Highly selective and ultra-sensitive electrochemical sensor behavior of 3D SWCNT-BODIPY hybrid material for eserine detection.

In this work, 4,4-difluoro-8-(4-hydroxyphenyl)- 2,6-diethynly-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (BODIPY) having double terminal ethynyl groups was synthesized. Three dimensional single walled carbon nanotube (SWCNT)-BODIPY hybrid material (3D SWCNT-BODIPY) was synthesized by the reaction of BODIPY bearing double terminal ethynyl groups with azido containing SWCNTs via "Click" reaction. The structural properties and electrochemical detection of eserine (a pesticide) on BODIPY functionalized SWCNTs as a three dimensional (3D) material were investigated. A glassy carbon electrode (GCE) was modified by 3D SWCNT-BODIPY hybrid material for the determination of eserine in the range of 0.25-2.25 µM. In the study by the square wave voltammetry (SWV), the bare GCE showed no response, while the new peak at - 0.6 V appeared in the case of the modified electrode. The detection limit and quantification were determined as 160 nM and 528 nM for eserine on the 3D SWCNT-BODIPY modified electrode, respectively. Eserine was also determined with a standard addition method in different brands of orange juices, and the recovery of eserine was obtained to be in the range of 102.09% and 103.22%. This study clearly indicates that the 3D SWCNT-BODIPY modified electrode tested as an electrochemical sensor was found to be highly selective and sensitive to eserine.

Determination of physostigmine and pyridostigmine in pharmaceutical formulations by capillary electrophoresis.

Physostigmine (PHY) and pyridostigmine (PYR) are two important anticholinesterase compounds with several clinical uses. Recently, PHY has been investigated for the treatment of senile dementia in Alzheimer's disease. However, both PHY and PYR have gained importance as antidotes for anticholinergic drugs. In military medicine, PYR is used as a prophylactic against nerve gas poisoning and was used in Saudi Arabia during the Gulf War in 1991. A new capillary zone electrophoresis (CZE) method for the rapid determination of PHY and PYR in pharmaceutical preparations has been developed. An untreated fused-silica capillary tube (75 microm i.d., 44 cm total length, 36.5 cm length to the detector) was employed with detection at 200 and 270 nm for PHY and PYR, respectively. The optimal separation conditions for PHY were: 50 mM boric acid-HCl buffer (pH 3.25) with 30 mM NaClO4, electrokinetic injection for 5 sec at -5 kV, temperature 25 degrees C, and separation voltage 15 kV. The optimal separation conditions for PYR were: 20 mM phosphate buffer (pH 7), electrokinetic injection for 20 sec at -10 kV, temperature 25 degrees C, and separation voltage 15 kV. The limits of detection (LOD, S/N = 3) were 70 and 60 ppb for PHY and PYR, respectively. The method can be used for the monitoring of possible main degradation products in tablets of military antidote formulations.

Micro-CLC as an interface between SLM extraction and CZE for enhancement of sensitivity and selectivity in bioanalysis of drugs.

This work demonstrates the high selectivity and sensitivity obtainable in bioanalysis using the supported liquid membrane (SLM) technique coupled on line with capillary zone electrophoresis (CZE) through a micro-column liquid chromatography (CLC) interface. The system utilizes two selective, sequential enrichment steps before the third analyte focusing and separation step with double-stacking CZE. The enantiomers of bambuterol in human plasma can be concentrated about 40,000 times (approx. 6 times by the SLM treatment, approx. 17 times by micro-CLC focusing, and approx. 400 times by double-stacking CZE) on their way through the system, and extremely high selectivity is obtained. Determinations in the subnanomolar region are achievable for the enantiomers despite relatively weak UV absorbance. Good performance of the entire procedure is demonstrated and a method to increase the sample throughput is presented.

Extraction of physostigmine from biologic fluids and analysis by liquid chromatography with electrochemical detection.

A rapid and simple method is described for the extraction of physostigmine (Phy) and its hydrolysis product, eseroline, from plasma, whole blood, and cerebrospinal fluid (CSF) and their subsequent quantitation by high-performance liquid chromatography (HPLC) with dual electrode electrochemical detection. Phy and eseroline were extracted from biologic fluids with cyano-phase columns eluted with 0.1 M citrate buffer, pH 4 containing 20% acetonitrile. Phy recovery from citrate buffer and CSF was nearly 100%. Phy recovery from plasma was 82% when methanol was used to precipitate proteins and 62% when HClO4 was used to precipitate proteins. Phy recovery from whole blood was only 17%. These results are discussed in the context of attempting to measure Phy in fluids of patients receiving this drug in clinical trials for the treatment of Alzheimer's disease.

Determination of physostigmine in plasma and brain by HPLC.

A specific, reliable, and accurate high performance liquid chromatographic method is described for the determination of physostigmine in plasma and brain using carbaryl as an internal standard. Plasma and brain containing physostigmine were first precipitated with TCA, and then carbaryl was added. This was followed by chloroform extraction and then evaporation. The residue was reconstituted in the mobile phase. Physostigmine, its hydrolyzed product eseroline, and carbaryl were separated on a reversed-phase column eluted with mobile phase containing octanesulfonic acid with phosphate buffer in a methanol and water solution. The eluted compounds were detected at 245 nm, and physostigmine was quantified from the ratio of the area of physostigmine to carbaryl peaks. The chromatography was complete within 15 min. The dynamic range of quantitation of physostigmine was 0.05 micrograms to 0.5 micrograms/mL plasma or per gram of brain. Analytical recoveries varied from 95 to 107% over this range. Coefficient of variation ranged from 1.7 to 9.5%. This method was applied to study plasma and brain concentration in rats after 650 micrograms/kg intramuscular administration of physostigmine. The ratio of brain to plasma was found to be 0.48 and 1.97 at 15 and 30 min, respectively.