Preparation of Solid Samples for Isotope Analysis
by Continuous Flow IRMS
D. J. Herman May 14, 1993
last update April 30, 2007
1. Samples must be milled down to a fine powder, about the texture of flour. For
plants, try preprocessing them in a Wiley mill or coffee mill, then finishing them in a ball mill or a wiggle bug. Soils should first be sieved down to 2 mm, then pulverized in a ball mill.
2. Determine the proper sample size. The upper limit for N at natural abundance is
about 400 g; as enrichment increases up to 90 atom % 15N, the upper limit becomes 20 g. The upper limit for C at natural abundance is about 2.5 mg.
3. Having decided on an appropriate sample size, try to measure that amount of
analyte consistently among all samples. A continuous flow IRMS is sensitive to sample size, so uniformity will help assure data quality. As an outside limit, the highest amount of C and/or N in a batch should not exceed twice the lowest. For calibration purposes, we need to know how much N and/or C to expect in the samples.
4. Measure the samples into tin capsules. Capsules should be wrapped into spherical balls with no edges (edges may cause samples to hang in the autosampler), and should not exceed 4 mm along any axis. Since air trapped inside the capsules is a source of background N2, try to wrap them as compactly as possible. However, if capsules are overworked, they may tear and spill sample. We do not attempt to analyze torn samples. Finally if total N or C is desired, record sample weights. Capsules are available from either:
Sercon, Ltd.
Wistaston Road Business Centre
Wistaston Road
Crewe, Cheshire, UK CW2 7RP
44-1270-580008
(tin capsules 8 x 5 mm, 250/pk, p/n SC0009)
or
Elementar Americas, Inc.
520 Fellowship Rd. Suite B-204
Mt Laurel, NJ 08054
1-856-787-0022
(tin capsules, 8 x 5 mm, 250/pk, p/n D1008)
5. Wrapped capsules may be stored and shipped in 96-well ELISA plates (e.g. Fisher Scientific catalog number 07-200-103 and 07-200-598).