## 6 Recent Advancements in Analytical Methods
### Instrumental Analysis
#### 6.4.4 GC-Ms  
GC-MS systems are also frequently used for the quantification of BPA. Helium is usually employed as a carrier gas at a constant flow ranged from 0.76 mL min\({}^{-1}\)[9] to 1 ml min\({}^{-1}\)[81]. Spitless injection mode has been applied, while the injection temperature was reported as 280-300 \({}^{\circ}\)C. The oven temperature was reported to start from 100-150 \({}^{\circ}\)C, and to reach 280-300 \({}^{\circ}\)C. The MS was mostly operated in electron ionization mode (70 eV) [88; 89; 111], however, MS operated in negative chemical ionization also has been reported [112]. Ion source temperature and MS quadrupole temperature was used at 230 and 150 \({}^{\circ}\)C, respectively [81; 88; 89; 111]. Before analysing samples by GC-MS, a derivatization step is needed to modify the slightly polar properties of BPA molecules thus producing a compound that is suitable for GC analysis (lower polarity, higher volatility, higher stability, and higher peak efficiency and detectability) [113]. Frequently used derivatization approaches include silylation [114], and acetylation [12]. Extracts obtained after clean-up steps were derivatized with commercially available derivatization reagents, such as acetic anhydride [9; 12; 14], N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) [115], N-methyl-N(trimethylsilyl)-trifluoroacetamide [6], and pentafluorobenzoylchloride (PFBCI, 5% \(v/v\) in hexane) [13].  
The mass spectrum of extracts derivatized with acetic anhydride displayed m/z 213 as the most abundant ion [9]. This is probably due to benzylic carbocation, resulting in the loss of methyl group from BPA. The resulting ion with m/z 213 was very stable resulting in it being the base peak in the mass spectrum [28]. [PERSON] et al. reported m/z 213 as the main ion with further fragments including m/z 228 (molecular ion), 110, and 91 [115]. While m/z 213 ion was used for the quantification, m/z 228, 255, 270, and 312 have been used for the qualification of BPA in extracts from meat and fish samples in GC-MS [81; 88]. On the other hand, mass spectrum of BPA derivatized with BSTFA containing 1% trimethylchlorosilane (TMCS) showed m/z 357 as the most abundant ion, used for the quantification, with m/z 372, 207, and 73 being used for the confirmation [114; 116]. [PERSON] et al. used selected ion monitoring mode for the analysis of BPA derivatized with PFBCI where the quantification ion was m/z 616, with m/z 408 being used for confirmation [13]. However, [PERSON] and [PERSON] reported m/z 601 and 616 as quantifier ions for GC-MS using electron ionization and negative chemical ionisation (Isobutane was used as ionization gas), respectively, while m/z 195 and 617 were used as qualifier ions [112]. Finally, the fragmentation pathway of BPA was studied using Orbitrap MS in negative ion mode. Product ions at m/z 211.07618, 133.06488, and 93.03336 were detected using this method probably due to the losses of CH4, phenol (C6H6O), and isopropylphenol (C9H10O) from the precursor ion [117].  
[PERSON] et al. reported the LOD and recovery of BPA from canned foods using GC-MS as 2 ug/kg and 81-103%, respectively [12]. On the other hand, [PERSON] and [PERSON] reported a LOQ of <10 ug/kg for foods of low-fat content (<1%) and <20 ug/kg for foods containing >1% fat [9]. In comparison to the reported values of BPA detected using LC-MS (LOD: 0.1-1.2 ug/kg, LOQ: 0.01-3.14 ug/kg, and recovery: 62-120%), meat samples analysed with GC-MS showed LOD: 0.00013-1 ug/kg, 0.0004-20 ug/kg, and recovery 42-112% (data reported in Table 5). Although acceptable ranges of LOD and LOQ of BPA from food samples has been mentioned in the literature, GC-MS is less used than LC because of the additional sample preparation associated with the derivatization step.