# Current Trends in Fully Automated On-Line Analytical Techniques for Beverage Analysis
## 1 Introduction  
Gas chromatography (GC) and liquid chromatography (LC) are by far the two most used analytical techniques in food analysis. These techniques are widely employed for the separation and identification of both volatile and non-volatile compounds present in beverages [1]. In most cases before the chromatographic analysis a sample preparation step is required, determining the analysis time once this stage is considered is equivalent to ca. 80% of the total analysis time [2].  
Because of the high complexity of some beverage matrices or the presence of contaminant compounds in very low quantities, choosing the proper sample preparation technique is of utmost importance to make an adequate sample clean-up that allows increasing the sensitivity of the detection stage. Sample preparation allows isolating the target analytes from the interfering components in the main matrix and enriches them, in order to identify and quantify them with precision. Although being a relatively simple process, it is critical because all errors that occur in this stage cannot be corrected, even with the best of separation or detection method available [2].  
Classical sample preparation techniques such as liquid-liquid extraction (LLE) and solid-phase extraction (SPE) [3] are the most commonly employed techniques; more recently, miniaturized solid phase techniques have also been playing a relevant role [2]. These techniques such as solid-phase microextraction (SPME) [4], in-tube SPME [5], and turbulent-flow chromatography (TFC) [6] have gained particular interest since they offer several advantages that include reduced analysis time, less solvent consume, less use of toxic solvents, automation of the extraction process, and on-line coupling to GC and LC systems.  
In a typical analysis, after the sample preparation step, the target analytes are transferred to the chromatographic system to be separated and detected, which can occur in two different ways: Off-line or on-line. In the off-line mode, the sample preparation step and chromatographic analysisare carried out separately, which means that the sample needs to be manually transferred from one system to the other. The on-line mode implies a physical connection between the sample preparation device and a chromatographic system. This mode usually employs either a valve or an interface to connect the two systems thus allowing the full automation of the analytical process [7]. Many different on-line couplings have been made to improve analysis performance, reduce the time required and increase productivity. Besides, this set up minimizes sample handling reducing analytes losses. These couplings depend on both the sample matrix and target analytes, as well as on the analytical performance required, the instruments available and the size and quantity of samples [8; 9; 10].  
Over the past years, sample preparation and analysis are moving towards the development of fully automated analytical techniques that permit extraction, separation, detection, and quantification in a single and continuous stage, usually employing tandem mass spectrometry (MS/MS) as the detector, which are becoming widely used methods in the analysis of beverages. The use of MS/MS allows the unequivocal identification and quantification of the target compounds at very low levels, improving selectivity and sensitivity especially when complex samples are analyzed. The sequential combination of sample preparation, chromatographic separation, and MS/MS systems benefits from their complementary advantages, resulting in a powerful tool able to cover the majority of challenges in beverages analysis, and simplifying routine methods [11].  
This review focuses mainly on extraction techniques and their on-line coupling with analytical instruments, mainly GC and LC. Principles, automation and on-line fully automated systems are described evidencing the main reported applications over the last decade, as well as the potential applications of this approach to the analysis of beverages in the coming decades.