Voltammetric detection of the α-dicarbonyl compound: Methylglyoxal as a flavoring agent in wine and beer

A simple, rapid and highly selective method for the determination of the most abundant α-dicarbonyl compound in wine and beer has been developed for the first time by employing square wave voltammetry. A novel electrochemical sensor, based on the electrodeposition of platinum nanoparticles onto single wall carbon nanotubes that were cast on a glassy carbon electrode (GCE) substrate, is presented in this paper. This modified electrode exhibited excellent catalytic activity in the electroreduction of methylglyoxal, showing much higher peak currents than those measured on an unmodified GCE. The effects of different experimental and instrumental parameters, such as solution pH and square wave frequency, were examined. The reduction peak current showed a linear range of from 0.1 × 10⁻⁶ to 100 × 10⁻⁶ M with a 0.9979 correlation coefficient; and a low detection limit of 2.8 × 10⁻⁹ M was also obtained. The proposed methodology was successfully applied to the quantitative analysis of methylglyoxal in wine and beer samples. The developed sensor possesses advantageous properties such as a high active surface area, stability, and rapid electron transfer rate, which cumulatively demonstrate high performance toward the electrocatalytic reduction and detection of methylglyoxal.     

Spectrophotometric Study of the Complexation of Indium(III) With the α-Diketone Bis(4-Phenyl-3-Thiosemicarbazones) Derived From Glyoxal,Biacetyl and Methylglyoxal

Abstract

Indium(III) reacts with α-diketone bisphenylthiosemicarbazones derived from glyoxal, biacetyl and methylglyoxal to form 1:1 and 1:2 (In: reagent) complexes in acid and basic medium, respectively. The effect of experimental variables was studied in detail on the acid site, and a new method for the spectrophotometric determination of indium(III) with meth-ylglyoxal bis(4-phenyl-3-thiosemicarbazone) (MGBPT) is proposed. The yellow 1:1 In-MGBPT complex is formed at pH 3.5–6 in a solution containing a 60 % V/V of dimethylforrnamide. The nature of the complex (? = 27,100 1 mol^?1 cm^?1 at 465 mm) and the effect of interferences were studied.     

Enzymatic analysis by means of the air-gap electrode determination of urea in blood

The newly developed air-gap electrode has been used for enzymatic assay of urea in serum and whole blood; analyses can be done accurately, reliably, simply and quickly. The determination is highly selective because the electrode senses only the ammonium ion, which is selectively released from urea by urease in a preliminary rapid incubation step. The reproducibility of the determination (standard deviation less than 2.4%) is sufficient for clinical purposes; the linear range of the method is 10^-2–lO^-4M urea. Since the electrode actually never touches the sample solution, the problems caused by the presence of proteins, blood cells etc. do not arise.     

Comparison of three different configurations of dual ultramicroelectrodes for the decomposition of S-Nitroso-L-glutathione and the direct detection of nitric oxide

Podoplanin (PDP) is a small transmembrane protein and widely present in various specialized cells throughout the human body. It is a specific marker for identification of lymphatic vessel and a candidate marker for cancer stem cells in squamous cell carcinoma of the lung. We report on method for the highly selective determination of PDP by using a surface plasmon resonance imaging (SPRI) that exploits the highly selective interaction between PDP and anti-human PDP monoclonal antibody (IgG). The sensor has a dynamic range between 0.25 and 1.0?ng?mL^?1, and a detection limit of 15?pg?mL^?1. It was applied to the determination of PDP in blood plasma and tissue homogenates from paired normal and lung tumor tissue.

Development of a method for the determination of advanced glycation end products precursors by liquid chromatography and its application in human urine samples

A liquid chromatographic method with fluorimetric detection has been developed to determine the most abundant α‐dicarbonyl compounds, generated as intermediates in the Maillard's reaction, previous derivatization to high fluorescent pteridinic derivatives. Hence, the biomarkers D‐glucosone, 3‐deoxyglucosone, glyoxal, methylglyoxal, diacetyl, 2,3‐pentanedione, and phenylglyoxal were quantified using a gradient elution mode. The experimental conditions of the derivatization reaction and mobile phase composition were optimized. Linearity ranges (peak area versus α‐dicarbonyl compound concentration) from 1.0 to 100.0 ng mL^?1 were obtained. Detection limits were comprised between 0.3 and 11.0 ng mL^?1. The high sensitivity of the method allows the determination of α‐dicarbonyl compounds present in human urine, such as D‐glucosone, 3‐deoxyglucosone, glyoxal, and methylglyoxal, that are used as biomarkers, in order to investigate their roles in several diseases, with special emphasis in diabetes mellitus. With the aim of avoiding the interferences due to pteridinic compounds present in urine, a cleanup step with an ISOLUTE ENV+ cartridge was carried out. The concentrations of these urinary biomarkers have been reported as a normalized ratio to urinary creatinine, and determined in healthy and in diabetic volunteers, of different ages and sex. In all urine samples, standard addition and external calibration procedures were applied and compared.     

Fluorimetric determination of hemoglobin using spiro form rhodamine B hydrazide in a micellar medium

A novel fluorimetric method for the determination of hemoglobin (Hb) using spiro form rhodamine B hydrazide (RBH) as fluorogenic reagent in the presence of sodium dodecylbenzene sulfonate (SDBS) surfactant micelles is described. The method employs the reaction of Hb with RBH, a colorless, non-fluorescent spirolactam hydrazide in SDBS micelles to generate highly fluorescent product rhodamine B and hence leads to a large increase in fluorescence intensity. The fluorescence increase is linearly related to the concentration of Hb in the range 0.2-12.0 nmol l⁻¹ with a detection limit of 0.086 nmol l⁻¹ (3σ). The optimal conditions for the detection of Hb are evaluated and the possible detection mechanism is also discussed. The proposed method has been applied to the determination of Hb in human blood.     

Chemiluminescence derivatization of methylglyoxal using 2-aminonicotinic acid

To develop a sensitive and selective chemiluminometric method for the determination of methylglyoxal, we used 2-aminonicotinic acid as the chemiluminescence derivatization reagent. 2-Aminonicotinic acid reacts with methylglyoxal in an acidic solution at 37 degrees C for 4 h and gave a chemiluminescence in N,N'-dimethylformamide containing sodium tert-butoxide. The detection limit (blank intensity plus three-times its standard deviation of methylglyoxal) for methylglyoxal is 233 fmol in the reaction mixture.     

Capillary GC Analysis of Glyoxal and Methylglyoxal in the Serum and Urine of Diabetic Patients After Use of 2,3-Diamino-2,3-dimethylbutane as Derivatizing Reagent

The dicarbonyl compounds glyoxal, methylglyoxal, and dimethylglyoxal have been separated by capillary GC on a 30 m × 0.32 mm i.d. HP-5 column after precolumn derivatization with 2,3-diamino-2,3-dimethylbutane at pH 4. Chromatographic separation was complete in 6 min. Nitrogen was used as carrier gas at a flow rate of 2 mL min^?1. Split injection was performed with a split ratio of 10:1 (v/v). The derivatives were monitored by flame-ionization detection, and linear calibration plots were obtained in the ranges 0.06–0.69, 0.05–1.01, and 0.07–1.33 μg mL^?1 for glyoxal, methylglyoxal, and dimethylglyoxal, respectively; the respective detection limits were 20, 10, and 10 ng mL^?1. Glyoxal and methylglyoxal were analyzed in serum and urine from diabetics and from healthy volunteers. Amounts of glyoxal and methylglyoxal in serum from diabetic patients were 0.19–0.33 and 0.20–0.29 μg mL^?1, respectively, with respective relative standard deviations (RSD) of 0.8–1.0 and 0.8–1.1%. Amounts of glyoxal and methylglyoxal in serum from healthy volunteers were 0.05–0.08 and 0.04–0.10 μg mL^?1, respectively, with respective RSD of 0.9–1.2 and 1.0–1.2%. Levels of glyoxal and methylglyoxal in urine from diabetic patients were 0.18–0.40 and 0.25–0.36 μg mL^?1, respectively.     

Analysis of methylglyoxal in water and biological matrices by capillary zone electrophoresis with diode array detection

We describe a new method for the determination of methylglyoxal in water and biological matrices, using o-phenylenediamine as derivatizing agent and solid-phase extraction followed by capillary zone electrophoresis with diode array detection. 25 mM sodium phosphate running buffers at pH 2.2, 30 kV, and 25 degrees C allowed the best instrumental conditions for the optimum separation of methylglyoxal in a suitable analytical time (< 10 min), using an uncoated fused-silica capillary of 75 microm inner diameter and an effective length of 45.1 cm with an extended light path and the wavelength set to 200 nm. Under optimized instrumental conditions, good reproducibility of the migration time (< 1.1%), precision (< 5%), an excellent linear dynamic range from 0.1 to 3.6 mg/L (r(2) = 0.9997), and low limits of detection (7.2 microg/L) were obtained for methylglyoxal measurements, using the internal standard methodology. Assays on laboratory-spiked tap and ground water samples allowed a remarkable accuracy, presenting yields of 95.0 +/- 4.3 and 94.0 +/- 1.1%, respectively, and good performance to determine methylglyoxal in beer and yeast cells suspensions matrices was also obtained at trace level. The present methodology is a cost-effective alternative for routine quality control analysis, showing to be reliable, sensitive, and with a low sample volume requirement to monitor methylglyoxal in water and biological matrices.     

Sensitive and rapid determination of nitric oxide in human serum using microchip capillary electrophoresis with laser-induced fluorescence detection

Microfluidic chip capillary electrophoresis with laser-induced fluorescence detection is employed for direct determination of trace nitric oxide in human blood using diaminorhodamines as the fluorescence probe. Factors influencing the separation and detection processes were systematically studied. Complete and fast separation of the highly fluorescent triazole formed was achieved within 45 s, and the relative standard deviations values of migration time and peak area were less than 3%. The detection limit of NO was 3.0 nmol.L^-1 (at a signal-to-noise ratio of 3) and the liner range was from 1.0?×?10^-8?mol.L^-1 to 3.0?×?10^-6?mol.L^-1. The method has been applied to the determination of NO in serum of healthy persons and patients suffering from diseases, with recoveries varying from 92.65 to 98.43%.     

Inductively coupled plasma mass spectrometric analysis of the total amount of platinum in DNA extracts from peripheral blood mononuclear cells and tissue from patients treated with cisplatin

We present a highly sensitive method for the determination of platinum (Pt) in DNA extracts of peripheral blood mononuclear cells (PBMCs) and tissue samples from patients treated with cisplatin. The method is based on the measurement of Pt by inductively coupled plasma mass spectrometry (ICP-MS) and allows quantification of Pt-DNA adducts in PBMCs isolated from 10 mL blood and 1 mg tissue. The lower limit of quantification is 0.75 pg Pt or 7.5 fg Pt μg⁻¹ DNA when using 100 μg DNA. The method proved to be accurate and precise. The results obtained using the ICP-MS method were in good agreement with results from the alternative ³²P-postlabelling assay. The ICP-MS method was, however, more sensitive and proved to be less laborious. The advantages of the presented ICP-MS technique were demonstrated by the analysis of PBMCs, normal gastric tissue, and gastric tumour tissue of patients treated with cisplatin.     

A new derivatization method for the determination of valproic acid in serum using tetramethylammonium hydroxide as a catalyst

Valproic acid (VPA) pharmacokinetics is highly variable and monitoring of blood levels is necessary to determine its appropriate dosage. This study aimed to establish and validate a novel derivatization method for the determination of VPA. The method was based on the catalytic effect of tetramethylammonium hydroxide using 2,4′‐dibromoacetophenone as a derivatization reagent. After derivatization, samples were injected into the HPLC system for analysis. The method showed a good linearity in the range of 1.0–200.7 μg mL^?1, and the limit of quantification was 1 μg mL^?1. All values of the accuracy and relative standard deviations were acceptable for the analyses of biological samples. The recoveries were in the range from 91.6 to 97.4% for VPA with RSD <3.9%. A novel and high conversion‐rate derivatization method has been developed and validated for the determination of VPA in human serum. It can be applied to the analysis of VPA in clinic serum samples.     

Bis-aroylhydrazones of α-diketones as reagents for colorimetric and fluorimetric determinations of calcium,cadmium and other cations

The bis(4-hydroxybenzoylhydrazones) of glyoxal, methylglyoxal and dimethylglyoxal form colored chelates with Ca²⁺, Cd²⁺, La³⁺, a Bi(III) species and other cations. The glyoxal derivative shows more selective reactions, and highly selective assays are possible for calcium and cadmium in the presence of cyanide and citrate, respectively; Beer's law was obeyed in the range 0–50 mM for both cations. The chelates were also fluorescent, the reaction for lanthanum being particularly sensitive. The formation of this type ofchelate is a general property of the bisaroylhydrazones of α-diketones.     

Direct spectrofluorimetric determination of glutathione in biological samples using 5-maleimidyl-2-(m-methylphenyl) benzoxazole

A new thiol fluorescence probe, 5-maleimidyl-2-(m-methylphenyl)benzoxazole (MMPB) has been developed for the direct determination of reduced glutathione (GSH) in real samples. Compared to the reported N-substituted maleimide type of thiol reagents, the main advantage of MMPB is its rather high selectivity for GSH to cysteine (Cys), which often coexists with GSH in biological samples. Under mild conditions similar to the physiological environment, MMPB reacted with GSH to give a highly fluorescent derivative with the excitation and emission wavelengths of 299.2 and 355.8 nm, respectively. In the presence of 0.40-fold (molar ratio) of Cys, a linear relationship was found in the range of 0-1.62×10⁻⁷ mol l⁻¹ with the detection limit (3σ) of 3.23×10⁻¹⁰ mol l⁻¹ for GSH determination. Many other amino acids (100-fold) did not interfere with the determination. Since the molar ratio of Cys to GSH in mammalian tissues and blood does not exceed the value of 0.40:1, the proposed method has been used in the direct determination of GSH in these kinds of biological samples, such as human blood, pig’s liver and heart with the recoveries of 94.3-104.5%     

A rapid spectrophotometric method for the determination of cobalt in industrial, environmental, biological, pharmaceutical and soil samples using bis(5-bromosalicylaldehyde)orthophenylenediamine

A very simple, ultra-sensitive and fairly selective spectrophotometric method is presented for the determination of cobalt at trace levels using bis(5-bromosalicylaldehyde)orthophenylenediamine (BBSOPD). The method is based on the reaction of nonabsorbent BBSOPD in a slightly acidic (0.001–0.0025 M H₂SO₄ or pH 3.4–4.0) and 50% N,N-dimethylformamide media with cobalt(II) to produce a highly absorbent orange colored chelate-product with an absorption maximum at 473 nm. The reaction is instantaneous and the absorption remains stable for 24 h. The average molar absorption coefficient and Sandell’s sensitivity were found to be 5.84 × 10⁴ l mol^-1 cm^-1 and 9.0 ng cm^-2 of cobalt(II), respectively. Linear calibration graphs were obtained for 0.02–4.0 mg l^-1 of Co(II). The stoichiometric composition of the chelate is 1:1 (Co(II):BBSOPD). A large excess of over 50 cations, anions and complexing agents do not interfere in the determination. The method was successfully used for the determination of cobalt in several standard reference materials (steels and alloys), environmental waters (potable and polluted), biological samples (human blood and urine), pharmaceutical and soil samples and solutions containing both cobalt(II) and cobalt(III) as well as some complex synthetic mixtures. The method has high precision and accuracy.     

Some observations on the solvent extraction and spectrophotometric determination of palladium using 3,4-dihydro-4,4,6-trimethyl-2(1H)-pyrimidine-thione as a selective reagent

A highly selective spectrophotometric method is described for the determination of palladium, using 3,4-dihydro-4,4,6-trimethyl-2(1H)-pyridinethione (DTPT). The intense yellow 1:2 complex is extractable in chloroform from aqueous solution of pH 5.5. The maximum absorption occurs at 420 nm, ε = 3.90 × 10⁴ liter/mol⁻¹ cm⁻¹ and the sensitivity of the determination is 0.023 μg/ml. Palladium can be determined over a range of 0.4–24.6 ppm. CN⁻ interferes in this determination and should be absent. The method is applied to the determination of palladium in hydrogenation catalysts.     

New Spectrophotometric Method for Sulfite Determination

Abstract

A highly selective spectrophotometric method for the determination of aqueous sulfite was developed. Sulfite was found to react with o-phthaldialdehyde in presence of ammonia yielding a deep blue colored complex the absorbance of which is sensitive to trace sulfite concentrations. The method is simple, very sensitive, and convenient for the determination of as little as 5X10^?6 M sulfite. The molar absorptivity of the colored complex is about 1.2X10⁴ L cm^?1 mol^?1. The proposed method is more sensitive and selective for sulfite than the widely used Ellman reagent method. Absorbance is measured at 628 nm which is the best of the two absorption maxima that are exhibited by the compound.     

<Superscript>226</Superscript>Ra and <Superscript>228</Superscript>Ra determination in environmental samples by alpha-particle spectrometry

A complete methodology for ²²⁶Ra and ²²⁸Ra determination by alpha-particle spectrometry in environmental samples is being applied in our laboratory using ²²⁵Ra as an isotopic tracer. This methodology can be considered highly suitable for the determination of these nuclides when very low absolute limits of detection need to be achieved. The ²²⁶Ra determination can be performed at any time after the isolation of the radium isotopes from the analyzed samples while the ²²⁸Ra determination needs to be carried out at least six months later through the measurement of one of its grand-daughters. The method has been validated by its application to samples with known concentrations of these Ra nuclides, and by comparison with other radiometric methods.     

Differential pattern of glycogen accumulation after protein phosphatase 1 glycogen-targeting subunit PPP1R6 overexpression, compared to PPP1R3C and PPP1R3A, in skeletal muscle cells

Background

Insulin is a hormone that regulates blood glucose homeostasis and is a central protein in a medical condition termed insulin injection amyloidosis. It is intimately associated with glycaemia and is vulnerable to glycation by glucose and other highly reactive carbonyls like methylglyoxal, especially in diabetic conditions. Protein glycation is involved in structure and stability changes that impair protein functionality, and is associated with several human diseases, such as diabetes and neurodegenerative diseases like Alzheimer's disease, Parkinson's disease and Familiar Amyloidotic Polyneuropathy. In the present work, methylglyoxal was investigated for their effects on the structure, stability and fibril formation of insulin.

Results

Methylglyoxal was found to induce the formation of insulin native-like aggregates and reduce protein fibrillation by blocking the formation of the seeding nuclei. Equilibrium-unfolding experiments using chaotropic agents showed that glycated insulin has a small conformational stability and a weaker dependence on denaturant concentration (smaller m-value). Our observations suggest that methylglyoxal modification of insulin leads to a less compact and less stable structure that may be associated to an increased protein dynamics.

Conclusions

We propose that higher dynamics in glycated insulin could prevent the formation of the rigid cross-β core structure found in amyloid fibrils, thereby contributing to the reduction in the ability to form fibrils and to the population of different aggregation pathways like the formation of native-like aggregates.     

Covalent modification of a glassy carbon electrode with penicillamine for simultaneous determination of hydroquinone and catechol

A simple and highly selective electrochemical method has been developed for the simultaneous determination of hydroquinone (HQ) and catechol (CC) at a glassy carbon electrode covalently modified with penicillamine (Pen). The electrode is used for the simultaneous electrochemical determination of HQ and CC and shows an excellent electrocatalytical effect on the oxidation of HQ and CC upon cyclic voltammetry in acetate buffer solution of pH 5.0. In differential pulse voltammetric measurements, the modified electrode was able to separate the oxidation peak potentials of HQ and CC present in binary mixtures by about 103 mV although the bare electrode gave a single broad response. The determination limit of HQ in the presence of 0.1 mmol L⁻¹ CC was 1.0 × 10⁻⁶ mol L⁻¹, and the determination limit of CC in the presence of 0.1 mmol L⁻¹ HQ was 6.0 × 10⁻⁷ mol L⁻¹. The method was applied to the simultaneous determination of HQ and CC in a water sample. It is simple and highly selective.