Analytica Chimica Acta 694 (2011) 90–94 Contents lists available at ScienceDirect Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca Flow injection determination of free fatty acids in vegetable oils using capacitively coupled contactless conductivity detection Ahmad Makahleh, Bahruddin Saad ∗ School of Chemical Sciences, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia article info Article history: Received 23 January 2011 Received in revised form 4 March 2011 Accepted 6 March 2011 Available online 31 March 2011 Keywords: Flow injection analysis (FIA) Capacitively coupled contactless conductivity detector (C 4 D) Free fatty acids Vegetable oil abstract A single line flow injection analysis (FIA) method that incorporated a preconcentrator column packed with C 18 particles and capacitively coupled contactless conductivity detector (C 4 D) was developed for the determination of free fatty acid (FFA) in vegetable oils. The carrier stream was methanol/1.5 mM sodium acetate (pH 8) 80:20 (v/v) at a flow rate of 1.0 mL min -1 . Calibration curve was well correlated (r 2 = 0.9995) within the range of 1–200 mg L -1 FFA (expressed as palmitic acid). Sampling rate of 40–60 h -1 was achieved. Good agreement was found between the standard non-aqueous titrimetry method and the proposed method when applied to the determination of FFA in palm (crude, olein, and refined, bleached and deodorised) and other vegetable (soybean, rice bran, walnut, corn and olive) oils. The proposed method offers distinct advantages over the official method, especially in terms of simplicity, high sam- pling rate, economy of solvents and sample, offering considerable promise as a low cost automated system that needs minimum human intervention over long periods of time. © 2011 Elsevier B.V. All rights reserved. 1. 1. Introduction Oil acidity, usually determined as free fatty acid (FFA) is an important quality parameter in the oleochemical industry. It is a measure of the extent to which hydrolysis has liberated the fatty acids from their ester linkage of the parent triglyceride molecule and is routinely measured during production and storage stages [1,2]. FFA is commonly determined by non-aqueous titrimetry, using phenolphthalein as indicator. The method, however, uses large amounts of organic solvents and involves manual operation. Flow approaches (e.g., flow injection analysis (FIA) [3–5], sequential injection analysis (SIA) [6]) have been introduced as alternatives, mainly to automate the analysis, thus enhancing laboratory pro- ductivity. FIA methods have been developed for the determination of acidity in vegetable oils (olive [3,4] and palm [5]). A SIA method for the determination of acidity in vegetable oils, although con- sume less chemicals and sample, but the sampling rate was rather low (12 h -1 ) [6]. These SIA and FIA methods use spectrophotomet- ric detection and their performance can be affected by samples of different viscosities. Acidity is also an important quality indicator in other samples such as fruit juices, soft drinks, etc. As an example, a slight change in the acidity of coffee resulted in marked differences in its taste and aroma [7]. In biodiesels, FFA is one of the main factors that ∗ Corresponding author. Tel.: +60 604 653 4047. E-mail address: bahrud@usm.my (B. Saad). affect the transesterification process [6]. FIA methods, either using spectrophotometric or conductimetric detectors have been applied for the determination of fruit juice [8–10], coffee [7], vinegar [11,12] and soft drink [12] acidities. The determination of individual FFA is traditionally done by derivatization to increase its volatility, followed by GC separation. High performance liquid chromatography (HPLC) and capillary electrophoresis (CE) methods have also been used [13,14]. Since fatty acids (FAs) lack chromophores, either derivatization or indi- rect UV detection is necessary. Ion chromatography and CE coupled with conductivity detection for the analysis of short chain and long chain FAs, respectively, were also reported [14,15]. CE with C 4 D detection for analysis of FA was also described [16]. Recently, we reported a HPLC method with C 4 D detection for the profiling of FAs in vegetable oils [17]. These HPLC methods require long analysis time and consume large amounts of solvent. In this paper, we describe a new FIA method for the rapid deter- mination of FFA using C 4 D. The analytical practicality of the method was demonstrated in the determination of FFA in a few types of vegetable oils. 2. 2. Experimental 2.1. Chemicals and reagents Myristic acid (99%), palmitic acid (≥99%), stearic acid (≥99%), oleic acid (99%), linoleic acid (99%), sodium hydroxide and potas- sium hydrogen phthalate were purchased from Sigma–Aldrich 0003-2670/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2011.03.033