Estimation of the measurement uncertainty of the high-performance anion-exchange chromatographic determination of carbohydrates in soluble (instant) coffee

The measurement uncertainty of the determination of free and total carbohydrates in soluble (instant) coffee using high-performance anion exchange chromatography with pulsed amperometric detection according to AOAC Method 995.13 and ISO standard 11292 was calculated. This method is important with regard to monitoring several carbohydrate concentrations and is used to assess the authenticity of soluble coffee. We followed the recommendations of the ISO, Eurachem, and Valid Analytical Measurement (VAM) guides: individual uncertainty contributions u(x) were identified, quantified, and expressed as relative standard deviations related to each specific source u(x)/x or RSD(x). Eventually, they were combined to yield the standard uncertainty and the relative standard uncertainty of a given carbohydrate concentration, c, that is respectively u(c) and u(c)/c. As a result of our study, we could demonstrate that the overall repeatability of the carbohydrate determination in duplicate, RSD(r); the repeatability of the integration of the peak area of the carbohydrate standards, RSD(r(area)(ST)); and the uncertainty of the linear calibration model used in our laboratory, RSD (linST), are the most significant contributions to the total uncertainty. The u(c)/c values thus determined differ for each carbohydrate and depend on their concentrations. The least standard uncertainties that can be achieved are about 2.5%. The question of trueness in the total carbohydrate assay (determination of monosaccharides obtained upon hydrolysis of coffee oligo- and polysaccharides) was addressed. For this purpose, we analyzed the data of 2 different collaborative trials in which our laboratory took part.     

Independent assessment of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) sample preparation quality: A novel statistical approach for quality scoring

Preparation of samples according to an optimized method is crucial for accurate determination of polymer sample characteristics by Matrix-Assisted Laser Desorption Ionization (MALDI) analysis. Sample preparation conditions such as matrix choice, cationization agent, deposition technique or even the deposition volume should be chosen to suit the sample of interest. Many sample preparation protocols have been developed and employed, yet finding the optimal sample preparation protocol remains a challenge. Because an objective comparison between the results of diverse protocols is not possible, “gut-feeling” or “good enough” is often decisive in the search for an optimum. This implies that sub-optimal protocols are used, leading to a loss of mass spectral information quality. To address this problem a novel analytical strategy based on MALDI imaging and statistical data processing was developed in which eight parameters were formulated to objectively quantify the quality of sample deposition and optimal MALDI matrix composition and finally sum up to an overall quality score of the sample deposition. These parameters can be established in a fully automated way using commercially available mass spectrometry imaging instruments without any hardware adjustments. With the newly developed analytical strategy the highest quality MALDI spots were selected, resulting in more reproducible and more valuable spectra for PEG in a variety of matrices. Moreover, our method enables an objective comparison of sample preparation protocols for any analyte and opens up new fields of investigation by presenting MALDI performance data in a clear and concise way.     

Carbohydrate Structure Database (CSDB): new features

Russian Chemical Bulletin - Carbohydrate Structure Database (CSDB) is a regularly updated database containing structural, taxonomic, bibliographic, NMR spectroscopic, and other information on...     

Origin assessment of green coffee (Coffea arabica) by multi-element stable isotope analysis of caffeine

The delta(13)C(VPDB), delta(2)H(VSMOW) and delta(18)O(VSMOW) values of caffeine isolated from Arabica green coffee beans of different geographical origin have been determined by isotope ratio mass spectrometry (IRMS) using elemental analysis (EA) in the "combustion" (C) and "pyrolysis" (P) modes (EA-C/P-IRMS). In total, 45 coffee samples (20 from Central and South America, 16 from Africa, six from Indonesia, and three from Jamaica and Hawaii) were analysed, as well as three reference samples of synthetic caffeine. Validation was performed by excluding isotope discrimination in the course of sample preparation and determining linear dynamic ranges for EA-P-IRMS measurements. The values for caffeine from green coffee ranged from -25.1 to - 29.9 per thousand, -109 to -198 per thousand, and +2.0 to -12.0 per thousand for delta(13)C(VPDB), delta(2)H(VSMOW), and delta(18)O(VSMOW), respectively. Data evaluation by linear discrimination analysis (LDA) and by classification and regression tree (CART) analysis revealed the delta(18)O(VSMOW) values to be highly significant. Use of LDA on the delta(2)H(VSMOW) and delta(18)O(VSMOW) data from coffee of African and Central/South American provenance led to error rates of 5.7% and 7.7% for adaption and cross validation, respectively.     

Application of infrared spectroscopy to the assessment of authenticity of tea

Diffusion reflectance fourier transform infrared spectroscopy in the mid-IR region was used to assess the authenticity of tea varieties. The differences between the spectra of 12 different tea varieties (seven black, two green, three semifermented grades) were sufficient to allow their discrimination by the soft independent modelling of class analogy classification method or linear discriminant analysis, despite a significant heterogeneity of the samples as revealed by variance analysis.     

A statistical approach by serial correlation to assessment of stability of analytical systems

The functional instability of infrared spectrometers can result in serious errors of analysis. This work shows that the stability can be tested by means of the serial correlation method, and the various causes of unstable conditions and equipment faults identified. Drift and large oscillations present separately or together can be detected by new statistics developed from the serial correlation method.     

Contribution to the statistical definition of the limits of reliable assay measurement

Summary Different analytical limits for a calibration experiment can be calculated by the use of external standards. Various definitions for the limits of qualitative and quantitative analysis are compared, and an illustrative example is given.

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Beitrag zur statistischen Definition der Grenzen analytischer Bestimmungen

Zusammenfassung Mit Hilfe externer Standards können verschiedene Grenzen für die analytische Bestimmung mittels Kalibrierung berechnet werden. Unterschiedliche Definitionen für die Grenzen qualitativer und quantitativer Analysen werden verglichen und durch ein experimentelles Beispiel illustriert.

     

Fabrication of electrospun poly(methyl methacrylate) nanofibrous membranes by statistical approach for application in enzyme immobilization

Response surface methodology based on a five-level, five-variable central composite rotatable design was used to model the average diameter of electrospun poly(methyl methacrylate) nanofibers. The effects studied include polymer concentration, distance, temperature, flow rate, and voltage. Fiber diameter was correlated to these variables by using a second-order polynomial function at a 95% confidence level. The analysis confirmed that polymer concentration, temperature, flow rate, and voltage were the significant factors affecting the diameter with the first three being the most significant ones. Also, no interaction effect terms were found to be significant. The coefficient of determination of the model was found to be 0.9443. The predicted fiber diameters were in agreement with the experimental results. The adequacy of the model was examined using additional independent experiments that were not employed in the model generation to fabricate 100–500 nm fibers with the average absolute relative deviation being 3.55%. A minimum fiber diameter of 36 nm was established and could be validated by experiments. When used for immobilization of Candida rugosa lipase by adsorption, the nanofibrous membranes provided enzyme loading as high as 332 mg lipase/g fibers, which is 5.2 times the reported maximum value.     

Quality assessment of organic coffee beans for the preparation of a candidate reference material

Summary A random sampling was carried out in the coffee beans collected for the preparation of the organic green coffee reference material in view of assessing the homogeneity and the presence of soil as impurity. Fifteen samples were taken for the between-sample homogeneity evaluation. One of the samples was selected and 10 test portions withdrawn for the within-sample homogeneity evaluation. Br, Ca, Co, Cs, Fe, K, Na, Rb, Sc and Zn were determined by instrumental neutron activation analysis (INAA). The F-test demonstrated that the material is homogeneous for Ca, Co, Cs, K and Sc, but not homogeneous for Br, Fe, Na, Rb and Zn. Results of terrigenous elements suggested negligible soil contamination in the raw material.     

Homogeneous nucleation: classical formulas as asymptotic limits of the Cahn-Hilliard approach

Classical expressions for the critical cluster work of formation approximate the nonclassical expressions based in the density functional theory of capillarity for the limit of low supersaturation degrees. However, the ratio between classical and nonclassical expressions for nucleation rates grows as the supersaturation degree decreases. Here, with the aim to obtain simple and more accurate expressions that approximate the modern nucleation rate formulas, an asymptotic expansion of the Cahn-Hilliard expression of the critical work of formation is developed within the limit of low supersaturation. In such asymptotic expansion, terms up to third order are retained. The ratios between the corrected classical expressions and the nonclassical ones are now decreasing for supersaturation degrees tending to zero. However, the corrected approximate formulas are as difficult to handle as the exact Cahn-Hilliard expressions. When only the two first low-order terms of the asymptotic expansion are retained, a simpler corrected classical expression is obtained but it can only approximate nonclassical expressions up to order unity. Finally, using a Becker-Doring model of nucleation, the kinetic prefactor of the critical nuclei rate of formation is modeled consistently with the Cahn-Hilliard approach to the critical work of formation.     

Detection limits in inductively coupled plasma atomic emission spectrometry: an approach to the breakdown of the ratios of detection limits reported for different equipments

Potential OH band interferences were studied for over 100 prominent lines emitted by an inductively coupled plasma (ICP). The basic information was derived from stepped spectral scans obtained with a 1.5-m echelle monochromator with predisperser (Spectrochim. Acta39B 1239 (1984)). The scans were made at both “high resolution” (HR) and “medium resolution” (MR) corresponding to spectral bandwidths of 4–5 pm and 11–16 pm, respectively.The seriousness of OH band interferences was assessed on the basis of the ratio of the limit of determination (c_D) and the limit of detection (c_L) as defined in Parts I and II (Spectrochim. Acta40B, 1085,1107 (1985)). It is shown that the results of an assessment based on this criterion do not strongly depend on the ICP operating conditions.Results are presented for a conventional argon ICP operated under compromise conditions. Appraisals are stated in generalized form for spectral bandwidths of 5 and 15 pm, independent of the apparatus used in this work. Out of the more than 100 prominent lines examined 7 were found to experience very serious OH band interference (c_D/c_L 30) at 5 and/or 15 pm bandwidth. Serious interference (10 c_D/c_L 30) at 5 and/or 15 pm bandwidth was established for 18 lines. OH band interference turned out to be non-existent or negligible for 83 prominent lines.The study also revealed that generally in the case of line overlap it is the limit of determination rather than the limit of detection that should be used as the criterion for the optimization of the ICP parameters.     

Influence of the surfactant bromide of cetyltrimetyl ammonium in the determination of chlorogenic acid in instant coffee and mate tea samples

In this study, two quantitative differential-pulse polarography (DPP) and square-wave voltammetry (SWV) methods were developed to determine total chlorogenic acid (CGA). Studies on this compound involve its reduction at a hanging mercury drop electrode in micellar media—a simple, fast, reliable, and sensitive method. The use of surfactant cationic cetyltrimethylammonium bromide (CTAB) was pivotal to the development of these methods, allowing for satisfactory changes in CGA reduction. The supporting electrolyte which provided the best-defined CGA determination was 0.04-mol L⁻¹ phosphate buffer at pH 6.0 in the presence of CTAB. Based on this use and under optimized conditions, the two new DPP and SWV methods for CGA analysis had detection limits of 2.36 × 10⁻⁷ and 1.34 × 10⁻⁹ mol L⁻¹, respectively, for a pure standard. Analysis of the standard in the presence of treated instant coffee and mate tea samples allowed for good average recovery rates, ranging from 97.06% to 105.90%.     

Homopolycyclotrimerization of A4‐type tetrayne: A new approach for the creation of a soluble hyperbranched poly(tetraphenylethene) with multifunctionalities

A tetraphenylethene‐containing A₄‐type tetrayne, named 1,1,2,2‐tetrakis(4‐ethynylphenyl)ethene is synthesized and its TaCl₅‐Ph₄Sn catalyzed homopolycyclotrimerization affords hyperbranched poly(tetraphenylethene) with high molecular weight (M_w = 280,000) in high yield (97%). The polymer shows good solubility and high thermal stability. It is aggregation‐enhanced emission (AEE)‐active and functions as a fluorescent chemosensor for explosive detection with a superamplification effect and large quenching constants up to 758,000 M^?1. The polymer shows high and tunable refractive indices (RI = 1.9288?1.6746) in a wide wavelength region. Porous fluorescent polymer thin film is prepared by breath figure (BF) methods and real‐time monitoring of the elusive BF formation process is realized. Photolithography of the thin films readily generates well‐resolved fluorescent photopattern without and with porous secondary structure. The polymer is metallified and pyrolysed to give magnetic ceramics with high magnetic susceptibilities (M_s = 83 emu/g) and near‐zero coercivity (H_c = 0.08 kOe). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4752–4764     

Limits of detection, identification and determination: a statistical approach for practitioners

 For the estimation of the limits of detection, identification and determination, considerations from analytical practice were applied to the statistics of the calibration line and its prediction interval. The detection limit was the concentration calculated from the maximum height of the prediction interval at zero spiking concentration. The identification limit was twice the detection limit and was the lowest concentration that could safely be detected. The determination limit was the lowest concentration fulfilling three criteria: 1. None of the signals resulting from determination limit concentration should interfere with any signal from detection limit concentration, thus providing an unambiguous separation between the two limits. 2. Recovery should be between 70% and 120%. 3. Lowest and highest predictable signal at determination limit concentration should not deviate more than ± 30% from the average. Practical analytical guidance and the necessary mathematical formulae are presented. Received: 12 November 1997 · Accepted: 7 December 1997     

Capillary electrophoresis for the analysis of meat authenticity

In this overview, different meat authenticity issues are presented, as well as a wide variety of methods available for meat authentication. Unlike chromatographic, traditional gel electrophoretic, or immunological methods, which have been routinely used in analytical laboratories, the application of capillary electrophoresis (CE) is relatively new in solving meat authentication issues. Several unique CE applications based on meat protein fingerprinting are discussed for the analysis of meat species in unheated meat products. For protein data interpretation, pattern recognition is used to account for the natural variability present within the same meat species. While gel DNA-based methods are widely used for determining meat species in heat processed products, few DNA-based methods utilizing CE have been reported. Moreover, the methods reported are qualitative or semiquantitative. Thus, the need for quantitative competitive PCR CE methods in the determination of meat species is addressed. For the determination of meat extenders, CE methods were either protein-based or based on specific markers. Polyphenols are used as specific markers for soy detection and hydroxyproline is used as a specific marker for collagen determination. Finally, the potential of electrophoretically mediated miroanalysis (EMMA) for the detection of meat that may have been previously frozen and retailed as "fresh" is highlighted.     

Enzymes in Organic Synthesis: Application to the Problems of Carbohydrate Recognition (Part 2)

Recognition of carbohydrates by proteins and nucleic acids is highly specific, but the dissociation constants are relatively high (generally in the mM to high μM range) because of the lack of hydrophobic groups in the carbohydrates. The high specificity of this weak binding often comes from many hydrogen bonds and the coordination of metal ions as bridge between sugars and receptors. Though weak hydrophobic interactions between sugars and proteins have also been identified, the unique shape of a complex carbohydrate under the influence of anomeric and exo anomeric effects (the glycosidic torsion angles are therefore often not flexible but are typically somewhat restricted) and the topographic orientation of the hydroxyl and charged groups contribute most significantly to the recognition process. Studies on the structure–function relationship of a complex carbohydrate therefore require deliberate manipulation of its shape and functional groups, and synthesis of oligosaccharide analogs from modified monosaccharides is often useful to address the problem. The availability of various monosaccharides and their analogs for the synthesis of complex carbohydrates together with the information resulting from structural studies (such a NMR or X-ray studies on sugar–protein complexes) will certainly provide a basic understanding of complex carbohydrate recognition. An ultimate goal is to develop simple and easy-to-make non-carbohydrate molecules that resemble the active structure involved in carbohydrate–receptor interaction or the transition-state of an enzyme-catalyzed transformation (for example, glycosidase or glycosyltransferase reactions) and have the approprite bioavailability to be used to control the carbohydrate function in a specific manner. In part one of this review we described various enzymatic approaches to the synthesis of monosaccharides, analogs, and related structures. We describe in this part enzymatic and chemoenzymatic approaches to the synthesis of oligosaccarides and analogs, including those involved in E-selectin recognition, and strategies to inhibit glycosidases and glycosyltransferases.