Extraction Induced by Microemulsion Breaking: A Novel Strategy for

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Extraction induced by microemulsion breaking: a novel strategy for Mg, Mn and Zn extraction from ethyl alcohol-containing gasoline Jonas Oliveira Vinhal, Priscila Oliveira Vicentino, Priscila Kimberlim A. da Silva, and Ricardo Jorgensen Cassella Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b04363 • Publication Date (Web): 30 Apr 2019 Downloaded from http://pubs.acs.org on May 3, 2019

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Energy & Fuels

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Extraction induced by microemulsion breaking: a novel strategy for Mg,

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Mn and Zn extraction from ethyl alcohol-containing gasoline

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Jonas O. Vinhal, Priscila O. Vicentino, Priscila Kimberlim A. da Silva, Ricardo J. Cassella*

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Departamento de Química Analítica, Universidade Federal Fluminense, Outeiro de São

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João Batista s/n, Centro, Niterói/RJ, 24020-141, Brazil.

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* Corresponding author

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Email address: [email protected]

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Tel.: + 55 21 2629 2344

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Fax: + 55 21 2629 2143

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Abstract

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The determination of metals in petroleum derivates is an important issue related to

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quality control of these products. Therefore, we conducted a research work to propose

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a simple strategy for the extraction of Mg, Mn and Zn from Brazilian automotive

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gasoline, which contains ethyl alcohol, followed their quantification by flame atomic

33

absorption spectrometry (FAAS). The extraction method consisted of two steps. In the

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first step, we formed a microemulsion with the gasoline sample and the acid

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extractant solution, using 1-porpyl alcohol as dispersant agent. Afterwards, we induced

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microemulsion breaking with addition of water, yielding two immiscible phases: (i) a

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gasoline phase on top, and (ii) a water/alcohol acid solution at the bottom. Mg, Mn

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and Zn extracted from the sample were in the bottom phase. The water/alcohol phase

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was collected for the determination of the analytes by FAAS. The experimental

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parameters of the method were optimized, as well as the calibration conditions. Under

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optimum conditions, we dispersed 100 µL of the extractant solution (3.5 mol L-1 HNO3)

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through the sample (9.20 mL) using 700 µL of 1-propyl alcohol. After that, we induced

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microemulsion breakdown with 300 to 600 µL of deionized water, depending on the

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analyte. The extracts (bottom phase) were collected and analyzed using a matrix-

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matching strategy, and the adjustment of the nebulizer aspiration flow rate was shown

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to be very important to achieve a satisfactory accuracy. The method presented the

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following limits of detection: 0.02, 0.03 and 0.03 mg L-1 for Mg, Mn and Zn,

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respectively; and the limits of quantification of 0.05, 0.1 and 0.09 mg L-1. Five samples

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of Brazilian gasoline were tested using the developed method, yielding concentrations

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of Mg, Mn and Zn between 0 and 0.05 mg L-1, 0.11 and 0.17 mg L-1, and 0.22 and 0.46

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mg L-1, respectively. The analysis of spiked samples was carried out to evaluate the

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method accuracy and recovery percentages between 90 and 120% were verified.

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Keywords: extraction induced by microemulsion breaking; metals; ethyl alcohol-

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containing gasoline; FAAS

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Energy & Fuels

1. Introduction

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Automotive gasoline is a mixture of substances and contains, essentially,

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hydrocarbons with 4 to 12 carbon atoms. A number of other compounds, such as

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paraffin, olefins and aromatic hydrocarbons, can be found in gasoline. They are

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incorporated into the gasoline directly from crude oil or formed during the refining

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process.1 Commercial gasoline also contains some additives, which are generally added

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to increase its stability and to reduce the precipitation of solids in the internal parts of

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the engine.2

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Brazilian gasoline presents special characteristics, since the current legislation

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in Brazil imposes the addition of anhydrous ethyl alcohol at 25 and 27.5% (v/v) to

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regular and premium gasoline, respectively. This composition confers specific physical-

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chemical properties to Brazilian gasoline and influences the performance of engines.3

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Some substances present in gasoline can react with the oxygen present in the

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atmosphere, resulting in the formation of solid deposits that adhere to the inner parts

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of engines. Several factors can influence the formation of these solids, such as

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temperature, storage time and the presence of metals, which catalyze the reactions

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with oxygen.3 On this basis, the estimation of the concentrations of Mg, Mn and Zn in

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gasoline is of fundamental importance due to their effect as catalysts in oil

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degradation.

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Metals are present in gasoline and other fossil fuels due to different factors.

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They are naturally found in crude oil, especially iron, nickel and vanadium,4 and can be

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directly transferred to the derivates. They can also be incorporated to the derivates as


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contaminants during the refining process, storage and transportation, and due to their

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presence in additives largely employed to improve fuel characteristics.5-7

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The quantification of metals in gasoline and petroleum derivates can be

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performed using a wide variety of sample preparation strategies and different

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analytical techniques.8 The current literature reports several approaches for metal

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determination in petroleum derivates, such as (i) direct analysis of the sample using

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the available instrumentation, (ii) direct analysis of the sample after its dilution with a

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suitable organic solvent, (iii) conversion of the sample into an emulsion/microemulsion

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prior to instrumental analysis, (iv) transference of the targeted metals to a simpler

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medium (in general, an aqueous solution) and (v) total mineralization of the samples in

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order to eliminate the high carbon content and simplify the matrix.

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Special attention should be given to sample preparation methods that involve

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an extraction process, since these methods allow the transference of the analytes to a

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phase that is, in general, less susceptible to interferences during the measurement

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step. In this field of study, we developed, in 2010, the extraction induced by emulsion

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breaking (EIEB).9 In the EIEB, the analytes are extracted from the complex organic

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liquid to the aqueous medium during the breakdown of an emulsion, mediated by a

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mineral acid. The emulsions are obtained through of vigorous agitation of the oil

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sample with an aqueous solution containing HNO3 and a surfactant, which acts as an

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emulsifying agent. Afterwards, the system is disrupted by centrifugation or elevating

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the temperature and the analytes are determined in the aqueous phase generated in

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the process. EIEB has been employed with success in the analysis of different types of

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oils, such as diesel oil,9-11 used lubricant oil,12,13 vegetable oils,14-16 mineral oil,17-18


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biodiesel18-20 and even crude oil.21-23 Recently, this approach was employed in the

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extraction and determination of Cu, Fe and Pb in automotive gasoline from Brazil.24

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The presence of ethyl alcohol in Brazilian gasoline makes difficult its

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emulsification with aqueous solutions of acids, impairing the application of EIEB for

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metals extraction from this kind of sample. To overcome this drawback, we proposed,

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in 2017, the extraction induced by microemulsion breaking (EIMB). EIMB was firstly

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tested for the extraction of Hg from the gasoline commercialized in Brazil, which

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contains approximately 25% of ethyl alcohol.25 In the first step of EIMB, a

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microemulsion was formed by dispersing the aqueous HCl solution (extractant)

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through the gasoline (sample) with the aid of 1-propyl alcohol (dispersant agent).

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Secondly, the microemulsion was disrupted by altering the proportion of water phase

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in the microemulsion, which was achieved with 300 µL of HCl solution. After elapsed

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few seconds, two phases were separated and the total Hg could be easily measured in

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the lower phase containing 1-propyl alcohol, ethyl alcohol and HCl by cold-vapor

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atomic absorption spectrometry (CV-AAS). Total extraction of Hg was observed under

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optimized conditions. The EIMB presented some advantages over EIEB, especially

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because the formation (spontaneous) and breakdown of the microemulsions were

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much faster than in the case of emulsions.

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In this work, we are proposing the employment of EIMB for the extraction and

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quantification of some metals (Mg, Mn and Zn) in the automotive gasoline

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commercialized in Brazil, which contains approximately one quarter (in terms of

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volume) of ethyl alcohol. The methodology was optimized in relation to experimental

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parameters and we used FAAS for the analysis of the obtained extracts.

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2. Materials and methods

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2.1. Instruments

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We employed a Varian, model AA240FS, flame atomic absorption spectrometer

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(Mulgrave, Australia) for the measurement of Zn, Mg and Mn analytical signals

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(absorbance) in the water/alcohol extracts from EIMB. The instrument was fitted with

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hollow cathode lamps of Mg, Mn and Zn, which were operated at 4.0, 5.0 and 5.0 mA,

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respectively. We measured the absorbance signals for Mg at 285.2 nm, for Mn at 279.5

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nm and for Zn at 213.9 nm, and using the nominal spectral resolutions of 0.5, 0.2 and

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1.0 nm, for Mg, Mn and Zn, respectively. The atomization of the analytes was carried

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out in an air-acetylene flame, which was obtained by mixing 2.0 L min-1 of acetylene

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(99.99% purity, Linde Gases, Macaé, Brazil) with 13.5 L min-1of compressed air. The

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analytical signals were measured in terms of peak height for all analytes.

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We used a roller mixer from Biomixer (Curitiba, Brazil), model MR-II, to shake

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the microemulsions at 110 rpm before their breaking. The centrifugation of the

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microemulsions after their breaking was performed at 3500 rpm in a model 5804

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centrifuge, supplied by Eppendorf (Hamburg, Germany).

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2.2. Reagents and solutions We always employed deionized water (18.2 MΩ cm) produced with a Direct-Q 3 system, which was supplied by Millipore (Bedford, USA).

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Working solutions of the analytes were prepared just before the experiments

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from dilution of the aqueous stock solutions of Mg(II), Mn(II) and Zn(II) with deionized

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water. The aqueous standard stock solutions used in this work presented a certified 6 ACS Paragon Plus Environment

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concentration of 1000 mg L-1 of the analytes and were purchased from Sigma Aldrich

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(Steinheim, Germany).

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Organometallic standards dissolved in base oil with 1000 mg kg-1 of Mg, Mn and

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Zn (Conostan, Bale, Canada) were used in the standard addition of the analytes to the

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gasoline samples. When necessary, these standard solutions were diluted using a

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convenient organic solvent, which was always the short-chain alcohol employed in the

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experiment as dispersant agent.

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HPLC grade solvents (ethyl alcohol, 1-propyl alcohol and 2-propyl alcohol) were

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purchased from Tedia (Fairfield, OH, USA), as well as the concentrated acids (HCl and

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HNO3) used in the experiments.

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The automotive gasoline samples evaluated in the present work were obtained

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in gas stations of different brands and contained at least one quarter (in terms of

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volume) of ethyl alcohol, as indicated by the Brazilian agency of petroleum (ANP –

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Agência Nacional do Petróleo). The entire study was performed using one sample of

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gasoline fortified with known concentrations of Mg, Mn and Zn, which were

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incorporated to this sample as organometallic substances (organometallic standards in

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base oil). The samples were protected from light incidence to avoid photochemical

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degradation. Also, they were stored at laboratory temperature (21 ± 2 °C).

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2.3. Extraction procedure (EIMB)

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The preparation and breaking of the microemulsions was performed in 15-mL

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falcon tubes made of polyethylene. In order to form the microemulsions, 9.2 mL of

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sample, 100 µL of HNO3 solution (3.5 mol L-1), and 700 µL of 1-propyl alcohol were

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mixed inside the falcon tube. Afterwards, the obtained microemulsion was 7 ACS Paragon Plus Environment

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homogenized on a roller mixer for 5 min, and then broken with the addition of either

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300 µL (for Mn and Zn determination) or 600 µL (for Mg determination) of deionized

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water. Two phases appeared:(i) the organic phase on top, constituted basically by the

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original gasoline without ethyl alcohol, and (ii) the water/alcohol phase, constituted by

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HNO3, water, ethyl alcohol (already present in the samples) and 1-propyl alcohol.

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After separation of the phases, the analytes were present in the water/alcohol phase

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due to the action of the acid. The water/alcohol phase, located at the bottom of the

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flask, was collected with a Pasteur pipette and taken for analysis by direct aspiration

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into the FAAS. It is important to highlight that each aliquot of sample was treated

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separately for the determination of only one analyte at a time.

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Simulated extracts were prepared with defined quantities of ethyl alcohol, 1-

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propyl alcohol and HNO3aqueous solution, in order to give a composition similar to

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those of the extracts obtained from the microemulsion breakdown. The analysis of the

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simulated extracts was performed by FAAS using the same experimental conditions

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used in the analysis of the real extracts.

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3. Results and discussion

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3.1. Optimization of the EIMB conditions

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As mentioned previously, we used a gasoline sample fortified with the analytes

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(Mg, Mn and Zn) throughout the development of the EIMB method proposed in this

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work. All of them were incorporated to this sample as organometallic compounds

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(Conostan standards). The experimental parameters involved in the extraction process

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were optimized one at a time. 8 ACS Paragon Plus Environment

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3.1.1. Evaluation of the influence of type and volume of short-chain alcohol used for

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water dispersion on microemulsion formation

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In the first study, we evaluated the use of ethyl alcohol, 1-propyl alcohol and 2-

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propyl alcohol as dispersant agents to prepare the microemulsions. Simultaneously, we

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investigated the best ratio sample/alcohol to be employed for microemulsion

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formation, always maintaining a final volume of microemulsion of 10 mL. The

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extraction was performed using 100 µL of a HNO3 solution (7.0 mol L-1). The

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microemulsions were homogenized by shaking during 5 min using a horizontal roller

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mixer at 110 rpm. After homogenization, they were disrupted with 200 µL of deionized

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water. The experiments were performed separately for each metal.

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Microemulsions were formed instantaneously with the three alcohols,

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indicating that they are suitable for water dispersion throughout the gasoline. The data

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shown in Fig. 1 indicate that the extraction of the analytes was possible using any of

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the three alcohols tested. However, higher responses were observed when 1-propyl

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alcohol was used as dispersant in Mg determination. This distinct behavior in the case

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of Mg is probably associated to the effect of the presence of 1-propyl alcohol in the

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final extracts, which enhances Mg signals more than the signals of the other elements

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under investigation. In this context, we decided to select 1-propyl alcohol due to its

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large application as a dispersant agent in microemulsion preparation procedures26-29

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and also because higher signals were observed for Mg when this alcohol was employed

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for the dispersion of the extractant solution (HNO3 solution).

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As expected, lower responses were observed for the three analytes when the

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volume of alcohol (dispersant agent) was increased, since the amount of sample

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decreased as a consequence of the increase in the amount of dispersant agent (Fig. 1). 9 ACS Paragon Plus Environment

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Therefore, the microemulsions were formed with 700 µL of 1-propyl alcohol, 9.20 mL

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of gasoline, and incorporating 100 µL of HNO3 solution as extractant. Again,

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microemulsion breakdown was induced with the addition of 200 µL of deionized

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water.

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aqueous/alcoholic extract to be used in the determination of the analytes by FAAS.

These

experimental

conditions

provided

a

satisfactory

volume

of

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3.1.2. Effect of the acid (type and concentration) on metals extraction

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The evaluation of the effect of the acid on EIMB process was investigated by

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testing the use of either HCl or HNO3 for metals extraction from gasoline. The

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concentration of HCl was varied in the range of 0 (deionized water) and 10.8 mol L-1,

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whereas the concentration of HNO3 was tested between 0 (deionized water) and 12.6

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mol L-1. Experimental conditions employed for microemulsion preparation, optimized

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in the previous experiments, were maintained (9.20 mL sample + 100 µL acid solution

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+ 700 µL 1-propyl alcohol). The homogenization of the microemulsions was performed

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as in the previous experiment (shaking for 5 min at 110 rpm) and 200 µL of deionized

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water was introduced to induce their breakdown.

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The results showed that Mn can be extracted to the aqueous/alcoholic phase

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(extract) using only water, since no differences were observed among the solutions

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tested for extraction. This result indicated that Mn was probably found as Mn(II) free

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ions in the samples, which were easily transferred to the polar aqueous/alcoholic

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phase because of the highest affinity of water soluble species (as Mn(II)) to this phase

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(Fig. 2B). In this case, we did not have to add any concentration of acid to displace

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Mn(II) from the organic matrix.


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Energy & Fuels

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On the other hand, the concentration of either HNO3 or HCl in the extractant

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solution affected the extraction efficiency of Zn and Mg (Fig. 2A and 2C). The use of

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only deionized water or a solution with the lowest acid concentration (1.2 mol L-1 in

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the case of HCl, and 1.4 mol L-1 in the case of HNO3) was not enough to promote Mg

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and Zn extraction, indicating that a significant amount of these elements should be

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present in the gasoline as organometallic species (organometallic substances or

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complexes), which had higher affinity to the organic non-polar phase. The increase in

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acid concentrations to the highest values (3.0 mol L-1 in the case of HCl, and 3.5 mol L-1

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in the case of HNO3) allowed maximum extraction of both Mg and Zn, certainly

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because the metals were displaced from organic structures at these conditions due to

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the action of H+. As there were no differences between the effect of HCl and HNO3, we

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concluded that the extraction process depended only on H+ concentration, and was

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not dependent on the redox characteristics of the acid.

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From the data obtained in this experiment, it was possible to conclude that the

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extraction process under evaluation was affected by the acid concentration of the

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extractant solution. On this basis, as we observed that maximum extraction of the all

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analytes could be achieved with 100 µL of a 3.6 mol L-1 HNO3 solution, we decided to

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use this condition for the EIMB method.

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3.1.3. Influence of extraction time

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As mentioned previously, under the selected conditions, the microemulsions

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were formed instantaneously and presented high stability. In EIMB, the extraction

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process begins just after the microemulsion formation, especially because the

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interfacial area between dispersed (water droplets) and continuous phases (sample) is 11 ACS Paragon Plus Environment

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very high. However, sometimes, despite this high interfacial area available for

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extraction, the time required to accomplish the transference is relatively long.

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Therefore, in order to evaluate the extraction kinetics, the microemulsions were

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shaken during defined time intervals to evaluate the effect of extraction time. We

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evaluated the extraction time between 0 and 60 min. However, the microemulsions

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were always shaken at 110 rpm to intensify the extraction process. The other

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experimental parameters were maintained as optimized previously.

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The data presented in Fig. 3 demonstrated no influence of the extraction time

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on the process, proving that the analytes are probably transferred to the extractant

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solution dispersed through the sample just after the microemulsion formation. Even

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so, we selected a 10 min extraction time for the subsequent experiments to guarantee

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that all Mg, Mn and Zn present in the samples could be extracted.

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3.1.4. Evaluation of microemulsion breaking conditions: effect of the volume of H2O

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and HNO3 solution

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The destabilization of the microemulsions can be achieved by changing the

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proportion of their components. Therefore, the simplest way to reach the separation

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of the phase was to add a small volume of an aqueous solution to the microemulsions.

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This strategy proved to be very efficient, since just after the addition of deionized

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water, it was possible to note the formation of small droplets in the bulk of the

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microemulsions, which coalesced to form the bottom phase.

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Taking into account that the separation of the phases is one of the most

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important steps of the EIMB, we studied the effect of some variables on this process.

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As reported previously, the microemulsions could be disrupted through the variation 12 ACS Paragon Plus Environment

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of the proportion between the phases, which was achieved by adding a small volume

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of either water or a solution of nitric acid (3.5 mol L-1 concentration). The volume of

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the solutions was evaluated in the range of 200–1200 µL.

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As displayed in Fig. 4, similar results were verified when deionized water and

298

nitric acid solution were employed for microemulsion breaking. In the cases of Zn and

299

Mn, the highest responses were verified using 200 to 400 µL of the solutions to induce

300

microemulsion breakdown. Beyond 400 µL, the responses suffered a slight decrease,

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certainly due to the increase in the volume of the bottom phase recovered in these

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cases with a consequent dilution of the extracts.

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In the case of Mg, the response increased continuously when we varied the

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volume of the two solutions from 200 to up to 600 µL to promote microemulsion

305

breaking. It is possible that this increase may be related to the fact that the additional

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amount of aqueous solution used to induce the microemulsion breaking has behaved

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as an extractant solution, thus enhancing the extraction process. However, the use of

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larger volumes of these solutions caused a decrease in the analytical response,

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probably because the extraction process ceased and the final extracts were only

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diluted with the addition of these larger volumes. Based on the obtained data, we

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selected 300 µL of deionized water to promote microemulsion breakdown in the

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determination of Zn and Mn, and 600 µL of deionized water in the determination of

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Mg.

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3.2. Evaluation of the influence of the aspiration flow rate

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The final extracts obtained after application of EIMB were composed of

317

different solvents, such as water (nitric acid solution, in fact), ethyl alcohol and 113 ACS Paragon Plus Environment

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propyl alcohol. At the end of the process, these extracts were separated as a mixture

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of these solvents in the bottom phase. In FAAS, the solvent presents a remarkable

320

influence on the aspiration rate and the nebulizer performance, since they are both

321

affected by the viscosity of the solutions. Additionally, the flame characteristics area

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modified when organic solvents are introduced into the nebulization system, since

323

they change flame temperature and stoichiometry,30 thus affecting atomization rates.

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Therefore, the influence of sample aspiration flow-rate was studied in detail in order

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to adjust the suitable conditions to achieve satisfactory accuracy.

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We performed this study with a gasoline sample fortified with three different

327

concentrations (low, medium and high) of Mg, Man and Zn. Organometallic standard

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solutions of the analytes were used to fortify the samples and the recovery

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percentages were employed to evaluate the suitability of each approach. It is

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important to highlight that calibration curves used in the calculation of recovery

331

percentages were constructed with standard solutions composed of the three solvents

332

in a proportion similar to that expected in the real extract. These solutions were called

333

of “simulated extract”. In the present case, the simulated extract was composed of 300

334

µL (for Mn and Zn) or 600 µL (for Mg) of deionized water, 100 µL of HNO3 solution (3.5

335

mol L-1), 700 µL of 1-propyl alcohol and 2.5 mL of ethyl alcohol. The volume of ethyl

336

alcohol used in the preparation of the simulated extract was estimated taking into

337

account that it is present at a concentration of 25% (v/v) in Brazilian gasoline and that

338

all ethyl alcohol present was transferred to the extract.

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The maximum aspiration flow rate allowed by the instrument was tested (9.0

340

mL min-1), in addition to two other aspiration flow rates: 4.0 and 6.5 mL min-1. The

341

recovery percentages varied with the variation of the sample aspiration flow rate for 14 ACS Paragon Plus Environment

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Energy & Fuels

342

Mn and Zn (Fig. 5B and 5C). On the hand, for Mg, the sample aspiration flow rate did

343

not influence the recovery percentages (Fig. 5A).

344

We observed a lack of accuracy for Mn and Zn determination when the extracts

345

were aspirated at 9.0 mL min-1. This phenomenon was probably associated with the

346

modification of atomization conditions (flame temperature and stoichiometry) due to

347

the introduction of the alcohols present in the final extracts, which intensified the

348

differences between the real and simulated extracts. The best accuracies for Mn and

349

Zn (recoveries close to 100%) were verified when the samples were introduced at 6.0

350

and 4.5 mL min-1, respectively. Then, these flow rates were set to the measurement of

351

these analytes. The same did not occur for Mg, which presented satisfactory accuracy

352

for all aspiration flow rates tested, certainly because the atomization of Mg is less

353

susceptible to the variation of flame conditions.30 Therefore, in the case of Mg

354

measurement, the samples were introduced into the nebulizer system at 9.0 mL min-1

355

to provide maximum sensitivity.

356

The results obtained in this experiment also allowed us to conclude that a

357

convenient calibration could only be achieved if a matrix-matching strategy and a

358

suitable sample aspiration flow rate were used. In all cases, the analytes were

359

incorporated into the solutions as organometallic standards.

360 361

3.3. Estimation of the extraction efficiency

362

The efficiency of the extraction process was estimated by performing two

363

sequential extractions of the metals from gasoline and comparing the amount

364

extracted in each step. To perform the experiments, the gasoline recovered after the

365

first extraction was submitted again to the same extraction procedure, yielding a 15 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 34

366

second extract that was also analyzed by FAAS. The obtained results indicated that the

367

EIMB method was efficient to extract Zn, Mg and Mn from samples after only one

368

extraction. In all cases, more than 90% of the amount of each analyte was transferred

369

to the aqueous/alcoholic phase after the first application of EIMB, indicating that only

370

a single extraction procedure is needed to reach a quantitative extraction of the

371

analytes from the samples.

372 373

3.4. Characterization of the EIMB method

374

The analytical performance of the proposed method was evaluated through the

375

determination of its figures of merit. For this purpose, we employed calibration curves

376

prepared in the simulated extract and the best instrumental conditions set in the

377

previous experiments. The equations of the calibration curves were: A = 0.426 [Mg] +

378

0.003 (r2 = 0.995) for Mg; A = 0.109 [Mn] + 0.001 (r2 = 0.999) for Mn, and A = 0.232 [Zn]

379

+ 0.004 (r2 = 0.997), for Zn. In all cases, A represents the absorbance, and the

380

concentrations of the analytes are given in mg L-1. The limits of detection (LOD) and

381

the limits of quantification (LOQ) were estimated as recommended by Miller and

382

Miller.31 The LOD for Mg, Mn and Zn, calculated using the 3σ criterion, were 0.02, 0.03

383

and 0.03 mg L-1, respectively. In the same way, the LOQ for Mg, Mn and Zn, calculated

384

using the 10σ criterion, were 0.05, 0.1 and 0.09 mg L-1, respectively. A

385

preconcentration factor of approximately 2 was taken into consideration in the

386

calculation of these limits. We estimated the precision of the EIMB method through

387

the calculation of the relative standard deviation (RSD) of ten independent

388

determinations of the analytes in a gasoline sample spiked (as organometallic


Page 17 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

389

standards) with 0.10 mg L-1 of each analyte. The RSD observed for Mg, Mn and Zn were

390

2.8%, 6.7% and 8.1%, respectively.

391

The proposed extraction was fast, yielding a method with high productivity. We

392

spent approximately 15 min to process each individual sample, taking into account the

393

shaking time and the time spent in the formation and breaking of microemulsion.

394

Although this time seems to be relatively high for the processing of one sample, it is

395

important to have in mind that several samples can be run simultaneously, depending

396

on the capacity of the shaker device employed in the procedure.

397 398 399

3.5. Sample analysis and recovery test After

method

development,

the

optimum

conditions

obtained

for

400

microemulsion formation and breakdown were used to extract Zn, Mg and Mn from

401

five Brazilian gasoline samples, with the aim of their quantification by FAAS. We also

402

carried out a recovery test to prove method accuracy.

403

The concentrations of Mn and Zn in the samples were above the LOQ of the

404

method in all samples under evaluation, whereas Mg could only be quantified in

405

sample G1 (Table 1). The amount of Mg present in the other samples was very low and

406

did not allow that LOQ could be achieved in the analysis of the extracts. The

407

concentration of Mn in the samples ranged from 0.11 to 0.17 mg L-1, and the

408

concentration of Zn was between 0.22 and 0.46 mg L-1. Sample G1 presented the

409

highest concentration of the three metals under study, indicating that this sample had

410

the lowest quality or the highest concentration of additives.

411

As no certified reference materials of gasoline are available, method accuracy

412

was estimated using a recovery assay. The recovery assay was carried out with samples 17 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 34

413

spiked with known concentrations (0.1 and 0.2 mg L-1) of the analytes, which were

414

incorporated to the gasoline as organometallic standards. Then, the EIMB optimized

415

method was applied and the amount of each analyte recovered was calculated taking

416

into account the amount determined in the non-spiked samples. The recovery

417

percentages were satisfactory for all analytes under evaluation (Table 1), indicating

418

that the method is really capable of extracting the metals from the samples to the

419

bottom phase and allow their measurement in the obtained extracts. Recovery

420

percentages varied from 100 to 110% in the case of Zn, from 100 to 115% for Mg, and

421

from 90 to 120% for Mn.

422

We also performed a recovery assay spiking the sample G1 with the analytes in

423

the inorganic form (as metallic cations) in order to test if the method would be able to

424

extract the analytes in a different form. The results are shown in Table 1 and

425

demonstrated that we achieved a quantitative extraction (90-105%) of the cations

426

Mg(II), Mn(II) and Zn(II), indicating that the method is also efficient for the extraction

427

of the analytes when they are found as metallic cations in the samples.

428 429

4. Conclusions

430

The extraction approach developed in this research was shown to be fast,

431

simple and efficient for the separation of Mg, Mn and Zn from the Brazilian gasoline,

432

making possible their preconcentration in a water/alcohol phase. Making some

433

adjustments in the calibration strategy and in the instrumental conditions, we were

434

able to quantify the total concentration of the elements of interest in the

435

water/alcohol phase using FAAS.


Page 19 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

436

When compared to the EIEB,9-12 the EIMB method presented some advantages.

437

Firstly, the preparation of microemulsions was much easier and faster than the

438

preparation of emulsions, since there was no need of agitation to achieve a convenient

439

dispersion of one phase into other. Additionally, as the formation of microemulsions is

440

a spontaneous process, their preparation was instantaneous, occurring as soon as the

441

components were mixed. The microemulsion breaking was also induced very easily, by

442

simple addition of a low volume (300 or 600 µL) of deionized water to the

443

microemulsion. The microemulsion breaking took no more than 60 s, yielding a sample

444

preparation approach with high productivity.

445

The studies performed in this work indicated that a quantitative extraction of

446

Mg, Mn and Zn from the Brazilian gasoline can be achieved in one single step with a

447

HNO3 solution of 3.5 mol L-1 concentration and that 1-propyl alcohol can be used as a

448

dispersant for microemulsion preparation. Furthermore, the microemulsions can be

449

disrupted with the addition of only deionized water, yielding the appearance of two

450

phases. One of them (water/alcohol phase at the bottom) contained the analytes

451

extracted from the sample.

452

The quantification of the Mg, Mn and Zn in the water/alcohol phase (extract)

453

was only possible using the matrix-matching strategy for calibration. In this case, we

454

used standards solutions with a general composition similar to real extracts, which was

455

denominated simulated extract. In addition, the adjustment of the aspiration flow rate

456

of the nebulizer was obligatory to achieve a satisfactory accuracy.

457

The developed EIMB methodology was successfully employed for the

458

quantification of the metals under study in the samples of Brazilian gasoline, which

459

contained approximately 25% (v/v) ethyl alcohol. Satisfactory recovery percentages 19 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 34

460

were obtained (90–120%) in the analysis of fortified samples, proving the applicability

461

of the developed method for the analysis of this kind of sample. We believe that the

462

proposed approach can be expanded to the analysis of other kinds of fossil fuels and

463

oiled samples using other analytical techniques.

464 465

Acknowledgments

466

The development of this work was only possible due to the financial support provided

467

by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, grant

468

number 408166/2018-5) and Fundação Carlos Chagas Filho de Amparo à Pesquisa do

469

Estado do Rio de Janeiro (FAPERJ, grant number E-26/202.288/2018). This study was

470

also financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível

471

Superior - Brasil (CAPES) - Finance Code 001.

472 473

References

474 475

(1) Pereira, R.C.C.; Pasa, V.M.D. Effect of alcohol and copper content on the stability of

476

automotive gasoline. Energy Fuels 2005, 19, 426–432.

477 478

(2) Jones, E.G.; Balster, L.M. Impact of Additives on the autoxidation of a thermally

479

stable aviation fuel. Energy Fuels 1997, 11, 610–614.

480 481

(3) Teixeira, L.S.G.; Souza, J.C.; dos Santos, H.C.; Pontes, L.A.M.; Guimarães, P.R.B.;

482

Sobrinho, E.V.; Vianna, R.F. The influence of Cu, Fe, Ni, Pb and Zn on gum formation in

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the Brazilian automotive gasoline. Fuel Process. Technol. 2007, 88, 73–76. 20 ACS Paragon Plus Environment

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(4) Vouk, V.B.; Piver, W.T. Metallic elements in fossil fuel combustion products:

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amounts and form of emissions and evaluation of carcinogenicity and mutagenicity,

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Environ. Health Perspect., 47, 201–225.

488 489

(5) Saint’Pierre, T.D.; Dias, L.F.; Maia, S.M.; Curtius, A.J. Determination of Cd, Cu, Fe, Pb

490

e Tl in gasoline as emulsion by electrothermal vaporization inductively couple plasma

491

mass spectrometry with analyte addition and isotope dilution calibration techniques.

492

Spectrochim. Acta Part B, 59, 551–558.

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(6) Aucelio, R.Q.; Curtius, A.J. Evaluation of electrothermal atomic absorption

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spectrometry for trace determination of Sb, As and Se in gasoline and kerosene using

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microemulsion sample introduction and two approaches for chemical modification. J.

497

Anal. At. Spectrom. 2002, 17, 242–247.

498 499

(7) Du, B.; Wei, Q.; Wang, S.; Yu, W. Application of microemulsions in determination of

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chromium naphthenate in gasoline by flame atomic absorption spectroscopy. Talanta

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1997, 44, 1803–1806.

502 503

(8) Korn, M.G.A.; dos Santos, D.S.S.; Welz, B.; Vale, M.G.R.; Teixeira, A.P.; Lima, D.C.;

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Ferreira, S.L.C. Atomic spectrometric methods for the determination of metals and

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metalloids in automotive fuels – A review. Talanta 2007, 73, 1–11.

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(9) Cassella, R.J.; Brum, D.M.; de Paula, C.E.R.; Lima, C.F. Extraction induced by

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emulsion breaking: a novel strategy for the trace metals determination in diesel oil

509

samples by electrothermal atomic absorption spectrometry. J. Anal. At. Spectrom.

510

2010, 25, 1704–1711.

511 512

(10) Cassella, R.J.; Brum, D.M.; Lima, C.F.; Caldas, L.F.S.; de Paula C.E.R. Multivariate

513

optimization of the determination of zinc in diesel oil employing a novel extraction

514

strategy based on emulsion breaking. Anal. Chim. Acta 2011, 690, 79–85.

515 516

(11) Cassella, R.J.; Brum, D.M.; Robaina, N.F.; Rocha, A.A.; Lima, C.F. Extraction induced

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by emulsion breaking for metals determination in diesel oil by ICP-MS. J. Anal. At.

518

Spectrom. 2012, 27, 364–370.

519 520

(12) Caldas, L.F.S.; Brum, D.M.; de Paula, C.E.R.; Cassella, R.J. Application of the

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extraction induced by emulsion breaking for the determination of Cu, Fe and Mn in

522

used lubricating oils by flame atomic absorption spectrometry. Talanta 2013, 110, 21–

523

27.

524 525

(13) He, Y-M.; Zhao, F-F.; Zhou, Y.; Ahmada, F.; Ling, Z-X. Extraction induced by

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emulsion breaking as a tool for simultaneous multi-element determination in used

527

lubricating oils by ICP-MS. Anal. Methods 2015, 7, 4493–4501.

528


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(14) Robaina, N.F.; Brum, D.M.; Cassella, R.J. Application of the extraction induced by

530

emulsion breaking for the determination of chromium and manganese in edible oils by

531

electrothermal atomic absorption spectrometry. Talanta 2012, 99, 104–112.

532 533

(15) He, Y-M.; Chen, J-J.; Zhou, Y.; Wang, X-J.; Liu, X-Y. Extraction induced by emulsion

534

breaking for trace multi-element determination in edible vegetable oils by ICP-MS.

535

Anal. Methods 2014, 6, 5105–5111.

536 537

(16) Bakircioglu, D.; Kurtulus, Y.B.; Yurtsever, S. Comparison of extraction induced by

538

emulsion breaking, ultrasonic extraction and wet digestion procedures for

539

determination of metals in edible oil samples in Turkey using ICP-OES. Food Chem.

540

2013, 138, 770–775.

541 542

(17) Cassella, R.J.; Brum, D.M.; Robaina, N.F.; Lima, C.F. Extraction induced by emulsion

543

breaking: A model study on metal extraction from mineral oil. Fuel 2018, 215, 592–

544

600.

545 546

(18) Lima, L.C.; Paixão, T.R.L.C.; Nomura, C.S.; Gaubeur, I. Combination of dispersive

547

liquid−liquid microextraction and emulsion breaking for the determination of Cu(II)

548

and Pb(II) in biodiesel and oil samples. Energy Fuels 2017, 31, 9491–9497.

549 550

(19) Pereira, F.M.; Zimpeck, R.C.; Brum, D.M.; Cassella, R.J. Novel extraction induced by

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emulsion breaking as a tool for the determination of trace concentrations of Cu, Mn


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and Ni in biodiesel by electrothermal atomic absorption spectrometry. Talanta 2013,

553

117, 32–38.

554 555

(20) Pereira, F.M.; Brum, D.M.; Lepri, F.G.; Cassella, R.J. Extraction induced by emulsion

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breaking as a tool for Ca and Mg determination in biodiesel by fast sequential flame

557

atomic absorption spectrometry (FS-FAAS) using Co as internal standard. Microchem. J.

558

2014, 117, 172–177.

559 560

(21) Trevelin, A.M.; Marotto, R.E.S.; de Castro, E.V.R.; Brandão, G.P.; Cassella, R.J.;

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Carneiro, M.T.W.D. Extraction induced by emulsion breaking for determination of Ba,

562

Ca, Mg and Na in crude oil by inductively coupled plasma optical emission

563

spectrometry. Microchem. J. 2016, 124, 338–343.

564 565

(22) Robaina, N.F.; Feiteira, F.N.; Cassella, A.R.; Cassella, R.J. Determination of chloride

566

in brazilian crude oils by ion chromatography after extraction induced by emulsion

567

breaking. J. Chromatogr. A 2016, 1458, 112–117.

568 569

(23) Wuyke, H.; Oropeza, T.; Feo, L. Extraction induced by emulsion breaking for the

570

determination of As, Co, Cr, Mn, Mo and Pb in heavy and extra-heavy crude oil

571

samples by ICP-MS. Anal Methods 2017, 9, 1152–1160.

572 573

(24) Leite, C.C.; de Jesus, A.; Kolling, L.; Ferrão, M.F.; Samios, D.; Silva, M.M. Extraction

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method based on emulsion breaking for the determination of Cu, Fe and Pb in Brazilian


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automotive gasoline samples by high-resolution continuum source flame atomic

576

absorption spectrometry. Spectrochim. Acta Part B 2018, 142, 62–67.

577 578

(25) Vicentino, P.O.; Cassella, R.J. Novel extraction induced by microemulsion breaking:

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a model study for Hg extraction from Brazilian gasoline. Talanta 2017, 162, 249–255.

580 581

(26) Brandão, G.P.; Campos, R.C.; Castro, E.V.R.; Jesus, H.C. Determination of

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manganese in diesel, gasoline and naphtha by graphite furnace atomic absorption

583

spectrometry using microemulsion medium for sample stabilization. Spectrochim. Acta

584

Part B 2008, 63, 880–884.

585 586

(27) Reyes, M.N.M.; Campos, R.C. Graphite furnace atomic absorption spectrometric

587

determination of Ni and Pb in diesel and gasoline samples stabilized as microemulsion

588

using conventional and permanent modifiers. Spectrochim. Acta Part B 2005, 60, 615–

589

624.

590 591

(28) Brandão, G.P.; Campos, R.C.; Luna, A.S. Determination of mercury in gasoline by

592

cold vapor atomic absorption spectrometry with direct reduction in microemulsion

593

media. Spectrochim. Acta Part B 2005, 60, 625–631.

594 595

(29) Cunha, F.A.Z.; Sousa, R.A.; Harding, D.P.; Cadore, S.; Almeida, L.F.; Araújo, M.C.U.

596

Automatic microemulsion preparation for metals determination in fuel samples using a

597

flow-batch analyzer and graphite furnace atomic absorption spectrometry. Anal. Chim.

598

Acta 2012, 727, 34–40. 25 ACS Paragon Plus Environment

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(30) Welz, B.; Sperling, M. Atomic absorption spectrometry: third, completely revised

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edition. Wiley-VCH, Weiheim, 1999.

602 603

(31) Miller, J.N.; Miller, J.C. Statistics for Analytical Chemistry, 3rd ed., EllisHorwood PTR

604

Prentice Hall, Chichester, UK, 1993.

605 606


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607 608

Energy & Fuels

Table 1. Results obtained in the analysis of Brazilian gasoline samples using the optimized EIMB method in µg mL-1. The results are expressed as mean ± standard deviation (n =3). The value between parentheses represents the recovery percentage verified in each assay.

609 Sample G1

G2

G3

G4

G5

Inorganic standard

Organometallic standard




0.05 ± 0.01

0.05 ± 0.01

< LOQ

< LOQ

< LOQ

< LOQ

0.10

0.16 ± 0.03 (110%)

0.14 ± 0.02(90%)

0.11 ± 0.01 (110%)

0.10 ± 0.02 (100%)

0.11 ± 0.02 (110%)

0.11 ± 0.01 (110%)

0.20

0.28 ± 0.05 (114%)

0.26 ± 0.03 (105%)

0.23 ± 0.03 (115%)

0.22 ± 0.02 (110%)

0.21 ± 0.08 (105%)

0.21 ± 0.01 (105%)

0

0.17 ± 0.03

0.17 ± 0.03

0.11 ± 0.02

0.12 ± 0.02

0.12 ± 0.03

0.13 ± 0.03

0.10

0.27 ± 0.03 (100%)

0.27 ± 0.02 (100%)

0.23 ± 0.01 (120%)

0.22 ± 0.02 (100%)

0.24 ± 0.04 (117%)

0.24 ± 0.01 (117%)

0.20

0.35 ± 0.03 (90%)

0.38 ± 0.04 (105%)

0.32 ± 0.02 (105%)

0.34 ± 0.01 (110%)

0.33 ± 0.05 (105%)

0.33 ± 0.03 (100%)

0

0.46 ± 0.04

0.46 ± 0.04

0.32 ± 0.04

0.32 ± 0.04

0.32 ± 0.04

0.22 ± 0.05

0.10

0.57 ± 0.02(110%)

0.57 ± 0.01 (110%)

0.43 ± 0.01 (110%)

0.43 ± 0.01 (110%)

0.42 ± 0.04 (100%)

0.33 ± 0.06 (110%)

0.20

0.68 ± 0.05 (110%)

0.65 ± 0.02 (95%)

0.52 ± 0.04 (100%)

0.53 ± 0.02 (105%)

0.52 ± 0.05 (100%)

0.44 ± 0.04 (110%)

Analyte

Addition (µg mL-1)


Mg

0

Mn

Zn

610 611


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

612

Page 28 of 34

List of Figures Captions

613 614

Figure 1. Influence of the volume of alcohol (ethyl alcohol, 1-propyl alcohol and 2-

615

propyl alcohol) on the extraction of (A) Mg, (B) Mn and (C) Zn from Brazilian gasoline

616

by EIMB. The total volume of microemulsion was always 10 mL. The extraction was

617

performed with 100 µL of a 7.0 mol L-1 HNO3 solution and the microemulsion was

618

broken with 200 µL of deionized water. The extraction was carried out by agitation on

619

a horizontal roller at 110 rpm for 5 min.

620 621

Figure 2. Influence of acid concentration (HCl and HNO3) on the extraction of (A) Mg,

622

(B) Mn and (C) Zn from Brazilian gasoline by EIMB.

623 624

Figure 3. Influence of the extraction time.

625 626

Figure 4. Influence of the volume of aqueous solution (deionized water and 3.5 mol L-1

627

HNO3 solution) employed to disrupt microemulsion in the EIMB procedure for (A) Mg,

628

(B) Mn and (C) Zn determination in Brazilian gasoline.

629 630

Figure 5. Influence of the nebulizer flow rate on the determination of (A) Mg, (B) Mn

631

and (C) Zn employing the EIMB procedure.

632 633 634


Page 29 of 34

Figure 1

0.40

(A)

ethyl alcohol 1-propyl alcohol 2-propyl alcohol

0.35

Response

0.30 0.25 0.20 0.15 0.10 0.05 0.00 1 0.2

2 0.7

3 1.2

4 3.2

Volume of alcohol (mL)

0.20

(B)


0.16

Response

635

0.12

0.08

0.04

0.00 1 0.2

2 0.7

3 1.2

4 3.2


0.45

(C)


0.40 0.35 0.30

Response

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.25 0.20 0.15 0.10 0.05 0.00 1 0.2

2 0.7

3 1.2

4 3.2



Energy & Fuels

636

Figure 2

1.2

(A)

Relative response

1.0

0.8

0.6

0.4

0.2 HCl HNO3

0.0 0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

-1

Acid concentration (mol L )

637 1.2

(B)

Relative response

1.0

0.8

0.6

0.4

0.2 HCl HNO3

0.0 0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

-1


638 1.2

(C)

1.0

Relatve response

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 34

0.8

0.6

0.4

0.2 HCl HNO3

0.0 0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

-1


639


Page 31 of 34

640

Figure 3

641

1.2

1.0

Relative response

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.8

0.6

0.4

0.2

Mg Mn Zn

0.0 0

10

20

30

40

50

60

70

Extraction time (min)

642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658


Energy & Fuels

659

Figure 4

1.2

(A)

Relative response

1.0

0.8

0.6

0.4

0.2 deionized water -1 HNO3 solution(3.5 mol L )

0.0 0.2

0.4

0.6

0.8

1.0

1.2

Volume used to disrupt microemulsion (mL)

660 1.2

(B)

Relative response

1.0

0.8

0.6

0.4

0.2 deionized water -1 HNO3 solution (3.5 mol L )

0.0 0.2

0.4

0.6

0.8

1.0

1.2


661

1.2

(C)

1.0

Relative response

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 34

0.8

0.6

0.4

0.2 deionized water -1 HNO3 solution (3.5 mol L )

0.0 0.2

0.4

0.6

0.8

1.0

1.2


662


Page 33 of 34

Figure 5

140

(A)

Concentration of analyte added -1 0.1 g mL -1 0.2 g mL -1 0.4 g mL

120

Recovery (%)

100 80 60 40 20 0 1 4.5

2 6.0

3 9.0 -1

Nebulizer Flow Rate (mL min )

140

(B)


120 100

Recovery (%)

663

80 60 40 20 0 1 4.5

2 6.0

3 9.0 -1


140

(C)


120 100

Recovery (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

80 60 40 20 0 1 4.5

2 6.0

3 9.0 -1



Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 34

664


Extraction Induced by Microemulsion Breaking: A Novel Strategy for

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