N tert butyldimethylsilyl n methyltrifluoroacetamide mtbstfa

Acetic acid was purchased from Thermo Fisher Scientific (Fair Lawn, NJ). Propionic acid, isobutyric acid, butyric acid, 2-methylbutyric acid, isovaleric acid, valeric acid, 2-methylpentanoic acid, 3-methylpentanoic acid, isocaproic acid, caproic acid, 2-methylhexanoic acid, 4-methylhexanoic acid, heptanoic acid, hexanoic acid-6,6,6-d₃ internal standard, N-tert-Butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA), and methoxyamine hydrochloride were purchased from Sigma-Aldrich (St. Louis, MO).

Fish skins were peeled off Tilapia specimens bred in the pilot aquaponics plant of the “Urban Farming Lab” of the Dept. of Innovation Engineering (University of Salento, Lecce, Italy), where they were distributed in glass aquaria filled with dechlorinated water and supported with two oxygen pumps. Skins were harvested when the small (length: 25.0 ± 1.1 cm, height: 9.4 ± 0.9 cm, weight: 320.8 ± 35.8 g, ST) and the big (length: 31.6 ± 0.6 cm, height: 10.9 ± 0.9 cm, weight: 606.7 ± 19.7 g, BT) adult size were reached. Non-fish-skin components (i.e., scales, fillet) were immediately eliminated with a knife. Then, fish skins were rinsed three times with distilled water and stored at −20 °C in polyethylene bag. Prior to use, samples were thawed at 4 °C.
Distilled water was obtained from Millipore Milli–U10 water purification facility from Merck KGaA (Darmstadt, Germany). N, N–dimethylformamide was provided by VWR International PBI S.r.l. (Milan, Italy). Acetic acid, chloroform, methanol, and CaCl₂, norleucine, and N–tert–butyldimethylsilyl–N–methyltrifluoroacetamide (MTBSTFA) were purchased from Sigma–Aldrich (Milan, Italy). If not otherwise stated, all other chemicals used were of analytical grade and purchased from Sigma–Aldrich (Milan, Italy).

Dichloromethane, ethanol, and ethyl acetate were of chromatography quality, purchased from Sigma-Aldrich (Madrid, Spain). Diatomaceous earth (Hydromatrix) was purchased from Agilent Technologies (Madrid, Spain). PTFE centrifuge filters (0.22 μm pore size) were purchased from Ciromfg (FL, USA). Derivatizing agents, N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide (MTBSTFA) and acetic anhydride from Sigma Aldrich (Madrid, Spain), were also used to improve the analytical signal. Neutral alumina (58 Å) was used as a sorbent for the clean-up and provided by Sigma-Aldrich (Madrid, Spain). Silica was activated according to Environmental Protection Agency proceedings (3630c, method EPA). Commercial polydimethylsiloxane (PDMS) stir bars [10 mm × 0.5 mm (length × film)] and a 15-position magnetic stirrer were purchased from Gerstel (Germany).
Standards for BP-3, OC, TCS, and the isotopically labeled internal standard benzophenone- 2,3,4,5,6-d5 were purchased from Sigma-Aldrich (Madrid, Spain). OTNE (synthetic fragrance) was purchased from Bordas Chinchurreta Destilations (Seville, Spain). Triclosan-d3 was purchased from LGC Standards (Barcelona, Spain). Table S1 indicates the main physicochemical properties of these PCPs.

Standards of 4-n-NP, BPA, BPF, MeP, PrP, ibuprofen, mefenamic acid, carbamazepine, diclofenac, allopurinol and paracetamol (all purity > 97%), NP technical grade (mixture of ring and chain isomers), N-(tert-butyldimethylsilyl)-N-methyl-trifluoroacetamide (MTBSTFA, purity ≥ 95%) with 1% tert-butyldimethylchlorosilane (TBDMCS) were acquired from Sigma-Aldrich (St. Louis, MO, USA). Ultrahigh purity water was obtained from a MilliQ water purification system (Millipore, Spain).
Acetonitrile (ACN), ethyl acetate (EtAc), and methanol (MeOH), for GC residue analysis, were supplied by Aldrich (Steinheim, Germany). Formic acid (purity ≥ 98%) was acquired from Acros Organics (Geel, Belgium). Ammonium hydroxide (NH₄OH, ≥32%) and primary secondary amine (PSA) bulk adsorbent were purchased from Scharlab (Barcelona, Spain).
Individual stock solutions (1 mg/mL) of each compound were prepared in ACN, except for diclofenac and paracetamol that were prepared in ACN:MeOH (90:10 v/v), allopurinol in dimethyl sulfoxide and mefenamic acid in EtAc. A working mixture solution at 1 μg/mL was prepared in ACN (except for carbamazepine and diclofenac that were at 4 μg/mL due to their low MS response). All the standard solutions were stored in amber vials at −20°C prior to use.

Standards of acrylamide (≥99.5%), D3-acrylamide (500 mg L⁻¹ in acetonitrile), and asparagine (99%), as well as both GC-grade derivatization reagents xanthydrol (≥99%) and N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA) (≥99%) with 1% tert-butyldimethylsilyl chloride (TBDMSCI), were obtained from Sigma Aldrich (Schnelldorf, Germany). For pH adjustments, Na₂CO₃ and acetic acid (80%) were purchased for VWR (Vienna, Austria).
Analytical-Grade fructose, glucose, maltose, and sucrose were purchased from Sigma Aldrich. LC-MS-grade acetonitrile and ammonium acetate, as well as ammonia (25%), were obtained from VWR. GC-MS grade ethylacetate, hexane, HCl (37% p.A.) and Carrez I and Carrez II solutions were purchased from VWR. Sample cleanup was performed using J.T. Baker BAKERBOND spe C18 polarplus 1 mL SPE (solid phase extraction) columns (Schwerte, DE). LC-MS-grade water (<0.055 μS cm⁻¹) from a Sartorius ultrapure water purification system (Göttingen, Germany) was used for sample preparation.
The grain and rye varieties (Secale cereale) used were obtained from Arnreiter Mühle GmbH (Wallern a der Trattnach, Austria), Plohberger Malz GmbH (Grieskirchen, Austria), and Saatgut Erntegut GmBH (Linz, Austria). Asparaginase (EC 3.5.1.1, hydrolase) was purchased as PreventAse (product #23156) from DSM (Heerlen, Netherlands), and CaCl₂ was purchased from Solvay (Brussels, Belgium).

Acetonitrile (ACN), n-hexane, and toluene of HPLC quality were purchased from Sigma-Aldrich (St. Quentin Fallavier, France).
Standards of 50 individual pesticides of Pestanal^® quality (>99% purity) and N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MtBSTFA) were purchased from Fluka (Sigma Aldrich, St. Quentin Fallavier, France), Dr Ehrenstorfer GmbH (Cluzeau Info Labo, Sainte-Foy-la-Grande, France), or Riedel de Haën (Sigma Aldrich, St. Quentin Fallavier, France). A mixture of these pesticides (SM1) was prepared at 10 mg L^–1 in ACN and stored at −18 °C. The list of pesticides under study is summarized in Supplementary Material S2.
Five internal standards (IS) were used, including trifluralin d₁₄, nitrophenol d₄, pp’-DDE d₈, pp’-DDT d₈, sand trans-cypermethrin d₆. These ISs were obtained from Sigma-Aldrich (L’Isle d’Abeau, France) and Cambridge isotope laboratories (Cluzeau Info Labo, Sainte-Foy-la-Grande, France). A mixture of these ISs at 10 mg L⁻¹ in ACN were prepared and used for the quantification of the 50 assessed pesticides.