The development of liquid and gas chromatographic methods for the determination of water

Abstract

<p>Two liquid chromatographic (LC) methods and one gas chromatographic (GC) method for the determination of water are developed. In the LC methods, water in various analytical samples is separated from the sample matrices on either a single cation-exchange column or two cation-exchange columns via an ion-exclusion mechanism and determined using spectrophotometric detection. The detection system is based on a shift in the equilibrium between cinnamaldehyde and cinnamaldehyde dimethylacetal in the methanol eluent. The shift in equilibrium is linearly proportional to the amount of water present and occurs only in the presence of an acid catalyst. The mechanism of this unique detection system is studied in detail. The conditions for chromatographic separation and detection are optimized so that water can be accurately determined in a very short time with good sensitivity;In the single-column LC method, a short column (2.5 cm x 2.1 mm i.d.) packed with cation-exchange resin in the H[superscript]+ form is used. Under favorable conditions, water in a wide variety of samples can be determined in as little as twenty seconds. In the two-column method, water is separated from the sample matrix on a neutral Li[superscript]+-form column which is followed by a short H[superscript]+-form column to catalyze the cinnamaldehyde-acetal equilibrium that is necessary for the detection of water. With this method, water in almost any kind of organic sample, including samples which interfere with the single-column method, can be determined quickly and accurately;A third water determining method is developed that is based on gas chromatographic (GC) technique. The amount of water in analytical samples is determined by reaction with an ortho ester (such as triethylorthoformate), followed by measurement of a product of the reaction by capillary-column GC. A low concentration of methanesulfonic acid is dissolved in the reagent to catalyze the reaction. Various experimental parameters are investigated to optimize the method. A complete analysis, including the reaction and chromatographic separation requires only about five minutes. Water is determined in a large variety of liquid and solid samples.</p>