Reported Methods of Analysis

Most of the reported methods of analysis of valproic acid and its sodium salt in biological fluids rely on the use of chromatography, especially gas chromatography, although high performance liquid chromatography (HPLC) is also reported. Other methods, such as flow injection analysis, enzyme-immunoassay, fluorescence-polarization capillary electrophoresis, and potentiometry are sometimes used. The reported methods can be classified as follows. 

Sodium valproate has been determined in pharmaceuticals using a valproate selective electrode [13,14]. The electroactive material was a valproate-methyl-tris (tetra-decyl)ammonium ion-pair complex in decanol. Silver-silver chloride electrode was used as the reference electrode. The electrode life span was 1 month. Determination of 90-1500 pg/mL in aqueous solution by direct potentiometry gave an average recovery of 100.0% and a response time of 1 min. 

Three anticonvulsant drugs including valproic acid were determined using different dyes as ion-pair reagents. Gentian violet was used for the spectrophotometric detection at 588 nm and acridine orange for the fluorimetric detection at 470 nm after excitation at 297 nm. Calibration graphs were linear for 5-50 pg/mL 2.5 0.50 pg/mL for the spectrophotometric and fluorimetric methods, respectively [15]. 

Nuclear magnetic resonance spectroscopy was investigated as a method to screen for organic substances (and metabolites) in patients with indications of a drug overdose [17]. Urine specimens containing valproic acid were examined by H-NMR spectroscopy at 300 MHz and the results compared with GC MS. 

A competitive fluorescence-polarization immunoassay method was described for the monitoring of 12 drugs including valproic acid [18]. Samples (serum or plasma) were deproteinated. Fluorescence from the fluorescein-labeled analyte used as tracer was excited at 488 nm and polarization of light emitted at 531 nm was measured. The calibration was stable for 4 weeks and the coefficient of variation was below 10%. A single measurement took 8-10 min. 

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European Commission, Residues Guidance for Generating and Reporting Methods of Analysis in Support of Pre-registration Data Requirements for Annex II (Part A, Section 4) and Annex III (Part A, Section 5) of Directive 91/414, SANCO/3029/99 rev. 4, 11.07.00. European Commission, Bmssels (2000). 

REPORTED METHODS OF ANALYSIS 6.1. Application and associated history... 

The first reported method of analysis for halo-thane in blood was by turbidimetric measurement. Halo-thane was extracted from blood with petroleum ether. 

It is in the study of this phenomenon where two-dimensional GC offers by far the most superior method of analysis. The use of chiral selector stationary phases, in particular modified cyclodextrin types, allows apolar primary and atropisomer selective secondary separation. Reported two-dimensional methods have been successful... 

In the case of the low abundance of some compounds, there are difficulties with signal overlap. To overcome these difficulties, there have been developments involving NMR hyphenation with techniques such as HPLC and mass spectrometry. In LC/NMR methods of analysis, NMR is used as the detector following LC separation and this technique is capable of detecting low concentrations in the nanogram range. This technique has been reported for the detection and identification of flavanoids in fruit juices and the characterization of sugars in wine [17]. 

CODEX alimentarius commission, Report of the 21st Session of the Codex Committee on Methods of Analysis and Sampling - ALINORM 97/ 23A, Rome, FAO, 1997. 

The mass of sample taken for analysis is primarily dependent on four factors (1) the amount of material available, (2) the concentration of the analyte, (3) the heterogeneity of the sample, and (4) the method of analysis. Most conventional solvent extraction techniques currently start with more sample than is required, use more extraction solvent than is necessary, and ultimately only analyze 0.1% of the material prepared, e.g., 1 pi from 1 ml. Micro-extraction techniques [468] can be used in conjunction with on-line LC-GC or LC-MS to utilize the whole extract in the final determinations. This approach can significantly reduce the size of sample required and the volume of solvent used. Many workers have reported the use of solid phase microextraction (SPME) in different environmental matrices for various pollutants [288,342,345,469 - 477]. 

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