Automatic Carbon, Hydrogen, Nitrogen, Sulfur Analyzer Ciiemistry of Sulfur Reactions

Many laboratories routinely analyze plant, animal and soil samples with elemental analyzers coupled to isotope ratio mass spectrometers, obtaining rapid results for nitrogen (%N, d 15 N) and carbon (%C, d 13 C) from the same sample. The coupled N and C measurements are possible because of a gas chromatography (GC) separation of N 2 and CO 2 gases produced in elemental analysis. Adding a second GC column allows additional measurement of sulfur (%S, d 34 S) from the same sample, so that combined N, C and S information is obtained routinely. Samples are 1-15 mg, and replicates generally differ by less than 0.1% for d S. An example application shows that the N, C, and S measurement system allows a three-dimensional view of element dynamics in estuarine systems that are undergoing pollution inputs from upstream watersheds. Extension of these GC principles should allow coupled H, C, N, and S isotope measurements in future work. Copyright # 2007 John Wiley & Sons, Ltd.Measuring several parameters together from the same sample is desirable for many reasons, partly to save time, cost and sample, but also because the resulting coupled data allow a multivariate view of scientific problems. This paper describes a new advance in the field of coupled elemental and isotope analysis, adding S analyses to existing systems that already measure N and C amounts and isotopes in routine laboratory settings. Sulfur isotopes are valuable tracers in biogeochemical studies of element cycling on ecological and geological time scales, 1,2 complementing and expanding tracer information gained from N and C isotope measurements. 3 This paper focuses mostly on the added S analyses, and gives practical guidelines on how to make routine these new N, C and S (hereafter NCS) measurements. Laboratory analyses of sulfur are traditionally difficult and performed separately from nitrogen and carbon analyses. [4][5][6][7] Problems encountered with sulfur derive mostly from production of SO 2 gas in elemental analyzers, with SO 2 often reacting with surfaces and behaving in a 'sticky' fashion as it slowly desorbs and moves through combustion systems. Current NC analysis uses a combined elemental analyzer-isotope ratio mass spectrometer (EA-IRMS) system with one gas chromatography (GC) column to separate N 2 and CO 2 gases for sequential analysis. The new main feature of the system described here is use of a second GC column to separate SO 2 from N 2 and CO 2 gases. The N 2 and CO 2 gases pass through both GC columns for N then C measurements, while the SO 2 is only slowly moving through the first column. Upon completion of the N and C measurements, the second GC column is switched out of the gas-handling system, allowing flow rates to increase by twofold, rapidly eluting the SO 2 to the mass spectrometer for S measurements. The system described here complements a recent report of an analyzer capable of coupled H, C, N, and S (hereafter HCNS) measurements, 8 with the main difference that the system described here separates gases with GC and avoids usin...

Section: Resultsmentioning

confidence: 99%

Coupled N, C and S stable isotope measurements using a dual‐column gas chromatography system

Fry

2007

“…This indicates that structural O in organic samples is used preferentially during SO 2 formation, although the approximate O amount of tank O 2 (∼13 mg O, calculated by the ideal gas equation) was always in excess of the amount of structural O supplied with the organic samples. The contribution of tank O 2 to the produced SO 2 was limited possibly because of a thermodynamic preference of tank O 2 for CO 2 , N 2 , H 2 O reactions prior to SO 2 22 or kinetic preference of structural O for the SO 2 formation.…”

Section: Resultsmentioning

confidence: 99%

δ³⁴S measurements on organic materials by continuous flow isotope ratio mass spectrometry

Yun

Mayer

Taylor

2005

Sulfur (S) isotope ratios of thoroughly dried organic samples were measured by direct thermal decomposition in an elemental analyzer coupled to an isotope ratio mass spectrometer in continuous flow mode (EA-CF-IRMS). For organic samples of up to 13 mg weight and with total S contents of more than 10 microg, the reproducibility of the delta34S(organic) values was +/-0.4 per thousand or better. However, the delta34S values of organic samples measured directly by online EA-CF-IRMS analysis were between 0.3 and 2.9 per thousand higher than those determined on BaSO4 precipitates produced by Parr Bomb oxidation from the same sample material. Our results suggest that structural oxygen in organic samples influences the oxygen isotope ratios of the SO2 produced from organic samples. Consequently, SO2 generated from organic samples appears to have different 18O/16O ratios than SO2 generated from BaSO4 precipitates and inorganic reference materials, resulting in a deviation from the true delta34S values because of 32S16O18O contributions to mass 66. It was shown that both the amount of structural oxygen in the organic sample, and the difference of the oxygen isotope ratios between organic samples and tank O2, influenced the magnitude of the observed deviation from the true delta34S value after direct EA-CF-IRMS analysis of organic samples. Suggestions are made to correct the difference between measured delta34S(organic) and true delta34S values in order to obtain not only reproducible, but also accurate S isotope ratios for organic materials by EA-CF-IRMS.

“…As samples were combusted in this reactor, copper became oxidized to CuO such that after the first few samples sample oxidation occurred via reaction with the EA O 2 pulse followed by the CuO oxidation zone. Placement of the copper wire in this packing arrangement kept copper hot, above the 830 °C temperature at which copper sulfate can form and cause low SO 2 yields 8. An alternate packing of this tube placed copper at 7–13cm from the bottom of the reactor tube to avoid melting of the copper.…”

Section: Methodsmentioning

confidence: 99%

“…Conventional sulfur isotopic compositions5,, 9 for samples are normally calculated relative to a working standard SO 2 gas where: In the above calculation, a difference of 10‰ in δ 18 O oxygen isotope composition of the SO 2 translates into a 0.9‰ error in the measured δ 34 S sulfur isotopic composition, which led to previous efforts to prepare samples and standard SO 2 with identical oxygen isotope values 4–8. In the present study, the oxygen isotope values were assumed constant for illustration of problems encountered in these conventional calculations.…”

Section: Methodsmentioning

confidence: 99%

Oxygen isotope corrections for online δ³⁴S analysis

Fry

Silva

Kendall

et al. 2002

Elemental analyzers have been successfully coupled to stable-isotope-ratio mass spectrometers for online measurements of the delta(34)S isotopic composition of plants, animals and soils. We found that the online technology for automated delta(34)S isotopic determinations did not yield reproducible oxygen isotopic compositions in the SO(2) produced, and as a result calculated delta(34)S values were often 1-3 per thousand too high versus their correct values, particularly for plant and animal samples with high C/S ratio. Here we provide empirical and analytical methods for correcting the S isotope values for oxygen isotope variations, and further detail a new SO(2)-SiO(2) buffering method that minimizes detrimental oxygen isotope variations in SO(2).