Original Research Papers Temperature-Programmed Packed Capillary Liquid Chromatography Coupled to Fourier-Transform Infrared Spectroscopy Inge Bruheim, Paal Molander*, Elsa Lundanes, Tyge Greibrokk Department of Chemistry, University of Oslo, P.O.Box 1033 Blindern, 0315 Oslo, Norway; e-mail: pal.molander@kjemi.uio.no Espen Ommundsen Borealis AS, 3690 Stathelle, Norway Ms received: May 18, 2000; accepted: July 17, 2000 Key Words: Packed capillary liquid chromatography; temperature programming; Fourier-transform infrared spectroscopy; polymer additives; pneumatic nebulization Summary Temperature-programmed packed capillary liquid chromatography has been coupled off-line to Fourier-transform infrared spectroscopy, utilizing a commercially available interface with a pneumatic nebuli- zer rebuilt to handle low flow rates at elevated temperatures. The modified interface showed excellent performance with regard to non- aqueous reversed phase separations of polymer additives, resulting in constructed Gram-Schmidt chromatograms comparable to chro- matograms obtained using UV detection. The spray of the in-house constructed nebulizer was not influenced by temperature changes of the column effluent, and hence temperature-programmed gradient separations could be used successfully. The relative standard devia- tion of peak height was 4.4% (n = 5) and the mass limit of detection was determined to be about 40 ng, using a polymer antioxidant as model compound. The present instrumental coupling has been used for characterization of the antioxidant Irgafos P-EPQ. 1 Introduction The combination of liquid chromatography (LC) and mass spectrometry (MS) has recently become a widely used and powerful tool for characterization of non-volatile analytes. However, structural information obtained from LC-MS is often not sufficient for solute characterization due to limited fragmentation. For instance, MS lacks the ability to discrimi- nate between isomers. Infrared spectroscopy (IR), however, is suitable for the characterization of functional groups in addition to differentiation between structural isomers. Hence, the coupling of LC and Fourier-transform-IR (FT-IR) is a useful complementary technique to LC-MS. Interest in LC- FT-IR has increased during recent years, and both on-line and off-line approaches have been employed [1]. Elimina- tion of the mobile phase background signal is considered favorable regarding the off-line approach, where the column effluent is usually nebulized and the solutes deposited on a moving substrate suitable for IR detection. To facilitate effluent removal, interfaces such as thermospray [2], particle beam [3], and ultrasonic nebulizers [4] have been used with conventional columns. The low flow rates typical for minia- turized modes of LC are obviously beneficial regarding detection techniques involving solvent elimination. This fact was nicely exploited by Fujimoto et al. in their pioneering work on packed capillary LC-FT-IR [5], where the column effluent was deposited on a moving KBr disc, prior to eva- poration of the mobile phase. In succeeding studies, others have utilized the combination of narrow bore LC-FT-IR with pneumatic nebulization [6–8] and packed capillary LC-FT- IR with electrospray nebulization [9], and achieved improved detection limits as compared to those of conven- tional systems. Furthermore, miniaturized LC offers several other advantages compared to conventional LC, such as reduced consumption of mobile and stationary phases, increased mass sensitivity, possibility of using temperature programming for retention control, and availability of longer columns to enhance the resolution of complex mixtures and overall efficiency [10]. Thus, the use of packed capillary col- umns in LC has increased recently. Solvent gradient elution is the traditional way to adjust the elution strength of the mobile phase in LC during the chro- matographic run. However, this technique is not simple with columns of small inner diameters, due to instrumental limita- tions with regard to the low flow rates required [11]. In addi- tion, gradual changes of the mobile phase composition can have a negative influence on nebulization processes, such as in LC-FT-IR. In this regard, temperature-programmed LC is believed to be expedient compared to solvent gradient elu- tion. Packed capillary columns are recognized for their excel- lent suitability for use with temperature programming for retention control, due to their low thermal mass [10]. Tem- perature-programmed packed capillary LC separations have still only been scarcely explored by a limited number of research groups [12 – 23]. The aim of this study was to explore temperature-pro- grammed packed capillary LC coupled to solvent elimination FT-IR, utilizing the only commercially LC-FT-IR interface J. High Resol. Chromatogr. 2000, 23, (9) 525–530 i WILEY-VCH Verlag GmbH,D-69451 Weinheim 2000 0935-6304/2000/0909–0525$17.50+.50/0 525