# Methods for Determining Polycyclic Aromatic Hydrocarbons (PAHs) in Milk: A Review
## 3 PAH Detection Methods in Milk and Dairy Products
### Instrumentals Detection Methods
#### 3.2.2 GC  
Gas chromatography (GC) uses gas as the mobile phase and is divided into gas-solid and gas-liquid chromatography depending on the type of stationary phase. Modern stationary phases used for the GC separation of PAHs are often metal-organic structures (MOFs), graphene sheets, or graphitic carbon nitride [25]. Detection by GC-MS is relatively challenging because of the low volatility of high-molecular-weight PAHs (dibenzopyrenes). Some PAHs also separate poorly in capillary columns. There may also be interference with PAHs that are not the target of the study (not among the PAHs of particular interest, e.g., triphenylene). Compared to the 16 US EPA PAHs, the separation of the 15 EU PAHs is further hampered by their higher level of structural similarity [85]. Despite the obstacles, GC-MS is a method frequently and effectively used to separate and identify PAHs in complex matrices such as milk. It requires a small sample volume, and combining it with the HeadSpace method, solid-phase microextraction (HS-SPME) can further facilitate the entire process. This combination bypasses complex extraction methods and potential matrix-derived interferences that can occur with other extraction methods [25]. [PERSON] et al. [65] used GC and MS to determine PAHs in various dairy matrices. They rated the efficiency of the method they developed as high, with limits of detection of 1-200 ng/kg, but all detected PAHs were of the lighter type. In addition, they used various milk-based matrices. Recoveries for individual PAHs varied depending on the product tested. All were above 80%. They did not detect any PAH contamination in the baby formulas, which are based on milk processed at high temperatures, which can affect the additional formation of PAHs in milk. A similar method, as well as a column (one of the most popular for testing PAHs HP-5 MS), was used by [PERSON] et al. [83] in a study of liquid milk. Among the lighter PAHs, they identified the heavy and most toxic BaP. They also recognized the most likely possible causes of milk contamination in the study area (Taiwan): communication and heavy industry. In doing so, they did not consider the possible impact of milk processing. They did not perform recovery measurements. [PERSON] et al. [75], using GC-MS, achieved recoveries of 67.90% (Chr) to 99.76% (IcP) and only determined BaA and Chr in raw milk samples from around Bangladesh. They determined this was low; the samples showed it was from regions with \"higher human activity\". [PERSON] et al. [95] used a DB-XLB column. Using raw milk, they also focused on environmental contamination. They showed that Flu had statistically higher contamination in samples around the cement factory. They did not investigate recovery. [PERSON] et al. [72] studied various matrices, including smoked cheese and liquid milk. They did not perform recovery measurements. They assumed that some of the contamination of dairy products by PAHs occurs during technological processing, such as pasteurization. In addition, they pointed out their failure to detect naphthalene in the samples, which they linked to its degradation or evaporation during laboratory work. They identified PAHs using retention times. [PERSON] et al. [74], using GG-MS, obtained recoveries of 62.81-105.18% for the 5 \(\upmu\)g/kg value and 68.46-113.86% for the higher level--10 \(\upmu\)g/kg. They pointed out the processing optimization to reduce the accumulation of PAHs in milk. [PERSON] et al. [82] and [PERSON] et al. [62] studied infant formulas, meaning heat-treated milk-based products. The first team obtained recoveries of 95-98%, while the second team obtained 50-120% recoveries. The differences in methodology were mainly based on extractions. [PERSON] team [82] studied the European samples and found low contamination levels. [PERSON] and his co-workers [62], operating in Iran, determined more worrisome levels of PAHs in the formulas. They also noted that their levels could rise as high as 100 \({}^{\circ}\)C during processing.