Pervaporation in chemical analysis

Abstract

Unlike thermal processes such as distillation, pervaporation relies on the relative rates of solute permeation through a membrane and is a combination of evaporation and gas diffusion. The analytical pervaporation systems consist of a membrane module suitable for liquid sample introduction and a vacuum (or a sweeping gas) on the permeate side. It has been used in a wide range of applications including the analysis of various organic and inorganic compounds, and sample concentration. It has been directly interfaced with gas chromatography, spectrophotometry, capillary electrophoresis, electrochemical detectors, liquid chromatography, and mass spectrometry. A wide range of liquids, slurries, and solids samples has been analyzed using these techniques. This review highlights the basic principles of the pervaporation and the state of its current development as applied to analytical chemistry.

Introduction

Membrane separation is an emerging technology that has undergone rapid development in recent years. Serving as a selective barrier, its primary function is the separation of two bulk phases and controls the mass transfer between them. This allows the enrichment of the species of the interest and their removal from the sample matrix. The movement of the solutes or analytes across a membrane maybe driven by a chemical, pressure, or an electrical potential gradient [1]. The use of the membranes in analytical applications has become a preferred sample preparation option where the membrane can perform multiple functions that range from extraction, concentration, to cleanup prior to the detection by instrument. This is largely due to the fact that they facilitate extraction without the mixing of two phases, thus eliminating problems such as emulsion formation and high solvent usage [2]. Moreover, the sample and the extractant can be continuously brought into contact, thus providing the basis of continuous, real-time process leading to automation and online interfacing to instruments [3]. Some major large scale applications of membrane separation techniques include desalination, dialysis, ultrafiltration, gas separation, dehumidification, osmosis, reverse osmosis, electrodialysis, and pervaporation [4], while analytical applications range from volatile/semi-volatile organics to inorganics and metals.

Pervaporation is a promising alternative to conventional energy intensive processes such as distillation and evaporation. It is often referred to as “clean technology”, especially for the treatment of volatile organic compounds. The separation is not based on relative volatilities as in the case of thermal processes, but rather on the relative rates of permeation through a membrane. It is a combination of evaporation and gas diffusion in a single module [5]. The analytical pervaporation systems consist of a suitable membrane in a module, a delivery system for liquid feed, and a vacuum or a sweeping gas on the permeate side. It has been used in a wide range of applications including the analysis of various organic pollutants [6], [7], [8], [9] and inorganic compounds [10], [11], [12], [13], and has been directly interfaced with gas chromatography (GC), spectrophotometry, capillary electrophoresis (CE), liquid chromatography (LC), and mass spectrometry (MS) [14], [15], [16], [17], [18]. In pharmaceutical and clinical fields, this technique has been reported in a variety of matrices such as tablets, toothpaste, and urine [19], [20], [21]. In food analysis, a number of publications have reported the analysis ranging from liquids, slurries, to solids [17], [22], [23], [24], [25]. In addition, the authors believe that there are many other applications that are yet to be explored. This review highlights the fundamental principles of pervaporation, and the current status of analytical applications.