Analytical Chemistry Research最新文献

Nutritionally important minerals are more readily absorbed by living systems when complexed with organic acids, resulting in higher consumer demand and premium prices for these products. These chelated metals are produced by reaction of metal oxides and acids in aqueous solution. However, unreacted dry blends are sometimes misrepresented as metal chelates, when in reality they are only simple mixtures of the reactants typically used to synthesize them. This practice has increased interest in developing analytical methods that are capable of measuring the extent of metal chelation for quality control and regulatory compliance. We describe a novel method to rapidly measure the percent chelation of citric and malic acids with calcium, magnesium, and zinc. Utilization of attenuated total reflectance (FTIR-ATR) provides for the direct, rapid measurement of solid samples. The inclusion of an internal standard allows independent determination of either free or chelated acids from integrated areas in a single spectrum.

We present an improved extraction and derivatization protocol for GC–MS analysis of amino/non-amino acids in Saccharomyces cerevisiae. Yeast cells were extracted with chloroform: aqueous-methanol (1:1, v/v) and the resulting non-polar and polar extracts combined and dried for derivatization. Polar and non-polar metabolites were derivatized using tert-butyldimethylsilyl (t-BDMS) dissolved in acetonitrile. Using microwave treatment of the samples, the derivatization process could be completed within 2 h (from >20 h of the conventional method), providing fully derivatized metabolites that contain multiple derivatizable organic functional groups. This results in a single derivative from one metabolite, leading to increased accuracy and precision for identification and quantification of the method. Analysis of combined fractions allowed the method to expand the coverage of detected metabolites from polar metabolites i.e. amino acids, organic acids and non-polar metabolites i.e. fatty alcohols and long-chain fatty acids which are normally non detectable. The recoveries of the extraction method was found at 88 ± 4%, RSD, N = 3 using anthranilic acid as an internal standard. The method promises to be a very useful tool in various aspects of biotechnological applications i.e. development of cell factories, metabolomics profiling, metabolite identification, ¹³C-labeled flux analysis or semi-quantitative analysis of metabolites in yeast samples.

A common problem in applying biosensors for the detection of genomic DNA is detecting short sequences in large amounts of long double stranded DNA. A gold electrode modified with a conductive nanocomposite, poly(3,4-ethylene-dioxythiophene), and gold nanoparticles was functionalized with 2,6-Pyridinedicarboxylic acid. Immobilization of a 20-mer DNA probe as the bioreceptor was successfully carried out via a peptide bond on the surface of the modified electrode. Two segments of 15 and 20 base probes were designed and named as Capture and Reporter probes respectively. The 20-mer Reporter probe was complementary to the bioreceptor and the 15-mer Capture probe was designed to bind on to the surface of the iron oxide magnetic nanoparticles. A 35-base Target DNA complementary to the Capture and the Reporter probes was used as Template in the ligation process, with the ligation between the Reporter and Capture probes mediated by T4 ligase. Iron oxide magnetic nanoparticles functionalized with carboxylic groups on their surface synthesized in a new method were attached to the 15-mer Capture probe. After the denaturation of the final ligation product, the separation of the attached probes was carried out using 5 G permanent magnets in a three step washing procedure in TE buffer. The hybridization of the DNA bioreceptor and the Reporter probe attached to the Capture probe-Fe₃O₄ was monitored via oxidation and reduction of the new redox marker (ruthenium complex) intercalated into the double helix.

This technique was found to be reliably repeatable. The indirect detection of genomic DNA using this method is significantly improved and showed high efficiency in small amounts of samples with the detection limit of 5.37 × 10⁻¹⁴ M.

A reagentless electrochemical biosensor for hydrogen peroxide was fabricated. The sensor carries a monolayer of nanocomplex composed of horseradish peroxidase and Au-nanoparticle, and responds to hydrogen peroxide through the highly efficient direct electron transfer at a mild electrode potential without any soluble mediator. Formation of the nanocomplex was studied with visible spectroscopy and size exclusion chromatography. The sensor performance was analyzed based on a hydrodynamic electrochemical technique and enzyme kinetics. The sensor was applied to fabrication of sensors for glucose and uric acid through further modification of the nanocomplex-carrying electrode with the corresponding hydrogen peroxide-generating oxidases, glucose oxidase and urate oxidase, respectively.

Chlorobium limicola belongs to the green sulphur bacteria that has a potential for technological applications such as biogas clean up oxidising hydrogen sulphide to elemental sulphur through photosynthetic process. In the present work, analytical methods are described for the determination of different sulphur species in C. limicola cultures – sulphide by GC-FPD, sulphate by ionic HPLC and elemental sulphur by RP HPLC. The latter method eliminates the need for chloroform extraction of water suspensions of elemental sulphur. Data from sulphide and elemental sulphur analyses have been compared with ones coming from more traditional analytical methodologies.

The calibration and quantitative measurement is the “Achilles heel” of the LIBS technique. This paper deals with a method developed for the direct measurement of K and Mg in plant samples. Instrumental parameters were optimized and the best condition found was a 50 μm spot size, 10 Hz laser repetition rate, 75 accumulated laser pulses with 25 mJ/pulse and 0.25 μs of delay time. For method calibration, the use of synthetic standard calibrating material prepared by the addition of increasing concentrations of K and Mg in wood, filter paper and babassu mesocarp was proposed in order to assess the feasibility of using these various matrices in plant samples analysis. The limits of detection of proposed method were 2–30 and 6–27 μg g⁻¹ for K and Mg, respectively. The use of the carbon emission wavelength at 247.856 nm was used as internal standard to improve the analytical results. Certified reference materials of plants were used to check the accuracy of the proposed method and recovery around 82% and 100% were obtained in all cases.

An electro-deposition approach was established to incorporate the gold nano-flakes onto the glassy carbon electrode in electrochemical cells (nano-Au/GC/ECCs). Using pulsed amperometric detection (PAD) without any gold oxidation for cleaning (non-oxidative PAD), the nano-Au/GC/ECCs were able to maintain their activity for oxidizing of carbohydrates in a normal alkaline medium. The reproducibility of peak area was about 2 relative standard deviation (RSD,%) for 6 consecutive injections. A dynamic range of carbohydrates was obtained over a concentration range of 5–80 mg L⁻¹ and the limits of detection (LOD) were of 2 mg L⁻¹ for fructose and lactose and 1 mg L⁻¹ for glucose and galactose. Moreover, the nano-Au/GC/ECC using the non-oxidative PAD was able to combine with the internal standard method for determination of lactose in fresh cow milk sample.

The present communication deals with the synthesis of luminescent Mn-doped ZnS quantum dots (QDs) anchored to surface imprinted polymer for the optical sensing of 3-phenoxy benzoic acid (3-PBA) in urine samples. The combination of sensing and surface functionalization not only improves the selectivity of the method, but also increases the optosensing ability of the material for non-phosphorescent substances. The developed material was utilized for the selective and sensitive detection of 3-PBA in urine samples. The proposed method shows good linearity with a regression coefficient (R²) of 0.98. The limit of detection was found to be 0.117 μM. The method has an acceptable precision and accuracy which are found to be less than 8% and 80–90% respectively at three different concentrations. The quenching constant of quantum dot-molecular imprinted polymer was found to be 3.4 times higher to that of the quantum dot-non imprinted polymer (QD-NIP) as calculated by Stern–Volmer equation. The sensing method developed has shown immense utility to detect 3-PBA in complex biological samples like urine.

The objective of the present work is to develop the stripping voltammetric method for determination of nephrotoxic drug cefitizoxime in pharmaceutical formulation and its application to wastewater analysis. Solubilized system of different surfactants viz. cationic, anionic and non-ionic influences the electrochemical response of cefitizoxime. Solubilized system of CTAB containing cefitizoxime enhanced the peak current while anionic and non-ionic showed an opposite effect. The current signal due to the reduction process is a function of concentration of the cefitizoxime, pH of medium, type of surfactant and accumulation time at electrode surface. The proposed SWCAdSV (Squarewave Cathodic Adsorptive Voltammtery) and DPCAdSV (Differential Pulse Cathodic Adsorptive Voltammetry) are linear over concentration range 1.732–6.901 μg/mL and 4.792–30.672 μg/mL with detection limit of 0.76 ng/mL and 2.63 ng/mL, respectively. The method is successfully applied for determination of cefitizoxime in pharmaceutical formulation and wastewater with mean percentage recovery of 99.73% and 98.51%, respectively.