Thank you very much indeed for carrying out these control experiments and for sharing the results with the list.
Beta-keratin sheets such as feather beta-keratin seem to be impervious to the autoclaving conditions you selected. At the very least, any minor breakdown that might happen is essentially so negligible as not to cause any statistically significant changes in its d13C and d15N values. By the same token this would suggest other beta-keratin materials such as beaks, claws (talons), and scales could also be safely autoclaved.
I have to admit I was expecting autoclaving to cause minor changes; minor but large enough to be measureable and to be statistically significant, e.g. for differences to be of the order of 3 to 5 sigma. Looks like I have been overanxious if not plain wrong. :-0
Well done. Now we know. I am sure there a lot of colleagues out there who will appreciate you haven taken the trouble to look into this. J
Just a note to pass on the results of bird feather autoclaving experiment I promised to update the list serve about some weeks ago (no need to read further if this isn't your sort of thing).
The question: Does autoclaving (120degrees C; 21minute cycle) change the stable C and N isotopic composition of bird feathers? [this question was motivated by biosecurity requirements to autoclave imported feathers prior to releasing samples from quarantine areas]
The answer: No.
Summary details: Two different bags of commercially available guinea fowl feathers were homogenised. Both homogenates were split into autoclaved and non-autoclaved sample sets and analysed several times for both d15N and d13C.
d15N of autoclaved feather homogenates were 3.12 (1sigma=0.11; n=8; Bag#1) and 3.75 (1sigma=0.09; n=8; Bag#2).
d15N of the non-autoclaved feather homogenates were 3.16 (1sigma=0.11; n=11; Bag#1) and 3.71 (1sigma=0.06; n=8; Bag#2).
d13C of autoclaved feather homogenates were -16.17 (1sigma=0.06; n=8; Bag#1) and -17.02 (1sigma=0.07; n=8; Bag#2).
d13C of the non-autoclaved feather homogenates were -16.27 (1sigma=0.10; n=11; Bag#1) and -17.00 (1sigma=0.04; n=8; Bag#2).
The Bag#1 non-autoclaved homogenates were analysed 11 times (instead of 8) as I wanted to run a few extras across a wider range in sample mass.
Not the biggest experiment, but these results suggest that autoclaving at 120degC for ~20minutes does not effect either the C nor N stable isotope compositions of keratin feathers.
All the best and especially to you Zach! You've always been a bass playing rockstar in my (more virtual) book.
University of Canterbury
P.S. Random other point: ideal sample mass was in the 0.5mg (~5V on mass28; ~1V on mass44) to 1.2mg (~13V on mass28; ~2.5V on mass 44) range.This was with a DeltaVplus; ConFloII; CosTechECS410; ~100ml/min UHP-He set-up. The middle of this ideal mass range equates to ~2-3mm of an unhomogenised penguin feather rachis of 1-2mm diameter (I did this experimental stuff in the lead up to some Adelie and Emperor penguin feather analyses; I gather the sample collection which I was not a part of will appear on a NatGeo show sometime soon...).
P.P.S. Homogenising samples lost an unexpectedly large amount of sample mass (SpexMill). Just a word of caution to any one out there wanting to homogenise small bird feathers: think about potential recovery issues during homogenisation.
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