GC-NICI-MS analysis of acetazolamide and other sulfonamide (R-SO2-NH2) drugs as pentafluorobenzyl derivatives [R-SO2-N(PFB)2] and quantification of pharmacological acetazolamide in human urine

Pentafluorobenzyl bromide - A versatile derivatization agent in chromatography and mass spectrometry: II. Analysis of organic acids and bases, and comparison with other perfluorinated reagents

Analytical derivatization is an important for the vast majority of substances an indispensable sample preparation step for their quantitative GC-MS and GC-MS/MS analysis in biological samples. Pentafluorobenzyl bromide (PFB-Br), pentafluorobenzoyl chloride (PFB-COCl), pentafluorobenzyl hydroxylamine (PFB-NHNH2), pentafluorophenyl hydrazine (PFPh-ONH2), pentafluoropropionic anhydride (PFPA), and heptafluorobutyric anhydride (HFBA) are versatile derivatization reagents in analytical chemistry. In the present work, the utility of the above mentioned derivatization reagents for the GC-MS analysis of carboxylic, aldehydic, hydroxylic and amine groups containing analytes including amino acids is reviewed and discussed. Derivatization requires different conditions for solvents, reaction temperature and time, and possibly for catalysts. The perfluorinated derivatives are electrically neutral and best soluble in water-immiscible organic solvents such as toluene. Under negative-ion chemical ionization (NICI) conditions, the perfluorinated derivatives readily and abundantly ionize that allows for sensitive analysis. In addition, the perfluorinated analyte derivatives emerge earlier from GC columns than protiated, thus enabling shorter analysis times. Externally added 2H-, 13C-, 15N and 18O-isotopologs for use as internal standards undergo similar changes during derivatization, extraction by organic solvents, ionization in the ion-source of GC-MS apparatus and have almost identical retention times with the analytes. Due to selective analytical derivatization, almost all classes of endogenous and exogenous low-molecular-mass analytes, including drugs and inorganic anions such as nitrite, nitrate, carbonate, and (pseudo)halogenides, become accessible to quantitative GC-MS and GC-MS/MS analysis. Thanks the high sensitivity of quantitative analytical methods based on GC-MS and GC-MS/MS, very low amounts of perfluorinated derivatization reagents are consumed. In consideration of the enormously high global warming potential (GWP) of F-containing derivatization reagents, this article discussed a potential abandonment of the use of perfluorinated reagents and their replacement by F-free reagents in GC-MS and GC-MS/MS.

Underlying Mechanisms of Chromatographic H/D, H/F, cis/trans and Isomerism Effects in GC-MS

Charge-free gaseous molecules labeled with deuterium 2H (D) atoms elute earlier than their protium-analogs 1H (H) from most stationary GC phases. This effect is known as the chromatographic H/D isotope effect (hdIEC) and can be calculated by dividing the retention times (tR) of the protiated (tR(H) ) to those of the deuterated (tR(D)) analytes: hdIEC = tR(H)/tR(D). Analytes labeled with 13C, 15N or 18O have almost identical retention times and lack a chromatographic isotope effect. Derivatives of cis- and trans-analytes such as cis- and trans-fatty acids also differ in their retention times. Analytes that contain trans-C=C-double bonds elute earlier in gas chromatography-mass spectrometry (GC-MS) than their cis-C=C-double bonds containing congeners. The chromatographic cis/trans-effect (ctEC) can be calculated by dividing the retention times of the cis- by those of the trans-analytes: ctEC = tR(c)/tR(t). In the present work, the hdIEC and ctEC values of endogenous and exogenous substances were calculated from previously reported GC-MS analyses and found to range each between 1.0009 and 1.0400. The examination suggests that the H/D-isotope effects and the cis/trans-effects observed in GC-MS are based on differences in the inter-molecular interaction strengths of the analyte derivatives with the stationary phase of GC columns. The deuterium atoms, being larger than the H atoms of the analytes, attenuate the interaction of the skeleton of the molecules with the GC stationary phase. The angulation of trans-analytes decreases the interaction of the skeleton of the molecules with the GC stationary phase, as only parts of the molecules are close enough to the GC stationary phase to interact. Other chromatographic effects caused by hydrogen (H) and fluorine (F) atoms and by stereo-isomerism are considered to be based on a similar mechanism due to the different orientation of the side chains.

Acetazolamide and human carbonic anhydrases: retrospect, review and discussion of an intimate relationship

Acetazolamide (AZM) is a strong pharmacological sulphonamide-type (R-SO2-NH2, pKa 7.2) inhibitor of the activity of several carbonic anhydrase (CA) isoforms, notably of renal CA II (Ki, 12 nM) and CA IV (Ki, 74 nM). AZM is clinically used for about eighty years in various diseases including epilepsy and glaucoma. Pharmacological AZM increases temporarily the urinary excretion of bicarbonate (HCO3-) and sodium ions (Na+) and sustainably the urinary pH. AZM is excreted almost unchanged over several hours at high rates in the urine. Closely parallel concentrations of circulating and excretory AZM are observed upon administration of therapeutical doses of AZM. In a proof-of-principle study, we investigated the effects of the ingestion of a 250-mg AZM-containing tablet by a healthy volunteer on the urinary excretion of organic and inorganic substances over 5 h (range, 0, 0.5, 1, 1.5, 2, 3, 4, 5 h). Measured analytes included: AZM, amino acids and their metabolites such as guanidinoacetate, i.e. the precursor of creatine, of asymmetrically (ADMA) and symmetrically (SDMA) dimethylated arginine, nitrite (O = N-O-, pKa 3.4) and nitrate (O2N-O-, pKa -1.37), the major metabolites of nitric oxide (NO), the C-H acidic malondialdehyde (MDA; (CHO)2CH2, pKa 4.5), and creatinine for correction of analytes excretion. All analytes were measured by validated isotopologues using gas chromatography-mass spectrometry (GC-MS) methods. AZM excretion in the urine reached its maximum value after 2 h and was fairly stable for the next 3 h. Time series analysis by the ARIMA method was performed. AZM ingestion increased temporarily the urinary excretion of the amino acids Leu + Ile, nitrite and nitrate, decreased temporarily the urinary excretion of other amino acids. AZM decreased sustainably the urinary excretion of MDA, a biomarker of oxidative stress (i.e. lipid peroxidation). Whether this decrease is due to inhibition of the excretion of MDA or attenuation of oxidative stress by AZM is unknown. The acute and chronic effects of AZM on the urinary excretion of electrolytes and physiological substances reported in the literature are discussed in depth in the light of its extraordinary pharmacokinetics and pharmacodynamics. Tolerance development/drug resistance to AZM in chronic use and potential mechanisms are also addressed.

Quality Control in Targeted GC-MS for Amino Acid-OMICS

Gas chromatography-mass spectrometry (GC-MS) is suitable for the analysis of non-polar analytes. Free amino acids (AA) are polar, zwitterionic, non-volatile and thermally labile analytes. Chemical derivatization of AA is indispensable for their measurement by GC-MS. Specific conversion of AA to their unlabeled methyl esters (d0Me) using 2 M HCl in methanol (CH3OH) is a suitable derivatization procedure (60 min, 80 °C). Performance of this reaction in 2 M HCl in tetradeutero-methanol (CD3OD) generates deuterated methyl esters (d3Me) of AA, which can be used as internal standards in GC-MS. d0Me-AA and d3Me-AA require subsequent conversion to their pentafluoropropionyl (PFP) derivatives for GC-MS analysis using pentafluoropropionic anhydride (PFPA) in ethyl acetate (30 min, 65 °C). d0Me-AA-PFP and d3Me-AA-PFP derivatives of AA are readily extractable into water-immiscible, GC-compatible organic solvents such as toluene. d0Me-AA-PFP and d3Me-AA-PFP derivatives are stable in toluene extracts for several weeks, thus enabling high throughput quantitative measurement of biological AA by GC-MS using in situ prepared d3Me-AA as internal standards in OMICS format. Here, we describe the development of a novel OMICS-compatible QC system and demonstrate its utility for the quality control of quantitative analysis of 21 free AA and metabolites in human plasma samples by GC-MS as Me-PFP derivatives. The QC system involves cross-standardization of the concentrations of the AA in their aqueous solutions at four concentration levels and a quantitative control of AA at the same four concentration levels in pooled human plasma samples. The retention time (tR)-based isotope effects (IE) and the difference (δ(H/D) of the retention times of the d0Me-AA-PFP derivatives (tR(H)) and the d3Me-AA-PFP derivatives (tR(D)) were determined in study human plasma samples of a nutritional study (n = 353) and in co-processed QC human plasma samples (n = 64). In total, more than 400 plasma samples were measured in eight runs in seven working days performed by a single person. The proposed QC system provides information about the quantitative performance of the GC-MS analysis of AA in human plasma. IE, δ(H/D) and a massive drop of the peak area values of the d3Me-AA-PFP derivatives may be suitable as additional parameters of qualitative analysis in targeted GC-MS amino acid-OMICS.

Diuretics in Different Samples: Update on the Pretreatment and Analysis Techniques

Diuretics are drugs that promote the excretion of water and electrolytes in the body and produce diuretic effects. Clinically, they are often used in the treatment of edema caused by various reasons and hypertension. In sports, diuretics are banned by the World Anti-Doping Agency (WADA). Therefore, in order to monitor blood drug concentration, identify drug quality and maintain the fairness of sports competition, accurate, rapid, highly selective and sensitive detection methods are essential. This review provides a comprehensive summary of the pretreatment and detection of diuretics in various samples since 2015. Commonly used techniques to extract diuretics include liquid-liquid extraction, liquid-phase microextraction, solid-phase extraction, solid-phase microextraction, among others. Determination methods include methods based on liquid chromatography, fluorescent spectroscopy, electrochemical sensor method, capillary electrophoresis and so on. The advantages and disadvantages of various pretreatment and analytical techniques are elaborated. In addition, future development prospects of these techniques are discussed.

Strategies for studying in vivo biochemical formation pathways and multilevel distributions of sulfanilamide metabolites in food (2012-2022)

Sulfonamide metabolites are a major source of food pollution worldwide. However, the formation of internal sulfanilamide metabolites has only been investigated for selected compounds. In this paper, the fragmentation mechanism and characteristic ions of sulfonamide metabolites are reviewed using density functional theory and Q-Orbitrap high-resolution mass spectrometry. The result of the protonation site, rearrangement and bond breaking induced fragmentations at C₆H₆NO₂S⁺m/z 156.01138, C₆H₆NO⁺m/z 108.04439, and C₆H₆N⁺m/z 92.04948. Mass shifts are calculated for derivative metabolites, including hydrogenation, acetylation, oxidation, glucosylation, glucosidation, sulfation, deamination, formylation, desulfonation and O-aminomethylation. Given their homologous series, it is demonstrated that similar metabolic reactions occur for all sulfonamides. The suspicious sulfonamide metabolites are confirmed by d-labelling experiments and reference standards. This is the first review of the latest advances in the field of sulfonamide metabolite prediction (2012-2022), and scheme design for metabolite multirresidue screening, as well as the challenges in the mass spectrometry evolution.

Development and validation of a fast ultra-high-performance liquid chromatography tandem mass spectrometry method for determining carbonic anhydrase inhibitors and their metabolites in urine and hair

A new, rapid, sensitive, and comprehensive ultra‐high‐performance liquid chromatography tandem mass spectrometry (UHPLC–MS/MS) method for quantifying diuretics (acetazolamide, brinzolamide, dorzolamide, and their metabolites) in human urine and hair was developed and fully validated. Twenty‐five milligrams of hair were incubated with 500‐μl M3® buffer reagent at 100°C for 1 h for complete digestion. After cooling, 1‐μl supernatant was injected onto chromatography system. Urine samples were simply diluted before injection. The chromatographic run time was short (8 min) through a column with a mobile phase gradient. The method was linear (determination coefficients always higher than 0.99) from limit of quantification (LOQ) to 500 ng/ml in urine and from LOQ to 10 ng/mg in hair. LOQs ranged from 0.07 to 1.16 ng/ml in urine and from 0.02 to 0.15 ng/mg in hair. No significant ion suppression due to matrix effect was observed, and process efficiency was always higher than 80%. Intra‐ and inter‐assay precision was lower than 15%. The suitability of the methods was tested with six urine and hair specimens from patients treated with acetazolamide, dorzolamide, or brinzolamide for ocular diseases or systemic hypertension. Average urine concentrations were 266.32 ng/ml for dorzolamide and 47.61 ng/ml for N‐deethyl‐dorzolamide (n = 3), 109.27 ng/ml for brinzolamide and 1.02 ng/ml for O‐desmethyl‐brinzolamide (n = 2), and finally, 12.63 ng/ml for acetazolamide. Average hair concentrations were 5.94 ng/mg for dorzolamide and 0.048 ng/mg for N‐deethyl‐dorzolamide (n = 3), 3.26 ng/mg for brinzolamide (n = 2), and 2.3 ng/mg for acetazolamide (n = 1). The developed method was simple and fast both in the extraction procedures making it eligible in high‐throughput analysis for clinical forensic and doping purposes.

Nitrous anhydrase activity of carbonic anhydrase II: cysteine is required for nitric oxide (NO) dependent phosphorylation of VASP in human platelets

The carbonic anhydrase (CA) family does not only catalyse the reversible hydration of CO₂ to bicarbonate, but it also possesses esterase and phosphatase activity. Recently, bovine CA II and human CA II have been reported to convert inorganic nitrite (O=N-O⁻) to nitric oxide (NO) and nitrous anhydride (N₂O₃). Given the ability of NO to mediate vasodilation and inhibit platelet aggregation, this CA II activity would represent a bioactivation of nitrite. There are contradictory reports in the literature and the physiological role of CA II nitrite bioactivation is still disputed. Here, we provide new experimental data in support of the nitrous anhydrase activity of CA II and the key role L-cysteine in the bioactivation of nitrite by CA II. Using washed human platelets and by measuring VASP phosphorylation we provide evidence that exogenous nitrite (10 µM) is bioactivated to NO in a manner strongly depending on L-cysteine (100 and 200 µM). The process is not inhibitable by acetazolamide, a potent CA inhibitor. The contradictory results of recently published studies in this area are thoroughly discussed.

GC-MS Studies on Derivatization of Creatinine and Creatine by BSTFA and Their Measurement in Human Urine

In consideration of its relatively constant urinary excretion rate, creatinine (2-amino-1-methyl-5H-imidazol-4-one, MW 113.1) in urine is a useful endogenous biochemical parameter to correct the urinary excretion rate of numerous endogenous and exogenous substances. Reliable measurement of creatinine by gas chromatography (GC)-based methods requires derivatization of its amine and keto groups. Creatinine exists in equilibrium with its open form creatine (methylguanidoacetic acid, MW 131.1), which has a guanidine and a carboxylic group. Trimethylsilylation and trifluoroacetylation of creatinine and creatine are the oldest reported derivatization methods for their GC-mass spectrometry (MS) analysis in human serum using flame- or electron-ionization. We performed GC-MS studies on the derivatization of creatinine (d₀-creatinine), [methylo-²H₃]creatinine (d₃-creatinine, internal standard) and creatine (d₀-creatine) with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) using standard derivatization conditions (60 min, 60 °C), yet in the absence of any base. Reaction products were characterized both in the negative-ion chemical ionization (NICI) and in the positive-ion chemical ionization (PICI) mode. Creatinine and creatine reacted with BSTFA to form several derivatives. Their early eluting N,N,O-tris(trimethylsilyl) derivatives (8.9 min) were found to be useful for the precise and accurate measurement of the sum of creatinine and creatine in human urine (10 µL, up to 20 mM) by selected-ion monitoring (SIM) of m/z 271 (d₀-creatinine/d₀-creatine) and m/z 274 (d₃-creatinine) in the NICI mode. In the PICI mode, SIM of m/z 256, m/z 259, m/z 272 and m/z 275 was performed. BSTFA derivatization of d₀-creatine from a freshly prepared solution in distilled water resulted in formation of two lMate-eluting derivatives (14.08 min, 14.72 min), presumably creatinyl-creatinine, with the creatininyl residue existing in its enol form (14.08 min) and keto form (14.72 min). Our results suggest that BSTFA derivatization does not allow specific analysis of creatine and creatinine by GC-MS. Preliminary analyses suggest that pentafluoropropionic anhydride (PFPA) is also not useful for the measurement of creatinine in the presence of creatine. Both BSTFA and PFPA facilitate the conversion of creatine to creatinine. Specific measurement of creatinine in urine is possible by using pentafluorobenzyl bromide in aqueous acetone.