Pyrazinamide

Reference standards of isoniazid (purity 98%), ethambutol dihydrochloride (purity 98%), pyrazinamide (purity 98%), isoniazid‐d₄ (purity 98%, isotopic purity 99.3%) and ethambutol‐d₄ dihydrochloride (purity 98%, isotopic purity 99.1%) were purchased from Toronto Research Chemicals. Acetonitrile, methanol, water, ammonium formate and formic acid were LC–MS grade and were obtained from Honeywell Riedel‐de Haën. Analyte‐free human plasma (blank plasma) with potassium EDTA as an anticoagulant was obtained from healthy and untreated volunteers (men and women aged 25–30 years).

Acetyl isoniazid, deacetyl rifabutin, desacetyl rifampicin, ethambutol, isoniazid, pyrazinamide, rifabutin and their deuterated internal standards: Acetyl isoniazid-d4 (isotopic purity: 99.4%), deacetyl rifabutin-d7 (isotopic purity: 98.5%), desacetyl rifampicin-d3 (isotopic purity: 99.6%), ethambutol-d4 (isotopic purity: 99.1%), isoniazid-d4 (isotopic purity: 99.3%), pyrazinamide-15 N,d3 (isotopic purity: 99.5%), and rifabutin-d7 (isotopic purity: 97.2%), were purchased from Toronto Research Chemicals (North York, Canada). Rifampicin reference material was purchased from the United States Pharmacopeia (Rockville, United States) and its deuterated internal standard, rifampicin-d3 (isotopic purity: 98.9%), was purchased from Toronto Research Chemicals (North York, Canada). Ammonium acetate, ascorbic acid, and dimethyl sulfoxide were purchased from Sigma-Aldrich (Darmstadt, Germany). Formic acid and ammonium bicarbonate were purchased from Merck (Darmstadt, Germany) and Acros Organics (Fair Lawn, United States), respectively. Acetonitrile and methanol were purchased from Honeywell (Charlotte, United States). LC-MS/MS grade millipore water was produced in-house (Merck-Millipore, Germany).