Development of a reliable method to determine water content by headspace gas chromatography/mass spectrometry with the standard addition technique

Abstract

A new and effective method for accurate water content determination using headspace gas chromatography/mass spectrometry (GC/MS) with the standard addition technique was developed. This method was applied to the analysis of commercially available water standards prepared in many kinds of solvent matrices. The results obtained were consistent with the standard specifications and the values obtained by Karl Fisher (KF) titration within the range of uncertainty. Furthermore, the method was also applied to biofuel samples such as biodiesel derived from palm. Finally, the results revealed that headspace GC/MS is a superior technique for water content analysis, and the developed method is applicable to a variety of analytes for which KF titration is not appropriate.

Determination of Trace Water Content in Petroleum and Petroleum Products

“…Thus, it is not surprising that the National Institute of Standards and Technology (NIST) has produced different reference materials to encompass different types of petroleum and petroleum products. Indeed, there has been some controversy and debate over the procedures used to produce some of the reference values even within this journal. ,− …”

“…The primary method used to determine water in petroleum and petroleum products is Karl Fisher titration (KFT). ,,,,, KFT has a wide dynamic range but can be problematic for samples having very low amounts of water. − , Under rigidly controlled conditions, KFT can have good precision, but the accuracy of problematic samples is open to question . The main problems of KFT are well-known, as indicated in Table .…”

“…A few alternatives to KFTs have been attempted for petroleum products, each having limited applicability and/or other analytical issues. For example, headspace gas chromatography (HSGC) has been attempted for the determination of water, ,,,− even though most stationary phases are not compatible with long-term exposure to water and/or provide poor peak shapes . With direct injection, volatile compounds often interfere with the water peak, while the nonvolatile compounds degrade in the injection port, producing unpredictable, slowly eluting peaks and column deterioration. ,, In HSGC, as in all trace water methods, atmospheric moisture is a significant problem .…”

“…For example, headspace gas chromatography (HSGC) has been attempted for the determination of water, ,,,− even though most stationary phases are not compatible with long-term exposure to water and/or provide poor peak shapes . With direct injection, volatile compounds often interfere with the water peak, while the nonvolatile compounds degrade in the injection port, producing unpredictable, slowly eluting peaks and column deterioration. ,, In HSGC, as in all trace water methods, atmospheric moisture is a significant problem . Indeed, this has given rise to a variety of attempts to reduce residual moisture by a variety of heating and dry gas purging procedures, even including placement of the entire GC apparatus and sample preparation area in a glovebox. ,, What is rarely discussed is that the dry purge gases as well as the GC carrier gases still may not be sufficiently dry to produce accurate and reproducible results for trace water analyses…”

“…1,4,5,10,11,19 KFT has a wide dynamic range but can be problematic for samples having very low amounts of water. [4][5][6][7][8][9][10][11]20 Under rigidly controlled conditions, KFT can have good precision, but the accuracy of problematic samples is open to question. 4 The main problems of KFT are well-known, as indicated in Table 1.…”