On-line desalting and carbohydrate analysis for immobilized enzyme hydrolysis of waste cellulosic biomass by column-switching high-performance liquid chromatography

A hybrid system integrating xylose dehydrogenase and NAD+ coupled with PtNPs@MWCNTs composite for the real-time biosensing of xylose

The wide application of xylose in the food, beverage, and pharmaceutical industries, as well as in the booming field of biorefinery, raises the demand for a rapid, accurate, and real-time xylose-sensing technique to rival the conventional methods based on chromatography, spectroscopy, and electrochemical analysis using non-specific enzymes or abiotic catalysts. Herein, a hybrid system comprising polyethylene glycerol swing-arm-tethered NAD⁺ and xylose dehydrogenase (XDH), coupled with platinum nanoparticles deposited on carbon nanotubes (PtNPs@MWCNTs), was constructed for the real-time sensing of xylose. The use of the PtNPs@MWCNTs composite enhanced the sensitivity of the electric response and reduced the oxidation potential of NADH significantly. Further, the NAD⁺ immobilization allowed an increase in its microenvironment concentration and facilitated cofactor regeneration. The screen-printed electrode cast with the hybrid system showed a wide xylose detection range of 0.5 to 10 mM or 3.33 to 66.61 mM, and a low detection limit of 0.01 mM or 3.33 mM (S/N = 3), when connected to a potentiostat or a homemade portable biosensor, respectively. The biosensor also exhibited excellent working stability as it retained 82% of its initial performance after 30 days. The analysis of various xylose-containing samples further revealed the merits of our portable xylose biosensor in real-time sensing, including its rapid response, inexpensive instrumentation, and high selectivity, suggesting its great potential in practical applications.

Liquid chromatographic isolation of individual carbohydrates from environmental matrices for stable carbon analysis and radiocarbon dating

Carbohydrates are among the most abundant organic molecules in both aquatic and terrestrial ecosystems; however, very few studies have addressed their isotopic signature using compound-specific isotope analysis, which provides additional information on their origin (δ¹³C) and fate (Δ¹⁴C). In this study, semi-preparative liquid chromatography with refractive index detection (HPLC-RI) was employed to produce pure carbohydrate targets for subsequent offline δ¹³C and Δ¹⁴C isotopic analysis. δ¹³C analysis was performed by elemental analyzer-isotope ratio mass spectrometer (EA-IRMS) whereas Δ¹⁴C analysis was performed by an innovative measurement procedure based on the direct combustion of the isolated fractions using an elemental analyzer coupled to the gas source of a mini carbon dating system (AixMICADAS). In general, four successive purifications with Na⁺, Ca²⁺, Pb²⁺, and Ca²⁺ cation-exchange columns were sufficient to produce pure carbohydrates. These carbohydrates were subsequently identified using mass spectrometry by comparing their mass spectra with those of authentic standards. The applicability of the proposed method was tested on two different environmental samples comprising marine particulate organic matter (POM) and total suspended atmospheric particles (TSP). The obtained results revealed that for the marine POM sample, the δ¹³C values of the individual carbohydrates ranged from -18.5 to -16.8‰, except for levoglucosan and mannosan, which presented values of -27.2 and -26.2‰, respectively. For the TSP sample, the δ¹³C values ranged from -26.4 to -25.0‰. The galactose and glucose Δ¹⁴C values were 19 and 43‰, respectively, for the POM sample. On the other hand, the levoglucosan radiocarbon value was 33‰ for the TSP sample. These results suggest that these carbohydrates exhibit a modern age in both of these samples. Radiocarbon HPLC collection window blanks, measured after the addition of phthalic acid (¹⁴C free blank), ranged from -988 to -986‰ for the abovementioned compounds, indicating a very small background isotopic influence from the whole purification procedure. Overall, the proposed method does not require derivatization steps, produces extremely low blanks, and may be applied to different types of environmental samples.

Membrane electrospray ionization for direct ultrasensitive biomarker quantitation in biofluids using mass spectrometry

The ability of rapid biomarker quantitation in raw biological samples would expand the application of mass spectrometry in clinical diagnosis. Up until now, the conventional chromatography-mass spectrometry method is time-consuming in both sample preparation and chromatography separation processes, while ambient ionization methods normally suffer from sensitivity. The membrane electrospray ionization (MESI) introduced in this study could not only achieve sensitive biomolecule quantitation, but also minimize the sample handling process. As a unique feature of MESI, both vertical and horizontal chemical separations could be achieved in real-time. With the capability of mass-selectively minimizing matrix effects from salts, small molecules, and macromolecules, ultrasensitive detection of cytochrome C (>500-fold sensitivity improvement) in raw urine samples was demonstrated in less than 20 min.

Immobilized enzyme reactors in HPLC and its application in inhibitor screening: A review

This paper sets out to summarize the literatures based on immobilized enzyme bio-chromatography and its application in inhibitors screening in the last decade. In order to screen enzyme inhibitors from a mass of compounds in preliminary screening, multi-pore materials with good biocompatibility are used for the supports of immobilizing enzymes, and then the immobilized enzyme reactor applied as the immobilized enzyme stationary phase in HPLC. Therefore, a technology platform of high throughput screening is gradually established to screen the enzyme inhibitors as new anti-tumor drugs. Here, we briefly summarize the selective methods of supports, immobilization techniques, co-immobilized enzymes system and the screening model.

Simultaneous analysis of aspartame and its hydrolysis products of Coca-Cola Zero by on-line postcolumn derivation fluorescence detection and ultraviolet detection coupled two-dimensional high-performance liquid chromatography

An innovative two-dimensional high-performance liquid chromatography system was developed for the simultaneous analysis of aspartame and its hydrolysis products of Coca-Cola Zero. A C8 reversed-phase chromatographic column with ultraviolet detection was used as the first dimension for the determination of aspartame, and a ligand-exchange chromatographic column with on-line postcolumn derivation fluorescence detection was employed as the second dimension for the analysis of amino acid enantiomers. The fluorimetric derivative reagent of amino acid enantiomers was o-phthaldialdehyde. The hydrolysis of aspartame in Coca-Cola Zero was induced by electric-heating or microwave heating. Aspartame was quantified by the matrix matched external standard calibration curve with a linear concentration range of 0-50 μg mL(-1) (r(2)=0.9984). The limit of detection (LOD) and the limit of quantification (LOQ) were 1.3 μg mL(-1) and 4.3 μg mL(-1), respectively. The amino acid enantiomers was analyzed by the matrix matched internal standard calibration method (D-leucine as the internal standard) with a linear concentration range of 0-10 μg mL(-1) (r(2)=0.9988-0.9997). The LODs and LOQs for L- and D-aspartic acid and L- and D-phenylalanine were 0.16-0.17 μg mL(-1) and 0.52-0.55 μg mL(-1), respectively, that was 12-13 times more sensitive than ultraviolet detection. The overall analysis accuracy for aspartame and amino acid enantiomers was 90.2-99.2% and 90.4-96.2%, respectively. The overall analysis precision for aspartame and amino acid enantiomers was 0.1-1.7% and 0.5-6.7%, respectively. Generally, the extent of aspartame hydrolysis increases with the increase of electro-thermal temperature, microwave power, and the duration of hydrolysis time. D-aspartic acid and D-phenylalanine can be observed with the electro-thermal racemization at the hydrolysis temperature 120°C for 1 day and only D-aspartic acid can be observed at the hydrolysis temperature 90°C for 2 and 3 days. For the microwave induced hydrolysis, only L-aspartic acid was detected at the power 560 W for 1 min and 320 W for 3 min.

Microbial and bioconversion production of D-xylitol and its detection and application

D-Xylitol is found in low content as a natural constituent of many fruits and vegetables. It is a five-carbon sugar polyol and has been used as a food additive and sweetening agent to replace sucrose, especially for non-insulin dependent diabetics. It has multiple beneficial health effects, such as the prevention of dental caries, and acute otitis media. In industry, it has been produced by chemical reduction of D-xylose mainly from photosynthetic biomass hydrolysates. As an alternative method of chemical reduction, biosynthesis of D-xylitol has been focused on the metabolically engineered Saccharomyces cerevisiae and Candida strains. In order to detect D-xylitol in the production processes, several detection methods have been established, such as gas chromatography (GC)-based methods, high performance liquid chromatography (HPLC)-based methods, LC-MS methods, and capillary electrophoresis methods (CE). The advantages and disadvantages of these methods are compared in this review.