# Methods for Determining Polycyclic Aromatic Hydrocarbons (PAHs) in Milk: A Review
## 3 PAH Detection Methods in Milk and Dairy Products  
### Extraction and Clean-Up Methods  
[PERSON] et al. [72] found differences in PAH levels depending on the form of milk (Table 2). In UHT liquid milk, PAH was at a level of about 6.07 ug/g, and in powdered milk 8.2 ug/g. The loss of low-molecular naphthalene due to degradation or volatilization during analysis was also noted. [PERSON] et al. [73] noticed that milk with a higher fat content contained more PAHs. Studies provided by [PERSON] et al. [74] indicated that high-molecular-weight PAHs were significantly lower in skimmed milk. The explanation is that PAHs are highly lipophilic compounds. Studies have shown a positive correlation between fat and PAHs in milk. Therefore, an important aspect during the preparation of samples for analysis is homogenization by thorough mixing, shaking or sonication of milk. Otherwise, the results may be unreliable. [PERSON] et al. [73] optimized the QuEChERS method in terms of the use of an appropriate mixture of extraction solvents and the use of deionized water in the EMR-Lipid procedure. It was found that the best recovery and precision parameters are obtained using acetonitrile  
Figure 3: Selecting a method for determining PAHs in milk and milk products. QuEChERS—SPE quick, easy, cheap, effective, rugged, and safe; HPLC—high-performance liquid chromatography; GC—gas chromatography; FLD—fluorescence detector; UV—ultraviolet detector; HS—HeadSpace; MS—mass spectrometer detector. and acetone in a volume ratio of 3:2. On the other hand, the recovery parameter was improved by using 3 mL of deionized water for the activation of EMR-Lipid. Also, [PERSON] et al. [75] used the QuEChERS method for PAH extraction. Only 16 PAH compounds standards were used for the study as an indicator of environmental pollution. Recovery in the range of 67.90 (for Chrysene)-99.76% (for Indeno(1, 2, 3-CD), pyrene was obtained at LOD values from 0.3 to 1.0 ng/g, and LOQ values from 1.0 to 4.0 ng/g). However, [PERSON] et al. [76] used HeadSpace solid-phase microextraction as a solvent-free method that does not require the pre-cleaning of the milk sample. It was not explained why a mixture of only 10 PAHs was used as a standard. [PERSON] and team [77] tested three liquid extraction methods for preparing milk samples for PAH determination using a gas chromatograph with flame ionization detector and mass detector. The first method was preceded by saponification and gave satisfactory results only for PAH with low molecular weight (LMW). The researchers [78] noticed a significant effect of saponification temperature on the analysis result. The higher the saponification temperature, the greater the losses in LMW. Also [PERSON] et al. [79] and [PERSON] et al. [80] used the saponification method using the same chemicals as [PERSON] [77]. However, saponification was carried out for 30 min at 60 \({}^{\circ}\)C, cyclohexane or acetonitrile was used for extraction. The researchers observed the relationship between the recovery and volatility of PAHs. The more volatile the compounds, the lower the recovery, i.e., the greater the analyte losses. [PERSON] and team [80], with the optimization of the method, tried three extraction solvents, i.e., hexane, cyclohexane, and toluene, and did not notice any differences in extraction efficiency. The dependence of extraction efficiency on saponification parameters such as sodium hydroxide concentration and ethanol concentration, and process time was also noted. The best PAH extraction results were observed at a concentration of 3-0.6 M NaOH and 60-100% ethanol. In the second method, they [77] used detergent solution extraction. One of the distinguishing features of the method was the use of a large volume of the sample for extraction, i.e., 250 mL of milk in a sample:detergent ratio of 1:1. Because the temperature of 90 \({}^{\circ}\)C was used in the extraction, a lower recovery of LMW was obtained than HMW PAHs. The third method tested by [PERSON] et al.