Selectivity of a Lithium‐Recovery Process Based on LiFePO4

The demand for lithium will increase in the near future to 713,000 tonnes per year. Although lake brines contribute to 80% of the production, existing methods for purification of lithium from this source are expensive, slow, and inefficient. A novel electrochemical process with low energy consumption and the ability to increase the purity of a brine solution to close to 98% with a single‐stage galvanostatic cycle is presented.     

High-precision quadruple isotope dilution method for simultaneous determination of nitrite and nitrate in seawater by GCMS after derivatization with triethyloxonium tetrafluoroborate

Quadruple isotope dilution mass spectrometry (ID⁴MS) has been applied for simultaneous determination of nitrite and nitrate in seawater. ID⁴MS allows high-precision measurements and entails the use of isotopic internal standards (¹⁸O-nitrite and ¹⁵N-nitrate). We include a tutorial on ID⁴MS outlining optimal experimental design which generates results with low uncertainties and obviates the need for direct (separate) evaluation of the procedural blank. Nitrite and nitrate detection was achieved using a headspace GCMS procedure based on single-step aqueous derivatization with triethyloxonium tetrafluoroborate at room temperature. In this paper the sample preparation was revised and fundamental aspects of this chemistry are presented. The proposed method has detection limits in the low parts-per-billion for both analytes, is reliable, precise, and has been validated using a seawater certified reference material (MOOS-2). Simplicity of the experimental design, low detection limits, and the use of quadruple isotope dilution makes the present method superior to the state-of-the-art for determination of nitrite and nitrate, and an ideal candidate for reference measurements of these analytes in seawater.     

Determination of UV filters in both soluble and particulate fractions of seawaters by dispersive liquid–liquid microextraction followed by gas chromatography–mass spectrometry

An analytical method to determine the total content (i.e., not only in the soluble fraction but also in the particulate one) of eight commonly used UV filters in seawater samples is presented for the first time. Dispersive liquid–liquid microextraction (DLLME) is used as microextraction technique to pre-concentrate the target analytes before their determination by gas chromatography–mass spectrometry (GC–MS). In order to release the UV filters from the suspended particles an ultrasound treatment is performed before DLLME. The ultrasound treatment time was studied in order to achieve a quantitative lixiviation of the target analytes. The type and volume of both disperser and extraction solvent, the sample volume, the pH and the ionic strength involved in the DLLME have been optimized to provide the best enrichment factors. Under the optimized conditions, the method was successfully validated showing good linearity, enrichment factors between 112 and 263 depending on the analyte, limits of detection and quantification in the low ng L⁻¹ range (10–30 ng L⁻¹ and 33–99 ng L⁻¹, respectively) and good intra- and inter-day repeatability (RSD <15%). No significant matrix effects were found. Finally, the method was satisfactorily applied to the analysis of three seawater samples from different origin. Results showed significant amounts of UV filters in the particulate fraction that would have been ignored if only the soluble fraction had been considered. This fact shows that the UV filters are also accumulated in the suspended particles contained in water, what should be taken into account from an environmental standpoint.     

Experimental Study of Stepped Solar Still Integrated with Reflectors and External Condenser

In this article, an experimental study of a modified stepped solar still with internal and external reflectors and an external condenser is presented. A suction fan is connected with the still to withdraw water vapor. A comparison between the modified stepped solar still and the conventional solar still is conducted. It is found that the productivity of the stepped still with a condenser and with both reflectors and a condenser are about 66% and 165% higher than that of the conventional still, respectively. Finally, the cost of 1 L of distillate for the modified stepped solar still and conventional solar still is estimated.     

Determination of Trace Metal Ions in SeaWater by Atomic Absorption Spectrometry After Separation/Preconcentration with Calmagite on Amberlite Xad-1180

A preconcentration/separation method for the atomic absorption spectrometric determinations of Cu(II), Ni(II) and Pb(II) ions in seawater have been established by using a chromatographic column filled Amberlite XAD-1180. The recoveries of Cu(II), Ni(II) and Pb(II) ions were quantitative (> 95%) at pH 8-9. The influences of the various analytical parameters including the amount of calmagite, amount of Amberlite XAD-1180, eluent type, etc. were investigated. The influence of the seawater matrix was also examined. Simultaneous enrichment and determination of copper, nickel and lead ions in seawater are possible with satisfactory results (recoveries > 95%, RSD <9%).     

In-syringe-stirring: A novel approach for magnetic stirring-assisted dispersive liquid–liquid microextraction

For the first time, the use of a magnetic stirrer within the syringe of an automated syringe pump and the resulting possible analytical applications are described. A simple instrumentation following roughly the one from sequential injection analyzer systems is used in combination with an adaptor, which is placed onto the barrel of a glass syringe. Swirling around the longitudinal axis of the syringe and holding two strong neodymium magnets, it causes a rotating magnetic field and serves as driver for a magnetic stirring bar placed inside of the syringe.     

缓蚀剂对船用钢在潮湿大气中的防蚀研究

模拟 90 7A钢在海水的潮湿大气环境和表面覆有薄层缓蚀剂液膜状态下其腐蚀受抑制的情况 ,利用恒电量仪连接ACM控头 ,监测其腐蚀状态 ,结合电化学阻抗谱 (EIS)的测量 ,探讨 90 7A钢在薄层缓蚀剂液膜下的腐蚀受到抑制机理 .结果表明 :此时大气腐蚀反应已转变为阳极过程控制占优势 ,在浸润后期的EIS呈现出由腐蚀介质扩散和电化学放电混合控制特征 ,如果利用恒电量激励下的等效电路模型解析 ,则可以更清楚地获知薄层缓蚀剂液膜下金属表面膜层的信息     

Determination of inorganic antimony species in seawater by differential pulse anodic stripping voltammetry: stability of the trivalent state

A simple method is described for the rapid and reliable determination of ultratrace concentrations of Sb(III) and Sb(V) in seawater by differential pulse anodic stripping voltammetry. It is based on the well-known dependence of Sb(III)/Sb(V) voltammetric response on acidity conditions. Under our optimised conditions (0.5 mol l⁻¹ HCl for Sb(III) and 5 mol l⁻¹ HCl for total Sb, respectively): (i) a detection limit of 11 ng l⁻¹ is obtained for a 10 min deposition time; (ii) no prior elimination of organic matter is needed; and (iii) antimony can be determined in the presence of natural copper levels. Particular care has been taken in order to understand the chemical processes taking place in all the solutions and reactions involved in the sampling and measuring procedures. Our results revealed the need to consider (i) the effect of photooxydation of synthetic and seawater samples on Sb speciation; and (ii) the stability of Sb(III) both in seawater samples and in the analytical solutions.     

关于过硫酸钾氧化-紫外分光光度法测定水中总氮方法改进探讨

针对海水中总氮的测定较繁琐,中间过程长,干扰物质多,分析时间长,重现性差,提出了采用硼酸-氢氧化钠缓冲体系,通过控制溶液酸碱度,消除海水中钙、镁离子对测定的干扰,实现用碱性过硫酸钾氧化-紫外分光光度法直接测定海水中总氮含量.对于成分复杂,色度较高且铵氮含量较高的地表水,采取延长消解时间,降低溶液酸碱性来抑制氨氮挥发所造...     

火焰原子吸收光谱法测定人工海水中铁的不确定度评定

对火焰原子吸收光谱法测定人工海水中铁的测量不确定度来源进行了分析,并对各不确定度分量进行了量化,求得合成标准不确定度和扩展不确定度分别为0.027mg/L和0.053mg/L.