Wood cellulose preparation methods and mass spectrometric analyses of delta13C, delta18O, and nonexchangeable delta2H values in cellulose, sugar, and starch: an interlaboratory comparison.

Interlaboratory comparisons involving nine European stable isotope laboratories have shown that the routine methods of cellulose preparation resulted in data that generally agreed within the precision of the isotope ratio mass spectrometry (IRMS) method used: +/-0.2 per thousand for carbon and +/-0.3 per thousand for oxygen. For carbon, the results suggest that holocellulose is enriched up to 0.39 per thousand in 13C relative to the purified alpha-cellulose. The comparisons of IRMS measurements of carbon on cellulose, sugars, and starches showed low deviations from -0.23 to +0.23 per thousand between laboratories. For oxygen, IRMS measurements varied between means from -0.39 to 0.58 per thousand, -0.89 to 0.42 per thousand, and -1.30 to 1.16 per thousand for celluloses, sugars, and starches, respectively. This can be explained by different effects arising from the use of low- or high-temperature pyrolysis and by the variation between laboratories in the procedures used for drying and storage of samples. The results of analyses of nonexchangeable hydrogen are very similar in means with standard deviations between individual methods from +/-2.7 to +/-4.9 per thousand. The use of a one-point calibration (IAEA-CH7) gave significant positive offsets in delta2H values up to 6 per thousand. Detailed analysis of the results allows us to make the following recommendations in order to increase quality and compatibility of the common data bank: (1) removal of a pretreatment with organic solvents, (2) a purification step with 17% sodium hydroxide solution during cellulose preparation procedure, (3) measurements of oxygen isotopes under an argon hood, (4) use of calibration standard materials, which are of similar nature to that of the measured samples, and (5) using a two-point calibration method for reliable result calculation.

Temperature dependencies of high-temperature reduction on conversion products and their isotopic signatures.

High-temperature reduction (HTR) is widely used for oxygen and hydrogen isotope determination. Decomposition of cellulose, sucrose and polyethylene foil by HTR is quantitative for temperatures around 1450 degrees C. For lower reaction temperature production of CO(2), water and the deposition of carbon inside the reactor are significant and thus the element of interest for isotopic analysis is split into different pools, leading to isotope fractionation. After reduction of cellulose or sucrose at 1125 degrees C less than 60% of the oxygen is found as CO, which is monitored with the isotope ratio mass spectrometer to determine the delta(18)O value. The remaining oxygen is unevenly distributed between CO(2) and H(2)O, preferentially as CO(2). Raising the reaction temperature to 1425 degrees C yields almost quantitative conversion of oxygen into CO and results in a 3 per thousand more positive delta(18)O value. Similarly, only 40-50% of the carbon of cellulose and sucrose is transformed into CO in the HTR reactor at 1125 degrees C. This is far from the stoichiometric expected value of 83% for quantitative carbon transfer for cellulose and 92% for sucrose. Of the carbon 40-50% is deposited in the reactor and the remainder can be found as CO(2). Based on the comparison of carbon isotope results from HTR and those obtained from combustion, we hypothesize that CO produced during the HTR originates partly from sample carbon and glassy carbon. A combined combustion and HTR carbon isotope determination may provide an insight into the intramolecular carbon distribution of organic substances. These results suggest that HTR should be carried out at temperatures above 1450 degrees C to make sure that fractionations associated with the reduction process are minimal. If this is not possible frequent calibration is required using reference materials of the same structure as the sample.

Rapid online equilibration method to determine the D/H ratios of non-exchangeable hydrogen in cellulose.

An improved method for the determination of deuterium-to-hydrogen (D/H) ratios of non-exchangeable hydrogen in cellulose is presented. The method is based on the equilibration reaction of the hydroxyl hydrogen of cellulose and water vapour of known isotopic composition. The equilibrated cellulose is pyrolysed and the total D/H ratio determined by subsequent online isotope ratio mass spectrometry (IRMS). With a mass balance system the D/H ratio of non-exchangeable hydrogen is recalculated after an empirical calibration has been performed, yielding a mean exchangeability of 0.239 and an equilibrium fractionation factor of 1.082 between the hydroxyl hydrogen of cellulose and water hydrogen at 110 degrees C. Equilibration takes 10 min per sample. Results obtained by this online equilibration method agree very well with values obtained by the nitration technique (R2 = 0.941). The uncertainty of the equilibration method is +/-4 per thousand resulting from a single standard deviation of +/-2.8 per thousand for the equilibration determined by standard cellulose and 2.8 per thousand from the variable exchangeability of the hydroxyl hydrogen in cellulose due to crystalline areas. The latter uncertainty may be lowered by minimising the crystallinity of the cellulose. Advantages of this new technique are (i) the considerably reduced sample amount required (as low as 0.2 mg, ideally 0.5 mg compared with 20 mg for the conventional nitration technique); (ii) an approximately 100-fold reduced process time; and (iii) no need for the hazardous chemicals used in the nitration technique.