Alabama Agricultural Experiment Station
roced es
used by the Aulbrn Universi
Depatment of A ronomy and Soils
March 1997
Agronomy and Soils Departmental Series No. 203
Alabama Agricultural Experiment Station
Auburn University, Alabama
James E. Marion, Director

TABLE OF CONTENTS
Page
INTRODUCTION ................................... 3
GENERAL LABORATORY PROCEDURES .......................... 4
C ourtesy ......................... . ..................................... 4
Safety..............................................................4
W aste D isposal ............................................................ 4
PLANT SAMPLE PREPARATION .................................... 5
Washing, Drying, Grinding, and Storing ...................... 5
Dry Ashing of Plant Samples ..................... 6
Wet Ashing of Plant Samples.................... 8
SOIL SAMPLE PREPARATION ................................. 10
Soil Testing Laboratory Procedure................ 10
Air-dried Samples.................................................10
M oist Sam ples ............................................................ 10
THE ICAP SPECTROMETER ...................................... 11
Principle of Operation .................................................. 11
Starting the ICAP ........................................................ 13
Shutting Down the ICAP .............................................. 14
Emergency Procedures .................................................. 15
ELEMENTAL 
ANALYSIS PROCEDURES 
............................
16
As in Plant Samples ..................................................1 16
B in Plant Samples .......................... 17
Ca in M ehlich I Soil Extract.........................0,0...........1 19
Cd in Plant Sam ples .................................................... 20
K in Mehlich I Soil Extract ..................... 21
Mg in Mehlich I Soil Extract..................... 22
Ni in Plant Samples ........................... 23
Pb in Plant Sam ples ................................................... 24
Se in Plant Samples ........................... 25
Se in Soil Sam ples ...................................................... 28
BIBLIOGRAPHY ........................................................ 30
AA Spectrometer Procedures..................... 30
General Analysis Procedures..................... 30
ICAP Spectrometer Procedures................... 30
Elemental Analysis Procedures Used by
the Auburn University Department of
Agronomy and Soils
J.W. ODOM AND M.B. KoNE
1
INTRODUCTION
This is a collection of elemental analysis procedures that
have been found useful for analysis of Alabama plants and soils.
All procedures are intended for use on existing equipment in the
Department of Agronomy and Soils or in the Soil Testing Labora-
tory. Some of the procedures in this collection were developed
over a long period of time by several people and most of the pro-
cedures are modifications of previously published methods.
The authors wish to thank the following people in the De-
partment of Agronomy and Soils for their assistance in the prepa-
ration of this document: William W. Wills, Research Technician
VII, and Cynthia D. Hunter, Research Technician IV, who helped
compile the ICAP procedures and reviewed the manuscript; and
Elizabeth A. Guertal, Assistant Professor, and Gregory L. Mullins,
Professor, who reviewed the manuscript.
1ODOM IS ASSOCIATE PROFESSOR AND KoNE IS FORMER GRADUATE STUDENT OF AGRONOMY
AND SOILS AT AUBURN UNIVERSITY. KoNE IS NOW EMPLOYED WITH THE GOVERNMENT OF
MAI IN WEST AFRICA.
GENERAL LABORATORY PROCEDURES
Courtesy
Most of the laboratories are not common use areas. Ask
the person in charge of a laboratory before using equipment or
chemicals. What looks like* trash may be someone's research.
Safety
Federal, state, local, and Auburn University safety regula-
tions will be followed. The following general safety procedures
will be used in our laboratories.
1. A first aid kit should be maintained in each main
laboratory.
2. Permanent technicians should attend first aid, CPR,
and laboratory safety classes conducted by Auburn
University.
3. Eye protection and appropriate protective clothing
should be used in chemical laboratories.
4. Eye washes and fire extinguishers should be kept
clear so they will be available in an emergency.
5. An inventory of all chemicals stored in the laboratory
must be kept.
6. Material Safety Data Sheets (MSDS) must be collected
for all chemicals used and stored in the laboratory.
Material Safety Data Sheets may be obtained from the
Office of Safety and Environmental Health.
Waste Disposal
Waste disposal guidelines are given in "A Guide to the
Handling and Disposal of Hazardous Wa ste at Auburn Univer-
sity,"9 which may be obtained from the Office of Safety and Envi-
ronmental Health. Most of the procedures in this manual generate
acidic wastes (pHs < 3) that must be neutralized before they can
be poured down the drain.
PLANT SAMPLE PREPARATION
Washing, Drying, Grinding, and Storing
1. If the plant is contaminated with nutrient spray or if Fe
is to be measured, wash the sample in 0.1% Tirton X-
100 solution while the material is fresh and rinse in
deionized water. The washing must be done quickly to
avoid leaching of K and Ca from the tissue.
2. Dry the plant material at 65
0
C for 24 hours or until dry.
Do not dry plant material in a 110C drying oven or in a
gravity convection oven. Do not store dried samples in
the plant driers. Dried samples will stay dry until ground
if stored in a closed plastic garbage bag.
3. For ease of manipulation and uniformity of composi-
tion, plant samples must be ground. Grinding becomes
very critical if less than 0.5 g of the sample is to be used
in the analysis. All the grinding mills cause some con-
tamination of the samples with trace elements. Trace
element contamination seems to be less with the Udy
mills that use a carborundum grinding ring.
4. Plant material should be redried for 24 hours at 65
0
C to
remove water picked up during grinding.
5. Samples should not be stored at room temperature in
Whirl-Pak bags for more than two months before being
analyzed. Samples that need to be kept for longer pe-
riods of time should be frozen in sealed containers.
Dry Ashing of Plant Samples
1. Principle of the Method:
The carbon in a known weight of dried plant material is
burned off by combustion with atmospheric oxygen in a muffle
furnace. The compounds in the ash are further oxidized using ni-
tric acid, brought into solution using hydrochloric acid, and made
to a known volume with deionized water. Silica is filtered out of
the solution before analysis.
2. Apparatus:
a. Muffle furnace
b..50 mL beakers with watch glass covers
c. Filter stand, funnels, and Whatman #40 filter
paper
d. 100 mL volumetric flasks
e. Storage bottles
3. Reagents:
a. Deionized 
water
b. 1 N HCl (83 mL concentrated HCl per liter)
c. 1 N HNO
3 
(64 mL concentrated HNO
3 
per liter)
4. Procedure:
a. Weigh 0.5 
g of previously 
dried and ground 
plant
material into a 50 mL beaker.
b. Cover the beakers with watch glasses and place
in a muffle furnace. Heat at 450
0
C for 4 hours or
overnight. Turn the furnace off, open the furnace
door, and allow the samples to cool before re-
moving them from the furnace.
c. Add 10 mL of 1 N HNO
3 
and evaporate slowly
to dryness on a hot plate in the fume hood. Take
'just to dryness and do not bake.
d. Add 10 mL of 1 N HCl to dissolve the residue.
The silica will not dissolve.
e. Warm nearly to boiling and transfer to a 100 mL
volumetric flask. Wash the beaker three times
with small amounts of deionized water.
f. Bring the contents of the flask to 100 mL volume
using deionized water and filter the contents into
a storage bottle. Do not wash the volumetric
flask or filter paper during this step.
5. Remarks:
a. Always carry a blank. through the procedure.
b. This ashing procedure 
is not suitable for N, 
B,
Hg, Si, or Se.
c. If trace elements are to be determined, increase
the sample size to 1 g.
d. The watch glass covers in step 4.b. are critical if
Ni is to be determined.
e. The muffle furnaces set at 4500C will actually be
about 4850C.
f. Step 4.c. is critical for P and -trace element deter-
minations.
g. If Ca, Mg, and K are to'be determined on the AA
spectrophotometer, dilute a portion of the digest
1:10.
6. S afety:
a. Obtain Material Safety Data Sheets (MSDS)
for nitric and hydrochloric acids and read
them.
b. Wear eye protection, a rubber or plastic apron,
and gloves while carrying out this procedure.
c. Use great care in step 4.b. The muffle furnace
is very hot.
Wet Ashing of Plant Samples
1. Principle of the Method:
The carbon in a known weight of dried plant material is
oxidized using nitric and perchloric acids. The digest is stabilized
by adding hydrochloric acid and made to a known volume using
deionized water. Silica is filtered out of the solution before analy-
sis.
2. Apparatus:
a. Digestion block in perchloric acid fume hood
b.'250 mL digestion tubes and rack
c. Filter stand, funnels, and Whatman #40 filter
paper
d. 100 mL volumetric flasks
e. Storage bottles
3. Reagents:
a. Deionized water
b. Acid Mix (700 mL concentrated HNO
3 
+ 300
mL concentrated HCIO
4
)
c. 1 N HCl (83 mL concentrated HCl per liter)
4. Procedure:
a. Weigh 0.5 g of previously dried and ground
plant material into a 250 mL digestion tube.
b. Add 10 mL of Acid Mix and allow the tubes to
stand overnight at room temperature in a fume
hood.
c. Heat the tubes in a block digestor at 190
0
C
until the digestion is complete. Add more Acid
Mix as needed to keep the tubes from going
dry. The digestion is complete when the
contents are light yellow and there is less than
3 mL of liquid in each tube.
d. Remove the tubes from the block and cool in
the perchloric hood.
e. Add 10 mL of 1 N HCl to each tube and
transfer the contents to a 100 mL volumetric
flask using deionized water.
f. Bring the contents of the volumetric flasks to
100 mL using deionized water and filter the
contents into a storage bottle. Do not wash the
volumetric flask or filter paper during this step.
g. Wash down the perchloric acid fume hood.
5. Remarks:
a. Always carry a blank through the procedure.
b. This ashing procedure is not suitable for N, B,
Hg, Si, or Se.
c. If trace elements are to be determined, increase
the sample size to 1 g.
d. Step 4.b. can be done in a conventional fume
hood.
e. Steps 4.c. and 4.d. must be done in the perchloric
acid fume 
hood in 
FS292.*
f. When the digestion is complete in step 4.c., the
samples will be light yellow because of Mn com-
pounds.
g. If Ca, Mg, and K are to be determined on the AA
spectrophotometer, dilute a portion of the digest
1:10.
6. Safety:
a. Obtain Material Safety Data Sheets (MSDS) for
nitric, perchloric, and hydrochloric acids and read
them.
b. Wear eye protection, a rubber or plastic apron,
and gloves while carrying out this procedure.
c. Use great care when handling perchloric acid.
Dry perchloric acid is explosive. Organic ma-
terials treated with perchloric acid and dried
are explosive. Samples allowed to go dry in
step 4.c. may explode.
d. The perchloric acid fume hood should be washed
down daily to remove dried perchloric acid.
*FS292 = FuNCHESS HALL ROOM 292.
9
SOIL SAMPLE PREPARATION
Soil Testing Laboratory Procedure
1. Dry soils in a forced air oven at 550C until dry.
Oven drying will affect K and Mn extraction.
.The ovens in FS225* are not temperature con-
trolled.
2. Dried samples are ground to pass a 10-mesh
sieve. The Braun pulverizer in FS225 will grind
pieces of rock that are in the sample. Samples
containing rock will need to be hand pulverized
with a mortar and pestle before they are screened.
Air-dried Samples
1. Air-dry samples by spreading them on trays in
the laboratory.
2. Dried samples that do not contain rocks can be
ground using the Braun pulverizer in FS225. If
the pulverizer is set too close it will grind min-
eral grains and change the extractable nutrients.
Dried samples that contain rocks should be care-
fully pulverized with a mortar and pestle and
screened with a 2 mm sieve to remove the rocks.
Moist Samples
Moist samples can be analyzed if they are thor-
oughly mixed and if a subsample is taken for
moisture determination.
*FS 225 = FUNCHESS HALL ROOM 225.
10
THE ICAP SPECTROMETER
Principle of Operation
The Jarrell-Ash ICAP 9000 spectrometer in FS27 1A* has
been upgraded by replacing the controller board, external com-
puter, and software to a Thermo-Jarrell-Ash ICAP 61. The ICAP
(or ICP-AES) uses a radio frequency generator to turn a stream of
argon gas containing droplets of a sample into a plasma by induc-
tion heating. Compounds in the plasma are reduced to ground state
atoms by the high temperature. Elemental emission lines are sepa-
rated by a polychromator and measured using photomultiplier
tubes. The ICAP 9000 has a set of exit slits and a photomultiplier
for each emission line measured (simultaneous spectrometer).
Samples for ICAP determination must be in aqueous solu-
tion. Organic solvents cannot be used unless the RF generator is
retuned. Solutions containing very high levels of salt cannot be
aspirated properly and will damage the torch. Samples containing
radioactive tracers cannot be analyzed using the ICAP 9000. The
torch ventilation system in FS27 1 A is not certified for radioactive
materials. The following elements are the only ones that can be
determined on the ICAP 9000 without adding more exit slits and
photomultiplier tubes.
ELEMENTS DETERMINABLE ON ICAP 9000
Atomic # Element Symbol Wavelength Order
nm
5 boron B 249.770 2
11 sodium Na 588.995 1
12 magnesium Mg 279.079 2
13 aluminum Al 308.215 2
14 silicon Si 288.160 2
15 phosphorus P 214.914 3
19 potassium K 766.491 1
20 calcium Ca 317.933 1
22 titanium Ti 334.941 1
24 chromium Cr 267.716 1
25 manganese Mn 257.610 2
26 iron Fe 271.441 2
27 cobalt Co 228.616 2
29 copper Cu 324.754 1
30 zinc Zn 213.860 2
42 molybdenum Mo 202.030 2
56 barium Ba 493.409 1
80 mercury Hg 546.074 1
82 lead Pb 220.350 2
*FS2l7A = FUNcHESS HALL ROOM 217A.
11
The following are the specifications 
published by Jarrell-
Ash for the ICAP 9000 spectrometer 
in their product brochure:
Optics: 0.75 m Rowland circle; Paschen-Runge
mount
Grating: 1510 lines/mm
Spectral Range: 190 - 800 nm (air spectrometer)
Linear Dispersion:
0.92 nm/mm, first order
0.46 nm/mm, second order
0.31 nm/mm, third order
Resolution:
0.045 nm, first order
0.023 nm, second order
0.015 nm, third order
Detection Limits and Upper Limits of the Linear
Range:
Atomic # Symbol
5 B
11 Na
12 Mg
13 Al
14 Si
15 P
19 K
20 Ca
22 Ti
24 Cr
25 Mn
26 Fe
27 Co
29 Cu
30 Zn
42 Mo
56 Ba
80 Hg
82 Pb
Upper limit
of linear
Detection limit range
ppm ppm
0.004 150
0.01 200
0.001 50
0.025 500
0.005 200
0.06 250
0.3 1,000
0.001 20
0.002 150
0.005 150
0.001 150
0.005 150
0.003 150
0.002 150
0.004 150
0.005 200
0.001 100
(No data for this wavelength)
0.025 200
RF Source: 2500 watts at 27.12 MHz
12
Starting the ICAP
1. Make sure that the circuit breakers on the RF genera-
tor are on. These breakers are left on during the week
but are turned off during weekends and holidays.
2. Make sure that the torch is centered in the induction
coils, then close the torch access door.
3. Aspirate fresh deionized water during the warm up
period.
4. Flip the automatic power control (APC) lever down
into the manual mode.
5. Rotate the power knob counterclockwise to OFF.
6. Open the argon main valve on the tank. Turn on the
coolant and plasma gas streams by flipping the toggle
switches up. Open the needle valve to the sample gas
stream by rotating the knob counterclockwise. At this
point there should be a mist in the premix chamber,
the blue light should be on, and the red light off. The
argon regulator pressure should be 40 psi and the
coolant gas flow should be 201pm.
7. Aspirate water for 3 minutes to purge air from the
system. Turn off the sample gas stream by turning the
needle valve clockwise. The mist should disappear
from the premix chamber. Wait 3 minutes to clear
water from the torch.
8. Push R.F. on. Both the blue and red lights should now
be 
on.
9. Alternate turning the power up with the power knob
and pushing the ignitor button until the plasma lights.
Do not press and hold the ignitor button. Operating
with the power in the red zone of the power meter will
melt the torch. If the torch glows red after ignition,
immediately push R.F. off. The torch may be over
heating.
10. Adjust the power to 1.4 on the power meter using the
power knob.
11. Penetrate the plasma by turning the sample needle
valve slowly counterclockwise. The plasma plume
should be hollow and there should be mist in the
premix chamber.
13
12. Flip the automatic power control up to the automatic
setting. The power level should drop to about 1.1.
13. Wait 30 to 45 minutes for the temperature to stabilize
inside the torch chamber.
14. While aspirating 1000 ppm yttrium (Y), position the
red tongue in the plasma from 0 to 2 mm above the
top of the torch by rotating the plasma gas control
knob.
15. Turn the computer on using the switch on the
standby power system.
16. Profile the spectrometer with the Hg lamp in the
verticle position (in the beam path). Aspirate water
during this procedure.
17. After profiling the spectrometer, rotate the Hg lamp
out of the beam path. Be careful not to drop the
access door onto the lamp.
18. Select a method appropriate for your samples.
19. Standardize the ICAP and run samples.
Shutting Down the ICAP
1. Aspirate water for 1 minute after final sample.
2. Push the RF OFF (blue) button.
3. Turn the Power knob to zero.
4. Flip the Automatic Power Control (APC) switch down
to MANUAL.
5. Close the argon main valve on the tank.
6. Let the gas lines bleed. The flowmeter balls will drop
to zero.
7. Flip the Coolant and Plasma gas levers down to turn
them off.
8. If you are the last operator scheduled on Friday after-
noon, turn the two main power breakers on the RF
Generator off. Skip this step if it is not Friday or if
there is someone scheduled after you.
9. Turn the computer off using the switch on the standby
power system.
14
Emergency Procedures
1. If the aspirator sucks up air and the alarm goes off, do
not panic.
a. Push the RF OFF (blue) button.
b. Turn the Power knob to zero.
c. Push the O.L. Reset (red) button on the RF
Generator.
d. Flip the Automatic Power Control (APC) lever
down to manual.
e. Re-light the plasma.
f. Re-standardize.
g. Continue sample analysis.
2. If there is a power surge or a main power outage, the
ICAP will have to be reset.
a. Push the Reset button on the back of the ICAP
near the main power breakers. This will reset
the power supply.
b. Push the Reset button on the controller panel
on the front of the ICAP. This will reset the
internal computer.
c. Re-light the plasma.
d. Re-standardize.
e. Continue sample analysis.
15
ELEMENTAL ANALYSIS PROCEDURES
As in Plant Samples
1. Principle of the Method:
Arsenic in plants is low enough that 
it must be run using
the graphite furnace atomic absorption technique 
(GFAA). Plant
samples should be wet ashed.
2. Standards: 0, 0.01, 0.05, 0.10, 0.25, and 0.50 ppm As
in 0.1 N HC1.
3. Matrix modifier: to 5 mL of each sample add 500 pL
of 0.5% (w/v) Ni(NO
3
)
2
.6H
2
0 + 10% concentrated
HNO
3
; to 10 mL of each standard add 1 mL of 0.5%
(w/v) Ni(NO
3
)
2
.6H
2
0 + 10% concentrated 
HNO
3
.
4. IL251:
a. Lamp: As at 8 ma; D2 at 25 ma
b. Wavelength: 193.7 nm
c. Slit width: 640
d. Integration: Pk Ht at 1/16 sec
e. Mode: (SB)A-B
f. Focus for maximum intensity
g. .HV: adjust until intensity is between 2 and 8
5. IL655 (with IL755 temperature sensor):
a. Coolflow: on at 20
0
C
b. Purge gas: argon at 45 psi and 30/5 SCFH
c. Mode: auto
d. Temperature feedback: on
e. Clean: off
f. Program:
Step Temperature Time Integrate Start
oC 
X5 sec.
1 150 0
2 150 1
3 750 4
4 1000 4
5 2300 0 *
6 2300 2
6. IL254:
a. Nebulizer flow: air at 40 psi and 2.8 LPM
b. Delay: 06
c. Deposit: 020
d. Repeat: 1
16
B In Plant Samples
1. Principle of the Method:
The carbon in a known weight of dried plant material is
burned off by atmospheric oxygen in a muffle furnace. The
compounds in the ash are brought into solution using hydrochlo-
ric acid and made to a known volume using deionized water.
Silica is filtered out of the solution before analysis on the ICAP
spectrometer.
2. Apparatus:
a. Muffle furnace
b. Porcelain evaporating dishes
c. Plastic funnels and Whatman #40 filter paper
d. 100 mL plastic volumetric flasks
e. Plastic storage bottles
3. Reagents:
a. Deionized water
b. HCl solution (dilute 83 mL concentrated HCl
to 100 mL with deionized water)
4. Procedure:
a. Weigh 1.0 g of previously dried and ground
plant material into a porcelain evaporating
dish.
b. Place the evaporating dishes in a muffle
furnace and heat at 450
0
C for 4 hours or over-
night. Turn the furnace off, open the furnace
door, and allow the samples to cool before
removing them from the furnace.
c. Moisten the cool samples with distilled water
and add 1 mL of HCl solution.
d. Transfer the sample 
to a 100 mL plastic 
volu-
metric flask using deionized water and a
plastic stirring rod. Make the flask to volume
with deionized water and allow the silica to
settle out.
e. Filter part of the contents of the volumetric
flask into a plastic bottle for storage. Do not
wash the volumetric flask or filter paper during
this step.
17
5. Remarks:
a. Always carry a blank through the procedure.
b..This ashing procedure is not suitable 
for N, P,
Hg, Si, or Se.
c. The final concentration of HCl in 
the digest is
0.1 N.
d. The muffle furnace set at 450
0
C will actually
be about 485
0
C.
6. Safety:
a. Obtain a Material Safety Data Sheet (MSDS)
for hydrochloric acid and read it.
b. Wear eye protection, an apron or 
lab coat, and
gloves while carrying out this procedure.
c. Use great care in step 4.b. The muffle 
furnace
is very hot.
18
Ca in Mehlich I Soil Extract
1. Principle of the Method:
Calcium in Mehlich I Soil Extract (double acid extract)
is concentrated enough to analyze using the flame atomization
technique on the atomic absorption spectrophotometer. Because
of interferences by phosphorus, the nitrous oxide-acetylene
flame must be used.
2. Standards: 0, 2, 4, 6, 8, and 10 ppm in Mehlich I
extracting solution.
3. Dilution: topsoil samples will need to be diluted
1/50, 1/100, 1/200, 1/1000, or 1/2000.
4. IL251:
a. Lamp: Ca at 7 ma; no D
2 
lamp
b. Burner: nitrous oxide-acetylene parallel to
and 1/2 inch below beam
c. Wavelength: 422.7 nm
d. Slit Width: 320
e. Integration: auto at 4 sec
f. Mode: (SB)A
g. Focus for maximum intensity
h. HV: adjust for intensity between 2 and 8
i. Oxidant: air at 40 psi and 20 scfh; nitrous
oxide at 30 psi
j. Fuel: acetylene at 15 psi and 8 scfh to
light; after switching to nitrous oxide, adjust
fuel for a red feather of 3/4 inch when not
aspirating water
k. Nebulizer: set for aspiration rate of 1 to
1.5 mL in 15 sec
19
Cd in Plant Samples
1. Principle of the Method:
Cadmiumn in plants is low enough that it must be run
using the graphite furnace atomic absorption technique (GFAA).
Plant samples may be digested using either wet or dry ashing.
2. Standards: 0, 0.005, 0.01, 0.02, 0.03 ppm Cd in 0.1 N
HC1
3. Matrix modifier: To 5 mL of each sample add 50 pL
of concentrated 
HNO
3 
and 50 pL concentrated 
H
3
PO
4
.
To 10 mL of each standard add 100 pL of concen-
trated HNO
3 
and 100 pL of 
concentrated 
H
3
PO
4
'
4. IL251:
a. Lamp: Cd at 3 ma; D
2 
at 25 ma
b. Wavelength: 228.8 nm
c. Slit width: 320
d. Integration: Pk Ht at 1/16 sec
e. Mode: (SB)A-B
f. Focus for maximum intensity
g. HV: adjust until intensity is between 2 and 8
5. IL655 (with IL755 temperature sensor):
a. Coolflow: on at 20
0
C
b. Purge gas: argon at 45 psi and 30/5 SCFH
c. Mode: auto
d. Temperature feedback: on
e. Clean: off
f. Program:
Step Temperature Time Integrate Start
oC 
X5 sec.
1 150 0
2 150 1
3 225 3
4 225 4
5 2250 0 *
6 2250 2
6. IL254:
a. Nebulizer flow: air at 40 psi and 2.8 LPM
b. Delay: 06
c. Deposit: 020
d. Repeat: 1
20
K in Mehlich I Soil Extract
1. Principle of the Method:
Potassium in Mehlich I Soil Extract (double acid extract)
is concentrated enough in topsoil extracts to analyze using the
flame emission mode on the atomic absorption spectrophoto-
meter.
2. Standards: 0, 10, 20, 30, 40, and 50 ppm K in
Mehlich I extracting solution.
3. Dilution: Topsoil samples can probably be run
undiluted.
4. IL25 1:
a. Lamp: none
b. Burner: air-acetylene perpendicular to and
1/2 inch below beam
c. Wavelength: 766.5 nm
d. Slit width: 320
e. Integration: auto at 1 sec
f. Mode: FE
g. HV: 460
h. Oxidant: air at 40 psi and 20 scfh
i. Fuel: acetylene at 15 psi and adjust flow for
blue flame
j. Nebulizer: set for aspiration rate of 1 to 1.5
mL in 1.5sec
21
Mg in Mehlich I Soil Extract
1. Principle of the Method:
Magnesium in Mehlich I Soil Extract (double acid extract) is
concentrated enough in topsoil extracts to analyze using the flame
atomization technique on the atomic absorption spectrophotometer.
2. Standards: 0, 2, 4, 6, 8, and 10 ppm in Mehlich I
extracting solution.
3. Dilution: topsoil samples will need to be diluted
1/10 or 1/50 with Mehlich I extracting solution.
4. IL251:
a. Lamp: Mg at 3 ma; no D
2 
lamp
b. Burner: air-acetylene perpendicular to and
1/2 inch below beam
c. Wavelength: 285.2 nm
d. Slit width: 320
e. Integration: auto at 1 sec
f. Mode: (SB)A
g. Focus for maximum intensity
h. HV: adjust for intensity between 2 and 8
i. Oxidant: air at 40 psi and 20 scfh
j. Fuel: Acetylene at 15 psi and adjust flow
for blue flame
k. Nebulizer: set for aspiration rate of 1 to
1.5 mL in 15 sec
22
Ni in Plant Samples
1. Principle of the Method:
Nickel in plants is low enough that it must be run using the
graphite furnace atomic absorption technique (GFAA). Plants samples
may be digested using either wet or dry ashing procedures.
2. Standards: 0, 0.01, 0.03, 0.05, 0.07, 0.10 ppm Ni in 0.1 N
HC1
3. Matrix modifier: To 5 mL of each sample add 50 VL of
concentrated HNO
3
. To 10 mL of each standard add 100 pL
of concentrated 
HNO
3
.
4. IL251:
a. Lamp: Ni at 10 ma; D
2 
at 30 ma
b. Wavelength: 232.0 nm
c. Slit width: 80
d. Integration: Pk Ht at 1/16 sec
e. Mode: (SB)A-B
f. Focus for maximum intensity
g. HV - adjust until intensity is between 2 and 8
5. IL655 (with IL755 temperature sensor):
a. Coolflow: on at 20
0
C
b. Purge gas: argon at 45 psi and 30/5 SCFH
c. Mode: auto
d. Temperature feedback: on
e. Clean: off
f. Program:
Step Temperature Time Integrate Start
oC 
X5 sec.
1 150 0
2 150 1
3 475 4
4 600 4
5 2250 0 *
6 2250 2
6. IL254:
a. Nebulizer flow: air at 40 psi and 2.8 LPM
b. Delay: 06
c. Deposit: 020
d. Repeat: 1
23
Pb in Plant Samples
1. Principle of the Method:
Lead in plants is low enough that it must be run using the
graphite furnace atomic absorption technique (GFAA). Plant samples
may be digested using either wet or dry ashing.
2. Standards: 0, 0.01, 0.03, 0.05, 0.07, 0.10 ppm Pb in 0.1 N
HCl
3. Matrix modifier: To 5 mL of each sample add 50 pL of
concentrated HNO
3
. To 10 mL of each standard add 100 pL
of concentrated 
HNO
3
.
4. IL251:
a. Lamp: Pb at 5 ma; D
2 
at 25 ma
b. Wavelength: 283.3 nm
c. Slit width: 320
d. Integration: Pk Ht at 1/16 sec
e. Mode: (SB)A-B
f. Focus for maximum intensity
g. HV: adjust until intensity is between 2 and 8
5. IL655 (with 1L755 temperature sensor):
a. Coolflow: on at 20
0
C
b. Purge gas: argon at 45 psi and 30/5 SCFH
c. Mode: auto
d. Temperature feedback: on
e. Clean: off
f. Program:
Step Temperature Time Integrate Start
1
2
3
4
5
6
oC
150
150
350
600
2200
2200
X5 sec.
0
1
3
4
0 *
2
6. IL254:
a. Nebulizer flow: air at 40 psi and 2.8 LPM
b. Delay: 06
c. Deposit: 020
d. Repeat: 1
24
Se in Plant Samples
1. Principle of the Method:
Plants growing on Alabama soils are extremely low in sele-
nium. The following fluorometric method (a modification of an
AOAC procedure) can be used to determine total Se in plant tissue.
The wet ashing procedure given here must be used for digestion of the
plant material. Use of the standard wet ashing procedure will result in
loss of Se by volatilization.
2. Apparatus:
a. 250 mL digestion tubes and rack
b. 50
0
C water bath
c. 50 mL Erlenmeyer flasks
d. Block digestor in perchloric acid fume hood
e. 125 mL separatory funnels
f. 15 mL centrifuge tubes
g. Centrifuge
h. Fluorometer
3. Reagents:
a. Acid mix (700 mL concentrated HNO
3 
+ 300
mL concentrated HCIO
4
)
b. 5 N NH
4
OH (34 mL concentrated NH4OH + 66
mL H20)
c. EDTA solution: Add 20 mL H20 to 1.9 g
EDTA (acid form). Slowly add 5 N NH40H
with stirring until the EDTA just dissolves. Dis-
solve 6 g hydroxylamine hydrochloride
(NH
2
OHHC1) in 100 mL H20. Combine the
solutions and dilute to 250 mL with H20.
d. Cresol red indicator: Dissolve 0.1 g cresol red
in 10 mL H20 and add one drop of saturated
NaOH solution (50%). Dilute to 50 mL with
H20.
e. 1000 ppm Se standard
f. Decalin (decahydronaphthalene)
g. 0.1 N HCl: Dilute 8.3 mL concentrated HCI to
1000 mL with H
2
O
h. 20% HCI (20 mL concentrated HCI + 80 mL
H20)
25
i. DAN (2,3-diaminonaphthalene) solution:
Prepare the DAN solution under yellow lights.
Add 100 mL 0.1 N HCI to 0.1 g DAN. Heat in
50
0
C water bath for 15 minutes. Cool to room
temperature and extract twice with 20 mL
decalin. Shake the flask vigorously and discard
the decalin. Filter the DAN solution through
Whatman #40 filter paper saturated with water.
Do not expose the DAN solution to white light.
The DAN solution must be made fresh daily.
4. Standards:
Standards containing 0, 0.2, 0.4, and 0.6 Vg Se
should be prepared by diluting the 1000 ppm Se standard. The
standards are carried through the same digestion procedure as
the samples. The 0 Vg Se standards also serve as reagent
blanks.
5. Procedure:
a. Weigh 1 g of previously dried and ground plant
material into a 250 mL digestion tube. Add 10
mL of acid mix and stopper the digestion tubes
by inverting 50 mL Erlenmyer flasks into their
tops. Allow the tubes to set overnight at room
temperature in a conventional fume hood.
b. Heat the digestion tubes in a 50
0
C water bath
for 2 hours. Leave the tubes covered during this
step.
c. Remove the 50 mL Erlenmyer flasks from the
digestion tubes and heat the samples at 200
0
C
using the heating block in the perchloric acid
fume hood. Continue heating until about 1 mL
of perchloric acid is left in the tubes.
d. Remove the tubes from the heating block and
add 1 mL of 20% HC1. Stopper the tubes with
inverted 50 mL Erlenmeyer flasks and return
them to the heating block for 5 minutes. Re-
move the tubes from the block and allow them
to cool.
e. Add 5 mL of EDTA solution and 2 drops of cre-
sol red indicator to each tube. Neutralize the solu-
tions to yellow using 5 N NH4OH and then acidify
the solutions to orange-pink using 20% HC1.
26
f. This and all the following steps must be carried 
out
under yellow lights. Prepare the DAN solution.g.
Add 5 mL of DAN solution and 20 mL of 0.1 N HCl
to each tube.
h. Heat the samples by setting the tubes in the 50
0
C water
bath for 25 minutes. Remove the tubes from the water
bath and cool by setting them in a pan of room temp-
erature water.
i. Pour the contents of the digestion tubes into separatory
funnels containing 10 mL of decalin. Shake the funnels
and discard the water layer.
j. Wash the contents of the separatory funnels twice 
using
25 mL of 0.1 N HCl each time.
k. Pour the organic layer from the separatory funnels into
15 mL centrifuge tubes and centrifuge at medium speed
for 2 minutes.
1. Pipette 3 ml of the organic layer from the centrifuge tubes
into fluorometer cuvettes and determine the fluorescence.
The fluorometer should be set to illuminate the sample at
a wavelength of 369 nm and to determine the fluorescence
at a wavelength of 525 nm.
m. Compare the fluorescence of the unknowns to the fluores
cence of the standards carried through the procedure to
determine Se in the unknowns.
27
Se in Soil Samples
1. Principle of the Method:
Soils in Alabama, with the exception of calcareous Black Belt
soils, are very low in plant available selenium. This procedure is a
modification of the boiling water extraction procedure for plant
available Se. Calcium chloride solution is used instead of deionized
water as an extracting agent because some Alabama soils disperse in
deionized water. Selenium in a large volume of extract is concentrated
by evaporation.
2. Apparatus:
a. 250 mL digestion tubes and rack
b. 50 mL Erlenmeyer flasks
c. 500 mL Erlenmeyer flasks and reflux apparatus
d. 50
0
C water bath
e. AA spectrophotometer with hydride generator
f. 150 mL fleakers
g. 500 mL fleakers
3. Reagents:
a. 0.01 M CaCl
2 
(1.47 g CaCl2 2H
2
0 per 1000 mL
of solution)
b. Acid Mix (700 mL concentrated HNO
3 
+ 300
mL concentrated HC10
4
)
c. Concentrated HCI
d. 0.3% NaBH
4 
in 1% NaOH: Add 1 g NaOH to
100 mL water in a 500 mL fleaker and mix.
Then add 0.3 g NaBH
4 
and mix.
e. 1 M CaCl2 (14.70 g CaCl
2 
2 H
2
0 per 100 mL of
solution.)
f. 1000 ppm Se standard
4. Standards:
Standards containing 0, 0.1, 0.2, 0.3, and 0.4 Vg of Se are
prepared in 150 mL fleakers by diluting the 1000 ppm Se standard.
To each fleaker, add 2 mL of 1 M CaCl
2 
and 33 mL of concentrated
HCL. Make the final volumes in the fleakers to 100 mL with H
2
0.
Blanks should be carried through the entire extraction procedure.
5. Procedure:
a. Place 60 g of previously dried and ground soil into a
500 mL Erlenmeyer flask. Add 300 mL of 0.01 M
CaCl
2 
and reflux the suspension for 30 minutes.
Filter the extract through Whatman #40 filter paper
into a beaker.
28
b. Transfer 200 mL of the filtrates to 250 mL digestion
tubes, add 10 mL of acid mix, stopper the tubes with
inverted 50 mL Erlenmeyer flasks, and heat the
tubes in a 50
0
C water bath for 2 hours. The water
bath should be in a conventional fume hood.
c. Unstopper the tubes and transfer them to the block
digestor in the perchloric acid fume hood. Evaporate
the extract and digest the sample by heating the
tubes at 300
0
C until the final volume is about 1 mL.
d. Remove the tubes from the block, add 33 mE of
concentrated HCl, stopper the tubes with inverted 50
ml Erlenmeyer flasks, and place the tubes back on
the block. When the acid starts to boil, remove the
tubes from the block and let them cool.
e. Transfer the contents of the digestion tubes to 150
mL fleakers and make the final volume in the
fleakers 100 mL with water.
f. Selenium is determined in the extracts, standards,
and blanks using the IL251 AA spectrophotometer
with the IL440 hydride generator accessory.
6. IL251:
a. Lamp: Se at 10 ma; no D
2 
lamp
b. Burner: special air-acetylene with attached quartz
cell
c. Wavelength: 196.0 nm
d. Slit Width: 320
e. Integration: Pk Area for 16 sec
f. Mode: (SB)A
g. Focus for maximum intensity
h. HV: adjust for intensity between 2 and 8
i. Oxidant: Air at 40 psi and 20 scfh
j. Fuel: Acetylene at 15 psi and adjust flow for yellow
flame.
k. Nebulizer: Set for aspiration rate of I to 1.5 ml in 15
sec.: aspirate water at all times.
7. 11440:
a. Inert gas: argon at 20 psi and 6 to 7 1pm
b. Reagent: 0.3% NaBH
4
in 1% NaOH
c. Reagent amount: 5
d. Reaction time: 0.5 mmn.
29
BIBLIOGRAPHY
AA Spectrometer Procedures
Emmel, R.H., J.J. Sotera, and R.L. Stux. 1977. Atomic absorption
methods manual. Instrumentation Laboratory, Inc.,
Wilmington, MA.
General Analysis Procedures
American Public Health Association. 1992. Standard methods for the
examination of water and wastewater. 18th ed. Am.Public
Health Assoc., Washington, DC.
Helrich, K. (ed.). 1990. Official methods of analysis of the Associa-
tion of Official Analytical Chemists. Assoc. of Official
Analytical Chemists, Inc., Arlington, VA.
Hue, N.V., and C.E. Evans. 1986. Procedures used by the Auburn
University Soil Testing Laboratory. Alabama Agri. Exp. Stn.,
Dept. of Agron. & Soils, Dept. Series 106.
Jackson, M.L. 1958. Soil chemical analysis. Prentice-Hall, Inc. Sixth
printing, 1970, by the author, Dept. of Soil Sci., Univ. of
Wisconsin, Madison, WI.
Page, A.L. (ed.). 1982. Methods of soil analysis. Part 2. 2nd ed.
Agron. Monogr. 9. ASA and SSSA, Madison, WI.
Walsh, L.M. (ed.). 1971. Instrumental methods for analysis of soils
and plant tissue. SSSA, Madison, WI.
Walsh, L.M., and J.D. Beaton (eds.). 1973. Soil testing and plant
analysis. Revised ed. SSSA, Madison, WI.
ICAP Spectrometer Procedures
Jarrell-Ash Div./Fisher Scientific Co. 1982. Jarrell-Ash ICAP-9000
plasma spectrometer. Jarrell-Ash Div./Fisher Scientific Co.,
Waltham, MA.
Thermo Jarrell Ash Corp. 1991. ICAP 61E plasma pectrometer
operator's manual. Thermo Jarrell Ash Corp., Franklin, MA.
30