Most soils contain inorganic nitrogen (N) in the form of ammonium (NHt) and nitrate (NO)"). Nitrite (NOz) also may be present, but the amount is usually too small to warrant its determination, except in cases where NHt or NHt-forming fertilizers are applied to neutral or alkaline soils. Several other forms of inorganic N have been proposed as intermediates during microbial transformations of N in soils, including hydroxylamine (NH20H), hyponitrous acid (H2N20 2), and nitramide (NH2N02), but these compounds are thermodynamically unstable and have not been detected in soil. Until the 1950s, inorganic N was believed to account for <2% of total soil N, on the assumption that NHt and NO)" are completely recovered by extracting soil with a neutral salt solution. The validity of this assumption was challenged by the finding that some soils contain NHt in a form that is not extracted by exchange with other cations (e.g., Rodrigues, 1954; Dhariwal & Stevenson, 1958; Stevenson & Dhariwal, 1959; Bremner & Harada, 1959; Bremner, 1959; Schachtschabel, 1960, 1961; Young, 1962), and by estimates that the proportion of soil N in this form can exceed 50% for some subsurface soils (Stevenson & Dhariwal, 1959; Young, 1962). In such cases, NHt is said to be fixed, and fixed NHt has subsequently been defined as the NHt in soil that cannot be replaced by a neutral potassium salt solution (SSSA, 1987), such as 1 or 2 M KCI or 0.5 M K2S04, in contrast to exchangeable NHt, which is extractable at room temperature with such a solution. Existing information indicates that fixed NHt occurs largely, if not entirely, between the layers of 2: I-type clay minerals, particularly vermiculite and illite (hydrous mica), and that fixation results from entrapment of NHt in ditrigonal voids in the exposed surfaces upon contraction of the clay lattice (Nommik & Vahtras, 1982). The term, nonexchangeable NHt, has been used by Bremner (1965) and Keeney and Nelson (1982) in previous editions of this publication as a more precise alternative to fixed NHt. The same term is used in the present treatment, with specific reference to NHt determined by the method described in "Determination of Nonexchangeable Ammonium," which involves digestion with an HF-HCI solution following treatment of the soil with alkaline KOBr to remove exchangeable NHt and labile organic-N compounds.

Nitrogen - inorganic forms.

Enzyme biocatalysis plays a very relevant role in the development of many chemical industries, e.g., energy, food or fine chemistry. To achieve this goal, enzyme immobilization is a usual pre-requisite as a solution to get reusable biocatalysts and thus decrease the price of this relatively expensive compound. However, a proper immobilization technique may permit far more than to get a reusable enzyme; it may be used to improve enzyme performance by improving some enzyme limitations: enzyme purity, stability (including the possibility of enzyme reactivation), activity, specificity, selectivity, or inhibitions. Among the diverse immobilization techniques, the use of pre-existing supports to immobilize enzymes (via covalent or physical coupling) and the immobilization without supports [enzyme crosslinked aggregates (CLEAs) or crystals (CLECs)] are the most used or promising ones. This paper intends to give the advantages and disadvantages of the different existing immobilization strategies to solve the different aforementioned enzyme limitations. Moreover, the use of nanoparticles as immobilization supports is achieving an increasing importance, as the nanoparticles versatility increases and becomes more accessible to the researchers. We will also discuss here some of the advantages and drawbacks of these non porous supports compared to conventional porous supports. Although there are no universal optimal solutions for all cases, we will try to give some advice to select the optimal strategy for each particular enzyme and process, considering the enzyme properties, nature of the process and of the substrate. In some occasions the selection will be compulsory, for example due to the nature of the substrate. In other cases the optimal biocatalyst may depend on the company requirements (e.g., volumetric activity, enzyme stability, etc).

Potential of Different Enzyme Immobilization Strategies to Improve Enzyme Performance

http://tautobiotech.com/en/download/REVIEW%20of%20HSCCC/Golden%20rules%20and%20pitfalls%20in%20selecting%20optimum%20conditions%20for%20high-speed%20counter-current%20chromatography.pdf

Golden rules and pitfalls in selecting optimum conditions for high-speed counter-current chromatography

There is at present an urgent need for trace detection of high explosives, with applications to screening of people, packages, luggage, and vehicles. A great concern, because of recent terrorist activities, is for the development of methods that might allow detection and identification of explosives at a stand off distance. Nearly every analytical chemical method has been or is being applied to this problem. This review outlines the properties of explosives that might be utilized in detection schemes, discusses sampling issues, presents recent method developments with particular attention to detection limits, speed of analysis, and portability, and looks towards future developments.

Instrumentation for trace detection of high explosives

Detection and determination of nitrate and nitrite: a review.

Activation analysis. Adhesives and Sealants. Air analysis. Alkaloids. Amino Acids. Amperometry. Amplification Reactions. Analytical reagents. Archaeometry and antique analysis. Arsenic (speciation). Asbestos. Atomic absorption spectrometry. Atomic emission spectrometry. Atomic fluorescence spectrometry. Atomic Mass Spectrometry. Bioassays. Bioluminescence. Bleaches and Sterilants. Blood and Plasma. Buffer Solutions. Building materials. Cadmium (speciation). Capillary Electrochromatography. Capillary Electrophoresis. Carbohydrates. Carbon. Cement. Centrifugation. Ceramics. Cerebrospinal Fluid. Chemical Warfare Agents. Chemiluminescence. Chemometrics. Chiroptical Analysis. Chlorofluorocarbons and other halocarbons. Chromatography. Clinical analysis. Coal and Coke. Colour Measurement. Computer Modelling. Conductimetry and oscillometry. Cosmetics and Toiletries. Derivatization of Analytes. Dioxins. Distillation. DNA Sequencing. Drug metabolism. Electrogravimetry. Electrolytes in physiological samples. Electron Energy Loss Spectrometry (EELS). Electron spin resonance spectroscopy. Electrophoresis. Elemental speciation. Endocrine Disrupting Chemicals. Environmental analysis. Enzymes. Essential Oils. Ethanol. Extraction. Extraction: solvent extraction. Fertilizers. Field Flow Fractionation. Fire Assay. Flow analysis. Flow injection analysis. Fluorescence. Foam Fractionation and Floatation. Food and nutritional analysis. Forensic sciences. Fourier transform techniques. Fuel. Functional group analysis. Gas chromatography. Gastric Juices. Geochemistry. Glasses. Gravimetry. Haemoglobins. Headspace analysis. Herbicides. History of Analytical Science. Hormones. Humic and Fulvic Compounds. Immunoassays. Indicators. Infrared spectroscopy. Ion. Ion exchange. Ion-selective electrodes. Isotope Dilution Analysis. Isotope Ratio Measurements. Kinetic methods. Lab-on-a-chip Technologies. Laser-based techniques. Lead. Lipids. Liquid chromatography. Mass spectrometry. Membrane. Mercury (speciation). Micellar Electrokinetic Chromatography. Micro Total Analytical Systems ( TAS). Microbiological techniques. Microelectrodes. Microscopy. Microwave Spectroscopy. Molecular Emission Cavity Analysis. Molecularly imprinted polymers. Nitric oxide: biological functions and detection. Nitrogen (speciation). Nitrosamines. Nuclear magnetic resonance spectroscopy. Nucleic acids. Optical spectroscopy. Ozone. Paints. Particle size analysis. Peptides. Perfumes. Personal Monitoring. Pesticides. pH. Pharmaceutical analysis. Pharmacokinetics. Phosphorescence. Phosphorus (speciation). Photoacoustic Spectroscopy. Pigments. Plastics. Polarography. Polychlorobiphenyls. Polycyclic aromatic hydrocarbons. Polymerase chain reaction (PCR). Polymers. Potentiometric Stripping Analysis. Precious Metals. Prions. Process analysis. Proteins. Proteins. Proteomics. Purines, pyrimidines and nucleotides. Qualitative analysis. Quality assurance. Radiochemical. Raman spectroscopy. Remote gas sensing. Sample dissolution for elemental analysis. Sample Handling. Sampling. Saponins. Segmented flow analysis. Selenium (speciation). Sensory Evaluation. Sequential injection analysis. Solvents. Speciation Analysis. Spectroelectrochemistry. Spectrophotometry. Spot Tests. Structural Elucidation. Sublimation. Sulfur and its Inorganic Compounds. Supercritical fluid chromatography. Surface analysis. Surfactants and detergents. Sweeteners. Textiles. Thermal analysis. Thin-layer chromatography. Thin-layer chromatography. Tin (speciation). Titrimetry. Toxins. Vitamins. Voltammetry. Volumetric gas measurements. Water analysis. Water determination. X-Ray techniques. Zone Refining.

Alan Townshend

Papers

Encyclopedia of analytical science

Determination of glucose in blood by flow injection analysis and an immobilized glucose oxidase column

Flow injection chemiluminescence determination of paracetamol.

Use of the terms "recovery" and "apparent recovery" in analytical procedures

Flow injection chemiluminescence determination of tetracycline