# Solid-Phase Microextraction Techniques and Application in Food and Horticultural Crops
## 1 Introduction  
The composition of food is incredibly diverse and complex, containing proteins, carbohydrates, minerals, vitamins, etc. Such complex compositions prompt the need for advanced methods in quality and safety evaluation. For example, most food products have a defined shelf-life. Thus, knowing the original and modified chromatographic patterns of fresh and processed/stored food products is essential in determining the compositional changes that food products may undergo over the time, such as microbial activity or the leaching of chemicals from packaging materials. In addition, the analysis of pesticides is a primary focus in the safety evaluation of food products. Ideally, a method for pesticide analysis in food should be rapid and easy to run with a minimum use of solvents, while providing a certain degree of selectivity and covering a wide scope of analyte-matrix combinations [1]. Additionally, more automated methods of analysis have the advantage of high sample throughput and minimize errors associated with human error [2]. Solid-phase microextraction (SPME) is able to meet most of these requirements via the integration of sampling, extraction, concentration, and sample introduction into a single solvent-free step. It was first developed and initially reported in the late 1980s/early 1990s by [PERSON] and co-workers [3; 4; 5]. It has since been developed as a sample preparation tool for a wide range of applications, such as food adulteration analysis, water analysis, food analysis, wine and beer analysis, pharmaceutical and biomedical analysis, soil analysis, etc. [6; 7; 8; 9; 10; 11; 12; 13]. The aim ofthis review is to focus on recent work that reports on the use of SMPE techniques in the analysis of food and horticultural crops. The major advantages of SPME include its easy miniaturization, automation of the analysis procedure, and convenience in coupling with gas chromatography (GC), high-performance liquid chromatography (HPLC) or capillary electrophoresis (CE). Due to the complexity of food matrices and the low concentration of the analytes analyzed, traditional sample preparation methods involve multiple sample pre-treatment steps; that is, the isolation/extraction of the components of interest from the sample matrix, purification, and then pre-concentration in order to reach sufficient sensitivity for a particular analytical method. Once the sample is prepared, the analysis is then run on the instrument of choice, such as a GC or a HPLC. In contrast to commonly used liquid-liquid extraction (LLE) or solid-phase extraction (SPE) sample preparation methods, SPME involves just two distinct analyte transfer steps: (1) the adsorption/extraction of the analyte into a layer of adsorptive material usually coated on a fused silica fiber, followed by (2) the transfer (desorption) of the adsorbed analytes from the fiber into the inlet of a chromatography column [14]. Extraction (on the SPME fiber) is carried out either via the direct immersion (DI) of the fiber into a liquid sample, or via exposing the fiber to the sample vapor phase containing volatile analytes (headspace extraction (HS)). Analytes then adsorb, and accumulate on the coated fiber. After a certain period of time, the analyte concentration in the SPME layer will reach an equilibrium level. The fiber is then removed and the sample is injected into a gas chromatograph via thermal desorption from the fiber (i.e., heating the fiber). For liquid chromatography, the desorption of analytes into a solvent occurs before the injection of the resultant solution into a HPLC column. Not only does the use of SMPE provide a simpler sample preparation process, decreasing the time required to process samples, but it should also lead to a reduction in errors associated with the procedure, as statistically, the amount of uncertainty in a method is directly related to the number of steps it contains. A SPME configuration which enables larger samples to be collected from a sample matrix is the prep and load solid-phase microextraction (PAL SPME) Arrow.