Tips for Preparing Your Solid Samples

Record sample weights

Sample weights must be recorded if total N or C measurements are required. Here is a sample weight sheet you may use. Otherwise, samples only need to be weighed to obtain optimal target weights. Be sure to keep a copy of your weight sheets.

Remove carbonates from calcareous soils before analysis for SOM-13C

Inorganic C in the form of carbonates can interfere with the measurement of organic 13C in soils. Remove inorganic C by acid fumigation. Weigh soil samples into silver capsules (tin decomposes when exposed to acid) and arrange samples in a 96-well plate. Add a small amount of water to each open capsule to wet the soil. Place the whole 96-well plate in a desiccator containing a beaker of concentrated (12M) HCl. Carbonates are released as CO2 in 6 to 8 hours. Dry the samples at 60°C and carefully crimp-seal the capsules. The capsules become brittle after drying. Be careful not to lose material when crimping. Alternatively, place the whole capsule into a new tin capsule and crimp it closed.

For more information, please refer to:
Harris, D., Horwath, W.R., and van Kessel, C., 2001.  Acid fumigation of soils to remove carbonates prior to total organic carbon or carbon-13 isotopic analysis.  Soil Science Society of America Journal 65: 1853-1856.

Use KHSO4 for ammonia diffusion traps

Use KHSO4 rather than H2SO4 on the ammonia trapping disk to avoid rapid corrosion of the tin capsule. Adjust the volume of extract to obtain optimal mass of N on the disk, ideally 100 µg N.

Use large tins for bulky samples

Large 9x10 mm tin capsules are helpful for encapsulating bulky items, like filter disks, which must be tightly packaged to maintain a compact form (no larger than 8mm wide X 8mm tall) in the autosampler. If samples are too large for a 96-well plate, ship them in a 24 or 48-well plate instead. Please do not force large samples into a 96-well plate, they will expand during shipping and we will not be able to extract these samples from their wells.

How to determine target sample weights for analysis of N & C

You need to know the carbon and nitrogen content of your material to determine your target sample weight ranges. To determine how much you sample you should weigh follow these steps using Table 1 & Table 2 below:
1) Find the min-max sample weight range in mg for N in Table 1 columns A & B
2) Find the min-max sample weight range in mg for C in Table 2 columns A & B
3) If the ranges overlap, then weigh your samples within the weight range of overlap (see examples below)
4) If the ranges do not overlap, find min-max ranges in columns C & D
5) If the ranges overlap, then use the range of overlap
6) If the ranges do not overlap because %N is low, find lower limit for N in column E
7) If the material is below 0.01%N, it may be necessary to analyze N and C on separate samples

Example: determining optimal weight ranges for weighing leaves and liver

TABLE 1		A	B	C	D	E
Nitrogen		Optimal	Optimal	Acceptable	Acceptable	Lower Limit
%N	µgN/mg	Min mg	Max mg	Min mg	Max mg	LL mg
0.01	0.1					75.00
0.02	0.2			75.00		50.00
0.03	0.3			66.67		33.33
0.04	0.4			50.00		25.00
0.05	0.5			40.00		20.00
0.06	0.6	75.00		33.33		16.67
0.07	0.7	71.43		28.57		14.29
0.08	0.8	62.50		25.00		12.50
0.09	0.9	55.56		22.22		11.11
0.1	1	50.00		20.00		10.00
0.2	2	25.00	75.00	10.00	75.00	5.00
0.3	3	16.67	50.00	6.67	66.67	3.33
0.4	4	12.50	37.50	5.00	50.00	2.50
0.5	5	10.00	30.00	4.00	40.00	2.00
0.6	6	8.33	25.00	3.33	33.33	1.67
0.7	7	7.14	21.43	2.86	28.57	1.43
0.8	8	6.25	18.75	2.50	25.00	1.25
0.9	9	5.56	16.67	2.22	22.22	1.11
1	10	5.00	15.00	2.00	20.00	1.00
2	20	2.50	7.50	1.00	10.00	0.50
3	30	1.67	5.00	0.67	6.67	0.33
4	40	1.25	3.75	0.50	5.00	0.25
5	50	1.00	3.00	0.40	4.00	0.20
6	60	0.83	2.50	0.33	3.33	0.17
7	70	0.71	2.14	0.29	2.86	0.14
8	80	0.63	1.88	0.25	2.50	0.13
9	90	0.56	1.67	0.22	2.22	0.11
10	100	0.50	1.50	0.20	2.00	0.10
20	200	0.25	0.75	0.10	1.00	0.05
30	300	0.17	0.50	0.07	0.67	0.03
40	400	0.13	0.38	0.05	0.50	0.03
50	500	0.10	0.30	0.04	0.40	0.02
TABLE 2		A	B	C	D	E
Carbon		Optimal	Optimal	Acceptable	Acceptable	Lower Limit
%C	µgC/mg	Min mg	Max mg	Min mg	Max mg	LL mg
0.03	0.3					66.67
0.04	0.4					50.00
0.05	0.5					40.00
0.06	0.6			75.00		33.33
0.07	0.7			71.43		28.57
0.08	0.8			62.50		25.00
0.09	0.9			55.56		22.22
0.1	1			50.00		20.00
0.2	2			25.00		10.00
0.3	3			16.67		6.67
0.4	4			12.50		5.00
0.5	5			10.00		4.00
0.6	6	75.00		8.33		3.33
0.7	7	71.43		7.14		2.86
0.8	8	62.50		6.25		2.50
0.9	9	55.56		5.56		2.22
1	10	50.00	75.00	5.00		2.00
2	20	25.00	40.00	2.50	75.00	1.00
3	30	16.67	26.67	1.67	50.00	0.67
4	40	12.50	20.00	1.25	37.50	0.50
5	50	10.00	16.00	1.00	30.00	0.40
6	60	8.33	13.33	0.83	25.00	0.33
7	70	7.14	11.43	0.71	21.43	0.29
8	80	6.25	10.00	0.63	18.75	0.25
9	90	5.56	8.89	0.56	16.67	0.22
10	100	5.00	8.00	0.50	15.00	0.20
20	200	2.50	4.00	0.25	7.50	0.10
30	300	1.67	2.67	0.17	5.00	0.07
40	400	1.25	2.00	0.13	3.75	0.05
50	500	1.00	1.60	0.10	3.00	0.04
60	600	0.83	1.33	0.08	2.50	0.03
70	700	0.71	1.14	0.07	2.14	0.03
80	800	0.63	1.00	0.06	1.88	0.03
90	900	0.56	0.89	0.06	1.67	0.02
100	1000	0.50	0.80	0.05	1.50	0.02

How to encapsulate samples

Please encapsulate solid samples in tin capsules so they remain intact and do not leak and contaminate other samples during shipping. Test your crimping-sealing method using a dummy sample in a tray. Shake and flip the tray to mimic agitation during shipping to see if the sample stays in its well or leaks from the tin. Very small or flat samples can escape their wells during shipping by slipping through the gap between the tray and cover. Do not underestimate the gap between the tray and cover! This is the number one cause of lost samples/data.

You can make a crimper plate (pictured below) to hold tins and use a metal dowel to compress them in the plate holes. Once compressed, the closed samples can be transferred directly into a 96-well plate.

Alternatively, you can manually seal the tins using two sets of forceps with blunt tips to form them into cubical or cylindrical shapes. First, pinch the top closed and fold it over. Then, press and hold the capsule top to bottom while using the other forceps to pinch the sides inward. Repeat until you have a compact tightly packed tin.

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