Agricultural Service Laboratory
Plant Tissue and Feed and Forage Analysis Procedures 

May 3, 2000

TABLE OF CONTENTS

Preparation of Plant Samples for Analysis  
Preparation and Determination of %100 Dry Matter in Feed and Forages 
pH Determination (Silage Only) in Feed and Forages 
Dry Ash Procedure for B & Al 
Dry Ash Procedure for P, K, Ca, Mg, Zn, Cu, Fe 
Wet Ashing Procedure Using HNO3+30%H202 for P, K, Ca, Mg, Zn, Mn, Cu, Fe, S 
Wet Ashing Procedure for P, K, Ca, Mg, Zn, Mn, Cu, Fe, S Using HNO3 and HCLO4 
Total Nitrogen by Combustion 
Kjeldahl Digestion for Total Nitrogen 
Determination of NH4-N by Steam Distillation 
Procedure for Distilling Samples on the Kjeltec 2300 Analyzer Unit 
Standardization of Acids and Bases 
Acid Detergent Fiber Determinations (ADF) 
Determination of ADF-N - Bound Protein 
Neutral Detergent Solution Determination - NDF 
Soluble Protein 
Determination of % Fat 
Determination of Sodium (Na) 
Determination of Nitrate Nitrogen (N03-N) by Specific Ion Electrode 
Determination of % Ash  
Determination of Phosphorous by Colorimetry 
Tubidimetric Determination of Sulfur as Sulfate 
Chloride (Total) Determination
Chloride (Soluble) Determination  
Washing Glassware 
Sample Storage and Disposal 

PREPARATION OF PLANT SAMPLES FOR ANALYSIS

INSPECTION

1. All fresh plant tissue should be carefully examined to determine physical 
condition, type of material, extent of contamination, and freedom from
disease.

2. When whole plants are received, remove the roots, stems and foreign material
if included in the sample.

3. Remove soil particles from plant tissue by gentle brushing. Washing under
cold water tap is sometimes necessary to remove water soluble contamination.
Remove excess water before drying.

4. Plant material that is decayed or moldy should be discarded.

5. Make note of the physical condition of the sample and what preparation steps
were taken if other than normal.

6. Assign laboratory number to sample bag, data sheet, and sample submission
form. The first digit of the lab number is 1 for plant. The second two
digits are the month, the last four digits are the sample number for the
year.

7. Check analyses desired on the data sheet.

DRYING

1. Oven-drying

a. Place paper sample bag (do not use waxed or plastic bags) in oven set at
70-80oC. Drying may require 12 to 24 hours depending on the original
condition of sample.

b. To facilitate rapid drying, loosen and separate plant parts in sample bag.

c. Samples should be dried to a crisp and brittle state and ground immediately.
Preparation of Feed and Forage Samples

2. Assign laboratory number to data sheet and sample submission form.

3. Use sharpie to write lab number on sample bag and oven dried paper bag.

4. The first digit of the lab number is 2 for feed, the next two digits are the
month, the last four digits are the sample number for the year.

5. Check analyses desired on the data sheet. Place an "A" next to the sample
number if the sample is to be analyzed "as-is".

Determination of %100 Dry Matter in Feed and Forages

1. For sample to be determined on an dry basis i.e., non- 'A' sample weigh
dried paper bag and record weight to 2 decimal places (keep extra bags in
oven set at 60oC). For sample to be determined on an as-sampled basis,
i.e., an 'A' sample, go to step 7.

2. Place a representative portion of the sample into the paper bag.

3. Weigh paper bag and sample and record weight to 2 decimal places.

4. Dry sample at 60oC overnight.

5. To prepare for the next morning, label 100 mL beaker. Weigh and record
weight to 2 decimal places.

6. After sample has been dried overnight, weigh bag and sample and record
weight to 2 decimal places.
(NOTE--When samples await grinding, they should be left in the oven with heat to
prevent moisture absorption by the dried material.)

7. Grind sample (see page 3).

8. Mix ground sample thoroughly then fill labeled glass vial with ground sample
for analysis.

9. Pour approximately 10 grams ground sample into pre-labeled and pre-weighed
100 mL beaker. Weigh and record weight to 2 decimal places.

10. Dry beaker plus sample at 105oC for 3 hours.

11. After sample has been dried overnight at 105oC, place in desiccator, then
weigh beaker and sample and record weight to 2 decimal places.

Calculation of non- 'A' samples

bag weight = a
bag weight plus sample = b
bag weight plus sample after drying overnight at 60oC = c
beaker weight = x
beaker weight plus sample = y
beaker weight plus sample after drying overnight at 105oC = z

% DM = (c-a)/(b-a) * (z-x)/(y-x) * 100

Calculation of 'A' samples

% DM = (z-x)/(y-x) * 100

Calculation for % Moisture

% MOISTURE = 100 - DM

GRINDING

1. Large Sample

a. Using a large Wiley mill, grind the samples to pass a 1 mm sieve.

b. Grind the entire sample and mix thoroughly before transferring the sample or an
aliquot to a labeled glass vial.

2. Small Sample

a. Grind in the small Wiley mill to pass a 20-mesh sieve.

3. Feed Sample to be Determined on an As-Sampled Basis - 'A' Sample

a. Pour about 50 grams of sample into coffee grinder. Grind for approximately 30
seconds.

b. Mix sample then transfer to a labeled glass vial.

NOTE -- When samples await grinding, they should be left in the oven with heat to
prevent moisture absorption by the dried material.

pH DETERMINATION (SILAGE ONLY) IN FEED AND FORAGES

1. Fill a 150 mL beaker half full with fresh silage and add sufficient water to set
sample leaving about 1/2 inch of free water over the top.

2. Stir and let stand 30 minutes.

3. Stir and remove the water from the silage by pouring into another beaker.

4. Read the pH of the solution immediately using a calibrated pH meter and buffers, pH
4.0 and pH 7.0. Record value with one decimal.

DRY ASH PROCEDURE FOR B & AL

REAGENTS

1. 1 N HYDROCHLORIC ACID - Dilute 83.3 mL conc. HCl to 1 L Deionized H2O (dH2O) or
170 mL to 2 liters d H2O).

APPARATUS

1. MUFFLE FURNACE

2. "HIGH FORM" PORCELAIN CRUCIBLES

3. 100 mL VOLUMETRIC FLASKS

4. 13 X 100 mm FLINT GLASS TEST TUBES

PROCEDURE

1. Weigh 1.000 g sample into "high form" porcelain crucible.

2. Place sample into furnace and increase temperature gradually until temperature
reaches 500oC.

3. Ash for 1 h after reaching temperature.

4. Remove sample from furnace and let cool.

5. Dissolve ash by adding 10 mL 1 N HCl to crucible.

6. Allow to equilibrate for 15 min.

7. Quantitatively transfer dissolved ash into 100 mL volumetric flasks.

8. Wash down sample with dH2O.

9. Dilute to volume with dH20 and shake.

10. Place aliquot into ICP test tube.

11. Record values directly from ICP sheet with no decimal.

Quality Control

1. Ash NIST peach sample as needed. Run solution along with standards and samples
daily. Prior to use, the NIST peach sample should be dried overnight at 80oC and
stored in the desiccator.

2. Check ICP standards at midpoints and end of run.

REFERENCES

See page Dry Ash Procedure.

DRY ASH PROCEDURE FOR P, K, Ca, Mg, Zn, Cu, Fe

REAGENTS

1. 1 N HYDROCHLORIC ACID - Dilute 83.3 mL conc. HCl to 1 L Deionized H20.

2. 6 N HYDROCHLORIC ACID - Dilute 50 mL conc. HCl to 100 mL deionized H20.

APPARATUS

1. MUFFLE FURNACE

2. "HIGH FORM" PORCELAIN CRUCIBLES

3. 100 mL VOLUMETRIC FLASKS

4. 13 X 100 mm FLINT GLASS TEST TUBES

PROCEDURE

1. Weigh 1.000 g sample into "high form" porcelain crucible.

2. Place sample into furnace and increase temperature gradually until temperature
reaches 500oC.

3. Ash for 3 h after reaching temperature.

4. Wet sample with a small amount of dH20, then add 5-10 mL of 6 N HCl and bring to
near dryness on hot plate.

5. Dissolve ash by adding 10 mL 1 N HCl to crucible.

6. Quantitatively transfer dissolved ash into 100 mL volumetric flasks.

7. Wash down sample with dH20.

8. Dilute to volume with dH20 and shake.

9. Place aliquot into ICP test tube.

REFERENCES

1. Ellis, R. J., Jr., J. J. Hanway, G. Holmgren, D. R. Keeney, and O. W. Bidwell.
Sampling and Analysis of Soils, Plants, Waste Waters, and Sludge-Suggested
Standardization and Methodology. Agricultural Exp. Station, Kansas State
University, Manhattan, Res. Pub. 170. North Central Regional Pub. 230.

2. Haynes, R. J. 1980. A Comparison of Two Modified Kjeldahl Digestion Techniques
for Multi-Element Plant Analysis with Conventional Wet and Dry Ashing Methods.
Comm. in Soil Sci. and Plant Anal. 11(5): 459-467.

WET ASHING PROCEDURE FOR USING HNO3+30%H202 FOR DETERMINING P, K, Ca, Mg, Zn, Mn, Cu, Fe, S

REAGENTS

1. CONCENTRATED NITRIC ACID - HN03

2. 30% HYDROGEN PEROXIDE - H202 (stored in refrigerator)

APPARATUS

1. DIGESTION BLOCK

2. 100 mL STRAIGHT DIGESTION TUBES - CALIBRATED AT 50 mL.

3. SILICONE-RUBBER STOPPERS

4. PIPET DISPENSERS

5. TEST TUBES FOR ICP AUTOSAMPLER

PROCEDURE

1. Weigh 0.5000 + 0.0005 g into labeled 100 mL digestion tubes.

2. Under hood, add 5 mL conc. HNO3 rinsing down sides during the addition.
Predigest samples for 30 min. by leaving under hood with no heat.

3. Place digestion tubes on digestion block and heat at 125oC for 1 and 1/2 h. Make sure
front and back shields are on rack. Close sash. Record ending heat time on
board.

4. Remove samples from block and let cool for a few minutes.

5. Add 3 mL 30% H202 slowly to each sample rinsing down sides during the addition.
Allow frothing to settle. Place tubes back on block. Close sash.

6. Heat for 1 h. Record ending heat time on board.

7. Repeat steps 4-6.

8. Increase block temperature to 200oC. Heat for 1 h. Record ending heat time on
board. This should bring the samples to dryness. If sample is still wet, heat a
little longer.

9. Remove dry samples one by one from the block adding 10 mL of 1:10 HN03. Set
samples in second rack under hood.

10. Let samples cool for 15 minutes.

11. Dilute to 50 mL with deionized water.

12. Stopper and shake vigorously.

13. Transfer aliquot to labeled ICP tubes.

14. For P, K, Ca, Mg, and S move decimal on ICP sheet two places to the left and
record 2 decimals. For Zn, Cu, Mn, and Fe record values directly from ICP sheet
with no decimals.

QUALITY CONTROL

1. Ash an NIST peach sample on Monday along with samples.
Prior to use, the NIST peach sample is dried at 80oC and stored in the
desiccator.

2. Save solution and run daily on ICP with standards and samples.

3. Check ICP standards at midpoints and end of run.

REFERENCES

1. Jones & Case. Analyzing plant tissue samples.

2. Jones, J. B., Wolf, B., and Mills, H. A. Plant Analysis Handbook. Micro-Macro
Publishing, Inc. p.197.

3. Plank, C. O. Plant Analysis Reference Procedures for the Southern Region of the
United States. Southern Cooperative Series Bulletin 368, May 1992. p.9.

WET ASHING PROCEDURE FOR DETERMINING P, K, Ca, Mg, Zn, Mn, Cu, Fe, S USING HN03 AND HCL04 (This procedure is not recommended for ICP analysis.)

REAGENTS

1. CONCENTRATED NITRIC ACID - HNO3

2. 70% PERCHLORIC ACID - HCl04

APPARATUS

1. PERCHLORIC ACID FUME HOOD

2. HOT PLATE*

3. 150 mL BEAKERS

4. WATCH GLASS COVERS

5. 100 mL VOLUMETRIC FLASKS

PROCEDURE

1. Weigh 1.000 g sample into 150 mL beakers.

2. Add 10 mL conc. HNO3.

3. Place beakers on hot plate and cover with watch glass covers and heat at 4.5 until
all organic matter is digested - clear yellow. Remove watch glasses and continue
to heat to reduce volume to near dryness (do not bring to dryness).

4. Remove beakers from hot plate and add 5 mL of 70% HCl04.

5. Return to hot plate and digest at 5.5 until white fumes appear and solution is
clear (silicates will be in bottom). If S is to be determined, allow to fume a
minimum of 1 1/2 h.

6. Remove beakers from hot plate. While still under the hood add about 10 mL of
dH20 to beakers to cool samples and stop fuming.

7. Quantitatively transfer sample into 100 mL volumetric flask with dH2O - cool to
room temperature.

8. Dilute to volume, stopper and shake flasks.

9. Allow silicates to settle and transfer aliquot to test tubes.

*The setting 4.5 on the hot plate corresponds to about 100oC, the setting 5.5
corresponds to about 200-250oC.

REFERENCES

1. Ellis, R. J., Jr., J. J. Hanway, G. Holmgren, D. R. Kenney, and O. W. Bidwell.
Sampling and Analysis of Soils, Plants, Waste Waters, and Sludge-Suggested
Standardization and Methodology. Agricultural Exp. Station, Kansas State
University, Manhattan, Res. Pub. 170. North Central Regional Pub. 230.

2. Haynes, R. J. 1980. A Comparison of Two Modified Kjeldahl Digestion Techniques
for Multi-Element Plant Analysis with Conventional Wet and Dry Ashing Methods.
Comm. in Soil Sci. and Plant Anal. 11(5): 459-467.

LECO FP528 NITROGEN COMBUSTION ANALYZER 

Start UP 

1. Wash hands.
2. Move carousel so that position 1 is one space right of arrow.
3. Delete previous results; select row 1 in gray – scroll through final record – right click – delete.
4. Run leak checks.

Blanks

EDTA 

Samples 

Print Report 

Clean Up 

If the power is out for an extended period of time and the furnace cools down, it must be powered up for at least 1 h before using.  Combustion furnace temp can be checked by clicking on Diagnostics - Ambients.  Temp should be 825 - 875 C.

If the sliding head is not sliding to drop the samples - Click Diagnostics - Solenoids.  Click 4th box down (Block Seal).  Click 1st box (Block open).  You should hear and see the block open.  Unclick both boxes.  Close.

KJELDAHL DIGESTION FOR TOTAL NITROGEN

REAGENTS

1. DIGESTION MIXTURE - 3 kg K2S04 and 600 g CuS04.5H20 (or 384 g CuS04 anhydrous)
(use CuS04.5H20 if available).
(This mixture can be purchased as Kjeltab catalyst tablets.)

2. CONC H2S04.

3. NITROGEN STANDARD - Accurately weigh 4.7166 g (NH4)2S04 (dried and stored in the
desiccator), dissolve in deionized water, then dilute to 100 mL. This will give
you a 1% N solution. To check distillation procedure, pipet 1 mL into digestion
tube, dilute with about 80 mL deionized water and follow the distillation
procedure. For calculations, 1 mL = 1 g.

4. Glycine - Weigh 0.1000 mg (stored in desiccator) and digest along with samples.
Value should be 18.66 + 0.9% N.

APPARATUS

1. DIGESTION BLOCK

2. FUME MANIFOLD

3. 250 mL DIGESTION TUBES

PROCEDURE

1. Weigh 0.500 g plant tissue or 0.500 g feed sample into a 250 mL digestion tube.

2. Add 2 Kjeltab catalyst tablets.

3. Add 12 mL of conc. H2S04.

4. Place on digestion block with front and back shields.

5. Heat at 400oC for 45 min. (should be 30 min. after samples have cleared).

6. Remove from block and allow to cool 15 - 20 min. with shields off.

7. Add approximately 75 mL dH20.

8. Sample is ready for distillation.

QUALITY CONTROL

1. Ash 0.1 g glycine along with samples on first set. Ensure value of N is 18.66 +
0.9%.

2. Prior to distilling samples, pipet 1 mL of (NH4)2SO4 solution into a digestion
tube for each distillation unit, dilute each with 80 mL deionized water, and
distill to ensure each sample is 1.00 + 0.05% N.

REFERENCES

1. Brenner, J. M. 1965. Total Nitrogen. In C. A. Black (ed) Methods of Soil
Analysis, Part II, SSSA., Madison, Wis. p.1149-1178.

2. Horwitz, W. (ed). 1970. Official Methods of Analysis of the AOAC, 11th Edition,
Washington, D. C. p.16-17.

3. Tecator Manual. Kjeltec System 2300 Distilling Unit. Tecator, Hoganas, Sweden.

DETERMINATION OF NH4-N BY STEAM DISTILLATION

REAGENTS

1. 40% NaOH solution (w/w) (16.67 N NaOH)

2. BORIC ACID INDICATOR SOLUTION - Dissolve 400 g H3B03 in about 2 L of hot
deionized water (use a 4 L beaker, heat and stir on a hot plate). When H3BO3 is
dissolved, transfer to 20 L carboy. Dilute to approximately 18 L with dH20. Add
200 mL of mixed indicator solution and dilute to 20 L. Adjust pH to 5.0 using
2 mL of 1.67 N NaOH.

STOPPER TIGHTLY!

3. STANDARDIZED H2S04 SOLUTION - Dilute 64 mL conc. H2S04 to 20 L with deionized
H20. Be sure to standardize solution by following the standardization of acids
and bases procedure. (Final concentration should be close to 0.1142 N.)

4. MIXED INDICATOR SOLUTION - Weigh 0.33 g Bromocresol green and 0.165 g Methyl
red. Transfer weighings to a 500 mL volumetric flask using an ethanol squirt
bottle. Dilute to volume with ethanol. Carefully slide a stir bar into flask
and stir until the bromocresol green and methyl red are dissolved. Remove stir
bar and store solution in plastic bottle.

5. NITROGEN STANDARD - Accurately weigh 4.6445 g (NH4)2S04 (dried and stored in
desiccator), dissolve in deionized water, then dilute to 100 mL. This will give
you a 1% N solution. To check distillation procedure, pipet 1 mL into digestion
tube, dilute with about 80 mL deionized water and follow the distillation
procedure. For calculation, 1 mL = 1 g.

APPARATUS

1. KJELTEC 2300 DISTILLATION UNIT

2. 250 mL DIGESTION TUBES

PROCEDURE FOR DISTILLING SAMPLES ON THE KJELTEC 2300 ANALYZER UNIT

OPERATION

1. Turn power on.

2. Turn printer on.

3. Turn water on.

4. Go to manual mode.

5. Flick titrating tube to get bubbles out. Dispense titrant several times to get
bubbles out.

6. Go to steam on. Press arrow key to turn steam on. Allow to warm up for 5
minutes.

7. Press arrow key to turn steam off.

8. Go to analysis mode.

9. Select program.

10. Go to result. Select blank.

11. Have tube containing water in place.

12. Close door.

13. Run at least two blanks. Make sure the blank value is around 0.10 or less.

14. Go to result and change to % Nitrogen. (The blank number above should read the
last blank value you ran.)

15. Put a tube with 1 mL of the 1% N solution standard and some water in place. Input
1.0 for the weight.

16. Close door and let run. Readout should be close to 1% (+ 0.05%).

17. Proceed with samples. Run the glycine check first. Input the correct weight for
each sample. (The result for the glycine check should be close to 18.66 % N.)

18. If you have blanks within the set run a tube with just water first to flush out
the system, then run the blank. (Change result to blank for running the blank
then back to % N for the samples. Input the weight for the samples as above.)

19. Record numbers from printout into nitrogen book and onto lab sheets with 2
decimals.

CALCULATIONS

%N = 14.01 x N H2SO4 x (mL acid)/(sample wt(g) x 10)

% Crude Protein = %N X 6.25

SHUT DOWN AND MAINTENANCE

Daily:

1. Place tube with water in unit. Select manual. Go to steam on. Press arrow key
and allow generator to run for about 5 minutes. Press arrow key to turn steam
off. Remove tube and dispose of contents.

2. Turn power off.

3. Turn water off.

4. Turn printer off.

5. Clean drip tray. Clean the shield. Rinse and inspect the rubber adapter. Wipe
any spillage with a damp cloth. Squirt water into titration vessel and onto pins
to clean.

6. Place empty tube in unit and close shield.

Weekly:

1. Check and clean around reagent tank screw caps to remove crystals.
Every one to three months:

2. Clean alkali pump. Put 2 L of warm distilled water in a beaker. Put alkali tube
into beaker. Select manual mode. Select add alkali several times. Empty
distillation tube as needed. (A rinse using a half a liter of warm water is
sufficient.) Replace hose into alkali tank. Flush out residual water and remove
entrapped air.

3. Clean receiver solution dispensing system as above only if contamination has
occurred.

4. Check volume of alkali. Go to manual mode. Select the pump you want. Measure
dispensed liquid. Adjust as necessary.

5. Check volume of receiver solution. Put drain tube into measuring cylinder. Go
to manual mode. Select add receiver. Adjust as necessary.

6. Clean splash head. Put 25 mL distilled water and 25 mL acetic acid into
distillation tube. Select manual. Go to steam on for 5 to 10 minutes. Turn off
steam. Replace tube with tube containing 50 mL distilled water. Distill for 5
minutes. Repeat the distillation three times with fresh water.

Yearly:

1. Inspect all tubing and connectors.

REFERENCES

1. Brenner, J. M. 1965. Total Nitrogen. In C. A. Black (ed) Methods of Soil
Analysis, Part II, SSSA., Madison, Wis. p.1149-1178.

2. Horwitz, W. (ed). 1970. Official Methods of Analysis of the AOAC, 11th Edition,
Washington, D. C. p.16-17.

3. Tecator Manual. Kjeltec System 2300 Distilling Unit. Tecator, Hoganas, Sweden.

STANDARDIZATION OF ACIDS AND BASES

PHENOLPHTHALEIN SOLUTION - Dissolve 0.5 g phenolphthalein in 85 mL 95% ethanol and
dilute to 100 mL with deionized H20.

STANDARDIZATION OF Na0H

1. Accurately weigh out three 0.2300 to 0.2500 g portions of KHP (Potassium Hydrogen
Phthalate) on weighing paper and quantitatively transfer to three 250 mL
Erlenmeyer flasks. (KHP must be dry; dry in oven before weighing and cool in
desiccator before using.)

2. Add 50 mL deionized water and dissolve by stirring.

3. Add 3 drops of phenolphthalein solution.

4. Titrate with unknown NaOH solution (approximately 0.05 M) to endpoint (very faint
persistent pink).

CALCULATIONS

# equivalents KHP = wt. KHP - 204.23 g/eq.

N NaOH = (# equivalents KHP)/(mL NaOH)(0.001)

STANDARDIZATION OF H2SO4

1. Pipet 20 mL standardized Na0H into four 150 mL beakers.

2. Add 3 drops of phenolphthalein solution.

3. Titrate with unknown H2SO4 solution to endpoint.

CALCULATIONS

N H2SO4 = (N NaOH x mL NaOH)/mL H2SO4

 (Take out the high and low numbers and average middle two. If there is too much
discrepancy, try again.)

REFERENCES

1. Peters, D. G., J. M. Hayes, and G. M. Hieftje. 1976. A Brief Introduction to
Modern Chemical Analysis, p.87-118. W. B. Sanders Company, Philadelphia.

ACID DETERGENT FIBER DETERMINATIONS (ADF)

REAGENTS

1. ADS - ACID DETERGENT SOLUTION - Weigh 400 g Hexadecyltrimethyl-ammonium
bromide in a 2 L beaker under the hood. (This material is harmful if inhaled or
absorbed through the skin so a respirator and gloves should be worn while making
this solution.) Add deionized water to this beaker and stir until mixture can be
poured. Transfer this solution to a 4 L beaker. Bring the volume up to about3 L with water 
and stir thoroughly with a long stirring rod. Very slowly add
556 mL conc. H2S04 to the solution and continue to stir vigorously with the
stirring rod. (If the acid is poured in too quickly without stirring, the
solution may turn brown. If this happens add a little more water and continue
to stir.) At this point there may still be some undissolved material, so place
the beaker on a heater/stirrer and stir with heat until the material is
dissolved. Transfer this solution to a 20 L carboy and dilute to 20 L with
deionized H20. This may be purchased as a concentrate or straight solution.

2. ACETONE

APPARATUS

1. ANKOM FIBER ANALYZER #F200

2. 3 3000 mL BEAKERS 

3. HOT PLATE

4. FILTER BAGS (ANKOM CO. #F57)  

5. HEAT SEALER #1915

6. BAG HOLDER

PROCEDURE

1. Prepare Filter Bags/Samples.

A. Weigh labeled filter bag (ANKOM Co. #F57). Record weight.  

B. Tare bag holder containing sample bag.  Weigh 0.5 g (+0.01 g) of sample 
into bag. Record weight of sample.

C. Seal the bag closed within 1 cm from the open edge using the heat sealer.

D. Spread sample uniformly inside the filter bag. This should be done by
shaking and tapping the bag to eliminate clumping. A uniform distribution
of the sample inside the bag is very important to achieving good precision
and accuracy in the analysis.

E. Place 24 bags in the bag suspender. The bag suspender is composed of 9
individual baskets and a center post. The 9th basket acts as a top of the
8th. Place three bags in each basket (separated 120 degrees apart). Stack
baskets on center post ensuring bags on different levels are not positioned
directly above each other in order to maximize the flow of solution around
each bag. (Run a check with each batch.)

2. Fill pressure vessel with 2000 mL of ambient temperature AD or ND solution. Less
bags and solution can be used per study but a minimum of 1500 mL of solution has
to be used in the digestion vessel. (See note below*.)

3. Place bag suspender with samples into the solution in vessel. Place weight on top
of samples.

4. Start timer (60 min. for ADF and 75 min. for NDF), screw down vessel top and turn
agitation and heat on.

5. While samples are being digested heat 9 L of rinse water to 90-100oC.

6. Turn heat and agitation off when indicated by timer, slowly open the valve and
exhaust hot solution before opening lid. NOTE: THE SOLUTION IN THE DIGESTION
VESSEL IS UNDER PRESSURE. THEREFORE, THE VALVE NEEDS TO BE OPENED FIRST IN
ORDER TO RELEASE THE PRESSURE BEFORE THE VESSEL LID CAN BE
OPENED.

7. After the solution has been exhausted close valve and open the lid. Add
approximately 2 L of hot rinse water. Lower lid and turn agitate on. Repeat hot water 
rinse three more times. For NDF assays add 4 mL of heat stable alpha-amylase 
(ANKOM Co. #FAA) to each of the first two rinses (8 mL total). Add amylase to 
beaker to mix before adding solution to vat.

8. Remove filter bags from bag suspender and gently press excess water out. Place
bags in a small beaker and pour in enough acetone (240 mL) to cover bags. Allow
bags to soak 3 min. Remove and lightly press excess acetone out.

9. Spread bags out and let air dry. Complete drying in oven (105oC) overnight.

10. Transfer samples to plastic bags. Take one fiber bag out at a time and close
plastic bag with remaining samples to exclude moisture. Weigh. Record weight.

11. Calculate percent fiber:

% Fiber = 100(C-(A*D))/B

Where:

A = Bag tare weight
B = Sample weight
C = Final bag weight after digestion and drying
D = Blank bag correction (final oven dried weight/original blank bag weight)

(use value of D=0.997)

*NOTE ADF

< 6 samples - hold until next day
7-15 samples - use 1500 mL ADF
16 samples - use 1600 mL ADF
17 samples - use 1700 mL ADF
18 samples - use 1800 mL ADF
19 samples - use 1900 mL ADF
20-24 samples - use 2000 mL ADF

12. Record values with one decimal.

QUALITY CONTROL

1. Run an NFTA check sample with each batch.

REFERENCES

1. Goering, H. K., and P. J. Van Soest. 1970. Forage Fiber Analysis (Apparatus,
Reagents, Procedures, and Some Applications). Agri. Handbook, No. 379, ARS,
USDA.

DETERMINATION OF ADF-N - BOUND PROTEIN

REAGENTS

1. ADS - see page 20 for ADF determination.

APPARATUS - see page 20.

PROCEDURE

1. Weigh out 0.500 g sample into a filter bag.

2. Use procedure for ADF determination (page 20).

3. Dry in oven at 100oC.

4. Place filter bag with sample into digestion tube. Run a blank (an empty filter
bag) before the sample. Determine % N by following Kjeldahl procedure (page 12)
with this exception: add 3 Kjeltab tablets and 18 mL H2S04.

5. Distill sample using procedure (page 14). (Press Blank Value on control unit
before running blank. This will automatically subtract the blank value from the
samples.)

6. Record values with two decimals.

CALCULATION

%N = 14.01 X N H2S04 X (mL acid used - mL acid for blank)/(sample wt (g) x 10)

 NEUTRAL DETERGENT SOLUTION DETERMINATION - NDF

REAGENTS

1. NEUTRAL DETERGENT SOLUTION - NDS - In a 4 L beaker combine 600 g sodium
lauryl sulfate, 200 mL ethylene glycol monoethyl ether, and 2 L deionized water.
Mix this solution thoroughly and pour it into a 20 L carboy. Combine 372.2 g
disodium ethylenediaminetetra-acetate (EDTA) dihydrate crystals and 136.2 g of
sodium borate decahydrate (Na2B407.10H20) with 3 L of deionized water in 4 L
beaker. Heat and stir this solution until the crystals are dissolved, then add
it to the 20 L carboy. Add 91.2 g of anhydrous sodium phosphate dibasic (Na2HP04)
to 1 L of deionized water, heat and stir to dissolve, then add it to the 20 L
carboy. Dilute this mixture to 20 L with deionized water and mix thoroughly.
pH should be between 6.9-7.1. This solution may be purchased ready made.

2. ANHYDROUS SODIUM SULFITE

3. ACETONE

4. ALPHA-AMYLASE (ANKOM CO. #FAA) (stored in refrigerator)

APPARATUS - see ADF determination.

PROCEDURE - see ADF Procedure.

*NOTE NDF

< 6 samples - hold until next day
7-15 samples - use 1500 mL NDS
16 samples - use 1600 mL NDS
17 samples - use 1700 mL NDS
18 samples - use 1800 mL NDS
19 samples - use 1900 mL NDS
20-24 samples - use 2000 mL NDS

use 1 g/(100 mL NDS) Na sulfite

Put solution in beaker, then sodium sulfite - stir w/stirring bar on stir plate.
Add 4 mL alpha amylase. Mix solution then pour into vat. Place basket with
samples into vat and weight on top.

See ADF Procedure.

CALCULATIONS - see ADF Procedure.

SOLUBLE PROTEIN

REAGENTS

1. DEIONIZED WATER

2. SODIUM PHOSPHATE, MONOBASIC, MONOHYDRATE (NaH2PO4.H20)

3. SODIUM TETRA BORATE, DECAHYDRATE (Na2B407.10 H20)

4. SODIUM BICARBONATE

SOLUTION PREPARATION

1. BUFFER SOLUTION - Carefully weigh exactly 89.10 g of Sodium Tetra Borate,
Decahydrate into a 250 mL beaker. Next, carefully weigh exactly 122.0 g Sodium
Phosphate mono-basic, mono-hydrate into a 250 mL beaker. To a 4 L beaker, add
approximately 3500 mLs deionized water and a stir bar (Large > 1"). With stir
bar rotating slowly, carefully add Sodium Tetra Borate, Decahydrate. Use a
squirt bottle containing deionized water to thoroughly rinse the weigh boat.
Next, add the Sodium Phosphate monobasic, monohydrate. Again, use squirt bottle
to thoroughly rinse weigh boat. Allow to stir until all crystals are dissolved.

IMPORTANT: DO NOT TURN STIRRER TOO HIGH AND CAUSE EXCESSIVE SPLASHING! After
all crystals are dissolved, with a clean, dry stir bar retriever, remove stir bar
from beaker. Rinse retriever and stir bar into beaker as bar is removed. DO NOT
EXCEED THE 4000 mL VOLUME LINE DURING THIS RINSE. Bring beaker to 4000 mL mark.
Transfer beaker contents into 20 L buffer carboy. Continue by adding 6000 mLs of
deionized water to the 20 L carboy. This addition of deionized water is used to
thoroughly rinse the beaker and bring the solution to the proper volume of 10 L
(concentration). Mix the contents of the carboy. Before using, measure the pH
of the solution. The normal range is 6.70-6.75.

To adjust pH up- use Sodium Bicarbonate.

To adjust pH down - use Hydrochloric Acid.

PROCEDURE

1. Weigh 0.5 g of sample into a clean, dry 250 mL Erlenmeyer Flask. Label flask with
sample number.

2. Add 50 mL of Borate-Phosphate buffer to each flask.

3. Place caps on flasks, swirl gently and let stand 1 h.

IMPORTANT NOTE 3: Soy Products (461,462,463,703,704,764) must be incubated in a
water bath at 39oC for 1 h.

4. After 1 h, samples are ready to filter. Filter samples through filter paper and
air dry overnight.

5. Analyze filter paper and residue for crude protein according to ADFN procedure
(page 23). This is insoluble protein.

6. Record values with 2 decimals.

CALCULATION

Soluble Protein % = (Sample CP% - Residue CP%) x 100/Sample CP%

 REFERENCES

1. NYDHIA

Cornell Nutrition Conference proceedings (10/23/92).

DETERMINATION OF % FAT

REAGENT

1. HEXANE

APPARATUS

1. SOXHLET EXTRACTION APPARATUS

2. THIMBLES (should be kept in oven at 100oC)

3. KIMWIPES

PROCEDURE

1. Weigh approximately 2 g of sample. Wrap sample up in kimwipe and place kimwipe
inside thimble.

2. Record weight to 4 decimal places.

3. Place thimble in labeled beaker. Dry overnight at 100oC, reweigh immediately from
oven and record weight to 4 decimals.

4. Place thimble inside extraction unit.

5. Fill boiling flask « to 2/3 full with hexane. (After cleaning flasks add a small
amount of zinc metal to serve as boiling chips.)

6. Turn on cooling water.

7. Turn on heating units.

8. Allow to extract for 6 h.

9. Remove thimbles and place in beakers. Pour excess hexane into reserve jug.

10. Place thimbles in oven at 100oC to dry overnight.

11. Weigh immediately from oven. Record weight to 4 decimal places.

12. Calculate fat % and record with one decimal.

CALCULATIONS

%FAT = ((wt. after drying) - (wt. after extraction)) x 100/(thimble and sample wt.) - (thimble wt.))

 QUALITY CONTROL

1. Analyze AAFCO check sample along with each set.

REFERENCES

1. Horwitz, W. (ed). 1970. Official Methods of Analysis of the Association of
Official Analytical Chemists, 11th Edition, Washington, D. C., p.128.

DETERMINATION OF SODIUM (Na)

APPARATUS

1. 150 mL BEAKERS

2. 18 X 150 mL TEST TUBES

3. METAL FILTER

PROCEDURE

1. Weigh 1.000 g sample into a 150 mL beaker.

2. Add 100 mL H20 and place on stirrer for 30 min.

3. Filter mixture with metal filter and pour filtrate into a large test tube.

4. Before analyzing, pour filtrate into ICP test tube.

5. Take reading directly from ICP printout with no decimals.

CALCULATION

Na (2.54) ppm = NaCl ppm

DETERMINATION OF NITRATE NITROGEN (N03-N) BY SPECIFIC ION ELECTRODE

REAGENTS

1. EXTRACTION SOLUTION - In a 4 L beaker, add 173.2 g Al2(S04)3, 12.8 g H 3B0 3, and
0.7218 g KNO3 and 25.2 g sulfamicacid (NH2S03H) to 3 L deionized water. Stir to
dissolve. Pour solution in carboy and dilute to 10 L with deionized water. Adjust
to pH 3.0 adding at least 15 mL conc. NaOH (may need more).

2. N03-N STANDARDS - To make 1000 ppm N stock solution, dissolve 0.7218 g KNO3 (dry
and stored in desiccator) in deionized water in a 100 mL volumetric flask. Add
1 mL preservation solution then dilute to 100 mL. (Make up blank, 10 ppm, and
100 ppm N03-N standards using stock solution and diluting with extracting
solution.)

3. OUTER FILLING SOLUTION - 0.04 M ammonium sulfate - Add 0.52 g (NH4)2S04 to 100
mL vol. flask. Dilute with H20.

4. INNER FILLING SOLUTION - Orion cat. 900002

5. PRESERVATION SOLUTION - Dissolve 6.2 g Boric Acid in 100 mL hot deionized water.
Allow to cool.

APPARATUS

1. ORION ION ANALYZER

2. NITRATE ION ELECTRODE (ORION 93-07)

3. REFERENCE ELECTRODE (ORION 90-02)

4. MAGNETIC STIRRER

PROCEDURE

1. Weigh 2 g plant or feed sample into 100 mL beaker. (When testing cotton petioles,
weigh 0.25 g sample, follow steps 2-11, then multiply final answer by 8).

2. Add 50 mL extraction solution.

3. Let stand for 30 minutes.

4. Check levels of inner and outer filling solutions in reference electrode (see
reference electrode manual for specifications).

5. To set up instrument, press 2nd function - 2 to select appropriate electrode.

6. Press speed-0 to calibrate N03-N.

7. Follow prompts - select 2 standards - Do blank correction. (Rinse electrodes and
blot dry before switching solutions.)

8. Set 10 ppm standard to read 25.

9. Set 100 ppm standard to read 250.

10. Measure N03-N in sample and multiply reading by 10. Record as ppm with no
decimal.

11. When finished place meter in standby mode by pressing speed-8. Submerge
electrodes in proper solutions.

REFERENCES

1. Baker, A. S., and R. Smith. 1969. Extracting Solution for Potentiometric
Determination of Nitrate in Plant Tissue. J. Agr. Food Chem. 17:1284-1287.

2. Barker, A. V. 1974. Nitrate Determination in Soil, Water, and Plants.
Massachusetts Agricultural Experiment Station Bulletin 611, p.35.

3. Cantliffe, D. J., G. E. MacDonald, and N. H. Peck, 1970. The Potentiometric
Determinations of Nitrate and Chloride in Plant Tissue. New York's Food and
Life Sciences Bulletin 3, p.7.

DETERMINATION OF % ASH

APPARATUS

1. MUFFLE FURNACE

2. PORCELAIN CRUCIBLES

PROCEDURE

1. Weigh crucible and record weight to 4 decimal places.

2. Weigh approximately 2 g into crucible.

3. Record weight to 4 decimal places.

4. Ash sample at 600oC for 2 h.  (Bring temperature rapidly to 600)

5. Cool in desiccator and weigh within 1 h after reaching room temperature.

6. Weigh ashed sample and record weight to 4 decimal places.

7. Calculate % Ash and record value with one decimal.

CALCULATION

% ASH = ((ashed wt.) - (crucible wt.)) x 100/((crucible and sample wt.) - (crucible wt.))

REFERENCE

St. John (1939), JOACI,XXII, 630.

 DETERMINATION OF PHOSPHOROUS BY COLORIMETRY

REAGENTS

1. ACID MOLYBDATE STOCK SOLUTION - In a 2 L volumetric flask, dissolve 125 g
ammonium molybdate in 400 mL deionized H20 by heating to 60oC until solution is
clear. Allow to cool, then dissolve 2.9 g antimony potassium tartrate in the
molybdate solution. Place the flask in an ice bath in the sink and very slowly add
1500 mL con. H2S04. Cool in the ice bath and very slowly dilute to 2 L with H20.
(It is very important to not let this solution get too hot. It may cause severe
burns if mishandled.) Store in brown bottle under refrigeration.

2. ASCORBIC ACID STOCK SOLUTION - Dissolve 211.2 g ascorbic acid in 1500 mL
deionized water and dilute to 2 L. Store in brown bottle under refrigeration.

3. WORKING SOLUTION (Prepare Fresh Daily) - Add 20 mL acid molybdate stock to about
800 mL water. Mix, then add 10 mL ascorbic acid stock and dilute to 1 L.

4. STANDARDS - 10, 80 ppm phosphorous. To make 1000 ppm P stock solution, dissolve
4.3937 g of dried KH2P04 in deionized H20 then dilute to 1 L. (10 ppm: 1 mL of
1000 ppm stock diluted to 100 mL dH20. 80 ppm: 8 mL of 1000 ppm stock diluted to
100 mL dH20.)

APPARATUS

1. SPECTROPHOTOMETER

2. TEST TUBES

PROCEDURE FOR PREPARING SAMPLES

1. Wet or dry ash sample as previously described.

2. Set diluter to 1:100.

3. Place hose from diluter into flask containing the P working solution.

4. Run diluter through several cycles to draw the working solution into diluter.

5. See diluter manual for instructions on diluting samples.

6. Use Vortex stirrer to insure proper mixing.

7. Allow color to develop for 30 minutes.

8. Set up spectrophotometer as follows.

SET UP OF SPECTROPHOTOMETER

1. Turn power on.

2. Let instrument run through self test.

3. Enter wavelength at 660 nm.

4. Press <Second Function> <Go To >.

5. Allow for a 30 min. warm up.

6. Press <T% / A/C> until you get to concentration mode.

7. Asp Blk by pressing <Sample> (hold under tubing until set up).

8. Press <Second Function> <100% T / Zero A>

9. After set up, remove Blk from tubing.

10. Asp high standard by pressing <Sample> (hold under tubing until set).

11. Enter value for high standard - Press <%T / A/C> (80 ppm corresponds to 80% in
sample).

12. Let set up then remove tube.

13. Read cks and samples by pressing <Sample>, record value, remove tube (can read
accurately to 140 ppm or 1.40% P in sample).

14. Clean cell, leaving water in cell.

15. Disconnect pump.

16. Turn power off.

17. Cover instrument.

REFERENCES

1. Murphy, J. and J. P. Riley. 1962. A Modified Single Solution Method for the
Determination of Phosphate in Natural Waters. Anal Chim. Acta. 27:31-36.

2. Nelson, W. L., A. Mehlich and E. Winters. 1953. The Development, Evaluation and
Use of Soil Tests for Phosphorus Availability. In W. H. Pierre and A. G. Norman
(ed.). Soil and Fertilizer Phosphorus, Vol. IV Agronomy, A Series of Monographs,
Academic Press, Inc., NY pp.153-188.

3. Watanbe, F. S. and S. R. Olsen. 1965. Test of an Ascorbic Acid Method for
Determining Phosphorus in Water and NaHC03 Extracts from Soil. Soil Sci. Soc.
Amer. Proceedings, 29:677-78.

TUBIDIMETRIC DETERMINATION OF SULFUR AS SULFATE

REAGENTS

1. CONDITIONING SOLUTION - Dissolve 150 g NaCl in 600 mL deionized water. Add 60
mL conc. HCl, 100 mL glycerine, and 200 mL 96% isopropyl alcohol. Add glycerine
first and mix well before adding isopropanol.

2. 2 N NH4OAc - Dissolve 150 g ammonium acetate (NH4OAc) in 1 L deionized water.

3. BaSO4 SEED SUSPENSION - (Prepare fresh daily.) - Dissolve 10 g BaCl2.2H20 in 50
mL hot demineralized water in a 250 mL Erlenmeyer flask. Add 1 mL of the 1000 ppm
S standard. Swirl and heat to boiling. Cool rapidly under flowing water. Add
5 mL of conditioning solution.

4. STANDARDS - Prepare a 1000 ppm Sulfur standard by dissolving 0.5435 g of
oven-dried K2S04 in 100 mL 0.1 N HCl. Prepare working standards of 10, 20, 30,
40 ppm S. Prepare S stock solution fresh weekly and prepare working standards
fresh daily.

5. EDTA REAGENT - (Used for cleaning cell in spectrophotometer.) Dissolve 20.2 g
ammonium chloride in 500 mL H20. Add 171 mL ammonium hydroxide and mix, then add
40 g of sodium (di)ethylene-diaminetetraacetate (EDTA) and dissolve. Dilute to
1 L with H20.

EQUIPMENT AND SUPPLIES

1. SPECTROPHOTOMETER

2. TEST TUBES

3. VORTEX MIXER

PROCEDURE

1. Wet ash sample as previously described.

2. Pipet 2 mL working standards and samples into clean test tubes.

3. Add 10 mL of 2 N NH4OAc.

4. Add 2 mL of conditioning solution.

5. Mix on vortex mixer.

6. Add 1.0 mL of seed suspension. (Swirl seed suspension frequently to insure
uniform distribution of BaS04 crystals.)

7. Mix each tube uniformly on the Vortex mixer. This step is important to insure
uniform precipitation of BaS04.

8. Wait 30 minutes and estimate turbidity using a visible spectrophotometer. See
page 32 for set up of spectrophotometer and make the following changes. Set
wavelength on 440 nm. 40 ppm S corresponds to 0.40% S in sample. Can read
accurately to 60 ppm or 0.60% S in sample.) Mix each sample on Vortex mixer
before reading.

REFERENCES

1. Butters, B., and E. M. Chenery. 1959. A Rapid Method for the Determination of
Total Sulfur in Soils and Plants. Analyst 84:239-245.

2. Massoumi, A., and A. H. Cornfield. 1963. A Rapid Method for Determining Sulfate
in Water Extracts of Soils. Analyst 88:321-322.

3. Standard methods for the examination of water and wastewater. 1960. 11th
edition. p.241-243. Am. Public Health Assoc., Inc., New York.

TOTAL CHLORIDE DETERMINATION

REAGENTS

1. CALCIUM OXIDE

2. ACETIC ACID (25%) - Dilute concentrated acid with distilled water, 1:4.

3. POTASSIUM CHROMATE INDICATOR - Dissolve 5 g K2Cr04 in 100 mL deionized water.

4. STANDARD SILVER NITRATE TITRANT, 0.03 N - Dissolve 5.0964 g AgN03 in
deionized water and carefully dilute to 1 L. This solution can be checked against
a standard sodium chloride solution if desired. Store silver nitrate solution in
a brown bottle and keep in the dark.

APPARATUS

1. 50 mL BURET, FUNNEL, AND STAND

2. 1 L VOLUMETRIC FLASK

3. 250 mL ERLENMEYER FLASKS

4. MAGNETIC STIRRER

5. FUNNEL, FUNNEL STAND, AND FILTER PAPER

6. HOT PLATE AND HOT WATER

PROCEDURE

1. Accurately weigh 1 g of ground sample into a porcelain crucible.

2. Add 0.25 g of calcium oxide and mix.

3. Weigh out 0.25 g of calcium oxide into a separate crucible to serve as a blank.
To each crucible add sufficient water to give a thin paste.

4. Place sample & blk into furnace and increase temperature gradually until
temperature reaches 550oC.

5. Ash at this temperature for at least 90 min.

6. Remove the sample & blk from the muffle furnace and cool.

7. Add about 15 mL of hot water to the crucibles and break the ash into a fine
powder.

8. Pour the mixtures through filter paper into 250 mL Erlenmeyer flasks and rinse
the crucibles with water into filter.

9. Wash the residue in the filters with five 10 mL portions of hot water. Bring up
the final volume to the 100 mL mark on the Erlenmeyer with dH20.

10. Cool the filtrate and add dilute acetic acid dropwise until the solution is about
pH 6.0 to 7.0. (Check pH with pH paper.)

11. Cool and add 5 drops of the potassium chromate indicator to the sample and to the
blank.

12. Titrate the blank, then the sample, with standard AgN03 to a persistent light
orange-red. (Be consistent in end-point recognition.)

13. Calculate value and report with 2 decimals.

14. Pour the waste into a carboy for pick up by the hazardous waste manager.

CALCULATION

%Cl = ((mL AgN03 for sample - mL AgN03 for blank) X NAgN03 X 3.545)/g sample

%NaCl = %Cl (1.65)

SOLUBLE CHLORIDE DETERMINATION

1.  Weigh 1 gram sample.

2.  Add 100 mL deionized water

3.  Stir or shake for 30 minutes.

4.  Filter.

5.  Analyze solution on ICP.

TEST TUBE WASHING

Pour acetone into bucket under hood. Swirl basket with test tubes in acetone to
remove numbers. Soak test tubes overnight in detergent solution. Fill clean
rinsing bucket with deionized water. Rinse test tubes in basket three times in
rinsing bucket using new water for each rinse. Dry test tubes in oven.

WASHING PIPETS

Put all pipets in one holder. Move pipet washer to sink. Place one alcotab
tablet (under sink)in bottom of washer. Insert holder with pipets. Fill with
water. Let stand 1 h. Rinse with water until no suds remain (make sure rinser
is refilling). Rinse with deionized water 2 or 3 times. Remove clean
pipets and drain tips up in racks.

Change acid water in pipet holders periodically. (2N HCL)

WASHING GLASSWARE

Run deionized water in dishpan adding some citranox detergent.
All glassware, plastic bottles, stirbars, etc. are washed with soap with the
exception of the volumetric flasks and their stoppers.
First wash glassware with soapy water, rinse three times thoroughly with
deionized water. Soak wet ash digestion tubes in a second dishpan of citranox
for 30 minutes. If yellow deposits remain on tubes, soak overnight. Rinse
three times with deionized water. If yellow deposits still remain, scrub with
brush. Drain on cart.
Next rinse stoppers or volumetric flasks three times thoroughly with deionized
water. Drain on cart.

SAMPLE STORAGE AND DISPOSAL

1. Fresh feed samples containing greater than 15% moisture are stored under
refrigeration for at least one month. Dried feed and plant samples are stored
in bins for at least one month. Dried and ground feed and plant samples are
stored in vials for at least two months. Samples are held for rechecks if
necessary.

2. After the holding period, samples are disposed of by a laboratory technician.