IDRC Practical Experiences with a Variety of Instrumentation for Diffuse Reflectance Measurments

Practical Experiences with a Variety of Instrumentation for Diffuse

Reflectance Measurements

Arnold Eilert

Unity Scientific

Overview

• “Real World” Deviations from the “Ideal”

• Diffuse Reflectance (I/Io) Measurement Approaches – Sample & Reference

• Sample Measurement Considerations, Challenges, Obstacles, and Strategies

• Various Examples to Illustrate

Diffuse Reflectance NIR Measurements

Diffuse Reflectance NIR

Specular Diffuse

Reflectance Modes

Diffuse Reflectance Theory

Ideal versus Reality

Impinging Radiation

Detectors

Sample Sample

Incident

Radiation

Return

Radiation

Sample

Integrating

Sphere

Close Proximity

Detectors

Fiber Optic

Bundle

Diffusely Reflected RadiationCollection Schemes

Remote

Non-Contact

“Absorbance” = -Log(R); R = I/Io

Various Referencing Schemes for Io

Particle Size Effects

Density Effects

Practical Diffuse Refl. NIR

Distance Effects

Residual Sample (Contaminant) Effects

“Practical” Diffuse Refl. NIR

• Flour – Compression/Compaction

• Tissue Paper - Compression

• Tissue Paper – “Infinite Thickness”

Diffuse Reflectance NIR Experiments(“Academic” Tests using Model 2600XT)

Variable Compaction Pressure StudyInfraAlyzer 400 & InfraAlyzer 500 w/ Edapt Probe

• Wheat flour placed in rotating cup on SpectraStar XT unit

• Uniform weights incrementally added to top of plunger

Flour Compaction PressureMeasurement Levels

0.034 PSI

0.689 PSI

Wheat Flour; Variable Compaction PressureAbsorbance Spectra; 680-2600 nm

Wheat Flour; Variable Compaction PressureAbsorbance + SNV + 1st Derivative Spectra; 680-2600 nm

Variable Compaction – Wheat Flour Protein

Variable Compaction – Wheat Flour Moisture

Variable Compaction – Wheat Flour Ash

A. Tissue Paper Compression

“Academic” Diffuse Refl. NIR

• 15 Layers of Paper Placed on Window

• Increasing Pressure Applied

B. “Infinite Thickness” Demonstration

• Consistent Pressure Applied

• Layers Peeled Off One-by-One

• Influence of Backing Evaluated

Tissue Paper (15 Thick) & Styrofoam Plate BackingAbsorbance Spectra

Styrofoam Plate (Backing)

Tissue Paper (15 Thick)

15 Layers Thick (Moderate Compression) = Approx. 0.25 inch Thick

Increasing Compaction

Pressure (PSI)0.05

Total Paper Thickness ~ 0.25 inch

Tissue Paper (15 Layers Thick)Absorbance Spectra; 680-2600 nm

Increasing

Weight

Tissue Paper (15 Layers Thick)Absorbance Spectra; 680-1900 nm

680-1100 nm

Tissue Paper (15 Layers Thick)Absorbance + 1st Derivative Spectra; 680-1900 nm

Tissue Paper (15 Layers Thick)Absorbance + SNV + 1st Derivative Spectra; 680-1900 nm

Tissue Paper (15 Layers Thick)Predicted “Pulp Viscosity” versus Compression Pressure

“Academic” Diffuse Refl. NIR

“Infinite Thickness” Demonstration

~ 0.6 PSI

15 Layers(0.25”)

1 Layer

Tissue Paper (Varying # of Layers)Absorbance Spectra

Polystyrene “Contaminant”

Tissue Paper (Varying # of Layers)Absorbance Spectra

Tissue Paper (Varying # of Layers)Absorbance Spectra; 1600-1900 nm

Tissue Paper (Varying # of Layers, 1 - 15)Absorbance Spectra; 680-1750 nm

Tissue Paper (Varying # of Layers, 1 - 15)Absorbance Spectra; 680-1400 nm

Tissue Paper (Varying # of Layers, 1 - 15)Absorbance + SNV + 1st Derivative Spectra

Tissue Paper (Varying # of Layers, 1 - 15)Absorbance + SNV + 1st Derivative Spectra; 680-1400 nm

To Grind, or Not to Grind???

Practical Diffuse Refl. NIR

Particle Size / Compaction

• To homogenize composition of a larger sample (i.e. representative subsampling)

• To get best results with for some properties with complex/layered products (seeds, coated products, . . .)

• To minimize variable particle size effects

• To minimize “macro” particle size effects

• Simply to make the sample presentable to the instrument

Why Choose the Grinding Option?

Rotating Transport Linear Transport

Particle Heterogeneity/Orientation Effects

Unground “Crystal” Ground “Crystal” Unground “High Impact”

Polystyrene Pellets – Ground & Unground

“Crystal” Pellets

“High Impact” Pellets

Gnd “Crystal” Pellets

Clear Layer / Transfl.

Polystyrene Pellets – ComparisonsAbsorbance Spectra

1000 1200 1400 1600 1800 2000 2200

High Impact Polystyrene, “Full Range” Spectra

SpectraStar 2200 RTW

512 Element InGaAs Diode Array

Analyzer

Diode Array Unit (512 Element): Ethylene Copolymer Pellets; 920-1700 nm

Absorbance Spectra

All Samples

Varying % Vinyl Acetate

Absorbance Spectra

Select Samples

Absorbance + 2nd Derivative Spectra

Select Samples

Absorbance + 2nd Derivative Spectra

Select Samples

Absorbance Spectra

2 Wavelength MLR Calibration:

# Samples = 10 + 1 Val Sample

R-Squared = 0.99940

S.E.C. = 0.306

Absorbance + 1st Derivative Spectra

2 Wavelength MLR Calibration:

# Samples = 10 + 1 Val Sample

R-Squared = 0.99993

S.E.C. = 0.103

512 Element Diode Array Unit: Ethylene Copolymer Pellets

Absorbance Spectra

All Samples

Smokeless Gunpowder

Graphite Coated Uncoated

Graphite Coated

Uncoated

Smokeless GunpowderAbsorbance Spectra

Soy White Flakes

Ground Unground

White Flake - UngroundAbsorbance Spectra

Measured on SpectraStar 2600 XT

12 Individual Cup Orientations

Measured on SpectraStar 2500 XL-R

White Flake - UngroundAbsorbance + SNV + 1st Derivative Spectra

Measured on SpectraStar 2600 XT

12 Repeated Measurements- Step Rotation

Soy White Flake - UngroundAbsorbance + SNV + 1st Derivative Spectra

12 Repeated Measurements- Step Rotation

12 Repeated Measurements- Continuous Rotation 90 deg/s

Grind & Rotation Comparison

1. Measurements at 12 Different Orientations

2. Step Rotation; 12 Measurements

3. Continuous Rotation 90 deg/s; 12 Measurements

A. Unground White Flake

1. Measurements at 12 Different Orientations

2. Step Rotation; 12 Measurements

B. Ground White Flake

Unground White Flake SampleAbsorbance Standard Deviation

Ground White Flake SampleAbsorbance Standard Deviation

(Expanded Y-Axis)

Unground White Flake Sample

Practical Implications using Spectra to Predict Percent Oil

Grinding – The Only Way to Go???

White, Yellow, Pink (w/ TiO2)

Red, Green, Blue, Violet (w/o TiO2)

Black (w/ Carbon Black)

Polypropylene Plastic Container Parts; Various ColorsGround Product Spectra; I/A 500 w/ Rotating Cup Drawer

3 Wavelength MLR Calibration for % Slip

Red, Green, & Blue Parts

Corr. Coef. = 0.993

S.E.C. = 0.080

Skew & Bias Adjusted for White Parts

S.E.P. = 0.144

Skew & Bias Adjusted for White Parts

S.E.P. = 0.144

Excluded

Particle Size / Compaction

• Calibrations estimating particle size

• Wheat hardness estimation (using MLR equation)

• Avoid heating / moisture loss caused by grinding

• Avoid grinding step – practical trade-off

Q: When might you NOT want to minimize variance due to particle size variation(using preprocessing, grinding, . . .)???

Diffuse Transflectance Mode

Q: Which sampling mode is most appropriate for the application?

A: Determined by the optical and physical characteristics of the product being analyzed:

• Powders / Granulates - Reflectance

• Formed Solids - Reflectance / Transmission

• Liquids / Films / Gels

Clear - Transmission / Transflectance

Semi-Opaque - Transflectance

Opaque - Reflectance / Transflectance

Liquid Cup + Transflectance Insert

Egg Yoke – SpectraStar 2400 RTW

0.1 mm Insert

0.2 mm Insert

0.3 mm Insert

0.4 mm Insert

Transflectance Mode; Absorbance Spectra

뫀л0.1 mm Insert

0.2 mm Insert

0.3 mm Insert

Egg Yoke – SpectraStar 2400 RTWTransflectance Mode; Absorbance Spectra

0.1 mm Insert

0.2 mm Insert

0.3 mm Insert

0.4 mm Insert

Egg Yoke – SpectraStar 2400 RTWAbsorbance + 1st Derivative Spectra

Egg Yoke – SpectraStar 2400 RTWAbsorbance + SNV + 1st Derivative Spectra

“Special Purpose” Compression Transflectance Cup

Caramel Sample Placed in SpectraStar Drawer

Final Tightening Step – Change with Position

Absorbance Spectra

Final Tightening Step – Change with Position

Final Tightening – Change with Position

Absorbance + SNV + 1st Derivative Spectra

Different Caramel Products

Absorbance Spectra

Absorbance + SNV + 1st Derivative Spectra

Different Caramel Products

Intact Measurement – The Only Way to Go???

Filled Sample Cup Placed for Measurement

Smear of an Individual Capsule Liquid onTransflectance-Mode Reflector Surface

Transflectance Reflector placed in Liquid CupAgainst Glass for Measurement (0.3 mm Path Length)

Bulk Capsules in Rotating Open CupReflectance Mode

Exctracted Liquid from Single CapsuleTransflectance Mode

Nutraceutical Capsules – SpectraStar 2500X RTWReflectance versus Transflectance Mode; Absorbance Spectra

Bulk Capsules in Rotating Open CupReflectance Mode

Exctracted Liquid from Single CapsuleTransflectance Mode

Individual Pack (Black) vs Average of 4 Packs (Red)

Nutraceutical Capsules – SpectraStar 2500X RTWBulk Capsules in Rotating Open Cup; Absorbance Spectra

Nutraceutical Capsules – SpectraStar 2500X RTWBulk Capsules in Rotating Open Cup; Absorbance + SNV + 1st Deriv Spectra

Individual Pack (Black) vs Average of 4 Packs (Red)800-2200 nm Range

Regions of Highest Degree of Undesirable Variance “Blotted Out”

Individual Pack (Black) vs Average of 4 Packs (Red)800-2200 nm Range

Confirmed misidentified (bad) sample in test set

A-Type CapsulesQuantitative Feasibility Evaluation

Regions of Highest Degree of Undesirable Variance “Blotted Out”

Discriminant Analysis Potential Evaluation

Nutraceutical Capsules – SpectraStar 2500X RTWBulk Capsules in Rotating Open Cup; Absorbance + SNV + 1st Derivative

Cluster Model Discriminant Analysis

Corn Syrup Types:

DE28DE63DE9942FCS55FCSHMCS

Corn Syrup Grades – SpectraStar 2400DTransflectance Mode; 0.3 mm PL; Absorbance Spectra

Corn Syrup Grades – SpectraStar 2400DTransflectance Mode; 0.3 mm PL; Absorbance + SNV + 1st Deriv Spectra

All Calibration Spectra

Corn Syrup Types:

Average Spectra for Each Type

Corn Syrup Types:

Average Spectra for Each Type1450-1820 nm

Average Spectra for Each Type2050-2350 nm

뫀лDE9942FCS

HMCS55FCS (HFCS)

Cluster Model for Corn Syrup Qualification; Scores Plot of Factor 3 vs Factor 2(Circles represent Factor Space Occupied by Corresponding Type)

Cluster Model Discriminant Analysis

10oC - 86oC RangeT

Temperature can influence band shape and peak position

• Sample presentation consistency (minimize controllable variables)

• Optimize optics, general performance of instrument, sampling mode

• Utilize the optimal spectral region

• Optimize the calibration (# factors / wavelengths, mathematical pretreatment, proper exclusion of outliers . . .)

Getting Optimal Results

• Keep an open mind . . .- but keep in mind the fundamentals

• Diffuse reflectance NIR doesn’t do it all- but it does a lot!

Summary

IDRC Practical Experiences with a Variety of Instrumentation for Diffuse Reflectance Measurments

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