Elsevier

Journal of Chromatography A

Volume 1466, 30 September 2016, Pages 129-135
Journal of Chromatography A

Performance and selectivity of dicyanuric-functionalized polycaprolactone as stationary phase for capillary gas chromatography

https://doi.org/10.1016/j.chroma.2016.08.070Get rights and content

Highlights

  • Unique amphiphilic selectivity for apolar to polar analytes.

  • High-resolution capability for structural and positional isomers.

  • Good column inertness for analytes prone to peak tailing.

Abstract

Dicyanuric-functionalized polycaprolactone (DPCL) was explored for its separation performance in gas chromatography (GC). The statically coated DPCL capillary column (0.25 mm, i.d.) showed column efficiency of 3460 plates/m determined by naphthalene at 120 °C. McReynolds constants and Abrahaḿs system constants were also determined to evaluate the polarity and possible molecular interactions of the stationary phase. As a result, DPCL column exhibited excellent separation performance for diverse types of analytes with good peak shapes. Most interestingly, it shows unique amphiphilic selectivity and high-resolution capability for both apolar to polar isomers. In addition, DPCL column had good column repeatability with the RSD values below 0.06% for run-to-run, 0.09–0.40% for day-to-day and 1.7–3.6% for column-to-column, and good thermal stability up to 280 °C. The high selectivity and resolving capability demonstrate the great advantages of the DPCL stationary phase for simultaneous determination of analytes of great variety in complex samples.

Introduction

Polymeric materials with good film-forming ability and stability have been used as stationary phases for gas chromatography (GC). Among them, polysiloxanes and polyethylene glycol (PEG, e.g. PEG–20 M) with polyether backbone structures are most widely used and well recognized [1], [2]. Developing stationary phases with high resolving capability has been the pursuit of researchers in GC to address the growing need for separation of analytes with high resemblance in complex samples, such as structural and positional isomers covering from nonpolar to polar ones. Over the past decade, the reported stationary phases for GC separation of such isomers mainly involved macrocycles [3], [4], [5], metal-organic frameworks [6], [7], [8], ionic liquids [9], [10] and liquid crystals [11]. Most of them showed high selectivity for nonpolar to weakly polar isomers such as alkanes and alkyl-substituted benzenes. It is not well documented for a GC stationary phase that possesses high resolution for both apolar and polar isomers due to their large difference in polarity.

Poly(Ɛ-caprolactone) (PCL) is a linear polyester with repeated hexanoate units. PCL-based macroporous biocomposites [12], [13] and amphiphilic polyesters [14], [15] were investigated for drug delivery and protein adsorption, respectively. PCL functionalized with dicyanuric units (DPCL, Fig. 1) showed the enhanced recognition ability of the polymer [16] through additional H-bonding interaction of cyanuric units with specific molecules [16], [17], [18]. Unlike PEG with a simple composition, DPCL is a linear polyester with amphiphilic nature, composed of repeated hexanoate units and benzoate, cyanuric and 1,2,3-triazole units. Its unique structure and physicochemical stability interested us to investigate its separation capability as GC stationary phase, especially its potential amphiphilic selectivity. Undoubtedly, a stationary phase with amphiphilic selectivity is essential for GC analysis of complex samples.

Herein, we present the investigation of DPCL stationary phase for GC separations regarding its polarity, selectivity, resolving ability and retention trend for analytes with a wide varying polarity, and their structural and positional isomers. Also, the separation ability of the DPCL stationary phase was evaluated in comparison with the typical polar PEG–20 M phase (using a commercial column). Moreover, column repeatability, reproducibility and thermal stability were evaluated. To the best of our knowledge, this is the first report on employing PCL-based polymers as stationary phases for chromatographic separations, showing their promising future in this field.

Section snippets

Materials and equipment

All chemicals and reagents used in this work were at least of analytical grade and used without purification. Octane, nonane, decane, undecane, nonanal, 2,3-butanediol, 1-octanol, methyl decanoate, methyl undecanoate, 2,6-dimethylaniline, 2-ethylhexanoic acid, 2, 6-dimethylphenol, methyl dodecanoate, o-dichlorobenzene, m-dichlorobenzene, o-cresol, p-cresol, o-dibromobenzene, p-dibromobenzene, m-dibromobenzene, o-diethylbenzene, p-diethylbenzene, m-diethylbenzene, 2,2,3-trimethylbutane, 2,

Characterization of DPCL stationary phase and capillary column

The thermal stability of the DPCL stationary phase was measured by thermal gravimetric analysis (TGA). As shown in Fig. 2, the DPCL stationary phase showed about 10% weight loss at 300 °C, suggesting its intrinsically good thermal stability. Moreover, the Golay curve relating the heights equivalent to a theoretical plate (HETP) with flow rates was determined by naphthalene at 120 °C, showing the minimum HETP of 0.288 mm at 0.40 mL/min with the column efficiency of 3460 plates/m.

Polarity of the DPCL

Conclusions

Herein, we present the first example of PCL-based stationary phases for GC separations. The statically coated DPCL column without any deactivation exhibits good separation performance and column inertness for analytes of different types with good peak shapes, including those that are labile to peak tailing. Most importantly, it exhibits interesting amphiphilic selectivity and high-resolution performance for analytes of high resemblance, especially their structural and positional isomers.

Acknowledgments

The authors are grateful for the financial support by the National Natural Science Foundation of China (21575013) and the 111 Project B07012 in China.

References (25)

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