Hyphenation of ion exchange high-performance liquid chromatography with Fourier transform infrared detection for the determination of sugars in nonalcoholic beverages

Procedure for automated background correction in flow systems with infrared spectroscopic detection and changing liquid-phase composition

This paper describes a partial least squares (PLS) based automatic procedure to correct for changes in the spectral contribution of the solvent or solvent mixtures from solute spectra recorded in these solvents. The procedure was developed for successful on-line Fourier transform infrared (FT-IR) detection in gradient high-performance liquid chromatography (HPLC) separations. It requires a reference FT-IR data set containing all possible combinations of the expected variation in solvent composition. Furthermore, a spectral region (A) in these spectra is required where the solvents show absorption but the analytes do not. This is the case for the system ACN:H(2)O, an often-applied solvent mixture in gradient HPLC, in the spectral region from 2300-2400 cm(-1). By focusing on (A) the developed numerical method selects an appropriate background spectrum from the reference data set, which is then subtracted from the analyte spectra. The method was programmed in Matlab and tested on different isocratic and gradient on-line reversed phase liquid chromatography-Fourier transform infrared spectrometry (LC-FT-IR) data sets. This work describes a successful method to perform eluent correction in on-line coupling of FT-IR spectrometry with gradient LC.

Analysis of the monosaccharide composition of purified polysaccharides in Ganoderma atrum by capillary gas chromatography

INTRODUCTION

Ganoderma, one of the best-known traditional Chinese medicines, has attracted considerable attention owing to the fact that dozens of polysaccharides isolated from it have shown diverse and potentially significant pharmacological activities. However, no work has been reported on the analysis of monosaccharide composition of polysaccharide isolated from the aqueous extract of Ganoderma atrum yet.

OBJECTIVE

To develop a simple and sensitive GC-based method for the analysis of monosaccharide composition of purified polysaccharides in Ganoderma atrum.

METHODOLOGY

The polysaccharide was first hydrolysed to give the constituent monosaccharides, which were subsequently derived into acetylated aldononitriles and analysed by gas chromatography using a capillary column packed with a (5%phenyl) methylpolysiloxane stationary phase with the addition of acetyl inositol as the inner standard. High-performance liquid chromatography was also used for comparison.

RESULTS

The stable derivatives of the most common monosaccharides could be separated and reproducibly determined with high sensitivity. The limits of detection and quantification were 0.013 and 0.043 mg/mL, respectively. The intermediary precision values (expressed as the RSD) were less than 10%. The mean recovery of the method was 100 + or - 3%, with RSD values of less than 5%. The results obtained from GC and HPLC methods were found to be close to each other within acceptable error ranges.

CONCLUSION

This study demonstrated that the developed method could be applied as an accurate method for the compositional analysis of monosaccharides in the field of biological and biochemical study.

Determination of Peroxide-Based Explosives Using Liquid Chromatography with On-Line Infrared Detection

A nondestructive analytical method for peroxide-based explosives determination in solid samples is described. Reversed-phase high-performance liquid chromatography in combination with on-line Fourier transform infrared (FT-IR) detection is used for the analysis of triacetonetriperoxide (TATP) and hexamethylenetriperoxide diamine (HMTD). In contrast to other liquid chromatographic methods with optical detection, no derivatization or decomposition of the peroxides is required. The peroxides are identified and quantified via their characteristic absorption spectra in the mid-infrared range of the electromagnetic spectrum. The detection limit of 0.5 mmol L-1 for HMTD and 1 mmol L-1 for TATP allows the identification of the explosives in complex matrixes.

Simultaneous Determination of Carbohydrates, Carboxylic Acids, Alcohols, and Metals in Foods by High-Performance Liquid Chromatography Inductively Coupled Plasma Atomic Emission Spectrometry

The applicability of the HPLC-ICP-AES coupling for the simultaneous determination of carbohydrates, carboxylic acids, alcohols, and metals in a single chromatographic run has been demonstrated in the present work. Five saccharides, glucose, fructose, sucrose, sorbitol, and lactose; five carboxylic acids, citric, tartaric, malic, lactic, and acetic; and three alcohols, glycerol, ethanol, and methanol, have been determined. A H+ cation exchange column has been used to separate these compounds. The chromatograms have been obtained by monitoring the carbon emission signal at 193.09 nm. The results obtained by HPLC-ICP-AES have been compared against those found with conventional detection systems (i.e., refractive index, UV, and photodyode array detectors). The HPLC-ICP-AES method has shown the following features: (i) organic compounds and metals can be simultaneously determined; (ii) the detection method is universal; (iii) for nonvolatile organic compounds, a complete calibration line can be obtained from a single injection; and (iv) it provides absolute limits of detection similar to or lower than those found with conventional detection systems (i.e., on the order of several tens of nanograms of organic compound). The methodology has been validated through the analysis of food samples such as juices, isotonic beverages, wines, and a certified nonfat milk powder sample.

On-line cut-off technique and organic modifier addition aided signal enhancement for trace analysis of carbohydrates in cellulase hydrolysate by ion exclusion chromatography–electrospray ionization mass spectrometry

Paper cellulose has been hydrolyzed with calcium alginate immobilized cellulase to produce carbohydrate products and the three trace sugars, galactose, arabinose, and mannose in the cellulase hydrolysate have been analyzed by HPIEC/ESI-MS. Applying the on-line cut-off technique to the HPIEC/ESI-MS can cut the high concentration glucose off to eliminate its interference on the peaks of minor sugars and enhance their signals from 1.1- to 1.6-fold. However, the on-line post column addition of 15% ethanol to the eluate can increase the signal of the three trace sugars, galactose, arabinose, and mannose up to 17-, 23-, and 11-fold, respectively, and make the corresponding detection limits as 0.04, 0.04, and 0.03 ppm. The accuracies of the quantitative analysis for the three trace sugars with the signal enhanced HPIEC/ESI-MS by the two enhancement methods were larger than 95%. The precisions of the analytical results were also greatly improved by the assistance of the two techniques and were less than 6.5%. The quantitative analysis of the three trace sugars was performed with the internal standard method and the internal standard (IS) was sorbitol. Overall, the signal enhancement of HPIEC/ESI-MS and quantification of the three trace sugars by the on-line cut-off technique and organic modifier addition was successful.

Flow-through microdispenser for interfacing μ-HPLC to Raman and mid-IR spectroscopic detection

A flow-through microdispenser has been coupled to a micro HPLC separation system and used as a solvent elimination interface for Fourier transform infrared (FTIR) and Raman spectroscopic detection of the separated compounds. Using the microdispenser picoliter sized droplets can be generated and deposited on an appropriate target placed on a computerized x, y-stage. Evaporation of volatile solvent and buffer is rapid and allows analysis of the obtained dry deposits by various techniques. Due to the destruction free character of Raman and FTIR spectroscopy they can be applied sequentially to interrogate the same deposit. In the reported application five phenolic acids typically present in wine have been separated on a C-18 column technique using a mixture of water, methanol and acetic acid as mobile phase. For spectrum acquisition infrared and Raman microscopes have been used. The spectra recorded from the dried deposits of the separated compounds agreed well with the reference spectra of corresponding components.

Development of an amperometric biosensing method for the determination of L-fucose in pretreated urine

The first amperometric biosensing method for the determination of L-fucose is described. L-Fucose is the objective of much current research, as it is considered as a potential marker for various pathologic disorders. Recombinant L-fucose dehydrogenase, having as cofactor beta-nicotinamide adenine dinucleotide phosphate (NAD+P), was cross-linked in a water-soluble photosensitive polymer matrix, that is, polyvinyl alcohol (PVA) modified with styrylpyridinium (SbQ), in the presence of BSA and glutaraldehyde. The resulting membrane was sandwiched between two polycarbonate membranes and was mounted in an amperometric cell. The oxidation of the enzymatically produced NADPH was monitored at a platinum anode at +0.25 V versus a silver pseudoreference electrode in the presence of ferricyanide. The system was fully optimized with respect to various analytical parameters. Regarding to the mechanical properties of the membrane and the storage stability of the immobilized enzyme, various parameters were also optimized. Several methods for the pretreatment of urine samples were investigated. Treatment of the samples with PbO2 found to eliminate the interference effect of various electroactive species exist in urine; optimum incubation time was determined since at prolonged incubation times L-fucose is also affected. Calibration curves for the direct and the mediated monitoring of NADPH were liner over the concentration ranges 0.04-1.0 mM (r2=0.9995) and 0.03-3.0 mM (r2=0.9997) fucose, respectively. The detection limits (S/N 3) were 2 and 1.5 microM fucose, respectively. The R.S.D. of the mediated biosensor is better than 1.5% (n=10, 0.5 mM fucose). The proposed biosensor correlates well with a reference enzymatic method and exhibits very good working and storage stability.

High-performance liquid chromatography with diamond ATR-FTIR detection for the determination of carbohydrates, alcohols and organic acids in red wine

A horizontal diamond attenuated total reflection (ATR) element has been incorporated in a flow-through cell with low dead volume and used for on-line mid-IR detection in high-performance liquid chromatography. The chemical inertness of the ATR element permitted the use of a strongly acidic mobile phase in the isocratic separation. The hyphenation was used for the analysis of organic acids, sugars and alcohols in red wine. In the case of co-eluting analytes multivariate curve resolution-alternating least squares (MCR-ALS) was successfully employed for quantitative analysis.

Micellar electrokinetic chromatography with on-line Fourier transform infrared detection

Micellar electrokinetic chromatography (MEKC) was successfully coupled to Fourier transform infrared (FTIR) detection, using a micromachined IR-transparent flow cell with an optical path length of 15 micro m for the on-line detection of five neutral analytes. Tight connections between the flow cell and the capillaries were achieved by creating a small O-ring of UV-curing epoxy adhesive on the sharply cut capillary ends. The background electrolyte consisted of 15 mM phosphate buffer at pH 7 and 40 mM sodium dodecyl sulfate (SDS). Five analytes (paracetamol, caffeine, p-nitro benzyl alcohol, m-nitrophenol and p-nitrophenol) were successfully separated, yielding detailed IR stack plots that could be used for quantification and identification. Linear calibration graphs were obtained for each individual analyte present in mixtures at concentrations up to 10 mM. The limit of detection (3 S/N) ranged between 1.1 and 1.5 mM (1.2-1.8 ng). Analytes were identified by comparing spectra obtained during the MEKC separation with those resulting from completely filling the capillary with each individual analyte dissolved in the micelle-containing electrolyte. Information on the specific functional groups of all analytes could be elucidated from the spectra. Since FTIR is a nondestructive detection technique, a conventional on-line UV detector was introduced directly after the developed IR flow cell to test the system's performance and to demonstrate that tandem FTIR and UV detection is feasible.

Separation methods for taurine analysis in biological samples

Taurine plays an important role in a variety of physiological functions, pharmacological actions and pathological conditions. Many methods for taurine analysis, therefore, have been reported to monitor its levels in biological samples. This review discusses the following techniques: sample preparation; separation and determination methods including high-performance liquid chromatography, gas chromatography, ion chromatography, capillary electrophoresis and hyphenation procedures. It covers articles published between 1990 and 2001.

On-line fourier transform infrared detection in capillary electrophoresis

The coupling of Fourier transform infrared (FT-IR) spectroscopy as a new on-line detection principle in capillary electrophoresis (CE) is presented. To overcome the problem of total IR absorption by the fused-silica capillaries that are normally employed in CE separations, a micromachined IR-transparent flow cell was constructed. The cell consists of two IR-transparent CaF2 plates separated by a polymer coating and a titanium layer producing an IR detection window, 150 microm wide and 2 mm long, with a path length of 15 microm. The IR beam was focused on the detection window using an off-axis parabolic mirror in an optical device (made in-house) attached to an external optical port of the spectrometer. The connections between the fused-silica capillaries and the flow cell were made by a small O-ring of UV-curing epoxy adhesive on the sharply cut ends of the capillaries, allowing the capillaries to be easily replaced. Aqueous solutions comprising mixtures of adenosine, guanosine, and adenosine monophosphate were used to test the system's performance. Conventional on-line UV detection was employed to obtain reference measurements of analytes after the IR detection flow cell. The limit of FT-IR detection for all analytes (in absolute amounts) was in the nano- to picogram range corresponding to concentrations in the low-millimolar range.

Improved high-performance liquid chromatographic method to estimate aminosugars and its application to glycosaminoglycan determination in plasma and serum

An improved isocratic high-performance liquid chromatography (HPLC) method for the analysis of L-(-)-fucose. D-(+)-galactosamine, D-(+)-glucosamine, D-(+)-galactose, obtained by hydrolysis of glycosaminoglycans (GAGs) and D-(+)-glucose and D-(+)-mannose is described. The presence in circulation of GAGs, acid polysaccharide sequences of alternate monosaccharide units, aminosugar and uronic acid (galactose in keratan sulfate), has been measured in terms of their sugar components. To evaluate concentration of these circulating sugars we considered blood samples obtained from healthy humans. Plasma or serum was filtered through weak anion-exchange Ecteola-cellulose either untreated or after mild alkaline treatment. GAGs adhering to resin were recovered by salt elution, and desalted on Bio-Gel P-2 resin. GAG fractionation by charge was carried out on a strong anion exchanger. GAG composition was evaluated in terms of galactose and aminosugars, measured in HPLC by the proposed procedure using anion-exchange resin and pulsed amperometric detection. The mobile phase consisted of 0.02 M NaOH and elution was carried out at flow-rate of 1.0 ml/min. The amperometric detector was set as follows: t1 (0.5 s), E1 (+0.1 V); t2 (0.09 s), E2 (+0.6 V); t3 (0.05 s), E3 (-0.6 V). The analysis required 14 min. Calibration standard curves for the six analytes were linear from 0.25 to 40 microM. RSD values for intra- and inter-day variabilities were < or = 5.3% at concentrations between 0.25 and 40 microM. Accuracy, expressed as percentage error, ranged from - 16 to 14%. The method was specific and sensitive with quantitation limits of 1 pmol for L-(-)-fucose, D-galactosamine and D-glucosamine, 3 pmol for D-(+)-galactose and D-(+)-glucose and 5 pmol for D-(+)-mannose. The results of the assay showed higher GAG concentrations in serum than in plasma.

Development of a simple gradient LC-IR interface for the detection of terpenoids from the alpha-pinene-ozone reaction

The development of a simple interface between liquid chromatography and infrared spectroscopy (LC-IR) using a coaxial sprayer is described for less volatile analytes. The system consists of a transfer capillary, in which the analytes are transported from the separation column of the gradient-LC to the outlet of the sprayer. This transfer capillary is coaxially surrounded at the outlet by a stainless steel sprayer capillary, which is resistively heated and flushed with nitrogen gas. The samples are sprayed in the manner that the eluent is vaporized by the heated nitrogen when exiting the capillary, while the analytes are deposited on a moving slide made of infrared transparent material (ZnSe or CaF2). Afterwards the deposited compounds are analyzed with an infrared microscope in transmission. First results from reaction products of the gas phase reaction of alpha-pinene with ozone are presented.

An inductively coupled plasma carbon emission detector for aqueous carbohydrate separations by liquid chromatography

An inductively coupled plasma atomic emission spectrometer is used to detect carbon-containing compounds following separation by high-performance liquid chromatography. A calcium form ligand exchange column with distilled and deionized water as the mobile phase is used to separate carbohydrates. The eluting species are detected by monitoring the carbon atomic emission line at 193.09 nm. The mass detection limits using a photomultiplier tube for sucrose and glucose are 50 ng, while that for fructose is 60 ng. The carbon emission detector should provide the same detection limit for any compound with a similar mass percent of carbon, whether or not the compound exhibits appreciable absorption characteristics. While the carbon emission detector will universally detect any organic compound, it will discriminate against species with high molar absorptivity that may be present at low concentration. Such species may act as interferences in chromatograms generated with conventional UV-visible absorption detectors. To demonstrate the utility of the carbon emission detector, three sugars (glucose, fructose, sucrose) are determined in apple, crangrape, and orange juice.

Liquid chromatography-Fourier-transform infrared spectrometry

Over the past years the coupling of liquid chromatography (LC) and Fourier-transform infrared spectrometry (FT-IR) has been pursued primarily to achieve specific detection and/or identification of sample constituents. Two approaches can be discerned in the combination of LC and FT-IR. The first and simpler approach is to use a flow cell through which the effluent from the LC column is passed while the IR spectra are continuously recorded. The second approach involves elimination of the LC solvent prior to IR detection using an interface which evaporates the eluent and deposits the analytes onto a substrate. This paper provides a general overview of flow-cell based IR detection and briefly discusses early solvent-elimination interfaces for LC-FT-IR. A more comprehensive description is given of interface systems which use spraying to induce rapid eluent evaporation, and which basically represent the state-of-the-art in LC-FT-IR. Finally, the interface systems suitable for reversed-phase LC are summarized and the perspectives of LC-FT-IR are discussed. The overview indicates that flow-cell LC-FT-IR has rather poor detection limits but can be useful for the specific and quantitative detection of major constituents of mixtures. Solvent-elimination techniques, on the other hand, provide much better sensitivity and enhanced spectral quality which is essential when unambiguous identification of low-level constituents is required.