Structural collapse of plant materials during freeze-drying

Structural collapse of plant materials, which affects quality of foods, was studied. Fresh and osmotically dehydrated plant materials were freeze-dried at several chamber pressures, to achieve initial sample temperatures that were below (?55?C), near (?45?C), or above (?28?C) their glass transition temperature (T _g=?45?C). Freeze-drying at ?55?C resulted in products retaining their original volume. When the initial sample temperature was increased aboveT _g, the resulting freeze-dried samples collapsed. When the initial sample temperature was increased above the temperature of ice melting (T′_m), the samples collapsed further.     

Radiochemical analysis of toxic elements in biological materials

A radiochemical method for simultaneous determination of toxic elements (Hg, Cd and Sb) in biological materials has been developed. The procedure involves the irradiation of samples with thermal neutrons and quantitative one-step separation in 0.1M 4-(5-nonyl)pyridine/benzene from 2.0M hydrochloric acid followed by gamma-ray spectrometry. The procedure is applied for the analysis and to the studies of distribution of these elements in IAEA-RMs, human serum and hair samples. Results obtained are found to be in good agreement with those reported in the literature.     

Analytical strategy for the chemical characterization of biological reference materials

The analytical strategy for the elemental chemical characterization of biological reference materials followed during a recently completed Reference Material development endeavour is discussed. Characterization, the assignment of reliable values to total elemental concentrations of a wide range of elements, poses the most difficult challenge in the scheme of reference material (RM) production. A review is presented of the many factors considered that significantly impinged on the conduct and outcome of the complex analytical characterization exercise. Major considerations were: (1) analytical elemental characterization philosophy, (2) analyte selection, (3) selection of analytical methodologies, (4) statistical protocols, (5) in-house characterization, (6) assessment of material homogeneity (7) cooperative interlaboratory characterization campaign, (8) data evaluation and (9) calculation of concentration values and associated uncertainties.Contribution no. 94-47 from Centre for Land and Biological Resources Research     

Dissolvable membranes as sensing elements for microfluidics based biological/chemical sensors

We demonstrate a chemical and biological sensing mechanism in microfluidics that transduces chemical and biological signals to electrical signals with large intrinsic amplification without need for complex electronics. The sensing mechanism involves a dissolvable membrane separating a liquid sample chamber from an interdigitated electrode. Dissolution of the membrane (here, a disulfide cross-linked poly(acrylamide) hydrogel) in the presence of a specific target (here, a reducing agent-dithiothreitol) allows the target solution to flow into contact with the electrode. The liquid movement displaces the air dielectric with a liquid, leading to a change (open circuit to approximately 1 kOmega) in the resistance between the electrodes. Thus, a biochemical event is transduced into an electrical signal via fluid movement. The concentration of the target is estimated by monitoring the difference in dissolution times of two juxtaposed sensing membranes having different dissolution characteristics. No dc power is consumed by the sensor until detection of the target. A range of targets could be sensed by defining membranes specific to the target. This sensing mechanism might find applications in sensing targets such as toxins, which exhibit enzymatic activity.     

Considerations in the preparation of biological and environmental reference materials for use in the study of the chemical speciation of trace elements

Summary The role that information on chemical speciation can play in the selection of reference materials for the analysis of biological and environmental samples is reviewed. Some considerations that might go into the preparation of materials designed for chemical speciation studies are explored. Individual steps in the preparation of lyophilized serum and urine reference materials are examined in relation to changes that could occur in the chemical speciation of trace elements.     

Determination of trace elements in biological materials using tetramethylammonium hydroxide for sample preparation

A method to prepare milk powder, bovine liver and bovine muscle samples for analysis by electrothermal atomic absorption spectrometry (ETAAS) is proposed. Samples are mixed with a small amount of tetramethylammonium hydroxide (TMAH) and a stable and homogeneous slurry is produced in ca. 2 h with heating at 60–70 °C. After such sample preparation and dilution with water, trace elements are determined in certified reference materials. Pyrolysis and atomisation temperatures are optimised for each element, and several modifiers are investigated. External calibration is used for every analyte. Limits of detection (LODs), precision and accuracy are reported for Cd, Pb, Ni, Cr, Cu and Ag and compared with those obtained after conventional acid digestion. The main advantages of the proposed method are the simplicity of sample preparation and the longer lifetime of the graphite tube.     

Nanotomography in the chemical, biological and materials sciences

Nanotomography is a technique of growing importance in the investigation of the shape, size, distribution and elemental composition of a wide variety of materials that are of central interest to investigators in the physical and biological sciences. Nanospatial factors often hold the key to a deeper understanding of the properties of matter at the nanoscale level. With recent advances in tomography, it is possible to achieve experimental resolution in the nanometre range, and to determine with elemental specificity the three-dimensional distribution of materials. This critical review deals principally with electron tomography, but it also outlines the power and future potential of transmission X-ray tomography, and alludes to other related techniques.     

Radiochemical separation methods for the determination of some toxic elements in biological reference materials

The present paper describes radiochemical separation procedures developed for the determination of the elements As, Cr, Hg, Sb and Se in biological reference materials. The methods chosen utilize ion exchange, retention on inorganic exchangers and solvent extraction techniques for the isolation of the elements of interest. These procedures are more rapid than previously used methods, such as distillation and precipitation. As to the sample dissolution, the following procedures were tested using radioactive tracers and reference materials: treatment of the materials in teflon bombs with a mixture of HNO₃+H₂SO₄ or HNO₃ only in a normal oven, and with HNO₃ in a microwave oven using specially designed digestion bombs.     

Analytical evaluation of comparative data on trace elements in biological materials

Large bodies of data on a given material from different sources appear a major advantage of intercomparison experiments and a sound basis for a straight statistical evaluation (as is the usual approach in the assignment of recommended or consensus values). On closer inspection of the results, however, it is usually found that only one or two techniques are represented in statistically significant numbers, most frequently AAS and NAA, and their distribution may not be normal. Correct results are sometimes hidden among laboratory means in the lower or upper part of the frequency distribution plots. Conventional statistics neglecting procedural details and the chemistry behind a procedure may result in incorrect assignment from the reported data, which can be affected by unidentified systematic effects. Generally, in the lowest concentration range contamination predominates as the systematic error determining the accuracy of results. Activation analysis being the least vulnerable to this type of error, it is, if applicable, in principle the most likely to give correct answers. Follow-up work was carried out in this laboratory on the IAEA reference samples of Milk Powder A-11, Muscle Tissue H-4, Fish Flesh MA-A-2 and the Soil-5, clearly demonstrating the potential of activation analysis as verification technique. By determining the same element in the destructive and nondestructive mode, and on the basis of two different isotopes, virtually independent approaches are achieved, often allowing the disclosure of different types of errors. Results are also reported for nickel by a new voltammetric technique enabling its determination at the microgram per kilogram level.     

An accurate procedure for multielement neutron activation analysis of trace elements in biological materials

A procedure for radiochemical neutron activation analysis of biological materials for As, Cd, Co, Cu, Ga, Hf, Mg, Mn, Na, Sb, Sc, Se, Zn, and the rare-earth elements (REE) has been developed. Maximum control over accuracy has been emphasized. Samples are digested under reflux in the presence of carrier for every element determined, and a chemical yield is measured for every element assayed. The procedure has been tested by replicate analysis of National Bureau of Standards bovine liver sample (SRM-1577). Values agree to within their uncertainties with those given by NBS for the 9 elements of this group that they have analyzed. Accuracies at the 90% confidence level for elements in the liver sample are estimated as better than ±10% for Cu, Na, and Zn, between ±10 and ±25% for As, Co, Hg, La, Mn, and Se, and between ±25 and ±50% for Cd, Sb, Sc, and Sm.     

A search for internal isotopic tracers in metallurgical materials

On the basis of the results obtained it can be concluded that none of the examined elements could be used as internal tracer for studying processes, which take place during production of steel in chosen steel-works. However, some of the examined elements could be used as inactive tracers. The results of the determination of lanthanum are particularly interesting in view of the fact that this element was used as inactive tracer for examination of the origin of exogenic inclusions.     

The freeze-drying of orange juice for the preparation of reference materials

Summary The possibility of producing fruit juice reference materials is conditioned by the availability of a method which allows the transformation of the original juice or concentrate into a better physically stable form. Therefore a feasibility study of the transformation of orange juice by freeze-drying was carried out. In general, the obtained powder is hygroscopic, and tends to agglomerate into large solid lumps. Under optimal conditions of freeze-drying combined with redrying of the powder before closing the bottles, a slightly cohesive but physically stable yellow orange powder can however be obtained. Compared to the original juice, this shows no loss of reducing sugars and has a normal glucose-fructose ratio. Moreover, most aminoacids e.g. asparagine, methionine, lysine and arginine are not affected by freeze-drying. Based on the study of a limited number of important fruit juice parameters, it may be concluded that freeze-drying seems very promising in order to obtain an orange juice reference material, which after redissolution in water keeps the original chemical orange juice properties.

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Gefriertrocknung von Orangensaft für die Herstellung von Referenzmaterialien

     

Radiochemical determination of some trace elements in biological materials using short-lived isotopes

A radiochemical procedure for the consecutive separation of vanadium and molybdenum, copper, manganese, rubidium and potassium is proposed for the analysis of biological materials. Vanadium and molybdenum are extracted together with 0.1% BPHA solution in toluene, copper followed by manganese are extracted as diethyldithio-carbamate complexes with chloroform and rubidium and potassium are precipitated as tetraphenylborates.     

Speciation of trace elements in biological materials: trends and problems.

In the determination of trace elements in biological materials, speciation is of particular importance as the essential effects or toxicity of an element and its metabolic behaviour depend to a large extent on the chemical forms in which it is present in the organism. Speciation is relatively easy if a property of a particular compound can be measured directly in the sample without interference from the other components of the material, e.g., the enzymic activities of the metallo-enzymes. Another possibility for speciation is immunoassay, which likewise allows direct determination of a particular trace element. At present, however, with most trace elements both fractionation methods and analytical procedures have to be combined and speciation has to be carried out by determining the elemental content in the separated fractions. The methods and apparatus used in taking, storing and preparing the samples can, therefore, not be selected solely according to the requirements of trace element determination, but it is also essential to ensure that the biological structures of the components to be separated remain intact. In this work the need for speciation in the investigation of the toxic and essential effects of trace elements is shown with the help of some examples, and the problems that can occur in the various steps of sampling, storage and sample preparation are discussed.     

Recombination of nanometric vesicles during freeze-drying

Concentrated dispersions of nanometric lipid vesicles (mean diameter 20 nm) in water/maltose solutions have been freeze-dried and then redispersed in water, yielding again dispersions of lipid vesicles. At each stage of the freeze-drying process, the organization of the vesicles in the dispersion and their size distribution were examined through small-angle neutron scattering and gel permeation chromatography. It was found that the osmotic deswelling of the vesicles caused them to recombine into larger vesicles. A single burst of recombination events occurred when the maltose concentration in the aqueous phase rose above 100 g/L. The final vesicle population was monopopulated, with a central diameter about twice as large as that of the original dispersion.     

Determination of trace elements in biological materials by instrumental epithermal neutron activation analysis

The use of reactor epithermal neutrons in instrumental activation analysis is described for the determination of trace elements via long-lived isotopes. A boron carbide filter is used. Results of analyses of human erythrocytes, plasma, urine and some biological reference materials are given to demonstrate the applicability of the method to biological samples. Bromine, iron, cesium, rubidium, selenium and zinc and cobalt are determined. The method provides accuracy and reliability similar to conventional thermal neutron activation but is faster. Limits of detection attainable with the two techniques are compared.     

Determination of 25 elements in biological standard reference materials by neutron activation analysis

Trace element analysis has been carried out on standard biological reference samples such as bovine liver, orchard and tomato leaves. Computer aided instrumental neutron activation analysis and, in some cases, preliminary chemical group separation followed by NAA were used. For Ca, Mg, Ni and Si special chemical separation and Cerenkov counting were applied. *** DIRECT SUPPORT *** A1353068 00003     

High reliability atomic absorption spectrometry of major and minor elements in biological materials

Summary Reliable analytical information is of fundamental importance for decisions of far-reaching impact in many regulatory, medical and scientific areas and disciplines. It is however at times elusive. Although the technique of atomic absorption spectrometry (AAS) as become widely established in analytical laboratories throughout the world for the determination of inorganic elements, only few AAS-based methods have reached official status and even fewer have attained reference method status. Research is underway to delineate impacts of a number of parameters on method performance to lead to protocols for standard and reference flame AAS (FAAS) methods for the reliable measurement of major and minor levels of elements of nutritional and toxicological pertinence in clinical and biological materials. Factors investigated include preparation of standards, calibration techniques, sampling and sample decomposition, solution preparation, instrumental parameters, and measurement protocols. Examples of some pronounced effects of sample decomposition and calibration techniques are presented as well as indications of the excellent performance of well-applied AAS procedures determined by use of standard reference materials and comparison with other techniques of analysis. Reference will be made to the determination of the major and minor nutrient elements Na, K, Mg, Ca, Mn, Fe, Cu and Zn in plant biological reference materials.Formerly at Plant Research Centre, Agriculture Canada, Ottawa, Ontario K1A OC6, CanadaContribution No. 1030 from Plant Research Centre     

Loss of elements in the oxygen flask decomposition of biological materials: A study by neutron activation analysis

Partial loss of elements in the oxygen flask method for the decomposition of biological materials is described. The irradiated sample is placed in a platinum wire gauze or quartz cup and burnt in an oxygen atmosphere in the presence of carrier solutions. The results obtained by radiochemical neutron activation analysis for the elements like Mn, As, Cu, Sb and Zn in different standard reference materials are presented with a discussion of the possible causes for the lower values.