Column liquid chromatography: equipment and instrumentation

Postcolumn renewal of sensor surfaces for high-performance liquid chromatography-surface plasmon resonance detection

The combination of high-performance liquid chromatography (HPLC) with surface plasmon resonance (SPR) for continuous separation and label-free detection of protein samples is described. The detection was realized by electrostatic adsorption of proteins bearing positive and negative charges onto chemically modified SPR sensors in two separate SPR channels. One SPR channel is coated with carboxymethylated dextran which facilitates the detection of positively charged proteins, whereas the other, devoted to the monitoring of negatively charged proteins, is covered with ethylenediamine molecules attached onto a dextran surface. Renewal of the sensor surface in the channels can be accomplished by introducing regeneration solutions through two six-port valves. The coupled technique (HPLC-SPR) was assessed for its analytical figures of merit and applied to the quantification of lysozyme in human milk samples. Unlike the SPR detection of bulk solution refractive index changes during chromatographic peak elutions, the highest sensitivity of SPR is retained in this work since the measurement is performed at the SPR sensor surface where the evanescent field is the strongest. The renewable SPR detection of continuous separations is reproducible and versatile and does not require the separated proteins to contain chromophores or to be prelabeled with a tag (e.g., a redox-active or fluorescent molecule). Such generality makes SPR complementary to other types of chromatographic detectors.

Retention mechanism of l-glutamide-derived noncrystalline stationary phases in reversed-phase high-performance liquid chromatography and application for separation of nucleic acid constituents

Double alkylated L-glutamide-derived noncrystalline stationary phases Sil-DSG and Sil-DBG have been prepared by coupling N',N''-dioctadecyl-N-[4-carboxybutanoyl]-L-glutamide (DSG) and N',N'',-dibutyl-N-[4-carboxybutanoyl]-L-glutamide (DBG) with aminopropylated silica (Sil-APS). TEM observations of DSG and DBG showed that lipid DSG can aggregate in organic solvents (methanol, chloroform, toluene, etc.) and self-assembled nano fibers are observed while such fibrous aggregations are not observed for DBG. The resulting chromatographic data have been provided information about its selective interaction with guest molecules (PAHs) in RP-HPLC. We have observed that the carbonyl groups in Sil-DSG exist in ordered state by forming a condensing thin layer over silica surface while DBG cannot form such an ordered state due to its lower order of short alkyl chain. The ordered carbonyl groups present in Sil-DSG promotes multiple carbonyl pi-benzene pi interactions with guest PAHs isomers which enhance the selectivity for these compounds. The contribution of pi-pi interactions was also supported by the substantial effects on the selectivity of benzene and nitrobenzenes. The effect of pi-electron containing solvent on the retention behavior of the PAHs was also studied. The selectivity for nucleic acid constituents, i.e. nucleosides and its bases were also evaluated by Sil-DSG and the selectivity for these compounds on Sil-DSG was compared with the selectivity of conventional polymeric ODS phase. It has been found that Sil-DSG provided higher selectivity for nucleic acid constituents than polymeric ODS and that HPLC packing materials can be efficiently employed for routine analysis of these compounds. The effect of methanol content on the separation behavior of nucleosides was also studied.

Detector for Liquid Chromatography Based on Acoustic Emissions from an Oscillating Flame

The acoustic flame detector (AFD) is examined as a novel detector for liquid chromatography (LC). It is based upon the acoustic emission frequency of an oscillating hydrogen/oxygen premixed flame and produces a universal response toward organic molecules. A stable frequency near 1000 Hz, which further depends on mobile-phase composition, is achieved for flow rates in the microliter per minute range. The mass flow sensitivity of the AFD demonstrates a linear response over 3 orders of magnitude and a detection limit (S/sigma = 3) of approximately 15 ng of C/s for a series of alcohols. For cyclopentanol, this amounts to an injected mass of approximately 77 ng based on a 0.5-microL injection of a 196 ppm solution in methanol (flow rate 20 microL/min methanol; peak width 30 s). Similar sensitivity is observed using a water mobile phase. Low-frequency (1/f ) noise contributions are dominant with or without mobile phase present. The AFD demonstrates a uniform molar sensitivity toward carbon compounds independent of their optical properties or volatility. Results suggest the device might serve as a simple, inexpensive universal LC detector.

Application of size exclusion electrochromatography to the microanalytical determination of the molecular mass distribution of celluloses from objects of cultural and historical value

The molecular mass distributions (MMD) of celluloses from paper and other sources were determined by size exclusion electrochromatography (SEEC). Prior to the separation the celluloses were chemically modified with phenyl isocyanate into their tricarbanilate derivatives (CTC). Sensitive UV detection of the CTC could be performed at a wavelength of 210 nm. The solvent used for separation was acetone. With this solvent, a high electroosmotic flow could be generated in columns packed with bare silica particles. With a column packed with particles with a nominal pore size of 30 nm, use of a mobile phase with a salt concentration of 0.1 mM was found to be optimal with respect to mass selectivity and efficiency. The workable mass range under these conditions was from 2 kDa to at least 500 kDa for (native) celluloses. The SEEC method was compared to classical pressure-driven size exclusion chromatography (PD-SEC). It is shown that the two methods give comparable results for the MMD of celluloses, while SEEC has important advantages in terms of speed and sample consumption. With SEEC, the analysis time was less than 20 min. The method was applied for the study of cellulose degradation during (artificial) aging of paper samples. A clear reduction of the average molecular mass of cellulose during aging was observed. With SEEC, the required sample amount is strongly reduced compared to classical PD-SEC. With a single paper fiber (after derivatization), multiple analyses could be carried out. It is argued that this is not only important for the analysis of unique objects but that it also allows the detection of MMD heterogeneities on a microscale. The strong reduction in sample size may be relevant when local heterogeneities in other types of polymer samples are studied.