Artifacts in trimethylsilyl derivatization reactions and ways to avoid them

doi:10.1016/S0021-9673(99)00267-8

Journal of Chromatography A

Volume 844, Issues 1–2, 4 June 1999, Pages 1-22

https://doi.org/10.1016/S0021-9673(99)00267-8 Get rights and content

Abstract

Trimethylsilyl derivatives are routinely employed in gas chromatography to increase the volatility and stability of organic compounds containing active hydrogens. Normally only the desired derivative is formed when organic compounds are derivatized with common silylation reagents. However, some compounds form additional unexpected derivatives or by-products (artifacts). Artifact formation leads to multiple peaks for the same compound or unexpected components in the gas chromatographic analysis of mixtures. This review includes silylation artifacts identified in our laboratory by mass spectrometry during the last 20 years and references to those found in the literature. Also, means of avoiding artifact formation are discussed in detail.

Introduction

Trimethylsilyl derivatives are routinely employed [1], [2], [3], [4], [5] in gas chromatography (GC) to increase the volatility and stability of organic compounds containing active hydrogens (see Fig. 1). Normally only the desired derivative is formed when organic compounds are derivatized with common silylation reagents such as BSA [N,O-bis(trimethylsilyl)acetamide] and BSTFA [N,O-bis(trimethylsilyl)trifluoroacetamide].

However, some functional groups such as aldehydes, amides, carboxylic acids, esters, ketones and phenols under certain conditions form additional unexpected derivatives from silylation reagents and their by-products (e.g., 1 and 2). We refer to these unexpected derivatives as silylation artifacts. Furthermore, even the derivatization reagent can react with itself, inorganic reagents, other organic reagents, or organic solvents to yield artifacts.

Artifacts are a common problem in analytical chemistry [6] and are noted in a wide variety of chromatography techniques. Artifact is either spelled artifact or artefact and both spellings are acceptable. The former spelling was employed in this article since searches [6] of several common databases showed that scientists prefer to spell the word with an “i”.

Artifact formation in silylation reactions leads to multiple peaks for the same compound or unexpected components in the gas chromatographic analysis of mixtures. This leads to confusion about the concentration of a component or the number of components present in the sample. For quantitative analyses, the responses for the multiple components can be summed (assuming equal responses) or derivatization conditions changed to avoid artifact formation. This report includes the types of artifacts noted in our laboratory during the last 20 years and references to those found in the literature. Also, means of avoiding artifact formation are discussed.

Section snippets

Instrumentation and sample preparation

Gas chromatography–mass spectrometry (GC–MS) data were obtained on Finnigan/MAT 4023, VG/Micromass 70, VG/Micromass Autospec, Hewlett-Packard MSD and Finnigan/MAT TSQ-700 mass spectrometers. The source temperature was set at 250°C on magnetic mass spectrometers and at 150°C on quadrupole mass spectrometers.

All reactions were performed in 2-ml disposable glass vials with crimp tops. Septa were sealed by crimping an aluminum top. Typically 1–5 mg of a sample were dissolved in 0.5 ml of a suitable

Results and discussion

In many of our examples, significant concentrations of silylation artifacts are only noted in the derivatization of reaction mixtures or crude samples, and not in the derivatization of pure samples. Apparently components not present in the pure samples lead to the formation of these artifacts. Many materials are reported [9] to catalyze the silylations of compounds with BSTFA and BSA. Catalysts reported include trimethylchlorosilane (TMCS), trifluoroacetic acid, hydrogen chloride, potassium

Summary of ways to avoid or minimize artifact formation

Normally silylation reactions yield the desired derivative with minimal optimization of reaction conditions. However, many different artifacts can be formed under certain circumstances. In addition, multiple peaks can be noted due to incomplete silylation of compounds. Several excellent references [1], [2], [3], [4], [5] discuss factors to consider in optimizing silylation reactions including reaction mechanisms, solvents, derivatization reagents/reagent mixtures, catalysts, temperatures,

Acknowledgments

I would like to thank Dr. John A. Hyatt and Dr. Robert J. Maleski at Eastman Chemical Company for useful mechanistic discussions in the preparation of this paper. I am also indebted to Dr. Henry M. Fales of the National Institutes of Health for useful suggestions for improving the text and for information on several silylation artifacts noted in his laboratory. I would also like to thank John L. Crawford, Nancy B. Depew and Robert J. Hale at Eastman Chemical Company for help in the acquisition

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ReviewArtifacts in trimethylsilyl derivatization reactions and ways to avoid them

Abstract

Introduction

Section snippets

Instrumentation and sample preparation

Results and discussion

Summary of ways to avoid or minimize artifact formation

Acknowledgments

Tetrahedron

J. Organomet. Chem.

J. Chromatogr.

J. Chromatogr.

Anal. Biochem.

Anal. Biochem.

J. Chromatogr.

Clin. Chim. Acta

Tetrahedron Lett.

J. Chromatogr.

Silylation of Organic Compounds

Handbook of Analytical Derivatization Reactions

Angew. Chem., Int. Ed. Engl.

Org. Mass Spectrom.

Anal. Chem.

J. Chromatogr. Sci.

Anal. Lett.

Review
Artifacts in trimethylsilyl derivatization reactions and ways to avoid them