In museum collections bivalve shells are traditionally dry stored, whereas gentle tissues are preserved in 70% ethanol, sometimes following fixation with 10% formalin. An inline soda lime CO trap was used to scrub CO 2 from the gas stream entering the gas chromatography column of the Natural products. IAEA N1 was utilised as a common, with an accepted worth of . 4 _ . 2% Extended term. common reproducibility is better than . 1% for samples nature, even samples between 5 and mg N provided reasonable information. There is also an upper limit to the volume of shell materials that can be loaded into the EA, but this was not evaluated here.

This method is robust simply because calcium carbonate com pletely decomposes about 8258C and the ash combustion in the EA was around 10208C, consequently, all N must be released from the matrix and carried to the IRMS. Moreover, previous reports have employed an EA IRMS system to combust Fig. 2 that the narrow and close to symmetrical peak shapes are equivalent for both shell carbonate and synthetic mixtures, which suggests that the two matrices are reacting similarly in the EA IRMS. We therefore argue that it is attainable to measure carbonates for d C assessment. It is clear from the traces in larger than 30 mg N. d N values are expressed in % vs. atmospheric nitrogen. Pure synthetic CaCO 3 had peaks similar to empty tin cups, empty tin cup 1/4 . 49 Vs) and therefore did not contribute a lot to the calculated delta values. The acetanilide regular had a d N worth of 2.

12 _ . 13% when it was run without having synthetic CaCO 3 and was _2. 02 _ . 11% when it was run with 98. 8 to 98. 4 excess weight % synthetic CaCO 3 powder and pure acetanilide. The strong line represents the suggest value of _2. 02% for data over mg N. The error bar represents the 1s of _. 11%. wileyonlinelibrary. com/journal/rcm Copyright 2011 John Wiley & Sons, Ltd. Quick Commun. Mass Spectrom. 2011, 25, 675 680 Letter to the Editor tissue is subject to metabolic turnover and is hence repre sentative for a particular time window, see HSP . although the shell samples averaged at least 1 yr of development. This tends to make comparing soft tissues with shell natural matrix difficult. Nevertheless, as proven in Delong and Thorp, tissues with slower turnover rates, such as the adductor muscle, are much better for comparisons with metabolically inactive shells.

Most earlier scientific studies that report differences among skeletal d N and gentle tissue d N do not consider the diverse quantities of time becoming averaged into contemplate ation. Moreover, several reports evaluate entire entire body tissue d N information to shell information even though it is known that different organs can have very distinct d N values, often as considerably as 5% in the very same animal. This may possibly clarify why Dtissue shell values for the exact same species of clam array from .