A capillary electrophoresis method for free fatty acids screening and acidity determination in biodiesel

Abstract

The advent of policies that incentivize or require alternative diesel fuels has increased the demand for the development of fast analytical methods aiming for the quality control of these fuels. This study approached an alternative method for the determination of biodiesel acidity employing capillary zone electrophoresis based on free fatty acids screening and quantification. Sample preparation comprised vortex-assisted liquid-liquid extraction of free fatty acids and was a crucial step for analysis. It was studied through a 3 2 full factorial design considering sample mass and the stirring time. Then, solvent suitability was evaluated univariately. The free fatty acid screening was carried out employing a capillary zone electrophoresis method able to separate C16:0, C18:0, C18:1 n-9, C18:2 n-6, and C18:3 n-3, major fatty acids in a variety of vegetable oils used for biodiesel synthesis. In addition to the straightforward sample preparation protocol, the running time of the developed method was only 12 min. Moreover, ultraviolet absorption indirect detection of analytes was approached to avoid analytes derivatization, considering the lack of chromophore groups in saturated fatty acids. Statistical tests did not evidence any significant differences in the biodiesel acidity determination expressed in percentage of free fatty acids when comparing the proposed capillary zone electrophoresis method and the traditional potentiometric titration approach within the 95% confidence interval, which demonstrates the suitability of this alternative method for the biodiesel quality control in routine.

Strategies for capillary electrophoresis: Method development and validation for pharmaceutical and biological applications—Updated and completely revised edition

“…This approach is somewhat similar to the one used in cloud-point extraction, where a surfactant above the CMC is used for the extraction [492][493][494]. These are both considered mature approaches, and most of the recent papers describe different modes to improve the extraction process using ultrasound (fluoxetine and norfluoxetine enantiomers [383]) or vortex (quinolone antibiotics in honey [491], free fattyacids in biodiesel [495]) as well as the application of those methods toward the analysis of specific molecules (such as antipsychotic, phenothiazine drugs in urine reaching LODs in the 2-10 nM range [496]). Last but not least, several groups performing for in vivo sampling have reported microdialysis [497][498][499][500], an approach that can now be performed using air-assisted flow gating [501].…”

Fatty acids analysis by capillary electrophoresis: Fundamentals, advantages and applications

“…Focusing on the use of TSH capillary, combined with the BGE composition of 15 mM NaH 2 PO 4 /Na 2 HPO 4 buffer (pH 7), 4 mM SDBS, 8.3 mM Brij R 35, 45% v/v ACN, and 2.1% v/v 1-octanol, this methodology was applied to determine FAs over the years. Hydrogenated vegetable fat, butter, margarine, and filled cookies [11], pequi fruits [30,34], extra virgin olive oil, virgin olive oil, soybean oil, and biodiesel [11,32,36], forages [29], analysis of FAs in liver rats submitted to a specific diet [31], chocolates [33], milk adulteration [35], and bottled butter [10], have been analyzed by CE, showing the potential of this method for the determination of a range of FAs in challenging samples and different applications. However, some works used the same BGE with TSP capillary for analysis of FAs in olive oil [26], in hydrogenated vegetable fat, and in spreadable processed cheese [27,28], in pumpkin seed oil and moisturizing cream with this oil in its composition [6], in encapsulated vegetable oil supplements [7], and in hops [38].…”

“…Nevertheless, this parameter is not only important in food analysis but also in other types of matrices, since determining acidity in biodiesel fuel is a strategy used to indicate product quality. Through the quantification of FAs, in this analysis, it is possible to identify errors in the production process and indicate the presence of water in the fuel [36].…”

“…Based on this, Sato et al were the first to report an acidity assay of biodiesel samples by CZE-UV since the classical method employed for this in quality control is potentiometric titration, which has certain limitations that can increase analysis time and reduce accuracy [36]. The novelty of this method, published in 2021, lies in the optimization of biodiesel sample preparation using a complete factorial design 3 2 , considering sample mass and stirring time as variables, which showed that 0.7 g of sample and 7 min of stirring time resulted in a nonsignificant baseline instability in the electropherograms [36]. After that, other solvents for sample solubilization were also tested including EtOH and isopropanol.…”

Separation of unsaturated C18 fatty acids using perfluorinated‐micellar electrokinetic chromatography: I. Optimization and separation process

“…Micellar electrokinetic chromatography (MEKC) can be used for the separation of FAs [ 6 , 7 , 8 ], including detection in real matrixes [ 9 , 10 , 11 ], as well as nonaqueous capillary electrophoresis [ 12 ]. In the latter case, the separation is performed using organic solvents (acetonitrile, methanol, and isopropanol) in the presence of aqueous ammonia or ammonium acetate.…”