# Methods for Determining Polycyclic Aromatic Hydrocarbons (PAHs) in Milk: A Review
## 3 PAH Detection Methods in Milk and Dairy Products
### Instrumentals Detection Methods
#### 3.2.1 HPLC  
Liquid chromatography (LC) uses a liquid as the mobile phase. It is used mainly for the analysis of organic compounds [25]. HPLC combined with a fluorescence detector (FLD) is widely used to determine PAHs in food matrices. It is most often chosen for its selectivity and sensitivity. Other detectors such as ultraviolet-visible (UV-Vis), diode-array (DAD), and fast-scanning fluorescence detector (FSFD) are also used, but to a lesser extent and often as a supplementary method to confirm results. The FSFS working method is based on measuring the outflow spectrum from the chromatographic column. The results are recorded at a fixed excitation (or emission) wavelength by scanning the emission (or excitation) wavelength at high speed, yielding three-dimensional chromatograms [86]. Methods can also be developed for the equipment available in a given laboratory. Liquid chromatography coupled with mass spectrometry (LC-MS) is not often the method of choice due to the difficulty of obtaining the adequate ionization of PAH molecules. The solution to this can be complicated without giving satisfactory results at the same time [25; 87]. PAHs are very stable molecules and are difficult to ionize at atmospheric pressure by commonly used methods (electrospary ionization (ESI) or atmospheric pressure chemical ionization (APCI)). The difficulty in ionizing these molecules arises from their non-polar nature. Atmospheric pressure photoionization, as employed by [PERSON]'s team [88], may offer a solution to this challenge. This method demonstrated a sensitivity 60 times higher for detecting PAH metabolites compared to conventional ionization techniques, which are typically ineffective for non-polar molecules [89]. Unlike GC, HPLC-FLD does not have problems caused by the low volatility of PAHs. However, some PAHs exhibit low fluorescence (e.g., cyclopenta[cd]pyrene), so analyzing deficient contamination levels is difficult [85]. [PERSON] et al. [80] used the HPLC-FLD method to analyze various dairy products: human, cow, condensed, and infant formula. They achieved recoveries of 90% and above. They concluded that this analytical method is suitable for testing various dairy products. [PERSON] [90] and his team used HPLC to analyze potential exposure to PAHs contamination, using markers that were OHPAHs. They are less lipophilic than PAHs and, as metabolic products of PAHs, can be a good indicator. They used fast-scanning fluorimetric detection. They obtained recoveries as low as 50%, depending on the extraction method. This indicates the need to adjust the method and the importance of choosing the extraction method. This is one of the few studies focusing on OHPAHs in PAHs hazard analysis. [PERSON] et al. [91] also tested differentiated samples--human milk and infant formula--but did not use markers, so the most popular HPLC-FLD method was used. They obtained results showing that human milk had higher contamination levels than infant formulas. This may have been due to the place of living of the motherswhose milk was tested. [PERSON]'s team [79] tested with the same chromatographic method and detector cow milk, goat milk, and plant drinks achieved varying levels of recovery (70-115%) depending on the specific PAH. They also included in the analysis the effect of solvents on recovery. They emphasized that technological processing (thermal treatment and skimming) can affect the content of PAHs in milk and beverages, which should be taken into account in planning legislation. Like [PERSON] et al. [90], [PERSON] et al. [92] investigated the metabolites, OHPAHs, and PAHs themselves. However, they used fluorescence detection rather than fast-scanning fluorometric detection. They obtained recoveries of 79-116%. They assessed that the behavior of PAHs and metabolites in media, especially aqueous media, makes quantitative analysis difficult. [PERSON]'s team [93] studied the content of PAHs in heat-treated milk. To confirm the results obtained with HPLC-FLD, they additionally used HPLC/UV-Vis-DAD/APCI-MS.