Determination of caffeine and its metabolites in urine by capillary electrophoresis-mass spectrometry

Synchronous analysis of acetaminophen, codeine, and caffeine in human fluids employing graphite screen-printed electrodes

A facile electrochemical approach is proposed for the synchronous determination of acetaminophen (ACP), codeine (COD) and caffeine (CAF) utilizing unmodified screen-printed electrodes (SPEs). The determination of ACP, COD and CAF has been explored across different supporting electrolytes including sulfuric acid (H2SO4), hydrochloric acid (HCl), phosphoric acid (H3PO4) and Briton Robinson (B.R) buffer solutions. It was found that a 0.05 mol L-1 sulfuric acid solution is an optimal supporting electrolyte utilized for voltammetric analysis of ACP, COD, and CAF with improved sensitivity, stability, and reproducibility. The electro-analytical sensing of ACP, COD and CAF was investigated using SPEs within linear concentration ranges of 3.0-35.0 μmol L-1, 10-160 μmol L-1 and 10-160 μmol L-1 and revealed competitively low limits of detection (3S/N) of 0.9, 4.8 and 6.3 μmol L-1 for ACP, COD and CAF, respectively. The results indicated the possibility of such a simple and quick electroanalytical protocol for online monitoring of pharmaceutical formulations comprising ACP, COD, and CAF drugs in human fluids with satisfactory recovery.

Quantification of caffeine in coffee cans using electrochemical measurements, machine learning, and boron-doped diamond electrodes

Electrochemical measurements, which exhibit high accuracy and sensitivity under low contamination, controlled electrolyte concentration, and pH conditions, have been used in determining various compounds. The electrochemical quantification capability decreases with an increase in the complexity of the measurement object. Therefore, solvent pretreatment and electrolyte addition are crucial in performing electrochemical measurements of specific compounds directly from beverages owing to the poor measurement quality caused by unspecified noise signals from foreign substances and unstable electrolyte concentrations. To prevent such signal disturbances from affecting quantitative analysis, spectral data of voltage-current values from electrochemical measurements must be used for principal component analysis (PCA). Moreover, this method enables highly accurate quantification even though numerical data alone are challenging to analyze. This study utilized boron-doped diamond (BDD) single-chip electrochemical detection to quantify caffeine content in commercial beverages without dilution. By applying PCA, we integrated electrochemical signals with known caffeine contents and subsequently utilized principal component regression to predict the caffeine content in unknown beverages. Consequently, we addressed existing research problems, such as the high quantification cost and the long measurement time required to obtain results after quantification. The average prediction accuracy was 93.8% compared to the actual content values. Electrochemical measurements are helpful in medical care and indirectly support our lives.

Urine caffeine metabolites are positively associated with cognitive performance in older adults: An analysis of US National Health and Nutrition Examination Survey (NHANES) 2011 to 2014

The aim of this study was to explore urine caffeine metabolites in relation to cognitive performance among 2011-2014 National Health and Nutrition Examination Survey participants aged ≥60 years. We hypothesized that urine caffeine metabolites were positively associated with cognition in older adults. Caffeine and 14 of its metabolites were quantified in urine by use of high-performance liquid chromatography-electrospray ionization-tandem quadruple mass spectrometry with stable isotope labeled internal standards. Cognitive assessment was based on scores from the word learning and recall modules. Participants were categorized based on the quartiles of caffeine and its metabolites level. The association between caffeine metabolites and each cognitive dimension was analyzed using multiple logistic regression analysis in adjusted models. Stratification analyses by gender were also performed. For CERAD test, there was a significant association between 1-methyluric acid (OR=0.62, 95% CI: 0.42 to 0.92), 7-methylxanthine(OR=0.49, 95% CI: 0.27 to 0.89), theophylline (OR=0.52, 95% CI: 0.29 to 0.92), as well as paraxanthine (OR=0.49, 95% CI: 0.27 to 0.88) and cognitive function. For animal fluency test, there was a positive association between theophylline (TP) (OR=0.44, 95% CI: 0.22 to 0.89) and cognitive function. The trend that the risk of low cognitive function decreased with increasing concentration of 1-methylxanthine (P trend=0.0229) was also observed. Furthermore, the same trend existed for 3-methylxanthine (p trend = 0.0375) in men. In conclusion, there was a significant positive association between urine caffeine metabolites and cognitive performance in older adults, particularly for theophylline, paraxanthine and caffeine; and the association might be dependent on gender.

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.

Metabolic Demethylation and Oxidation of Caffeine during Uptake by Lettuce

Pharmaceuticals can be metabolized after being taken up by plants. The metabolites could manifest similar or equivalent bioactivity to the parent compound, promoting the critical need to understand the metabolism in plants. Caffeine has been frequently detected in agriculture produce; however, little attention is given to its metabolites in vegetables. This study examined uptake and metabolism of caffeine in lettuce in a hydroponic system. Caffeine and its metabolites in aqueous solution and lettuce were identified and quantified using a liquid chromatography coupled to a QTrap tandem mass spectrometry instrument. After 144 h, over 50% of applied caffeine dissipated in the hydroponic lettuce system, and eight caffeine metabolites were identified primarily in the shoots. Caffeine underwent demethylation reactions, which were confirmed with authentic standards, and the total amount accounted for 20% of the initially applied caffeine. Other metabolism pathways included oxidation and hydroxylation, and the amount of metabolites increased over uptake time.

Integrating nanohybrid membranes of reduced graphene oxide: chitosan: silica sol gel with fiber optic SPR for caffeine detection

Caffeine is the most popular psychoactive drug consumed in the world for improving alertness and enhancing wakefulness. However, caffeine consumption beyond limits can result in lot of physiological complications in human beings. In this work, we report a novel detection scheme for caffeine integrating nanohybrid membranes of reduced graphene oxide (rGO) in chitosan modified silica sol gel (rGO: chitosan: silica sol gel) with fiber optic surface plasmon resonance. The chemically synthesized nanohybrid membrane forming the sensing route has been dip coated over silver coated unclad central portion of an optical fiber. The sensor works on the mechanism of modification of dielectric function of sensing layer on exposure to analyte solution which is manifested in terms of red shift in resonance wavelength. The concentration of rGO in polymer network of chitosan and silica sol gel and dipping time of the silver coated probe in the solution of nanohybrid membrane have been optimized to extricate the supreme performance of the sensor. The optimized sensing probe possesses a reasonably good sensitivity and follows an exponentially declining trend within the entire investigating range of caffeine concentration. The sensor boasts of an unparalleled limit of detection value of 1.994 nM and works well in concentration range of 0-500 nM with a response time of 16 s. The impeccable sensor methodology adopted in this work combining fiber optic SPR with nanotechnology furnishes a novel perspective for caffeine determination in commercial foodstuffs and biological fluids.

Derivation of uncertainty functions from validation studies in biological fluids: application to the analysis of caffeine and its major metabolites in human plasma samples

Procedures for estimating the measurement uncertainty (MU) of the concentration of a given analyte in a sample are of major concern for analytical chemists. Unfortunately, it is still unclear how and why MU should be assessed. While several possibilities exist, an appropriate approach consists in using method validation data for the evaluation of MU. This was demonstrated by a validation study achieved in the framework of a clinical study related to caffeine in sports medicine, where the results were used for the evaluation of MU. After validation of the method developed using ultra-high pressure liquid chromatography-mass spectrometry for caffeine and its three main metabolites, accuracy profiles were built for each analyte. The first important conclusion is that the developed method was valid for all compounds and met the given specifications for the application (fit for purpose). Relevant estimates of combined standard uncertainty were computed to obtain uncertainty functions, which allow obtaining values of MU as a function of the concentration of the analyte. The great advantage of both uncertainty function and uncertainty profile is the development of a continuous model that enables easy calculation of the standard, expanded and relative expanded uncertainty at any concentration within the validation domain. In fact, the expanded uncertainty interval is assumed to contain 95% of all possible measurements, regardless of the concentration. Finally, the uncertainty function enables the determination of the lowest limit of quantification by selecting adequate acceptance limits, with the limit of quantification being defined as the point where the relative uncertainty equals the acceptance limit threshold. It has to be noted that further discussions remain mandatory to establish which criteria should be applied to define an adequate decision threshold, and the proposal afforded in this work may open new avenues in this direction.

Voltammetric determination of caffeine in beverage samples on bare boron-doped diamond electrode

A sensitive and selective electrochemical method for the caffeine determination using bare boron-doped diamond electrode was developed. It was found that caffeine provided highly reproducible and well-defined irreversible oxidation peak at very positive potential. The effects of supporting electrolyte, pH and scan rate on the voltammetric response of caffeine oxidation were studied to select the optimum experimental conditions. Linear response of peak current on the concentration in the range from 4×10(-7) to 2.5×10(-5)M, good repeatability (RSD of 2.1%) and detection limit of 1.5×10(-7)M without any chemical modifications and electrochemical surface pretreatment were evaluated. The effect of possible interferents appeared to be negligible which evidently proved very good selectivity. The proposed method was successfully applied for the caffeine determination in commercially available beverage samples, with results in a close statistical agreement to those declared by manufacturer and HPLC used as independent method.

Identification and fragmentation pathways of caffeine metabolites in urine samples via liquid chromatography with positive electrospray ionization coupled to a hybrid quadrupole linear ion trap (LTQ) and Fourier transform ion cyclotron resonance mass spectrometry and tandem mass spectrometry

Liquid chromatography (LC) with positive ion electrospray ionization (ESI+) coupled to a hybrid quadrupole linear ion trap (LTQ) and Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) was employed for the simultaneous determination of caffeine and its metabolites in human urine within a single chromatographic run. LC/ESI-FTICRMS led to the unambiguous determination of the molecular masses of the studied compounds without interference from other biomolecules. A systematic and comprehensive study of the mass spectral behaviour of caffeine and its fourteen metabolites by tandem mass spectrometry (MS/MS) was performed, through in-source ion trap collision-induced dissociation (CID) of the protonated molecules, [M+H](+). A retro-Diels-Alder (RDA) process along with ring-contraction reactions were the major fragmentation pathways observed during CID. The base peak of xanthine precursors originates from the loss of methyl isocyanate (CH(3)NCO, 57 Da) or isocyanic acid (HNCO, 43 Da), which in turn lose a CO unit. Also uric acid derivatives shared a RDA rearrangement as a common fragmentation process and a successive loss of CO(2) or CO. The uracil derivatives showed a loss of a ketene unit (CH(2)CO, 42 Da) from the protonated molecule along with the loss of H(2)O or CO. To assess the potential of the present method three established metabolite ratios to measure P450 CYP1A2, N-acetyltransferase and xanthine oxidase activities were evaluated by a number of identified metabolites from healthy human urine samples after caffeine intake.

Determination of caffeine in coffee products by dynamic complexation with 3,4-dimethoxycinnamate and separation by CZE

A method based on the formation of pi-complexes with chlorogenate-like species was proposed for the determination of caffeine in regular (nondecaffeinated) and decaffeinated coffee. Both caffeate and 3,4-dimethoxycinnamate were able to transform caffeine--a neutral species in aqueous solutions--into an anionic species. The usage of 3,4-dimethoxycinnamate in the running electrolyte is advantageous, because of its greater chemical stability and the improved resolution of the peaks of caffeine, theobromine, and theophylline. Negative peaks were registered with a capacitively coupled contactless conductivity detector when solutions of these alkylxanthines were analyzed with a BGE composed of 20 mmol/L 3,4-dimethoxycinnamic acid and pH adjusted to 8.5 with Tris. This behavior was expected, because the complex is larger and thus should move slower than the free anion. Caffeine was determined in ground and instant coffee with precision and accuracy that meet Brazilian norms about such products. The LOD was estimated as 33 mg/L, which corresponds to 0.8 and 0.3 mg of caffeine per gram of dry instant coffee and ground coffee, respectively. For the case of decaffeinated coffee, ten times preconcentration with dichloromethane was carried out to allow the quantitation of caffeine, which should not exceed the concentration of 1 mg/g in dry matter.

Sample treatments prior to capillary electrophoresis-mass spectrometry

Sample preparation is a crucial part of chemical analysis and in most cases can become the bottleneck of the whole analytical process. Its adequacy is a key factor in determining the success of the analysis and, therefore, careful selection and optimization of the parameters controlling sample treatment should be carried out. This work revises the different strategies that have been developed for sample preparation prior to capillary electrophoresis-mass spectrometry (CE-MS). Namely the present work presents an exhaustive and critical revision of the different samples treatments used together with on-line CE-MS including works published from January 2000 to July 2006.

Capillary electrophoresis-mass spectrometry, an attractive tool for drug bioanalysis and biomarker discovery

The coupling of CE with MS detection, a relatively recent hyphenated technique, has gained increasing respect in the field of bioanalytical applications over the past few years. The first part of this review presents CE-MS applications dealing with drug bioanalysis, including forensic analysis and metabolism studies. Practical considerations to achieve a robust and sensitive CE-MS coupling are also presented. It is indeed essential to strictly control some critical electrospray parameters, such as the sheath liquid composition and flow rate, the nebulizing gas pressure as well as the capillary outlet position. The second part of the review critically describes the applications of CE coupled on-line to MS for the identification of biomarkers in body fluids for diagnostic purposes. Since the sample preparation procedures strongly differ according to the intended use (drug bioanalysis or biomarker discovery), they are discussed separately, taking into account the particular properties of plasma and urine matrices.

Recent advances in the applications of CE to forensic sciences (2001–2004)

The present article reviews the applications of CE in forensic science covering the period from 2001 until the first part of 2005. The overview includes the most relevant examples of analytical applications of capillary electrophoretic and electrokinetic techniques in the following fields: (i) Forensic drugs and poisons, (ii) explosive analysis and gunshot residues, (iii) small ions of forensic interest, (iv) forensic DNA and RNA analysis, (v) proteins of forensic interest, and (vi) ink analysis.