Novel extraction induced by emulsion breaking as a tool for the determination of trace concentrations of Cu, Mn and Ni in biodiesel by electrothermal atomic absorption spectrometry

How to overcome the difficulty in assaying Ni in biodiesel samples? Extraction induced by microemulsion breaking and square wave adsorptive stripping voltammetry could be the answer

Herein, a simple, green, and relatively inexpensive approach to determine nickel (Ni) in biodiesel samples by square wave adsorptive cathodic stripping voltammetry (SWAdCSV) is presented. A method based on the accumulation of Ni as Ni(II)-dimethylglyoxime (Ni(II)(HDMG)2) on the glassy carbon electrode was carried out in a solution containing the aqueous phase extract (APhEx) obtained from an extraction induced by microemulsion breaking (EIMB), which was achieved by adding a few microliters of ultrapure water to a microemulsion composed of biodiesel, n-propanol and a diluted HNO3 solution. The LOD and LOQ were 0.2 μg L-1 and 0.8 μg L-1, respectively, and the accuracy was evaluated by recovery assays of spiked samples and by analyzing a standard reference material. Results obtained from a comparative method (HR-CS GF AAS) were also used for this evaluation. The method was applied to biodiesel samples produced from different feedstocks. To the best of the authors knowledge, it is the first time that: 1) Ni in biodiesel is determined by a voltammetric method; 2) EIMB is applied to extract Ni from this matrix and 3) this type of sample preparation method is used with adsorptive stripping voltammetry.

A simple, fast and inexpensive approach to quantify low concentrations of iron in biodiesel by voltammetry after extraction induced by microemulsion breaking

An alternative approach to assay iron (Fe) in biodiesel by differential pulse adsorptive cathodic stripping voltammetry (DPAdCSV) is presented herein. The sample treatment involved a simple, rapid, but effective extraction of Fe from biodiesel into an aqueous phase after microemulsion (ME) breaking. Then, Fe was determined as the complex Fe(III)-PAN (1-(2-pyridylazo)-2-naphthol) on a glassy carbon electrode (GCE) in the presence of bismuth (Bi(III)). The extraction induced by microemulsion breaking (EIMB) was achieved by adding 0.80 mL of ultrapure water into a water-in-oil ME containing 7.00 mL biodiesel, 2.70 mL n-propanol and 0.30 mL of 0.25 mol L-1 HNO3 solution. No deliberate addition of surfactant was necessary to form and maintain the ME. The EIMB resulted in a 1.30 mL lower aqueous phase extract (APhEx) and an upper oily phase. DP voltammograms were recorded with a portable potentiostat, showing the potentiality of carrying out the determination out of a central laboratory. Another feature was the non-necessity of deaerating the solution to eliminate the dissolved O2. The limits of detection (LOD) and quantification (LOQ) were 1.7 μg L-1 (140 mg kg-1) and 5.5 μg L-1 (455 mg kg-1), respectively. The accuracy of the method was evaluated by recovery assays of spiked samples, by analyzing a standard reference material and by comparisons with high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS).

Ionic liquid assisted extraction induced by emulsion breaking for extraction of trace metals in diesel, gasoline and kerosene prior to ICP-OES analysis

This study describes a novel and greener ionic liquid assisted extraction induced by emulsion breaking (ILA-EIEB) method for extraction of As, Ba, Cd, Cr, Ni Pb, Sb, Sn, Tb, Te and V in fuel oils. The most influential extraction parameters were ionic liquid concentration [(1-Ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl)], HNO3 concentration, Triton X-100 concentration, and sample mass and were optimised by using full factorial and Box-Behnken designs. The optimum conditions obtained were 0.035 % 1-Ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) concentration, 18 % v/v HNO3 concentration, 15 % w/v Triton X-100 concentration, and 0.1 g sample mass. The emulsions were fully broken by using a controlled heating water bath at temperature of 80 ± 2 °C for 30 ± 4 min, followed by centrifugation at 3500 rpm for 15 min. Under the optimum conditions, the proposed ILA-EIEB method was accurate (80.1-101 %) and precise (1.9-4.7 %) for all the investigated metals. The method detection limits were 0.107, 0.013, 3.494 and 0.560 μg/g for Ba, Na, Ni and V, respectively. The optimised ILA-EIEB method was then applied in real fuel samples and metal concentration levels ranged from 0.072 to 8.610 μg/g, which were consistent with other literature reported work. Therefore, this study suggests that the examined metal ions present in fuel oils commercialised in Johannesburg, South Africa are in tolerable concentration levels and are not a threat.

A novel automatic flow-batch extraction induced by emulsion breaking platform for on-line copper determination in edible oil samples by atomic absorption spectrometry

A novel automatic flow-batch platform coupled with atomic spectrometry for on-line acidic extraction induced by emulsion breaking with heating (FB-EIEBH) for metal determination in edible oils (corn, sunflower and olive oil), was developed for the first time. The proposed system was demonstrated for copper determination in conjunction with flame atomic absorption spectrometry. The extraction of metal is accomplished after the oil emulsification with an aqueous solution consisted of Triton X-114 and nitric acid, in an on-line programmed manner. All the main parameters affecting the extraction procedure, such as oil dilution, type and concentration of surfactant and nitric acid as well as temperature and time for the emulsion breaking and phase separation, have been investigated and optimized. A mixture of oil/xylene at 10:2 proportion was found to be appropriate to use in the flow manifold. Optimum conditions were verified employing 8.0 mL of oil sample, 990 μL of extractant solution containing 10.0% m/v Triton X-114 and 10.0% v/v HNO₃. Emulsion breaking and phases separation were completed at temperature 90 °C, and time 300 s. The detection and quantification limit for copper determination was found to be 5.8 μg L^-1 and 19.3 μg L^-1, employing aqueous standards, which are proved to produce similar performance characteristics with oil-based standards. Recovery tests were executed by appropriate additions of oil-based standard solution of copper and the recoveries ranged between 94.2 and 102.4%.

Extraction Induced by Emulsion and Microemulsion Breaking for Metal Determination by Spectrometric Methods - A Review

This review focuses on extraction induced by the destabilization of emulsified systems combined with spectrometric techniques for metal analysis in oily samples. This approach is based on the formation and breaking of an emulsion (extraction induced by emulsion breaking - EIEB) or microemulsion (extraction induced by microemulsion breaking - EIMB) to transfer the analytes from the oil sample to the aqueous phase, which is separated in the process. Its simplicity, speed, and low cost have contributed to its growing popularity among researchers. However, the potential of EIEB and EIMB is far from being fully exploited. Therefore, this paper aims to provide relevant information to expand the applicability of these methods. The principle of the methods is discussed, and a brief description of emulsified systems is presented. The parameters affecting the extraction efficiency and calibration strategy are also critically discussed. Furthermore, the analytical applications of the methods are reviewed. Trends and opportunities in this field are also considered.

Extraction induced by emulsion breaking to assay Cr, Cu and Mn in asphalt samples by high-resolution continuum source atomic absorption spectrometry and its comparison with other sample preparation methods

This paper reports the development of a method based on the extraction induced by emulsion breaking (EIEB) for the determination of Cr, Cu and Mn in asphalt by high-resolution continuum source atomic absorption spectrometry. In optimized conditions, the extraction efficiency ranged from 88.6 for Cu to 104.5% for Mn. Measurements were carried out at the primary lines of the three analytes. The limits of detection were 0.02 μg g^-1 for Cr, 0.01 μg g^-1 for Cu and 7.11 ng g^-1 for Mn. The precision, expressed as the relative standard deviation, ranged from 1.0 for Cu to 9.1% for Cr. The performance of the proposed method was compared to previously reported sample preparation procedures, including microwave-assisted acid digestion (MW-AD), ultrasound-assisted acid extraction (USE), emulsification (E), and direct dilution in organic solvent (DD). The parameters evaluated were matrix effects, limits of detection and quantification, characteristic mass, precision, accuracy, sample stability and applicability for routine analysis. The methods most suitable for Cu determination were EIEB, MW-AD, USE and E. For Cr and Mn, the best results were obtained by EIEB, MW-AD and DD procedures.

Development of an extraction method for the determination of inorganic anions (chloride, sulfate and phosphate) in edible oils from different origins by ion chromatography

The present work reports the development of ion chromatography conductivity based detection analytical method for the determination of some inorganic anions (chloride, sulfate and phosphate) in vegetable oils. The analytes were extracted from samples prior to injection into the chromatographic system, employing a simple two-step procedure. In the first step, 4.5 g of the sample was vigorously mixed with 15 mL of deionized water and then mixed for 15 min on a horizontal roller. Afterwards, the mixture was sonicated for 15 min in an ultrasonic bath. Then, the mixture was centrifuged for 15 min at 5000 rpm and, after filtration through a 0.22 μm membrane, the aqueous phase was used for the determination of the analytes. A clean-up step was introduced in the analysis of olive oils in order to correct an increase of the baseline of the chromatograms. The limits of detection and quantification of the proposed method were, respectively, 0.005 and 0.02 μg g^-1 for chloride, 0.02 and 0.06 μg g^-1 for phosphate and 0.008 and 0.03 μg g^-1 for sulfate. Vegetable oils from corn, canola, soybean, sunflower and olive were analyzed and recovery tests (94.8 ± 10.1% mean recovery) were performed to attest the accuracy of the proposed method.

Extraction of trace elements by ultrasound-assisted emulsification from edible oils producing detergentless microemulsions

The aim of this study is to develop a new method for the extraction and preconcentration of trace elements from edible oils via an ultrasound-assisted extraction using ethylenediaminetetraacetic acid (EDTA) producing detergentless microemulsions. These were then analyzed using ICP-MS against matrix matched standards. Optimum experimental conditions were determined and the applicability of the proposed ultrasound-assisted extraction method was investigated. Under the optimal conditions, the detection limits (μg kg(-1)) were 2.47, 2.81, 0.013, 0.037, 1.37, 0.050, 0.049, 0.47, 0.032 and 0.087 for Al, Ca, Cd, Cu, Mg, Mn, Ni, Ti, V and Zn respectively for edible oils (3Sb/m). The accuracy of the developed method was checked by analyzing certified reference material. The proposed method was applied to different edible oils such as sunflower seed oil, rapeseed oil, olive oil and cod liver oil.

Development of a method for total Hg determination in oil samples by cold vapor atomic absorption spectrometry after its extraction induced by emulsion breaking

This work reports the development of a novel extraction method for total Hg determination in oil samples. After extracting Hg from samples it was quantified in the extracts by cold vapor atomic absorption spectrometry (CV-AAS), employing a laboratory-made gas-liquid separator (GLS) and NaBH4 as reducing agent. The extraction of Hg from samples was carried out by extraction induced by emulsion breaking (EIEB), which is based on the formation and breaking of water-in-oil emulsion between the oil samples and an extractant solution containing an emulsifying agent (surfactant) and nitric acid. Operational parameters of the GLS were evaluated in order to set the best performance of the measurement system. In these studies it was proven that the volume of sample and the concentration of HCl added to the sample extracts had significant influence on Hg response. The best conditions were achieved by adding 0.5 mL of a 0.3 mol L(-1) HCl solution on 1 mL of sample extract. The extraction conditions were also optimized. The highest efficiency was observed when 4 mL of a solution containing 2.5% triton X-100 and 15% v/v HNO3 were employed for the extraction of Hg contained in 20 mL of sample. Emulsion breaking was performed by heating at 80 °C and took approximately 20 min. The limit of quantification of the method was 1.9 µg L(-1) and recovery percentages between 80% and 103% were observed when spiked samples (2 and 10 µg L(-1)) of diesel oil, biodiesel and mineral oil were analyzed.