。方法在1-200 ng之间呈线性相关,相关系数在0.999 8以上,平均回收率为82.2%-89.0%,相对标准偏差为6.24%-9.83%,对螺旋霉素、泰乐菌素的检出限分别为0.005 4 mg.kg-1与0.031 mg.kg-1。     

固相萃取-抑制电导离子色谱法测定水产品中有机酸

建立了梯度淋洗-抑制型电导离子色谱法检测水产品中有机酸的方法。在2～3个数量级范围内,该方法对目标化合物的检测线性良好。酒石酸的线性范围为15～500 ng/mL,检测限为0.05 mg/kg;柠檬酸线性范围为8～500 ng/mL,检测限为0.03 mg/kg。以大黄鱼、中华绒螯蟹、南美白对虾、文蛤为空白样品,加入酒石酸和柠檬酸质量分数分别为0.05,0.07和0.10 mg/kg,酒石酸的加标回收率介于84.4%～89.2%,RSD<6.5%,柠檬酸的加标回收率介于87.5%～93.8%,RSD<5.9%。     

高效液相色谱快速测定水产品中孔雀石绿、结晶紫及其无色产物的残留量

采用高效液相色谱同时检测水产品中孔雀石绿、结晶紫及无色孔雀石绿和无色结晶紫的残留量,样品经提取、净化处理后所得残渣用乙腈溶解后,通过采用C_(18)色谱柱,以乙腈(A)和pH3.0的0.02 mol·L~(-1)磷酸二氢钾缓冲溶液(B)按不同比例混合进行梯度淋洗,实现孔雀石绿、结晶紫及其代谢物的分离。用自制的二氧化铅柱氧化无色孔雀石绿及无色结晶紫。在588 nm波长处,测定4种物质的质量浓度在0.3～6.0 mg·L~(-1)范围内与其峰面积呈线性关系,相对标准偏差(n=6)小于2.5%,检出限(3S/N)小于1.9μg·kg~(-1),分析时间20 min。以凤尾鱼罐头为基体进行回收试验,方法的回收率在71.5%～88.6%范围。     

水产品中14种磺胺类药物残留的HPLC法同时测定

建立了HPLC法同时分离并检测鱼、虾等水产品中14种磺胺类抗菌药物。样品经无水硫酸钠脱水后,乙腈提取药物,再用乙腈饱和正己烷脱脂净化。以乙腈-3％冰醋酸为流动相,采用梯度淋洗,于268nm波长处检测．该法的检出限为0．01～0．02mg／kg,样品的加标回收率为66％～92％。     

高效液相色谱法测定水产品中喹乙醇的残留量

建立了水产品中喹乙醇残留量的测定方法。主要研究了样品的预处理方法,提出了以水为提取剂,以硼砂一硫酸锌为高效蛋白去除剂的样品处理方法。该方法灵敏、准确,适合于水产品中微量喹乙醇残留量的测定。方法的检出限为40μg／kg。