## 3 Sample Treatment and Analysis Methods  
### Sample Treatment Methods  
Cleanup and concentration procedures of target compounds in environmental samples are the key to the full performance of analytical methods. Table 1 shows typical sample treatment methods. One of the characteristics of recently developed methods is the miniaturization. Liquid extraction (LE) using organic solvents is the most basic extraction method for solid materials such as airborne particulates and soils. Accelerated solvent extraction (ASE) uses a pressurized extractor to increase the extraction efficiency [27]. LE includes Soxhlet extraction and supercritical fluid extraction (SFE) as well. As organic solvents, acetone, dichloromethane, \(n\)-hexane, benzene-ethanol, and \(n\)-hexane-dichloromethane are widely used. Sonication, microwaves, heating, and pressure increase the extraction efficiency with these solvents [28]. Soxhlet extraction is the most conventional method for extracting PAHs and their oxidative derivatives, such as NPAHs and OPAHs, from materials such as filters. By reflux and siphon extracting in solvents such as \(n\)-hexane, organic compounds are extracted. This is often used for extracting PAHs and NPAHs collected on polyurethane form (PUF), but the conventional LE method requires large volumes of hazardous solvent, and further concentration of these organic solvents is necessary. SFE uses the state shift of supercritical fluid between gas and liquid, depending on the critical temperature and pressure. Organic compounds are extracted into the SF solvent (liquid)and concentrated by solvent volatilization. As SF extractants, carbon dioxide (CO\({}_{2}\)), nitrous oxide (N\({}_{2}\)O), ammonia (NH\({}_{3}\)), sulfur hexafluoride (SF\({}_{6}\)), ethane, and heptane are used. CO\({}_{2}\) is the most common, because of its critical temperature close to room temperature. Liquid-liquid extraction (LLE) uses two immiscible solvents with different solubilities of chemical compounds. The addition of salt and adjusting pH can increase the extraction efficiency. LLE is effective for aqueous samples such as rain, snow, river water, and marine water. Liquid-phase microextraction (LPME), which is regarded as a miniaturized LLE, uses small volume (<mL) of hydrophobic organic solvent to extract organic analytes from aqueous solution [29]. The enrichment factor increases with decreasing the volume of extractant. LPME contains single-drop microextraction (SDME) and dispersive liquid-liquid microextraction (DLLME), which uses small volume extractant immiscible with water. From DLLME, solidification of floating organic drop-dispersive liquid-liquid microextraction (SFO-DLLME) has been developed. This uses an organic solvent with a density lower than water and a melting point close to room temperature. After mixing with the sample solution, the extractant containing organic compounds becomes solid and floats on the surface of the water solution by cooling. These methods have been effectively used for extracting trace levels of NPAHs in aqueous solutions along with OPAHs and the parent PAHs [30; 31; 32; 33]. Solid-phase extraction (SPE) uses a stationary phase to purify and concentrate organic chemicals in environmental and biological samples. Core-shell indium (III) coated with organic phase has been developed for the pretreatment of aqueous phase NPAHs [34]. Solid-phase microextraction (SPME) attracts attention because it does not require sample treatment before gas chromatograph-mass spectrometry (GC-MS) analysis. As solid phases, polydimethylsiloxane/divinylbenzene (PDMS/DVS), cold fiber (CF)--a stainless-steel wire coated with zeolitic imidazolate frameworks--and metal-organic nanotubes (MONTs), have been developed [35; 36; 37; 38; 39]. These techniques have been applied for high-performance liquid chromatography (LC)-MS/MS analysis of NPAHs [40]. Advances in the above sample treatment methods for analysis of NPAHs have been detailed elsewhere [41].