Isotope pairing technique

Risgaard-Petersen, N., Nielsen, L. P., and Blackburn, T. H. (1998). Simultaneous measurement of benthic denitrification, with the isotope pairing technique and the N-2 flux method in a continuous flow-through system. Water Research. 32(11), 3371—3377. 

Master, Y., Shavit, U., and Shaviv, A. (2005). Modified isotope pairing technique to study N transformation in polluted aquatic systems Theory. Environ. Sd. Technol. 39, 1749-1756. 

Steingruher, S. M., Friedrich, J., Gachter, R., and Wehrh, B. (2001). Measurement of denitrification in sediments with the isotope pairing technique. Appl. Environ. Microbiol. 67, 3771—3778. 

It has been a serious draw-back in studies of nitrogen transformations that a useful radioisotope of nitrogen does not exist. The isotope, N, is available only at accelerator facilities and has a half-life of 5 min, which strongly limits its applicability. Instead, the stable isotope, N, has been used successfully as a tracer in studies of nitrogen transformations in the marine environment. For example, the use of N03 by the isotope pairing technique has offered possibilities to study the process of denitrification of NOj" to (Nielsen 1992). The NO3" is added to the water phase over the sediment and is allowed to diffuse into the sediment and gradually equilibrate with NO3 in the pore water. By analyzing the isotopic composition of the formed N, i.e. 

The reverse isotope dilution technique can be applied for accurate determination of the Mg contents in a sample, sample, on applying equation 7, by measuring the isotope ratio of a selected pair of stable isotopes, in a weighed mixmre of the sample with an isotopically enriched CRM. The average atomic masses m and the isotopic ratios R of Mg in the enriched CRM and in nature are known. The method was applied for determination of Mg in plant material using a CRM isotopically enriched with Mg, measuring with an ICP/MS instruments. ... 

Rysgaard, S., Risgaard-Petersen, N., Nielsen, L.P., and Revsbech, N.P. (1993) Nitrification and denitrification in lake and estuarine sediments measured by the 15 N dilution technique and isotope pairing. Appl. Environ. Microbiol. 59 2093-2098. 

Lohse, L., Kloosterhuis, H. T., Raaphorst, W. V., and Helder, W. (1996). Denitrification rates as measured by the isotope pairing method and by the acetylene inhibition technique in continental shelf sediments of the North Sea. Mar. Ecol. Prog. Ser. 132, 169—179. 

MEVIS/IPM, membrane inlet mass spectrometry/isotope pairing method TCD, gas chromatography-thermal conductivity detector AIT, acetylene inhibition technique IPM, isotope pairing method with isotope ratio mass spectrometry MIMS, membrane inlet mass spectrometry Stoichiometery, benthic flux DICiDIN stoichiometry MIMS + N03, membrane inlet mass with N03 amendment 15N2 production, 15N03 or 15NH4 conversion to 15N2. 

Denitrification is the reduction of N03 N02 NO N2O —> N2 gas that is mediated by bacteria under anaerobic conditions, most generally in microbial mats and sediments. There are a number of methods to measure denitrification acetylene inhibition, isotope pairing, changes in N2 fluxes, and changes in the N2 to argon (Ar) ratio. Each of the techniques has their pros and cons and none is clearly superior under all conditions (see reviews by Cornwell et al, 1999 Chapter 6 by Devol, this volume). 

It is obvious that none of the above methods is perfect in assigning metal-ligand vibrations. Furthermore, these methods encounter more difficulties as the structure of the complex (and hence the spectrum) becomes more complicated. Fortunately, the metal isotope technique which was developed in 1969 may be used to obtain reliable metal-ligand assignments [89]. Isotope pairs such as (H/D) and ( 0/ 0) had been used routinely by many spectroscopists. However, isotopic pairs of heavy metals such as ( Ni/ Ni) and ( °" Pd/ °Pd) were not employed until 1969 when the first report on the assignments of the Ni—P vibrations of fra 5-Ni(PEt3)2X2 (X = Cl and Br) was made. The delay in their use was probably due to two reasons ... 

The dIoxygen ligand may coordinate to a metal in the end-on or side-on fashion. These two structures can be distinguished by using the isotope scrambling technique. Andrews first applied this method to the structure determination of the ion-pair complex Li O a mixture of Oa, and O2... 

Ruttenburg KC (1992) Development of a sequential extraction method for different forms of phosphorus in marine sediments. Limnol Oceanol 37(7) 1460-1482 Rysgaard S, Risgaard-Petersen N, Nielsen LP, Revsbech NP (1993) Nitrification and denitrification in lake and estuarine sediments measured by the N dilution technique and isotope pairing. Appl Environ Microbiol 59(7) 2093-2098 Shaked Y, Erel Y, Sukenik A (2002) Phytoplankton-mediated redox cycle of iron in the epilimnion of Lake Kiimeret. Environ Sci Technol 36(3) 460-467 Shukla SS, Syers JKJ, Williams DH (1971) Sorption of inorganic phosphate by lake sediments. Soil Sci Soc Am Proc 35(2) 244-249 Song JM (1997) Chemistry of Sediment-Seawater Interface of China s Seas. China Ocean Press, Beijing, pp. 1-222 (in Chinese)... 

The initial yields of the ions have been determined from gamma radiolysis in cyclohexane at a pressure of 55 torr by isotopic labelling techniques. In Table 6 we show the initial yields of the various ions together with those obtained from mass-spectrometric determinations at very low pressure. The yields are given as ion-pair yields, i.e. the yield of species per ion pair produced. The ion-pair yield M/N can be converted into species produced per unit energy absorbed, by multiplication by the yield of ionization G = 4.4 (lOOeV)" We see that the decomposition of the parent ion is appreciably suppressed in the gas at 55 torr, due to collisional deactivation. 

One of the most important attributes of a liquid scintillation counter relevant to metabolic studies is the ability to determine two isotopes simultaneously in the same sample, and this does away with the requirement for weighing a sample. For this technique to be successful, the )S-spectra of the two isotopes must be sufficiently different to be amenable to separation by pulse-height analysis. This is the case for the isotope pairs most commonly used such as and and and and and Where... 

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