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Laser Lab
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STANDARD OPERATING PROCEDURE Date: July 31, 2014
Code: METH 06V01 Title: Method for analysing soil samples for particle size distribution using Laser Diffraction
Author: Emily Mwake Barasa
3 | L A S E R S O P
SCOPE AND APPLICATION
Soil particle size distribution is a characteristic that affects important soil properties. The
pipette method is the traditional means for determining soil particle size distribution (PSD). It is
however, a lengthy procedure based on a number of assumptions with the possibility of
considerable differences between operators. Laser diffraction has become widely accepted
technique for soil particle sizing because it is faster than the pipette method and provides a
broad range of continuous size information between 3,000 and 0.01 microns. Typical analysis
time is 2 to 3 minutes per sample, depending upon the degree of instrument automation. The
use of standard operating procedures for sample handling and treatment means that
reproducibility between different operators is very good.
Prior to the analysis, efficient soil dispersion is achieved by a combination of chemical and
physical procedures. Laser-light scattering analysis does not have the perfect agreement with
standard techniques. However, it does provide data rapidly and reproducibly for the full range
of particle sizes. It is particularly useful for mapping spatial variability of soil PSD over a
landscape. This SOP describes the analytical method followed at ICRAF Soil-Plant Spectral
Diagnostic Laboratory to analyze particle size distribution in soil samples using Horiba LA 950
Laser Scattering Particle Size Distribution Analyzer.
PRINCIPLE
This method is based on diffraction and diffusion phenomenon and Fraunhofer and Mie theory
to obtain the particle size. When a particle is lightened by a monochromatic source (laser
source) a diffraction pattern is obtained. This diffraction pattern gives the light scattering
intensity as a function of the diffraction angle. It is composed of concentric rings. The distance
between the different rings depends on the particle size. To observe this diffraction pattern at a
defined distance, a convergent lens is applied between the laser beam and the sensors. The
sensors (multi-cell) are placed at the focal length and allow measurement of the diffraction
pattern at infinity. Based on viable and proper use of this equipment it is deemed necessary
that any user must seek to know how to maintain the instrument in general whether it is being
STANDARD OPERATING PROCEDURE Date: July 31, 2014
Code: METH 06V01 Title: Method for analysing soil samples for particle size distribution using Laser Diffraction
Author: Emily Mwake Barasa
4 | L A S E R S O P
used for wet or dry mode analysis since both the laser source and detector unit are all
encapsulated in to one unit.
ABBREVIATIONS AND DEFINITIONS
LA Laser Analyzer LDPSA Laser diffraction particle size analyzer PSD Particle size distribution MSDS Material Safety and data sheet.
RELATED DOCUMENT
METH 13 WF 05:Particle Size Distribution Analysis by Laser Diffraction method with
HORIBA LA 950 workflow EQUP 02:Laser diffraction MSDS
RELATED FORMS
Recording sheet Logging form Sample check list Sample submission form
SAFETY AND ENVIRONMENT
Personal protection:
Safety glasses and protective gloves are recommended whenever reagents or samples are handled. For other precautions and safety procedures, consult the Material Safety Data Sheets (MSDS) for each chemical used.
Electrical hazards: Electrical systems must conform to the ICRAF standards. Shock hazards exist inside the instruments. Only an authorized service representative or an individual with training in electronic repair should remove panels or circuit boards where voltages are greater than
STANDARD OPERATING PROCEDURE Date: July 31, 2014
Code: METH 06V01 Title: Method for analysing soil samples for particle size distribution using Laser Diffraction
Author: Emily Mwake Barasa
5 | L A S E R S O P
20 V. The instruments require a third-wire protective grounding conductor. Three-to-two wire adapters are unsafe for these instruments.
Sodium Hexametaphosphate (Calgon) This is a dispersive agent which is highly hygroscopic. Always wear protective gloves and wipe the bench in case of any spills since it can corrode the bench surface. The chemical should not be left exposed.
REQUIREMENTS
Supplies
a. Vacuum bags (room G143F, cabinet 6)
Equipment Equipment Location a. Spatula G143F, cabinet 10 b. Balance G143G c. Magnetic Stirring rods G143F, cabinet 10 d. Stir (Stuart) G1433, cabinet 5 e. Disposing bucket G143F f. Disposing bottles G143F g. Central Water purifier G143F
Reagents and chemicals: Item Storage location Storage condition Sodium hexametaphosphate (Calgon) sln 1% cabinet 10 room temperature
PROCEDURE
Sample processing
The soil samples are air dried ground gently and sieved through 2-mm sieve, soil fines
are then mixed thoroughly and sub sampled via coning and quartering method (ISO
23909:2008) and eventually subjected for analysis on both wet and dry mode of analysis
on Laser Diffraction Particle Size analyzer.
Sample analysis procedure on la-950v’2 (laser diffraction particle size analyzer) a. Switch on the power (mains) then switch on the UPS if OFF.
STANDARD OPERATING PROCEDURE Date: July 31, 2014
Code: METH 06V01 Title: Method for analysing soil samples for particle size distribution using Laser Diffraction
Author: Emily Mwake Barasa
6 | L A S E R S O P
b. Switch on the instrument then thee computer and monitor
c. Click on LA 950software and select operation mode whether WET (Manual) or DRY
(Refer to EQUP02V01).
If wet mode (manual):
Click on LA Navigator menu.
Using scroll bar on your RHS select NEW SEQUENCE FINAL_2 in case you’re not
using AUTOSAMPLER.
Go to CONDITION MENU, and then set condition for the next measurement
sub -menu, measurement dialog Windows opens.
On measurement dialog Window click on load tab and select 2 TEST SOIL IN
WATER 4 DEBUBBLE WITH US and then click OK on the file load menu then click
OK to load the correct condition file
You are ready for a run on the manual mode once you’ve done all of the above.
Just click on start button to begin your run
If dry mode:
First ensure you‘ve placed the correct cell i.e. dry cell on flow cell unit after
removing the dry cap cover and aligning the dry cell with the laser source and
the detector by placing it on the red arrow mark.
Place the sample shoot on its holder
Switch on the dry cell unit
Switch on the compressor and the vacuum cleaner via the mains power switch*
On LA navigator menu select ICRAF SOIL IN AIR 2010 DRY-SEQ-EQ1
Click on condition menu and condition set for the next measurement
Then select SOIL IN AIR 2% TCHANGE then click OK on the file load menu then
click OK to load the correct condition file.
You are ready for a run on the manual mode once you’ve done the entire above,
click on start button to begin your run.
QUALITY CONTROL
In wet mode, after saving the data you need to compare the mean and median sizes of
the replicates. The 1st reading is taken just after the sample is introduced into the water
bath and without ultrasonic. The next 3 readings are taken consecutively after
STANDARD OPERATING PROCEDURE Date: July 31, 2014
Code: METH 06V01 Title: Method for analysing soil samples for particle size distribution using Laser Diffraction
Author: Emily Mwake Barasa
7 | L A S E R S O P
introducing ultra-sonic during measurement in the sequence .A loop can be introduced
where the 3 replicates taken during sonification are averaged. To have a good
repeatability do not wait for too long as this tends to allow small particles to settle on
the system e. g tubes or water bath container thus creating a shift towards larger
particles 2min wait through the sequence is preferred.
In dry mode- check if the two replicates fall within the same range.
REFERENCES
J S R 1622-1995-General rules for sample preparation of particle size analysis
J S R 1629-1997-Determination of particle size distribution for fine ceramic raw powder by laser diffraction method
EQUP02V01 * Compressor and vacuum cleaner are kept ON permanently and only switched on via the
mains.
STANDARD OPERATING PROCEDURE Date: July 31, 2014
Code: METH 06V01 Title: Method for analysing soil samples for particle size distribution using Laser Diffraction
Author: Emily Mwake Barasa
8 | L A S E R S O P
ANNEX Annex 1.Laser Diffraction Particle Size Analysis Work Flow
STANDARD OPERATING PROCEDURE Date: July 31, 2014
Code: METH 06V01 Title: Method for analysing soil samples for particle size distribution using Laser Diffraction
Author: Emily Mwake Barasa
9 | L A S E R S O P
De-ionized Water
1% Calgon preparation
Calgon/water
Switch on the machine and
Align cells
· Weigh 15g
calgon using
weighing boats
· Mix with 1500ml
to make 1%
calgon solution
Data Acquisition
· Results obtained as a cumulative curve of
distribution
Data Conversion· Data converted to flat tables using LA-950 for
windows (E)
· Then obtain PSA and frequency tables using
R-Script
TO DATABASE
Sample Analysis
· Run the sample following
the automated sequence on
the SOP
Unprocessed Sample
Sieve Sample
to 2mm
Processed/unprocessed sample
Processed Sample
Switch on the machine and
Align cells
Sample Analysis
Calgon
Run the sample following the
automated sequence on the
SOP
Start Wet Mode
StartDry Mode
Action point
Decision point
Terminal Point
Tape notes
Stored data
Process route
Samples
sieved at 2mmPreparation
From soil processing Factory
Laser Diffraction Particle Size
Analysis Workflow
LEGEND
This laboratory involves use of laser diffraction pattern to determine
particle distribution for wet and dry soils
Objective:
To achieve a high-throughput, non destructive and fine resolution analysis
of soil particle distribution for accurate and precise data
Annex 2. QUALITY CONTROL FACT SHEET
STANDARD OPERATING PROCEDURE Date: July 31, 2014
Code: METH 06V01 Title: Method for analysing soil samples for particle size distribution using Laser Diffraction
Author: Emily Mwake Barasa
10 | L A S E R S O P
PROCESS DESCRIPTION
Aligning of detectors Both blue and red transmittances should read 100% during alignment
NIST STD (Commercial STD) for wet mode Mean diameter approx. 1.020 µm∓ 0.22 µm
Polydisperse particle STD for dry mode Mean diameter is approx. 40.66µm∓ 0.22 µm.
Katumani Wet mode: Mean diameter approx. 129µm and median size approx. 45µm for Dry mode: Mean diameter approx. 401µm and median size approx. 326µm
Red upland Agricultural Clay
Wet mode: Mean diameter approx. 78µm µm and median size approx. 48µm for Dry mode: Mean diameter approx. 48µm and median size approx. 384 µm.
White sand Wet mode: Mean diameter approx. 91µm and median size approx. 90 µm. Dry mode: Mean diameter 86µm and median size approx.89µm.
Check distribution curves There should be a shift towards smaller particles
Check number of readings Wet mode: 4 readings per sample Dry mode: 2 readings per sample
