A rapid procedure for the determination of caffeine, theophylline and theobromine in urine by micellar liquid chromatography and direct sample injection

Comprehensive profiling and semi-quantification of exogenous chemicals in human urine using HRMS-based strategies

Chemicals infiltrate our daily experiences through multiple exposure pathways. Human biomonitoring (HBM) is routinely used to comprehensively understand these chemical interactions. Historically, HBM depended on targeted screening methods limited to a relatively small set of chemicals with triple quadrupole instruments typically. However, recent advances in high-resolution mass spectrometry (HRMS) have facilitated the use of broad-scope target, suspect, and non-target strategies, enhancing chemical exposome characterization within acceptable detection limits. Despite these advancements, establishing robust and efficient sample treatment protocols is still essential for trustworthy broad-range chemical analysis. This study sought to validate a methodology leveraging HRMS-based strategies for accurate profiling of exogenous chemicals and related metabolites in urine samples. We evaluated five extraction protocols, each encompassing various chemical classes, such as pharmaceuticals, plastic additives, personal care products, and pesticides, in terms of their extraction recoveries, linearity, matrix effect, sensitivity, and reproducibility. The most effective protocol was extensively validated and subsequently applied to 10 real human urine samples using wide-scope target analysis encompassing over 2000 chemicals. We successfully identified and semi-quantified a total of 36 chemicals using an ionization efficiency-based model, affirming the methodology's robust performance. Notably, our results dismissed the need for a deconjugation step, a typically labor-intensive and time-consuming process.

Supercritical fluid extraction-supercritical fluid chromatography of saliva: Single-quadrupole mass spectrometry monitoring of caffeine for gastric emptying studies†

Saliva is an attractive sampling matrix for measuring various endogenous and exogeneous substances but requires sample treatment prior to chromatographic analysis. Exploiting supercritical CO₂ for both extraction and chromatography simplifies sample preparation, reduces organic solvent consumption, and minimizes exposure to potentially infectious samples, but has not yet been applied to oral fluid. Here, we demonstrate the feasibility and benefits of online supercritical fluid extraction coupled to supercritical fluid chromatography and single-quadrupole mass spectrometry for monitoring the model salivary tracer caffeine. A comparison of ¹³ C- and ³² S-labeled internal standards with external standard calibration confirmed the superiority of stable isotope-labeled caffeine over nonanalogous internal standards. As proof of concept, the validated method was applied to saliva from a magnetic resonance imaging study of gastric emptying. After administration of 35 mg caffeine via ice capsule, salivary levels correlated with magnetic resonance imaging data, corroborating caffeine's usefulness as tracer of gastric emptying (R²  = 0.945). In contrast to off-line methods, online quantification required only minute amounts of organic solvents and a single manual operation prior to online bioanalysis of saliva, thus demonstrating the usefulness of CO₂ -based extraction and separation techniques for potentially infective biomatrices.

Novel Purine Alkaloid Cocrystals with Trimesic and Hemimellitic Acids as Coformers: Synthetic Approach and Supramolecular Analysis

In this work, benzene-1,3,5-tricarboxylic (trimesic acid, TMSA) and benzene-1,2,3-tricarboxylic acid (hemimellitic acid, HMLA) were used as coformers for cocrystal synthesis with chosen purine alkaloids. Theobromine (TBR) forms cocrystals TBR·TMSA and TBR·HMLA with these acids. Theophylline (TPH) forms cocrystals TPH·TMSA and TPH·HMLA, the cocrystal hydrate TPH·TMSA·2H₂O and the salt hydrate (TPH)⁺·(HMLA)^-·2H₂O. Caffeine (CAF) forms the cocrystal CAF·TMSA and the cocrystal hydrate CAF·HMLA·H₂O. The purine alkaloid derivatives were obtained by solution crystallization and by neat or liquid-assisted grinding. The powder X-ray diffraction method was used to confirm the synthesis of the novel substances. All of these solids were structurally characterized, and all synthons formed by purine alkaloids and carboxylic acids were recognized using a single-crystal X-ray diffraction method. The Cambridge Structural Database was used to determine the frequency of occurrence of analyzed supramolecular synthons, which is essential at the crystal structure design stage. Determining the influence of structural causes on the various synthon formations and molecular arrangements in the crystal lattice was possible using structurally similar purine alkaloids and two isomers of benzenetricarboxylic acid. Additionally, UV-vis measurements were made to determine the effect of cocrystallization on purine alkaloid solubility.

Fluorescence Sensing of Caffeine in Tea Beverages with 3,5-diaminobenzoic Acid

A rapid, selective and sensitive method for the detection of caffeine in tea infusion and tea beverages are proposed by using 3,5-diaminobenzoic acid as a fluorescent probe. The 3,5-diaminobenzoic acid emits strong fluorescence around 410 nm under the excitation of light at 280 nm. Both the molecular electrostatic potential analysis and fluorescent lifetime measurement proved that the existence of caffeine can quench the fluorescence of 3,5-diaminobenzoic acid. Under the optimal experimental parameters, the 3,5-diaminobenzoic acid was used as a fluorescent probe to detect the caffeine aqueous solution. There exists a good linear relationship between the fluorescence quenching of the fluorescent probe and the concentration of caffeine in the range of 0.1–100 μM, with recovery within 96.0 to 106.2%, while the limit of detection of caffeine is 0.03 μM. This method shows a high selectivity for caffeine. The caffeine content in different tea infusions and tea beverages has been determined and compared with the results from HPLC measurement.

Micellar liquid chromatography in doping control

The issue of doping control in sport involves the development of reliable analytical procedures and efficient strategies to process a large number of samples in a short period of time. Reversed-phase LC techniques with aqueous-organic mobile phases and MS or diode-array detection yield satisfactory results for the identification of prohibited substances in sport. However, time-consuming sample pretreatment steps are required, which reduces sample throughput. Micellar LC (MLC) that uses hybrid mobile phases of surfactant above its critical micellar concentration and organic solvent has been revealed as an interesting alternative. The surfactant sodium dodecyl sulfate solubilizes the protein components of urine, serum and plasma, which permits their direct injection into the chromatographic system. Only dilution and filtering of the samples may be required. Most MLC analyses are performed in isocratic mode, with short retention times and good selectivity. The sensitivity of MLC allows the detection of a variety of doping substances at least 24-48 h after being administered.

Determination of methylxanthines in urine by liquid chromatography with diode array UV detection

A liquid chromatography-diode array UV detection (LC-UVDAD) method for the simultaneous determination of four methylxanthines (caffeine, theobromine, paraxanthine and theophylline) is described. The chromatographic separation was achieved on a LC-18-DB column using 20:80 methanol:buffer (5mM citric acid adjusted to pH 5 with triethylamine) as mobile phase. The method has been applied to urine samples. The overall procedure had % recoveries ranging from 81.6 +/- 2.6 (theophylline) to 99.3 +/- 6.3 (theobromine). The within-day (n = 5) and between-days (n = 5 over 5 days) coefficients of variation in urine ranged from 2.9% (theophylline) to 3.4% (theobromine) and from 5.2% (theophylline) to 6.2% (theobromine). Estimated LOD and LOQ in urine ranged from 0.15microg/ml (theophylline) to 0.3microg/ml (theobromine) and from 0.8microg/ml (theophylline) to 1.2microg/ml (theobromine), respectively. Urine samples naturally contaminated with the target analytes were found.

Effect of a variety of organic additives on retention and efficiency in micellar liquid chromatography

The effect of 21 organic additives (alkanols, alkane diols, dipolar aprotic solvents, alkanes) on the chromatographic behavior (retention, elution strength, efficiency) of probe solutes of widely differing hydrophobicity, such as benzene and 2-ethylanthraquinone, have been examined using a C18 stationary phase and sodium dodecyl sulfate (SDS) micellar mobile phases. The mobile-phase elution strength parallels the octanol-water partition coefficients of the additives or their ability to bind to the SDS micellar system, due to the increased solubility in the mobile phase and reduced affinity for the additive-modified surfactant-coated stationary phase. The comparison of the elution strength of micellar mobile phases with that of a reference acetonitrile-water system indicates that the elution strength is lower for micellar systems and depends on the nature of the eluted solute. The displacement of the solute-micelle and solute-stationary phase binding equilibria is quantified for several probe solutes eluted with micellar mobile phases in the presence of 1-propanol, 1-butanol, 1-pentanol, and acetonitrile. A correlation was also observed between the number of theoretical plates and the hydrophobicity of the alcohol additives: the efficiency initially increased steeply and reached a plateau. Compared to benzene, a more hydrophobic additive was needed to attain the maximum efficiency for the more hydrophobic 2-ethylanthraquinone analyte. Dipolar aprotic solvents appear to be somewhat more effective in enhancing the efficiency than alcohols. The results are rationalized in terms of the ability of the organic additives to alter the composition, structure, dynamics, and properties of the micelles and the surfactant-coated stationary phase.

Direct injection of physiological fluids in micellar liquid chromatography

Micellar liquid chromatography (MLC), which uses mobile phases of surfactants above the critical micellar concentration, provides a solution to the direct injection of physiological samples by solubilizing the protein components, and coating the analytical column with surfactant monomers to avoid clogging. A review showing the advantages and limitations of this technique over other chromatographic techniques used in drug analysis, working protocols, and examples of application is presented. The possibility of direct sample introduction simplifies and greatly expedites the treatments with reduced cost, improving the accuracy of the procedures. Surfactant monomers and micelles appear to displace drugs bound to proteins, releasing them for partitioning to the stationary phase. The versatility of MLC encompasses the wide range of drug classes normally monitored, such as analgesics, anticancer drugs, antidepressants, bacteriostats, beta-blockers, bronchodilators, catecholamines, diuretics and steroids, among others. Analytical procedures have been developed in urine, plasma, serum and cow milk samples. Most of them utilize sodium dodecyl sulphate as surfactant and a C18 column. UV detection is usual, but enhanced detection has been reported by measuring the absorbance in the visible region of drug derivatives formed precolumn, and with a variety of other techniques, such as fluorimetry, amperometry, inductively coupled plasma-mass spectrometry and immunoassay. Column-switching with on-line surfactant-mediated sample clean-up is shown as an attractive enrichment technique, which expands the practical use of MLC beyond the singular dimensional chromatographic process.