## 2 Solid-Phase Microextraction
On the other hand, autistic children exhibited lower concentrations of methoxy-phenyl-oxime, 3-ethyl-pyridine, acetophenone, and 2-heptanone compared to the control group. In 2016, asimple glass device was constructed for the extraction of cyanide and thiocyanide ions from environmental and biological fluids [21]. The system consisted of a glass tube equipped with two valves and a movable glass slide positioned at its center (Figure 3). It incorporates an acceptor phase comprising a polyurethane foam treated with a Hg(II) dithiamate complex, fixed in a cylindrical tube. The principle of the method is based on the interaction of the acceptor phase with the headspace, followed by measuring the absorbance of mercury (II) dithiamate recovered from the polyurethane foam sorbent. The complex was formed in acidic conditions using 1.5 M H\({}_{2}\)SO\({}_{4}\). The method was applied for the determination of both ions in saliva samples obtained from smoker and non-smoker volunteers. One of the disadvantages of the method is the utilization of the highly toxic mercury. A polyamide/graphene oxide/polypyrrole nanofiber was synthesized using electrospinning and utilized for the HS-SPME of methamphetamine in urine samples [20]. The sorbent was characterized by Fourier transform infrared spectroscopy (FT-IR) and field emission-scanning electron microscopy (FESEM). The experimental parameters were optimized using a rotatable central composite design. It was concluded that the sample  
Figure 3: Schematic representation of the designed glass device. (Adopted from [21] with permissions). Figure 2: Schematic representation of the MOF-based SPME fiber fabrication and comparison of slopes of the calibration curves using direct immersion and HS sampling modes. (Adopted from [16] with permissions). pH of 11.5 containing 750 mg NaCl was sufficient to obtain an LOD of 0.9 \(\upmu\)g/L. After sampling at 40 \({}^{\circ}\)C, the analytes were thermally desorpted in the GC inlet at 240 \({}^{\circ}\)C for 3 min. The fiber-to-fiber reproducibility was found to be less than 12.3%, while the accuracy of the method ranged between 5.8 and 13.5% expressed as relative error. According to the authors, the manufactured nanofibers offered a high surface-to-volume ratio and sufficient mechanical, thermal, and chemical stability. Amphetamine-like stimulants have been determined in human urine using GC-MS after microextraction [19]. The analytes were extracted using acid-oxidized multiwalled carbon nanotubes coated onto a stainless-steel wire. The attachment of sorbent on the wire was performed using a simple physical adhesion approach. The SPME was thermally conditioned at 250 \({}^{\circ}\)C, while the urine sample was incubated at 80 \({}^{\circ}\)C for 10-60 min. An HP-5 MS capillary column was used for the separation of the analytes using a thermal gradient program up to 175 \({}^{\circ}\)C. The quantitation of the compounds was carried out in selected ion monitoring (SIM) mode with one and two quantification and confirmation ions, respectively. The linearity of the method ranged between 1 and 1000 \(\upmu\)g/L with adequate sensitivity (LODs: 0.2-1.3 \(\upmu\)g/L) for this type of analysis. The method was applied to the analysis of urine samples obtained from young persons who were suspected of the consumption of amphetamine-type stimulant drugs. The research group of [PERSON] developed a magnetic HS adsorptive microextraction for lung cancer diagnosis [22]. Two endogenous aldehydes, namely hexanal and heptanal, were identified as lung cancer biomarkers in saliva. The method is based on a modification of magnetic headspace adsorptive microextraction followed by GC-MS analysis. A neodymium magnet is employed to hold the magnetic sorbent (containing magnetic nanoparticles) in the headspace vial. The saliva samples were collected using Salivette swabs and centrifuged at 6000 rpm to remove phlegm and food leftovers. The acetonitrile used for the analytes desorption resulted in an extraction recovery of 61-97% following a simplex-centroid mixture design.