Determination of trace levels of acetamide, propanamide, and butyramide in surface and drinking water using gas chromatography–mass spectrometry after derivatization with 9-xanthydrol

Exploring the Sensing Potential of g-C3N4 versus Li/g-C3N4 Nanoflakes toward Hazardous Organic Volatiles: A DFT Simulation Study

Ab initio calculations were performed to determine the sensing behavior of g-C3N4 and Li metal-doped g-C3N4 (Li/g-C3N4) quantum dots toward toxic compounds acetamide (AA), benzamide (BA), and their thio-analogues, namely, thioacetamide (TAA) and thiobenzamide (TAA). For optimization and interaction energies, the ωB97XD/6-31G(d,p) level of theory was used. Interaction energies (Eint) illustrate the high thermodynamic stabilities of the designed complexes due to the presence of the noncovalent interactions. The presence of electrostatic forces in some complexes is also observed. The observed trend of Eint in g-C3N4 complexes was BA > TAA > AA > TBA, while in Li/g-C3N4, the trend was BA > AA > TBA > TAA. The electronic properties were studied by frontier molecular orbital (FMO) and natural bond orbital analyses. According to FMO, lithium metal doping greatly enhanced the conductivity of the complexes by generating new HOMOs near the Fermi level. A significant amount of charge transfer was also observed in complexes, reflecting the increase in charge conductivity. NCI and QTAIM analyses evidenced the presence of significant noncovalent dispersion and electrostatic forces in Li/g-C3N4 and respective complexes. Charge decomposition analysis gave an idea of the transfer of charge density between quantum dots and analytes. Finally, TD-DFT explained the optical behavior of the reported complexes. The findings of this study suggested that both bare g-C3N4 and Li/g-C3N4 can effectively be used as atmospheric sensors having excellent adsorbing properties toward toxic analytes.

An Orthogonal Approach for Determination of Acetamide Content in Pharmaceutical Drug Substance and Base-Contaminated Acetonitrile by GC and GC-MS External Method

Acetamide is a potential genotoxic impurity; it should control in drug substance based on daily dosage level. It forms from base-contaminated acetonitrile and by-product of some drug substances. The available methods for acetamide in drug substance and water samples were determined by GC-MS using internal standard with critical procedures. These developed and validated methods can assist in evaluating the reaction between acetonitrile and different bases and also determine trace level acetamide in drug substances. The method development was initiated with DB-624, 30 m, 0.32 width and 1.0-μm column. The column was used to validate at the 600 ppm TTC value. Similarly, the CP-SIL 5CB, 60 m, 0.32 width, the 5-μm column was used for the remaining TTC values. The validation study was performed for all TTC limits. The % RSD for precision at 600, 60, 20, 10 and 2.5 ppm was <15%. The % recovery at all TTC level was in between the 70 and 130%. Solution stability study was performed up to the 24 h. At 2.5 ppm, the results were <15% variation from the initial value. The linearities from the 50 to 150% concerning TTC values were more than limit of 0.98 correlation coefficient. The limit of detection and limit of quantitation values were 0.4 to the 1.3 ppm, respectively, for 2.5 ppm TTC limit method.

The 3rd degree of biomimetism: associating the cavity effect, ZnII coordination and internal base assistance for guest binding and activation

The synthesis and characterization of a resorcinarene-based tetra(imidazole) ligand is reported. The properties of the corresponding ZnII complex are studied in depth, notably by NMR spectroscopy. In MeCN, acid-base titration reveals that one out of the four imidazole arms is hemi-labile and can be selectively protonated, thereby opening a coordination site in the exo position. Quite remarkably, the 4th imidazole arm promotes binding of an acidic molecule (a carboxylic acid, a β-diketone or acetamide), by acting as an internal base, which allows guest binding as an anion to the metal center in the endo position. Most importantly, the presence of this labile imidazole arm makes the ZnII complex active for the catalyzed hydration of acetonitrile. It is proposed that it acts as a general base for activating a water molecule in the vicinity of the metal center during its nucleophilic attack to the endo-bound MeCN substrate. This system presents a unique degree of biomimetism when considering zinc enzymes: a pocket for guest binding, a similar first coordination sphere, a coordination site available for water activation in the cis position relative to the substrate and finally an internal imidazole residue that plays the role of a general base.

Exposure Assessment of Acetamide in Milk, Beef, and Coffee Using Xanthydrol Derivatization and Gas Chromatography/Mass Spectrometry

Acetamide has been classified as a possible human carcinogen, but uncertainties exist about its levels in foods. This report presents evidence that thermal decomposition of N-acetylated sugars and amino acids in heated gas chromatograph injectors contributes to artifactual acetamide in milk and beef. An alternative gas chromatography/mass spectrometry protocol based on derivatization of acetamide with 9-xanthydrol was optimized and shown to be free of artifactual acetamide formation. The protocol was validated using a surrogate analyte approach based on d₃-acetamide and applied to analyze 23 pasteurized whole milk, 44 raw sirloin beef, and raw milk samples from 14 different cows, and yielded levels about 10-fold lower than those obtained by direct injection without derivatization. The xanthydrol derivatization procedure detected acetamide in every food sample tested at 390 ± 60 ppb in milk, 400 ± 80 ppb in beef, and 39 000 ± 9000 ppb in roasted coffee beans.