Talanta 77 (2009) 1534–1538 Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta Multicommutated flow system for the determination of glucose in honey with immobilized glucose oxidase reactor and spectrophotometric detection Alexandra Sixto, Moisés Knochen ∗ Universidad de la República, Facultad de Química, Cátedra de Química Analítica. Av. Gral. Flores 2124, 11800 Montevideo, Uruguay article info Article history: Received 7 August 2008 Received in revised form 19 September 2008 Accepted 22 September 2008 Available online 27 September 2008 Keywords: Multicommutated flow system Glucose oxidase Honey Immobilized abstract A new automated method for the determination of glucose in honey is proposed. The method is based on multicommutated flow analysis (MCFA) and employs an immobilized glucose oxidase reactor and spectrophotometric detection at 505nm of the red quinoneimine formed (Trinder’s method). The calibration curve obeyed a second order equation in the range 0–0.14gL -1 (h = -2.2199 C 2 + 1.3741C + 0.0077, r 2 = 0.9991, where h is the peak height (absorbance) and C the concentration in g L -1 ). The method was validated analyzing eight commercial samples, both by the AOAC 954.11 and 977.20 official methods. According to Student’s t-test of mean values, at the confidence level of 95% the results obtained with the proposed method were in agreement with those obtained by the official methods. Precision (s r (%), n =10) was 3% and the sampling frequency of the system was 20 samples h -1 . © 2008 Elsevier B.V. All rights reserved. 1. Introduction Sugars are the principal constituents of honey. Aside from deter- mining its nutritious and energetic value, they influence some of its important physical characteristics. Glucose is the monosaccha- ride responsible for the crystallization; honeys with high fructose content and low glucose content are less susceptible to crystalliza- tion, which is a phenomenon that decreases the acceptation of this natural product by the consumers. Honey acidity is also strongly related to the glucose content, and the rate fructose/glucose is related to the genuinity, a value below 1 indicating adulteration or the proliferation of osmophiles yeast [1]. The determination of sugars in honey may be achieved by clas- sical procedures, such as those specified in the AOAC standard method [2]; these methods are usually slow and tedious, involving the isolation of the analyte from the matrix. In the aforementioned AOAC method this is carried out by means of classical chromatog- raphy involving a column filled with activated carbon and Celite ® followed by two different volumetric titrations. The column sep- aration step takes no less than 2 h per sample to which the time necessary for two volumetries should be added. Alternatively glu- cose may be determined by HPLC with a refractive-index detector [3]. ∗ Corresponding author. Tel.: +598 2 9241808. E-mail address: mknochen@fq.edu.uy (M. Knochen). A simpler way to achieve the desired selectivity is employing an enzymatic reaction that is inherently selective. Most com- mon selective procedures for the determination of glucose are based on the catalytic activity of glucose oxidase. Conventional enzymatic methods are costly due to the high consumption of enzymatic reagent, but this disadvantage has been success- fully overcome by using immobilized enzymes. This strategy has been widely used in flow injection analysis (FIA) [4,5] where a number of papers have been published describing the use of microcolumns filled with immobilized enzymes as a part of flow systems [6–14]. Various alternatives such as physical adsorption, microencapsulation in membranes, sol–gel entrapment, cross link- ing or covalent attachment have been explored in the design of suitable flow-through packed-bed, open-tubular reactors or optical/electrochemical biosensors. The advantage of employing a column reactor in comparison to integrated biosensors is the ability of entrapping a much large amount of enzyme. A different flow-based approach is sequential injection analysis (SIA) [15,16]. This technique has been developed to address some drawbacks of FIA, namely the high consumption of reagents and the use of multi-channel manifolds. Methods exploiting this technique for the determination of glucose employing enzymes, have been reported [17,18]. More recently, a different flow technique called multicommu- tated flow analysis (MCFA) was introduced [19–21]. MCFA shows interesting advantages for automation. It is based on flow systems, where a number of solenoid valves, acting as independent commu- tators configure a flow network. Solenoid valves are independently 0039-9140/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2008.09.030