Hsin-Lung Wu

Derivatization-GAS Chromatographic Determination of Perindopril

Abstract A capillary gas chromatographic method is described for the determination of perindopril, an anti-hypertensive agent. The method is based on the derivatization of perindopril with pentafluorobenzyl bromide in acetone, using potassium carbonate as a base catalyst. Under a mild condition, the highly polar and nonvolatile perindopril was derivatized into a derivative with suitable chromatographic properties. The resulting derivative was separated on an SE-54 capillary column and detected by a flame-ionization detector. Several parameters affecting the derivatization of perindopril were investigated. The linear range of the method for the determination of perindoplil was over 20–300 nmol. The detection limit (signal to noise ratio of 5) of perindopril in 0.2 mL acetone solution was about 3 nmol. Application of the method to the analysis of perindopril in tablets proved to be feasible.

Pentafluorobenzyl p-toluenesulphonate as a new derivatizing reagent for gas chromatographic determination of anions

A new derivatizing agent, pentafluorobenzyl p-toluenesulphonate, has been synthesized, which is designed to enhance the volatility of analytes and introduce a detector-oriented tag into the molecules for gas chromatography (GC) with electron-capture detection. The derivatization of several inorganic anions was studied, and a new GC method for their simultaneous determination has been developed. Bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulphide can be simultaneously derivatized to their pentafluorobenzyl derivatives using tetra-n-amylammonium chloride as the phase transfer catalyst. The derivatives were subsequently determined by GC with flame ionization detection. This method has also been applied to the determination of carboxylic acids or phenols, the derivatives of which were identified using mass spectrometry. The derivatives from bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulphide were pentafluorobenzyl bromide, pentafluorobenzyl iodide, pentafluorobenzyl cyanide, pentafluorobenzyl thiocyanate, α-nitro-2,3,4,5,6-pentafluorotoluene, pentafluorobenzyl nitrate and bis(pentafluorobenzyl) sulphide, respectively. The effects of added acid or base, and of the reaction time, on the pentafluorobenzylation are discussed.

Electron-capture gas chromatographic determination of cyanide as pentafluorobenzyl cyanide

Abstract A simple, sensitive and specific method was established for the determination of cyanide as pentafluorobenzyl cyanide, based on the derivatization of cyanide anion in an alkaline medium with pentafluorobenzyl bromide. The derivative formed in the reaction solution was injected directly into a gas chromatograph equipped with an electron-capture detector. The detection limit was about 0.2 ng of cyanide anion in 0.1 ml of aqueous sample (2 ppb). The effects of base, amount of pentafluorobenzyl bromide, solvents, reaction temperature and reaction time on the derivatization were investigated, and the optimal derivatization conditions were established. Interferences due to some anions commonly found in wastewater were examined and were found to be minimal except for thiocyanate ion. The proposed method was applied to the determination of cyanide in industrial wastewater and the results agreed well with those obtained using the pyridine—pyrazolone spectrophotometric method.

Simultaneous gas chromatographic determination of iodide, nitrite, sulphide and thiocyanate anions by derivatization with pentafluorobenzyl bromide

Abstract A gas chromatographic method is described for the simultaneous determination of iodide, nitrite, sulphide and thiocyanate anions as their pentafluorobenzyl derivatives. The method is based on transfer of the anions from the aqueous solution by n-hexadecyltrimethylammonium bromide into the dichloromethane organic phase, where derivatization with pentafluorobenzyl bromide occurs. Several parameters affecting the transfer and/or derivatization of the anions were investigated, including the phase-transfer catalyst, concentration of acid and base added, organic solvent, reaction time and the amount of derivatizing agent needed. Individual and simultaneous determinations of the anions could be achieved at sub-μmol levels initially in the aqueous phase, by use of a flame ionization detector.

Simultaneous gas chromatographic determination of cyanide, iodide, nitrite, sulphide and thiocyanate anions by derivatization with pentafluorobenzyl bromide and using a kryptand as phase-transfer catalyst

Abstract An improved gas chromatographic method has been established for the simultaneous determination of cyanide, iodide, nitrite, sulphide and thiocyanate anions as their volatile pentafluorobenzyl derivatives. The method is based on kryptate formation using Kryptofix 222 B polymer as complexing agent and phase-transfer catalyst to transfer the anions from aqueous alkaline solution to the dichloromethane organic phase for derivatization with pentafluorobenzyl bromide to be effected. Structural identification and correction of the cyanide derivative was studied. The parameters affecting the partition and/or derivatization of the anions were investigated, including the concentrations of acid and base in the aqueous phase. Individual and simultaneous determinations of the anions are attainable at sub-micromole levels with flame ionization detection.

Trace determinationof cyanide by derivatization and flame thermionic gas chromatography

Abstract A sensitive gas chromatographic method for the determination of cyanide at trace levels is described. The method is based on the derivatization of cyanide to benzonitrile, which is extracted with benzene and determined by flame thermionic gas chromatography. In the derivatization reaction, aqueous cyanide reacts with aniline and sodium nitrite in the presence of copper(II) sulphate and forms benzonitrile. Cyanide at concentrations between 3 ng/ml and 1.0 μg/ml can be detected with a linear response. Several anions tested do not interfere. The method was evaluated by analysing wastewater samples collected from various factories and by comparing the values obtained with those obtained by the pyridine-pyrazolone method, which has been used widely for the determination of cyanide. Good agreement was found between the two methods.

Derivatization of inorganic anions with pentafluorobenzyl methanesulphonate for gas chromatography

A new derivatizing reagent, pentafluorobenzyl methanesulphonate, has been synthesized and used to determine inorganic anions by gas chromatography. Bromide, iodide, cyanide, thiocyanate, nitrite and sulph iodide, cyanide, thiocyanate, nitrite and sulphide in water at mM levels could be simultaneously pentafluorobenzylated in dichloromethane, using tetra-n-amylammonium chloride as a phase-transfer catalyst. The resulting derivtives were subsequently determined by gas chromatography with flame ionization detection. In water at μM levels, except for cyanide and nitrate, the anions could also be derivatized to their pentafluorobenzyl derivatives in the biphasic reaction system and be detected by gas chromatography with electron-capture detection. In addition to the biphasic reaction method, bromide, iodide and thiocyanate were simultaneously pentafluorobenzylated in an homogen in an homogeneous reaction system of aqueous acetone or aqueous methanol, without the use of a phase-transfer catalyst.

Simultaneous determination of trace amounts of bromide and iodide by methylation with dimethyl sulphate and electron-capture gas chromatography

Abstract A specific sensitive gas chromatographic method is described for the simultaneous determination of trace quantities of bromide and iodide. Bromide and iodide are methylated with dimethyl sulphate at 70°C to form methyl bromide and methyl iodide, respectively. The resulting methyl derivatives are simultaneously determined by gas chromatography with electron-capture detection. The detection limits are 0.1 μ g -ml bromide application of the method of determination of bromide and iodide in spring-water is demonstrated. The results reveal that the recoveries are over 90% for both halides.

Butylation of inorganic anions for simultaneous determination by gas chromatography

Abstract Some aqueous inorganic anions were extracted into the organic layer as their tetra- n- butylammonium salts and then treated with n- butyl p- toluenesulphonate to yield their n- butyl derivatives which were determined by gas chromatography with flame ionization detection. Bromide, iodide, thiocyanate and nitrate were thereby derivatized and determined. The n- butyl derivatives were identified by comparison of the retention times as n- butyl bromide, n- butyl iodide, n- butyl thiocyanate and n- butyl nitrate, respectively. The effects of added base or acid, shaking time and phase-transfer catalyst on the extraction of the anions were discussed. By this method the anions could be determined simultaneously in the concentration range 10–50 m M .

Derivatization-Gas Chromatographic Determination Of Mercaptans

Abstract After being precipitated as silver mercaptides, mercaptans were converted into their pentafluorobenzyl derivatives in high yields by reaction with sodium sulfide and then with pentafluorobenzyl bromide. The derivatives were analyzed down to sub-ppm levels by gas chromatography with a flame ionization detector. It is possible that the above method is developed for the trace analysis of mercaptans in environmental matrices.