Total major and trace elements in soil

obtained with an automated digestion

system

Annie Guerin, P. Deboffles, E. Dubromel, D. Ducristel, G. de

Jaeger, L. Andrzejewski and N. Proix

PLATINAAE

Laboratoire d’Analyses des Sols INRA ARRAS FRANCE

Meetings of the Heads of the Laboratories – ICP Forests

Pallanza, 7th – 8th sept. 2017

.02

Total digestion of soils in LAS-INRA

NF X 31-147 (French standard)

Method :

5ml HF + 1.5ml HClO4

Hot block (120 °C and 160 °C, 7 hours)

Final medium : diluted HNO3

0.25 g of ashed soil / final vol : 50 ml

Time-consuming

Manual addition of very dangerous acids

.03

VULCAN (Questron Technologies Corp)

Safety : only put bottles of acids in a box

Availability of technicians

.04

Automated method of digestion

Problems :

Max volume transferable is 35 ml (not enough for the

analysis of all the elements)

Blanks too high (> quantification limits)

Steps of the program :

Addition of HF and HClO4

Acid evaporationVol adjusted to

50 ml with HNO3Stirring

Transferring intoa tube

New program :

End = addition of diluted HNO3 with a final vol of 30 ml

Steps of stirring, transferring and adjusting the vol to 50ml

are done manually

30

.05

Question :

?

LAS is accredited for total analysis of soil

Analysis of monitoring experiments

.06

Total digestion of soils

Soil samples :

Soils from the International Soil-Analytical Exchange (ISE,

Wageningen evaluating programs for analytical laboratories)

Experiments :

Automated digestion of 56 soils, 1 replicat / soil

Automated digestion of 8 soils, 2 replicats / soil, repeated 5

times

comparison of results : automated method versus manual

method (data from 2014 to 2017)

calculation of z-scores

accuracy profils (NF V 03-110)

estimation of uncertainties

.07

Analytical methods

ICP-AES (radial)

Al, Ca, Fe, K, Mg, Mn, Na, P

ICP-AES (axial)

Co, Cr, Cu, Ni, Pb, Zn - S

ICP-MS

As - Cd, Mo, Pb,Tl

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Results : exemples of Fe and As

y = 0,9985xR² = 0,9965

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6 7

Fe -

Vu

lcan

(g/

10

0g)

Fe - Manual (g/100g)

Total Fe

y = 0,9917xR² = 0,9974

0

10

20

30

40

50

0 10 20 30 40 50

As

-V

ulc

an (

mg/

kg)

As - Manual (mg/kg)

Total As

« Automated » and

« manual» results seem to

be not significantly

differents

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Results : exemples of K and Cr

y = 1,0232xR² = 0,9866

0

0,5

1

1,5

2

2,5

0 0,5 1 1,5 2 2,5

K -

Vu

lcan

(g/

10

0g)

K - Manual (g/100g)

Total K

y = 0,9677xR² = 0,9399

0

50

100

150

200

250

300

0 50 100 150 200 250 300

Cr

-V

ulc

an (

mg/

kg)

Cr - Manual (mg/kg)

Total Cr

Open digestion systems

(manual and automated)

induce variable losses of Cr

Analytical problem

suspected

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Results : number of z-scores ≥ 3

0

1

2

3

4

5

6

Al Ca Fe K Mg Mn Na P As Cd Co Cr Cu Mo Ni Pb V Zn

Nb

of

z_sc

ore

K : analytical results must be checked

Soil 856 : 5 outliers (Ca, Cd, K, P, Zn) problem of

digestion

Cr : only 1 outlier, despite variability (large standard

deviation of ISE)

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Results : Accuracy profil and uncertainty

60%

70%

80%

90%

100%

110%

120%

130%

140%

0 1 1 2 2 3 3 4

Re

cove

ry(%

)

Theorical concentrations (g/100g)

Accuracy profil of Fe

Recouvrement(justesse) (%)

Limite bassetolérance (%)

Limite hautetolérance (%)

Limite d'acceptabilitébasse (%)

Limite d'acceptabilitéhaute (%)

Expanded uncertainty (k=2) : 5%

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Conclusion

First results :

Concentrations obtained with automated digestion are globaly

in accordance with previous results (manual digestion method)

Conform results for Fe

Some problems :

K : truness

Cr : precision

Next steps :

Finish exploitation of the results

Check K results

Present results and conclusions to the COFRAC (French

comitee of accreditation)

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.014

LOQ Total HF digestion of soil

LQ unity LQ unity LQ unity LQ unityAl ICP-AES (rad) 0,02 g/100g 1,0 mg/l Ni ICP-AES (ax) 1 mg/kg 5,0 µg/lCa ICP-AES (rad) 0,02 g/100g 1,0 mg/l Pb ICP-AES (ax) 2 mg/kg 10 µg/lFe ICP-AES (rad) 0,02 g/100g 1,0 mg/l Zn ICP-AES (ax) 5 mg/kg 25 µg/l

K ICP-AES (rad) 0,02 g/100g 1,0 mg/l Co ICP-AES (ax) 1 mg/kg 5,0 µg/l

Mg ICP-AES (rad) 0,02 g/100g 1,0 mg/l V ICP-AES (ax) 0,5 mg/kg 2,5 µg/lMn ICP-AES (rad) 10 mg/kg 0,05 mg/l S ICP-AES (ax) 4 mg/kg 20 µg/l

Na ICP-AES (rad) 0,02 g/100g 1,0 mg/l Mo ICP-MS 0,04 mg/kg 0,2 µg/lP2O5 ICP-AES (rad) 0,001 g/100g 0,05 mg/l Cd ICP-MS 0,02 mg/kg 0,1 µg/lCd ICP-AES (ax) 0,5 mg/kg 2,5 µg/l Tl ICP-MS 0,01 mg/kg 0,05 µg/lCr ICP-AES (ax) 2 mg/kg 10 µg/l Pb ICP-MS 0,1 mg/kg 0,5 µg/lCu ICP-AES (ax) 1 mg/kg 5,0 µg/l