An enzymatic flow analysis method for the determination of phosphatidylcholine in sediment pore waters and extracts

A sensitive and selective flow injection method for the determination of phosphatidylcholine (PC) in sediment pore waters and extracts is described. It involves the use of phospholipase C, alkaline phosphatase and choline oxidase co-immobilized on controlled pore glass in a packed column reactor. The final product of the enzymatic reaction of phosphatidylcholine is hydrogen peroxide, and this is detected by measuring the chemiluminescence emission resulting from cobalt(II) catalysed reaction with luminol. The flow injection method is rapid (30 injections/h), reproducible (1.4% R.S.D. at 3 μM PC, n = 10) with a detection limit of 0.14 μM (estimated from 3σ_n−1 of the measured blank). A linear calibration response was obtained over a concentration range of 0.5-9 μM (r = 0.999). The method has been applied to the determination of phosphatidylcholine in sediment extracts and sediment pore waters.     

Selective and sensitive electrochemical detection of glucose in neutral solution using platinum-lead alloy nanoparticle/carbon nanotube nanocomposites

Electrodeposition of Pt-Pb nanoparticles (PtPbNPs) to multi-walled carbon nanotubes (MWCNTs) resulted in a stable PtPbNP/MWCNT nanocomposite with high electrocatalytic activity to glucose oxidation in either neutral or alkaline medium. More importantly, the nanocomposite electrode with a slight modification exhibited high sensitivity, high selectivity, and low detection limit in amperometric glucose sensing at physiological neutral pH (poised at a negative potential). At +0.30 V in neutral solution, the nanocomposite electrode exhibited linearity up to 11 mM of glucose with a sensitivity of 17.8 μA cm⁻² mM⁻¹ and a detection limit of 1.8 μM (S/N = 3). Electroactive ascorbic acid (0.1 mM), uric acid (0.1 mM) and fructose (0.3 mM) invoked only 23%, 14% and 9%, respectively, of the current response obtained for 3 mM glucose. At −0.15 V in neutral solution, the electrode responded linearly to glucose up to 5 mM with a detection limit of 0.16 mM (S/N = 3) and detection sensitivity of ∼18 μA cm⁻² mM⁻¹. At this negative potential, ascorbic acid, uric acid, and fructose were not electroactive, therefore, not interfering with glucose sensing. Modification of the nanocomposite electrode with Nafion coating followed by electrodeposition of a second layer of PtPbNPs on the Nafion coated PtPbNP/MWCNT nanocomposite produced a glucose sensor (poised at −0.15 V) with a lower detection limit (7.0 μM at S/N = 3) and comparable sensitivity, selectivity and linearity compared to the PtPbNP/MWCNT nanocomposite. The Nafion coating lowered the detection limit by reducing the background noise, while the second layer of PtPbNPs restored the sensitivity to the level before Nafion coating.     

In situ chemo-synthesized multi-wall carbon nanotube-conductive polyaniline nanocomposites: characterization and application for a glucose amperometric biosensor

A new glucose amperometric biosensor, based on electrodeposition of platinum nanoparticles onto the surface of multi-wall carbon nanotube (MWNT)-polyaniline (PANI) nanocomposites, and then immobilizing glucose oxidase (GOD) with covalent interaction and adsorption effect, was constructed in this paper. Firstly, the MWNT-PANI nanocomposites had been synthesized by in situ polymerization and were characterized through transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, and ultraviolet and visible (UV-vis) absorption spectra. The assembled process of the modified electrode was probed by scanning electron microscopy (SEM) and cyclic voltammetry (CV). Chronoamperometry was used to study the electrochemical performance of the resulting biosensor. The glucose biosensor exhibited a linear calibration curve over the range from 3.0 μM to 8.2 mM, with a detection limit of 1.0 μM and a high sensitivity of 16.1 μA mM⁻¹. The biosensor also showed a short response time (within 5 s). Furthermore, the reproducibility, stability and interferences of the biosensor were also investigated.     

Reusable and robust high sensitive non-enzymatic glucose sensor based on Ni(OH)2 nanoparticles

Nickel hydroxide nanoparticles were successfully electrodeposited on graphite electrode (Gr/NiONP) and employed as a robust non-enzymatic glucose sensor. The results of cyclic voltammetry (CV) and chronoamperometry demonstrated that the Gr/NiONP electrode displayed high electrocatalytic activity toward glucose. The oxidation current is directly related to the glucose concentration from 1 μM to 15 mM. Besides, the glucose sensor displayed high sensitivity (2400 μA mM⁻¹ cm⁻²) with a detection limit of 0.53 μM (S/N = 3) in basic solution. Moreover, the sensor showed excellent selectivity, reproducibility and stability properties. The relative standard deviation is 1.2% for 10 successive measurements in 16 μM glucose. Interestingly, the signal for glucose was maintained at 95% of its initial value even after 6 months of storage under ambient conditions. Gr/NiONP electrode has also been tested to detect glucose in human serum with satisfactory results.     

Microchip capillary electrophoresis with amperometric detection for several carbohydrates

Microchip capillary electrophoresis (μCE) with amperometric detection at Cu electrode benefited fast separation and direct detection of carbohydrates. The working electrode of 50-μm Cu wire attached nearly against the channel outlet—4 μm, where it benefited collecting detection current and suppressing overwhelming noise. The use of alkaline medium was essential to separating and detecting carbohydrates, which dissociated into the sensitive alcolate anions. The 10-cm serpentine chip, though lengthening the migration time, it provided better efficiency. Sucrose, cellobiose, glucose, and fructose migrated from the outlet in 400 s +2000 V. The linear calibration plots ranging from 10 to 1000 μM with regression coefficients better than 0.996 were obtained. The injection-to-injection reproducibility of 1.24% (n=7) for glucose in peak current and 0.6% for migration times were excellent. The detection limit was low, down to 2.3 μM for glucose (S/N=3) or 27.6 attomole in mass detection.     

Electrodeposited nitrogen-doped graphene/carbon nanotubes nanocomposite as enhancer for simultaneous and sensitive voltammetric determination of caffeine and vanillin

A nitrogen-doped graphene/carbon nanotubes (NGR–NCNTs) nanocomposite was employed into the study of the electrochemical sensor via electrodeposition for the first time. The morphology and structure of NGR–NCNTs nanocomposite were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. Meanwhile, the electrochemical performance of the glassy carbon electrode (GCE) modified with electrodeposited NGR–NCNTs (ENGR–NCNTs/GCE) towards caffeine (CAF) and vanillin (VAN) determination was demonstrated by cyclic voltammetry (CV) and square wave voltammetry (SWV). Under optimal condition, ENGR–NCNTs/GCE exhibited a wide linearity of 0.06–50 μM for CAF and 0.01–10 μM for VAN with detection limits of 0.02 μM and 3.3 × 10⁻³ μM, respectively. Furthermore, the application of the proposed sensor in food products was proven to be practical and reliable. The desirable results show that the ENGR–NCNTs nanocomposite has promising potential in electrocatalytic biosensor application.     

Composite poly(dimethylsiloxane)/glass microfluidic system with an immobilized enzymatic particle-bed reactor and sequential sample injection for chemiluminescence determinations

A three-layer poly(dimethylsiloxane) (PDMS)/glass microfluidic system for performing on-chip solid-phase enzymatic reaction and chemiluminescence (CL) reaction was used for the determination of glucose as a model analyte. A novel method for the immobilization of controlled-pore-glass based reactive particles on PDMS microreactor beds was developed, producing an on-chip solid-phase reactor that featured large reactive surface and low flow impedance. Efficient mixing of reagent/sample/carrier streams was achieved by incorporating chaotic mixer structures in the microfluidic channels. A conventional sequential injection (SI) system was adapted for direct coupling with the microfluidic system, and combined with hydrostatic delivery of reagents to achieve efficient and reproducible sample introduction at 10 μl levels. A detection limit of 10 μM glucose (3σ), and a precision of 3.1% RSD (n=7, 0.2 mM glucose) were obtained using the SI-microfluidic-CL system integrated with a glucose oxidase (GOD) reactor. Carryover was <5% at a throughput of 20 samples/h.     

A novel enzyme-mimic nanosensor based on quantum dot-Au nanoparticle@silica mesoporous microsphere for the detection of glucose

QD-Au NP@silica mesoporous microspheres have been fabricated as a novel enzyme-mimic nanosensor. CdTe quantum dots (QDs) were loaded into the core, and Au nanoparticles (NPs) were encapsulated in the outer mesoporous shell. QDs and Au NPs were separated in the different space of the nanosensor, which prevent the potential energy or electron transfer process between QDs and Au NPs. As biomimetic catalyst, Au NPs in the mesoporous silica shell can catalytically oxidize glucose as glucose oxidase (GOx)-mimicking. The resultant hydrogen peroxide can quench the photoluminescence (PL) signal of QDs in the microsphere core. Therefore the nanosensor based on the decrease of the PL intensity of QDs was established for the glucose detection. The linear range for glucose was in the range of 5–200 μM with a detection limit (3σ) of 1.32 μM.     

Sensitive DNA biosensor improved by Luteolin copper(II) as indicator based on silver nanoparticles and carbon nanotubes modified electrode

A novel and sensitive electrochemical DNA biosensor has been developed for the detection of DNA hybridization. The biosensor was proposed by using copper(II) complex of Luteolin C₃₀H₁₈CuO₁₂ (CuL₂) as an electroactive indicator based on silver nanoparticles and multi-walled carbon nanotubes (Ag/MWCNTs) modified glassy carbon electrode (GCE). In this method, the 4-aminobenzoic acid (4-ABA) and Ag nanoparticles were covalently grafted on MWCNTs to form Ag/4-ABA/MWCNTs. The proposed method dramatically increased DNA attachment quantity and complementary ssDNA detection sensitivity for its large surface area and good charge-transport characteristics. DNA hybridization detection was performed using CuL₂ as an electroactive indicator. The CuL₂ was synthesized and characterized using elemental analysis (EA) and IR spectroscopy. Cyclic voltammetry (CV) and fluorescence spectroscopy were used to investigate the interaction between CuL₂ and ds-oligonucleotides (dsDNA). It was revealed that CuL₂ presented high electrochemical activity on GCE, and it could be intercalated into the double helices of dsDNA. The target ssDNA of the human hepatitis B virus (HBV) was quantified in a linear range from 3.23 × 10⁻¹² to 5.31 × 10⁻⁹ M (r = 0.9983). A detection limit of 6.46 × 10⁻¹³ M (3σ, n = 11) was achieved.     

Modification of polypyrrole nanowires array with platinum nanoparticles and glucose oxidase for fabrication of a novel glucose biosensor

A novel glucose biosensor, based on the modification of well-aligned polypyrrole nanowires array (PPyNWA) with Pt nanoparticles (PtNPs) and subsequent surface adsorption of glucose oxidase (GOx), is described. The distinct differences in the electrochemical properties of PPyNWA–GOx, PPyNWA–PtNPs, and PPyNWA–PtNPs–GOx electrodes were revealed by cyclic voltammetry. In particular, the results obtained for PPyNWA–PtNPs–GOx biosensor showed evidence of direct electron transfer due mainly to modification with PtNPs. Optimum fabrication of the PPyNWA–PtNPs–GOx biosensor for both potentiometric and amperometric detection of glucose were achieved with 0.2 M pyrrole, applied current density of 0.1 mA cm⁻², polymerization time of 600 s, cyclic deposition of PtNPs from −200 mV to 200 mV, scan rate of 50 mV s⁻¹, and 20 cycles. A sensitivity of 40.5 mV/decade and a linear range of 10 μM to 1000 μM (R² = 0.9936) were achieved for potentiometric detection, while for amperometric detection a sensitivity of 34.7 μA cm⁻² mM⁻¹ at an applied potential of 700 mV and a linear range of 0.1–9 mM (R² = 0.9977) were achieved. In terms of achievable detection limit, potentiometric detection achieved 5.6 μM of glucose, while amperometric detection achieved 27.7 μM.     

Bismuth-dispersed xerogel-based composite films for trace Pb(II) and Cd(II) voltammetric determination

We report for the first time the synthesis of bismuth-modified (3-mercaptopropyl) trimethoxysilane (MPTMS) and its application for the determination of lead and cadmium by anodic stripping voltammetry. Xerogels made from bismuth-modified MPTMS and mixtures of it with tetraethoxysilane, under basic conditions (NH₃·H₂O), were characterized with scanning electron microscopy, energy dispersive spectroscopy, infrared spectroscopy and electrochemical methods. Bismuth-modified xerogels were mixed with 1.5% (v/v) Nafion in ethanol and applied on glassy carbon electrodes. During the electrolytic reductive deposition step, the bismuth compound on the electrode surface was reduced to metallic bismuth. The target metal cations were simultaneously reduced to the respective metals and were preconcentrated on the electrode surface by forming an alloy with bismuth. Then, an anodic voltammetric scan was applied in which the metals were oxidized and stripped back into the solution; the voltammogram was recorded and the stripping peak heights were related to the concentration of Cd(II) and Pb(II) ions in the sample. Various key parameters were investigated in detail and optimized. The effect of potential interferences was also examined. Under optimum conditions and for preconcentration period of 4 min, the 3σ limit of detection was 1.3 μg L⁻¹ for Pb(II) and 0.37 μg L⁻¹ for Cd(II), while the reproducibility of the method was 4.2% for lead (n = 5, 10.36 μg L⁻¹ Pb(II)) and 3.9% for cadmium (n = 5, 5.62 μg L⁻¹ Cd(II)). Finally, the sensors were applied to the determination of Cd(II) and Pb(II) ions in water samples.     

A disposable electrochemical sensor for vanillin detection

A disposable electrochemical sensor was developed for the detection of vanillin in vanilla extracts and in commercial products. An analytical procedure based on square-wave voltammetry (SWV) was optimised and a detection limit of 0.4 μM for vanillin was found. A relative standard deviation of 2% was calculated for a vanillin concentration of 100 μM. The method was applied to the determination of vanillin in natural concentrated vanilla extracts and in final products such as yoghurt and compote. The obtained results were compared with those provided by a reference method based on HPLC. The electrochemical behaviour of other compounds (vanillic acid, p-hydroxybenzaldehyde, p-hydroxybenzoic acid, etc.), generally present in natural oleoresins, were also studied, to check for interferences with respect to the vanillin voltammetric signal.     

Optimized chromatographic and bioluminescent methods for inorganic pyrophosphate based on its conversion to ATP by firefly luciferase

Two new methods for inorganic pyrophosphate (PPi) quantification are described. They are based on the enzymatic conversion of PPi into ATP by firefly luciferase (Luc, E.C. 1.13.12.7) in the presence of dehydroluciferyl-adenylate (L-AMP) followed by the determination of ATP by one of two different procedures, either UV-monitored (260 nm) ion-pair-HPLC (IP-HPLC) (method A) or luciferase-dependent bioluminescence in the presence of its substrate, firefly luciferin (d-LH₂) (method B). These methods were subjected to optimization using experimental design methodologies to obtain optimum values for the selected factors: method A—incubation time (t_inc = 15 min), inactivation time of the enzyme (t_inac = 2 min), pH of the reaction mixture (pH 7.50) and the concentrations of L-AMP ([L-AMP] = 40 μM) and luciferase ([Luc] = 0.1 μM); method B—concentrations of L-AMP ([L-AMP] = 2 μM), luciferase ([Luc] = 50 nM) and luciferin ([LH₂] = 30 μM). Method A has a linear response over the range of 0.1-20 μM of PPi, with a limit of detection (LOD) of 0.5 μM and a limit of quantitation (LOQ) of 1.8 μM. Precision, expressed as relative standard deviation (R.S.D.), is 7.4% at 1 μM PPi and 5.9% at 8 μM PPi. Method B has a linear response over the range of 0.75-6.0 μM of PPi, with LOD and LOQ of 0.624 and 2.23 μM, respectively, and a R.S.D. of 5.1% at 2.5 μM PPi and 4.9% at 5 μM PPi. Under optimized conditions sensitive and robust methods can be obtained for the analysis of PPi impurities in commercial nucleotides and tripolyphosphate (P₃).     

Solid phase selective separation and preconcentration of Cu(II) by Cu(II)-imprinted polymethacrylic microbeads

Ion-imprinted polymer (IIP) particles are prepared by copolymerization of methacrylic acid as monomer, trimethylolpropane trimethacrylate as crosslinking agent and 2,2′-azo-bis-isobutyronitrile as initiator in the presence of Cu(II), a Cu(II)-4-(2-pyridylazo)resorcinol (Cu(II)-PAR) complex, and PAR only. A batch procedure is used for the determination of the characteristics of the Cu(II) solid phase extraction from the IIP produced. The results obtained show that the Cu(II)-PAR IIP has the greatest adsorption capacity (37.4 μmol g⁻¹ of dry copolymer) among the IIPs investigated. The optimal pH value for the quantitative preconcentration is 7, and full desorption is achieved by 1 M HNO₃. The selectivity coefficients (S_Cu/Me) for Me = Ni(II), Co(II) are 45.0 and 38.5, respectively. It is established that Cu(II)-PAR IIPs can be used repeatedly without a considerable adsorption capacity loss. The determination of Cu(II) ions in seawater shows that the interfering matrix does not influence the preconcentration and selectivity values of the Cu(II)-PAR IIPs. The detection and quantification limits are 0.001 μmol L⁻¹ (3σ) and 0.003 μmol L⁻¹ (6σ), respectively.     

Prussian blue modified glassy carbon electrodes-study on operational stability and its application as a sucrose biosensor

Stabilisation of electrochemically deposited Prussian blue (PB) films on glassy carbon (GC) electrodes has been investigated and an enhancement in the stability of the PB films is reported if the electrodes are treated with tetrabutylammonium toluene-4-sulfonate (TTS) in the electrochemical activation step following the electrodeposition. A multi-enzyme PB based biosensor for sucrose detection was made in order to demonstrate that PB films can be coupled with an oxidase system. A tri-enzyme system, comprising glucose oxidase, mutarotase and invertase, was crosslinked with glutaraldehyde and bovine albumin serum on the PB modified glassy carbon electrode. The deposited PB operated as an electrocatalyst for electrochemical reduction of hydrogen peroxide, the final product of the enzyme reaction sequence. The electrochemical response was studied using flow injection analysis for the determination of sucrose, glucose and H₂O₂. The optimal concentrations of the immobilisation mixture was standardised as 8 U of glucose oxidase, 8 U of mutarotase, 16 U of invertase, 0.5% glutaraldehyde (0.025 μl) and 0.5% BSA (0.025 mg) in a final volume of 5 μl applied at the electrode surface (0.066 cm²). The biosensor exhibited a linear response for sucrose (4-800 μM), glucose (2-800 μM) and H₂O₂ (1-800 μM) and the detection limit was 4.5, 1.5 and 0.5 μM for sucrose, glucose and H₂O₂, respectively. The sample throughput was ca. 60 samples h⁻¹. An increase in the operational and storage stability of the sucrose biosensor was also noted when the PB modified electrodes were conditioned in phosphate buffer containing 0.05 M TTS during the preparation of the PB films.     

Sensitive detection of endocrine disrupters using ionic liquid--single walled carbon nanotubes modified screen-printed based biosensors

Simple and low cost biosensor based on screen-printed electrode for sensitive detection of some alkylphenols was developed, by entrapment of HRP in a nanocomposite gel based on single-walled carbon nanotubes (SWCNTs) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) ionic liquid. Raman and FTIR spectroscopy, CV and EIS studies demonstrate the interaction between SWCNTs and ionic liquid. The nanocomposite gel, SWCNT-[BMIM][PF₆] provides to the modified sensor a considerable enhanced electrocatalytic activity toward hydrogen peroxide reduction. The HRP based biosensor exhibits high sensitivity and good stability, allowing a detection of the alkylphenols at an applied potential of −0.2 V vs. Ag/AgCl, in linear range from 5.5 to 97.7 μM for 4-t-octylphenol and respectively, between 5.5 and 140 μM for 4-n-nonylphenol, with a response time of about 5 s. The detection limit was 1.1 μM for 4-t-octylphenol, and respectively 0.4 μM for 4-n-nonylphenol (S/N = 3).     

A simple and green analytical method for determination of iron based on micro flow analysis

A simple, inexpensive and reagent-less colorimetric micro flow analysis (μFA) system was implemented in a polymethyl methacrylate (PMMA) micro fluidic manifold. A T-shaped micro channel on a PMMA chip was fabricated by laser ablation and topped with molded polydimethylsiloxane (PDMS). The fabricated μFA system was integrated with the optical components as detector and applied to the determination of iron in water samples. It is based on the measurement of Fe(III)-nitroso-R salt complex at 720 nm formed by the reaction between Fe(III) and nitroso-R salt in an acetate buffer solution pH 5. The proposed μFA consumed very small amount of reagent and sample, it released waste of less than 2.0 mL h⁻¹. The relative standard deviation (R.S.D.) was less than 2% (n = 11) with the recovery of 98.7 ± 0.12 (n = 5). The linear range for the determination of iron in water samples was over the range of 0.05-4.0 μg mL⁻¹ with a correlation coefficient (r²) of 0.9994. The limit of detection (3σ) and limit of quantitation (10σ) were 0.021 μg mL⁻¹ and 0.081 μg mL⁻¹, respectively with a sample throughput of 40 h⁻¹.     

Synthesis of Zn(II) ion-imprinted solid-phase extraction material and its analytical application

Zn(II) ion-imprinted polymer materials used for solid-phase extraction (SPE) column were prepared by the copolymerization of 8-acryloyloxyquinoline (8-AOQ) monomer and a crosslinker ethylene glycol dimethacrylate (EGDMA) in the presence of 2,2′-azobisisobutyronitrile (AIBN) as an initiator. After removing Zn(II) ion from the polymer, molecularly imprinted polymers (MIPs) capable of selectively rebinding Zn(II) ion were obtained. The maximum adsorption capacity of Zn(II) on MIPs beads was about 3.9 mg g⁻¹. The effect of pH and flow rate for quantitative enrichment was also investigated. The Zn(II)-imprinted microbeads have a greater affinity for Zn(II) with respect to Cu(II), Co(II) and Ni(II) ions. A detection limit of 0.65 μg L⁻¹(3σ) and a relative standard deviation (R.S.D., n = 7) of 2.9% were obtained. The MIPs-SPE preconcentration procedure showed a linear calibration curve within concentration range from 0.65 to 130 μg L⁻¹. Zn(II) ion-imprinted beads enabled the selective extraction of zinc ions from a complex matrix, and after 20 times of adsorption and desorption cycle, the recovery of adsorption capacity of Zn(II) on MIPs beads was only decreased 3.2%. The results suggested that these MIPs can be used several times without considerable loss of adsorption capacity.     

Visual and trap emission spectrometric detections of Ag (I) ion with mesoporous ZnO/CdS@SiO2 core/shell nanocomposites

A new method for the preparation of mesoporous ZnO/CdS@SiO₂ core/shell nanostructure (CSN) has been developed. The mesoporous silica shells allow Ag⁺ to enter into the interior of the nanostructures to contact with ZnO/CdS core, accordingly causes the quenching of its band edge emission (475 nm) along with a simultaneous enhancement of red emission at around 595 nm. So, a novel visual fluorescence detection strategy for Ag⁺ ion is proposed based on a common core/shell Quantum dots nanostructure. Under optimal conditions, the enhanced fluorescence intensity at 595 nm increased linearly with the concentration of Ag⁺ ion ranging from 0.03 μM to 0.24 μM with a detection limit (3σ) of 3.3 nM.     

Amperometric determination of bonded glucose with an MnO(2) and glucose oxidase bulk-modified screen-printed electrode using flow-injection analysis

A screen-printed amperometric biosensor based on carbon ink double bulk-modified with MnO₂ as a mediator and glucose oxidase as a biocomponent was investigated for its ability to serve as a detector for bonded glucose in different compounds, such as cellobiose, saccharose, (-)-4-nitrophenyl-β-d-glucopyranoside, as well as in beer samples by flow-injection analysis (FIA). The biosensor could be operated under physiological conditions (0.1 M phosphate buffer, pH 7.5) and exhibited good reproducibility and stability. Bonded glucose was released with glucosidase in solution, and the free glucose was detected with the modified screen-printed electrode (SPE). The release of glucose by the aid of glucosidase from cellobiose, saccharose and (-)-4-nitrophenyl-β-d-glucopyranoside in solution showed that stoichiometric quantities of free glucose could be monitored in all three cases.The linear range of the amperometric response of the biosensor in the FIA-mode flow rate 0.2 mL min⁻¹, injection volume 0.25 mL, operation potential 0.48 V versus Ag/AgCl) extends from 11 to 13,900 μmol L⁻¹ glucose in free form. The limit of detection (3σ) is 1 μmol L⁻¹ glucose. A concentration of 100 μmol L⁻¹ yields a relative standard deviation of approximately 7% with five injections. These values correspond to the same concentrations of bonded glucose supposed that it is liberated quantitatively (incubation for 2 h with glucosidase).Bonded glucose could be determined in beer samples using the same assay. The results corresponded very well with the reference procedure.