The disclosure describes a method for simultaneous determination of nitrogen and oxygen isotope compositions of natural nitrate and nitrite, which quantitatively converts natural nitrate and nitrite into an organic ester and a nitro-compounds respectively, and then nitrate and nitrite δ.sup.18O and δ.sup.15N are simultaneously determined by adopting a gas chromatography/pyrolysis/gas chromatography/isotope ratio mass spectrometry coupling technology (GC/Py/GC/IRMS). According to the method for simultaneously determining the nitrogen and oxygen isotope compositions of the natural nitrate salt and nitrite salt, the small amount of sample does not result in the loss, acquisition, exchange and fractionation of nitrogen and oxygen.

Methods and systems for the detection and quantification of multiplicity of ionic analytes comprising CrO.sub.4.sup.2−, AsO.sub.4.sup.3−, SeO.sub.4.sup.2−, and ClO.sub.4.sup.−, and optionally F.sup.−, Cl.sup.−, NO.sub.2.sup.−, NO.sub.3.sup.−, SO.sub.4.sup.2−, using ion chromatography and suppressed ion conductivity. The method comprises loading a sample loop with a sample; injecting the sample from the sample loop into a column with an eluent, wherein the column comprises a guard column and an analytical column; separating, with the column, the injected sample at an effective separation temperature the injected sample in the presence of an organic modifier into a multiplicity of detectable ionic analytes; suppressing, with a suppressor, background signal; and detecting, with a detector, the multiplicity of ionic analytes.

Methods of quantifying N.sup.2-carboxyethyl-2′-deoxyguanosine (CEdG) levels in biological samples and comparing those levels to known normal levels can diagnose a number of disorders, including diabetes and cancer. Methods can also determine whether therapies for disorders are effective by measuring CEdG levels before and after treatment. Measurement of CEdG levels occurs using liquid chromatography electrospray ionization tandem mass spectrometry.

A system for determining isotopic composition of a gaseous sample. The system includes at least one gas chromatograph for separating the gaseous sample into gaseous components. Furthermore, the system includes a combustion furnace operatively coupled with the at least one gas chromatograph for oxidizing the gaseous components. Moreover, the system includes a water separator operatively coupled with the combustion furnace. Furthermore, the system includes an isotope-ratio mass spectrometer operatively coupled with the water separator. Moreover, the isotope-ratio mass spectrometer comprises an ion source for generating ion beams associated with each of the oxidized gaseous components and a mass analyser for receiving the generated ion beams from the ion source, wherein the mass analyser is operable to determine isotopic concentrations associated with each of the ion beams. Furthermore, the isotope-ratio mass spectrometer is operable to use the determined isotopic concentrations to determine the isotopic composition of the gaseous sample.

A zircon ID-TIMDS Pb isotope determination method by multiple ion counters with a dynamic multi-collection protocol is provided. Compared with a commonly used multi-ion counter static determination method, the method provided by the present invention completely eliminates influences of gain differences of the different ion counters on determination results of Pb isotopes. Compared with a conventional single-ion counter determination method with five times of peak-jumps, the method provided by the present invention can obtain all of Pb isotope ratios with two times of peak-jumps, which increases the collection efficiency of Pb isotope ion beams and decreases influences of ion beam stability on Pb isotope analysis results. Consequently, compared with a multi-ion counter static method and a single-ion counter peak-jumping method, the method provided by the present invention improves the Pb isotope analysis precision for the single-grain zircon ID-TIMS U—Pb dating method (with a .sup.205Pb tracer), having application potentials.

The present disclosure provides methods of identifying or certifying an animal that consumed a traceable diet comprising a C.sub.1 metabolizing microorganism.

A sorbent tube holder (100) for securing a sorbent tube (10) in position in a fluid-flow system, the sorbent tube holder (100) comprising: an mounting element (126) having first and second opposed ends (126a, 126b) which define a tube mounting axis (A-A); at least one fastener (128) in communication with the mounting element (126) for providing a releasable tube retaining force; at least one sorbent tube (10) engaged with the mounting element (126); and a holder frame (130) to which the mounting element (126) is attached to prevent or limit movement of the mounting element (126) perpendicular to the tube mounting axis. A method of preventing or limiting unintentional damage to a sorbent tube, and a portable tube holder are also provided.

The present invention is a method for detecting a specific disease based on the result of a measurement in which the amount of a peptide serving as a biomarker contained in a biological sample is determined by using an LC-MS. A pretreatment process performed before the measurement using the LC-MS includes the steps of preparing a mixed sample solution by adding a stable isotope reagent and a trifluoroacetic acid to the biological sample, where the stable isotope reagent is prepared beforehand by labeling the peptide with a stable isotope; boiling the mixed sample solution; injecting the mixed sample solution after boiled into a solid-phase extraction column to make the peptide be retained in the solid-phase extraction column; and passing a water-soluble organic solvent through the solid-phase extraction column to elute the peptide retained in the solid-phase extraction column and collect the eluate.

The present disclosure relates to a method performed in an interface system, the interface system comprising a reactor and a reaction-product-separator, the method comprising: (a) guiding a liquid containing analytes to and through the reactor and causing a component comprised by the analytes to react to a reaction product in the reactor, to thus create a post-reactor liquid comprising the reaction product, (b) guiding the post-reactor liquid from the reactor to the reaction-product-separator and through the reaction-product-separator, and separating the reaction product from the post-reactor liquid, to thus create a post-separator fluid, and (c) guiding at least one rinsing liquid through at least one of the reactor and the reaction-product-separator. The present invention also relates to an interface system, wherein the system is configured to perform the method, wherein the interface system comprises the reactor and the reaction-product-separator.

A method and a system for measuring the pore structure of tight sandstone are provided. The method comprises the following steps: carrying out the desorption experiment of a core sample saturated by a specific gas containing isotope element to obtain the pressure of the specific gas and the total isotope ratio at each sampling moment; acquiring a single isotope ratio of each pore diameter at each sampling moment according to a physical model containing pore diameter parameter and the pressure of the specific gas at each sampling moment; and obtaining the proportion of a pore of each pore diameter in the core sample. The method and the system for measuring the pore structure of the tight sandstone provided by the disclosure can quickly obtain the pore distribution of the tight sandstone without damaging a sample.