Determination of valproic acid in human serum and pharmaceutical preparations by headspace liquid-phase microextraction gas chromatography-flame ionization detection without prior derivatization

Occurrence, detection and ecotoxicity studies of selected pharmaceuticals in aqueous ecosystems- a systematic appraisal

Pharmaceutical compounds (PCs) have globally emerged as a significant group of environmental contaminants due to the constant detection of their residues in the environment. The main scope of this review is to fill the void of information on the knowledge on the African occurrence of selected PCs in environmental matrices in comparison with those outside Africa and their respective toxic actions on both aquatic and non-aquatic biota through ecotoxicity bioassays. To achieve this objective, the study focused on commonly used and detected pharmaceutical drugs (residues). Based on the conducted literature survey, Africa has the highest levels of ciprofloxacin, sulfamethoxazole, lamivudine, acetaminophen, and diclofenac while Europe has the lowest of all these PC residues in her physical environments. For ecotoxicity bioassays, the few data available are mostly on individual groups of pharmaceuticals whereas there is sparsely available data on their combined forms.

Use of TLC-Densitometric Method for Determination of Valproic Acid in Capsules

Determination of valproic acid in the drug was carried out on the aluminum silica gel 60F₂₅₄ plates and using acetone-water-chloroform-ethanol-ammonia at a volume ratio of 30:1:8:5:11 as the mobile phase, respectively. Two methods of detection of valproic acid were used. The first was a 2% aqueous CuSO₄×5H₂O solution, and the second was a 2',7'-dichlorofluorescein-aluminum chloride-iron (III) chloride system. The applied TLC-densitometric method is selective, linear, accurate, precise, and robust, regardless of the visualizing reagent used for the determination of valproic acid in Convulex capsules. It has low limits of detection (LOD) and limits of quantification (LOQ), which are equal to 5.8 μg/spot and 17.4 μg/spot using a 2% aqueous CuSO₄×5H₂O solution as visualizing agent and also 0.32 μg/spot and 0.97 μg/spot using a 2',7'-dichlorofluorescein-aluminum chloride-iron (III) chloride system as visualizing reagent, respectively. The described analytical method can additionally be used to study the identity of valproic acid in a pharmaceutical preparation. The linearity range was found to be 20.00-80.00 μg/spot and 1.00-2.00 μg/spot for valproic acid detected on chromatographic plates using a 2% aqueous CuSO₄×5H₂O solution and the 2',7'-dichlorofluorescein-aluminum chloride-iron (III) chloride system, respectively. A coefficient of variation that was less than 3% confirms the satisfactory accuracy and precision of the proposed method. The results of the assay of valproic acid equal 96.2% and 97.0% in relation to the label claim that valproic acid fulfill pharmacopoeial requirements. The developed TLC-densitometric method can be suitable for the routine analysis of valproic acid in pharmaceutical formulations. The proposed TLC-densitometry may be an alternative method to the modern high-performance liquid chromatography and square wave voltammetry in the control of above-mentioned substances, and it can be applied when other analytical techniques is not affordable in the laboratory.

Determination of valproic acid and 3-heptanone in plasma using air-assisted liquid-liquid microextraction with the assistance of vortex: Application in the real samples

Introduction: Valproic acid (VPA) is an antiepileptic drug used to treat epilepsy and bipolar disorder. Adverse effects of VPA were studied in many reports, however, a dose-response relationship between VPA and its metabolites in epilepsy patients are extremely limited. In this paper, a high efficient method was developed for the preconcentration and determination of VPA and its main metabolite in plasma. Methods: For the extraction and preconcentration of the selected analytes, a volume of an extractant was placed at the bottom of the microtube containing pretreated plasma. The mixture was repeatedly withdrawn from the microtube and pushed-out into it using a 1.0-mL glass syringe and resulted in a cloudy mixture. For further turbidity, the mixture was shaken on a vortex agitator. This procedure was used to analyze the plasma samples of patients with epilepsy (n = 70). Results: The results revealed that in most patients with a low level of VPA relative to its expected level, 3-heptanone concentrations were high. The limits of quantification of 3-heptanone and VPA were 0.04 mg L-1 and 0.2 mg L-1, respectively. A suitable precision at a concentration of 2 mg L-1 for each analyte was obtained (relative standard deviation ≤ 9%). Conclusion: The obtained results indicated that this procedure is easy, sensitive, and reliable, and can be used for the analysis of the selected analytes in the plasma samples of patients with epilepsy.

Synergistic effect of MoS2 and diamond nanoparticles in electrochemical sensors: determination of the anticonvulsant drug valproic acid

The authors describe an electrochemical sensor based on the use of diamond nanoparticles (DNPs) and molybdenum disulfide (MoS₂) platelets. The sensor was applied to the voltammetric determination of the anticonvulsant valproic acid which was previously derivatized with ferrocene. The MoS₂ platelets were obtained by an exfoliation method, and the DNPs were directly dispersed in water and subsequently deposited on a glassy carbon electrode (GCE). The sensor response was optimized in terms of the solvent employed for dispersing the MoS₂ nanomaterial and the method for modifying the GCE. Sensors consisting of a first layer of MoS₂ dispersed in ethanol/water and a second layer of DNPs give better response. The single steps of sensor construction were characterized by atomic force microscopy and electrochemical impedance spectroscopy. The differential pulse voltammetric response of the GCE (measured at +0.18 V vs. Ag/AgCl) was compared to that of sensors incorporating only one of the nanomateriales (DNPs or MoS₂). The formation of a hybrid MoS₂-DNP structure clearly improves performance. The GCE containing both nanomaterials exhibits high sensitivity (740 µA ⋅ mM^-1 ⋅ cm^-2), a 0.27 μM detection limit, and an 8% reproducibility (RSD). The sensor retained 99% of its initial response after 45 days of storage. Graphical abstract Electrochemical sensor by co-immobilization of MoS₂ and diamond nanoparticles (DNP). The formation of a hybrid MoS₂-DNP structure enhances the performance of the sensor towards valproic acid derivatized with a ferrocene group, when compared with sensors incorporating only DNP or MoS₂.

The Influence of Plasma Albumin Concentration on the Analysis Methodology of Free Valproic Acid by Ultrafiltration and Its Application to Therapeutic Drug Monitoring

BACKGROUND

Free drug analysis is increasingly becoming popular in therapeutic drug monitoring (TDM). Centrifugal ultrafiltration (CF-UF) is the primary method to separate free drug from that of bound drug. However, the volume ratio of ultrafiltrate to sample solution (Vu/Vs) affects the accuracy of CF-UF, which highly depends on the different plasma conditions. Plasma protein concentrations in patients are different from those observed in healthy subjects, and there are also significant differences among patients with different diseases. Only very few studies have reported on the effect of protein concentration on the analysis methodology of free drug by CF-UF.

METHODS

In this study, valproic acid was used as the representative drug, and plasma samples with different albumin concentrations were analyzed by CF-UF and hollow fiber centrifugal ultrafiltration (HFCF-UF).

RESULTS

There was no significant difference of free drug concentrations by HFCF-UF and CF-UF when plasma albumin concentrations ranged 40-60 g/L. However, at low albumin concentrations (<40 g/L), a considerable difference was detected, and the difference was increased with the decrease of plasma albumin concentration. When the albumin concentration was as low as 10 g/L, the free drug concentration was 17.3 mcg/mL by CF-UF, whereas it was 10.2 mcg/mL by HFCF-UF.

CONCLUSIONS

The accuracy of free drug measurement by CF-UF was albumin concentration dependent. However, such an effect was not observed when samples were prepared by HFCF-UF, which was more suitable for TDM of plasma samples from different patients. Therefore, this method could be readily applied to the measurement of free valproic acid plasma concentrations for TDM in patients.

A new derivatization method to enhance sensitivity for the determination of low levels of valproic acid in human plasma

A novel and sensitive high-performance liquid chromatographic (HPLC) method has been developed and validated for the determination of valproic acid (VPA) in human plasma. The method was based on derivatization of VPA using 2-bromo-2'-acetonaphthone as a new derivatization reagent. Caprylic acid was used as an internal standard (IS). Under the optimized extraction and derivatization conditions, the method showed good linearity in the range of 0.05-200 μg mL(-1) and the limit of detection was as low as 0.01 μg mL(-1). The relative standard deviation for intra-day and inter-day (n = 5) was <5%. The recovery ranged from 95.2 to 101.4%. The proposed method is proved to be highly sensitive, simple and rapid, and was successfully applied to the analysis of VPA in plasma samples from patients with generalized epilepsy.

A rapid and highly sensitive UPLC-MS/MS method using pre-column derivatization with 2-picolylamine for intravenous and percutaneous pharmacokinetics of valproic acid in rats

A rapid, highly sensitive and specific ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) for the detection of valproic acid (VPA) in rat plasma following the topical application was developed and validated. This method was carried out with pre-column derivatization using 2-picolylamine (PA) which reacts with the carboxylic acid group of VPA. The derivatization was completed in 10min and the resulting PA-VPA derivative enabled the sensitive detection of VPA in selected reaction monitoring (SRM) mode. Sample preparation was done with simple liquid-liquid extraction and chromatographic separation was achieved within 5min on a C18 column using a gradient elution with the mobile phase of 2mM ammonium formate containing 0.1% formic acid and methanol. The standard curves were linear over the concentration range of 0.07-200μg/mL with a correlation coefficient higher than 0.99. The limit of detection (LOD) and the lower limit of quantification (LLOQ) was 0.03 and 0.07μg/mL, respectively with 100μL of plasma sample. The intra- and inter-day precisions were measured to be below 10.7% and accuracies were within the range of 94.1-115.9%. The validated method was successfully applied to the pharmacokinetics of VPA in the rat following topical and intravenous applications.

Microextraction techniques in therapeutic drug monitoring

Therapeutic drug monitoring (TDM), as part of clinical process of medical treatments, is commonly used to maintain 'therapeutic' drug concentrations. TDM is useful to identify the causes of unwanted or unexpected responses, to prevent unnecessary diagnostic testing, to improve clinical outcomes, and even to save lives. The determination of drug concentration in blood samples requires an excellent sample preparation procedure. Recent trends in sample preparation include miniaturization, automation, high-throughput performance, on-line coupling with analytical instruments and low-cost operation through extremely low or no solvent consumption. Microextraction techniques, such as liquid- and solid-phase microextraction, have these advantages over the traditional techniques. This paper reviews the recent developments in microextraction techniques used for drug monitoring in serum, plasma or blood samples.

Liquid-phase microextraction in bioanalytical sample preparation

Liquid-phase microextraction (LPME) emerged in the mid-to-late 1990s, facing up to the main shortcomings of the classical liquid-liquid extraction. Since its origin, this new technique has been in continuous development driven by its successful and widespread use in the analytical sciences. Its inherent properties, such as low sample volume requirement, high preconcentration factors achieved and excellent sample clean-up, make LPME a very useful technique for bioanalytical sample preparation. This review focuses on the main LPME-related techniques, predominantly single-drop microextraction and supported hollow-fiber LPME, paying particular attention to the bioanalytical applications. A general view of the essential trends, including the description of promising extraction modes and solvents, is also highlighted.

Single-drop microextraction in bioanalysis

Bioanalysis usually requires a preparation procedure for sample cleanup or preconcentration. Conventional sample preparation techniques are often time consuming and labor intensive. Among recent progress in sample preparation, single drop microextraction (SDME) is one of the most efficient techniques providing both sample cleanup and preconcentration capabilities. In SDME, analytes are extracted from a sample solution into an acceptor drop and the drop is introduced to subsequent analysis. Since the volume of the acceptor drop is 1–10 µl or less, the consumption of solvents can be minimized and the preconcentration effect is enhanced. In this review, the basic principles of two-phase and three-phase SDME are described briefly and then recently developed modes of SDME, coupling with analytical instruments, and methods to enhance the drop stability are discussed. Recent applications of SDME to biological samples, including urine, blood and saliva, for the analysis of drugs, metal ions and biomarkers are reviewed.

Brain delivery of valproic acid via intranasal administration of nanostructured lipid carriers: in vivo pharmacodynamic studies using rat electroshock model

The treatment of brain disorders is one of the greatest challenges in drug delivery because of a variety of main barriers in effective drug transport and maintaining therapeutic concentrations in the brain for a prolonged period. The objective of this study was delivery of valproic acid (VPA) to the brain by intranasal route. For this purpose, nanostructured lipid carriers (NLCs) were prepared by solvent diffusion method followed by ultrasonication and characterized for size, zeta potential, drug-loading percentage, and release. Six groups of rats each containing six animals received drug-loaded NLCs intraperitoneally (IP) or intranasally. Brain responses were then examined by using maximal electroshock (MES). The hind limb tonic extension:flexion inhibition ratio was measured at 15-, 30-, 60-, 90-, and 120-minute intervals. The drug concentration was also measured in plasma and brain at the most protective point using gas chromatography method. The particle size of NLCs was 154 ± 16 nm with drug-loading percentage of 47% ± 0.8% and drug release of 75% ± 1.9% after 21 days. In vivo results showed that there was a significant difference between protective effects of NLCs of VPA and control group 15, 30, 60, and 90 minutes after treatment via intranasal route (P < 0.05). Similar protective effect was observed in rats treated with NLCs of VPA in intranasal route and positive control in IP route (P > 0.05). Results of drug determination in brain and plasma showed that brain:plasma concentration ratio was much higher after intranasal administration of NLCs of VPA than the positive control group (IP route). In conclusion, intranasal administration of NLCs of VPA provided a better protection against MES seizure.

Development of single-drop microextraction and simultaneous derivatization followed by GC-MS for the determination of aliphatic amines in tobacco

In this work, for the first time, headspace (HS) single-drop microextraction and simultaneous derivatization followed by GC-MS was developed to determine the aliphatic amines in tobacco samples. In the HS extraction procedure, the mixture of derivatization reagent and organic solvent was employed as the extraction solvent for HS single-drop microextraction and in situ derivatization of aliphatic amine in the samples. Fast extraction and simultaneous derivatization of the analytes were performed in a single step, and the obtained derivatives in the microdrop extraction solvent were analyzed by GC-MS. The optimized experiment conditions were: sample preparation temperature of 80 degrees C and time of 30 min, HS extraction solvent (the mixture of benzyl alcohol and 2,3,4,5,6-pentafluorobenzaldehyde) volume of 2.0 microL, extraction time of 90 s. With the optimal conditions, the method validations were also studied. The method has good linearity (R(2) more than 0.99), accepted precision (RSD less than 13%), good recovery (98-104%) and low limit of detection (0.11-0.97 microg/g). Finally, the proposed technique was successfully applied to the analyses of aliphatic amines in tobacco samples of seven different brands. It was further demonstrated that the proposed method offered a simple, low-cost and reliable approach to determine aliphatic amines in tobacco samples.