Onsite Oil Analysis with ASTM Compliant FTIR Instruments

Dr Steve DyeBusiness Development ManagerParker Kittiwake

Why use FTIR in Oil Analysis? § One of the most widely used laboratory tools for oil analysis

§ Fast - capable of detecting multiple oil analysis parameters simultaneously§ e.g. water, glycol, soot, oxidation, nitration…

§ Easy to use - no extensive sample preparation or wet chemistry required

§ Inexpensive – after capital outlay, per measurement costs are minimal

§ Quick - replaces tedious and time-consuming physical and chemical methods

Infrared Radiation§ Part of the Electromagnetic Spectrum

§ Longer wavelength than Visible light – “heat” energy§ Absorbed by molecules (not atoms)

§ Gives molecular information, not elemental§ Absorption increases molecular vibrations and/or rotations

§ associated with the internal bonds between the atoms of the moleculeThe Electromagnetic Spectrum

VisibleLight

Wavelength(m)

Frequency(Hz)

Wavenumber(cm-1)

10-11 10-10 10-9 10-8 10-7 10-6 10-410-5 10-3 10-2 10010-1 101 102 103

1019 1018 1017 1016 1014 1013 1012 1011 1010 109 108 107 106 105

1Å 1nm 10nm 1μm 10μm 100μm 1mm 1cm

Hard X-ray

SoftX-ray

UV IR

Microwave

VHF Short Mid Long

RadiowaveMid FarNear

Near

Far

Spectral Regions

Gammarays

1000 100 105000

Infrared Absorption§Molecules have several types of vibrations. (3n-5 for linear, 3n-6 for non-linear)

§ Associated with the internal bonds, some (not all) are IR active.

§ IR radiation absorbed at a characteristic energy (frequency / wavelength).§ Qualitative analysis – “fingerprint” identifies which molecules are present

§ Amount of energy absorbed per unit volume depends on concentration.§ Quantitative analysis – signal intensity reflects how much present (ppm or %)

H

O

HH

O

HH

O

H

H

O

H

H

O

H

H

O

H

H

OH

H HO

H H

O

IR Radiation

Stretching

Bending,In Plane

Bending,Out of Plane

A

wavelength (µm)

An example; Water (H2O):

Water Molecule Vibrations

Traditional scanning IR spectroscopy§ First developed in the 1950s§ Step wise scanning of a dispersive element and recording of signal

§ Time consuming§ Drift issues§ Need a reference to obtain the “instrument function”

§ Virtually all instruments are now of the Fourier Transform Interferometer design

FTIR Spectroscopy§ Development started in the late 1960s by analytical chemists borrowing from early work of physicists.

§ Michelson Morley Interferometer was the classic example

§ First commercial FT instrument released in 1969.

§ Uses an interferometer to generate an interference pattern of infrared radiation.§ Divide infrared radiation into two paths.§ Vary the path length along one of the arms§ Recombine the radiation.§ Record signal intensity as a function of change in pathlength difference (speed, time)

§ Interference pattern (interferogram) is in the time domain.§ We need frequency (wavenumber, Hz).

§ Conversion is by Fourier Transform.§ Extremely quick these days with computer FFT1 algorithms

FTIR Spectrometer Principle

Infrared Light Sample

MovingMirror

Fixed Mirror

Detector

InterferogramBeamsplitter

Moving mirror speed ->

Signal

-

>

0

0

Principle of FTIR Spectroscopy

Sample Interferogram

Background Interferogram

Ratio

A = -logTData

Fast Fourier TransformAlgorithm

Transmittance Spectrum

Transmittance Spectrum Absorbance Spectrum

Single Beam Spectra

Advantages of FTIR Spectroscopy§ All wavelengths scanned simultaneously (Fellget’s Advantage)

§ Reduction in data collection time by a factor of N§ Increase in signal-to-noise ratio (SNR) by a factor of N 1/2 by multiple scanning

§ Greater amount of source energy to detector (Jacquinot’s Advantage)§ No rectangular slit aperture§ Much greater throughput compared to conventional IR

§ Fixed internal wavelength reference source§ Typically a small HeNe laser§ Provides high wavelength accuracy

Transmission (Sample) Cell§ Fixed pathlength: Typically between 50-200μm

§ Note: ASTM standard mandates 100µm cell pathlength§ Other cell pathlengths allow for different concentrations

§ Short pathlengths for strong absorbers / high concentration§ Longer pathlengths for weak absorbers / low concentration

§ Cell window material choices:§ Water insoluble ZnSe or CaF2

§ Water soluble KBr, NaCl or KCl

Sample: Fixed Pathlength

IR Transparent Cell Windows

IR Radiation To Detector

FTIR Spectrum of an Oil Sample§ Load cell with sample and collect sample spectrum

§ The FTIR oil sample spectrum will reflect the molecular composition of the oil§ For example, an ester based oil:

Wavenumber (cm-1)

Absorbance

3500 3000 2500 2000 1500 1000

e.g. Ester Based Oil

C

-

H Stretch

C=O Stretch

C

-

O Stretch

CH

2

, CH

3

Bending

CH

2

Rocking

IR

How can I use FTIR for oil analysis?§ Most commonly used as a screening tool

§ FTIR is a rapid method to identify samples that have problems

§ Provides general information about the identity and condition of the oil § Degradation by-products, additive depletion, contaminants

§ FTIR supplements other methods to help diagnose any problems§ For example, elemental analysis methods, viscosity measurements, chemical analyses.

Collecting an FTIR Spectrum§ Specify FTIR instrument parameters:§ Resolution (usually 2, 4 or 8 cm-1)

§ Lower wavenumber means higher resolution§ Number of scans

§ Increasing the scans improves the signal-to-noise ratio by a factor of N1/2

§ Apodization§ Corrects for interferogram side lobes and affects spectral band shapes

§ Collect background single beam spectrum § Air or empty cell reference

Sampling Oil for FTIR Analysis§ Oil should be filtered to remove large particles.

§ Shake well to give a representative sample.

§ Most common sample cell is a transmission cell– Manual loading or continuous flow pumping system

Example of Used Oil FTIR Spectrum

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Absorbance

1000 1500 2000 2500 3000 3500

Wavenumber (cm-1)

Water

Soot

Oxidation

Nitration

Antiwear

Sulfate

Fuel

Qualitative or Quantitative?FTIR measurements can be either:

§ Qualitative§ Identify constituents§ Observe changes in peak intensities or absorbance – better/worse assessment

OR§ Quantitative§ Obtain a definite result in units of concentration (ex: ppm, g/L, %w/v)§ Calibration using standards of known concentrations of the constituent or

parameter of interest§ Correlate concentrations with absorbance to obtain regression coefficients§ Prediction of concentrations in unknown sample using these coefficients

Quantitative Analysis - Example§ Concentration of water in crankcase lubricants:

0.10 0.20 0.30 0.40

0.0

0.1

0.2

0.3

0.4

0.5

Water (%w/w)

Absorbance

.1

0

.2

.3

3800 3600 3400 3200

0.5%

0.4%

0.3%

0.2%

0.1%0.05%

0.0%

Wavenumber (cm-1)

Absorbance

Considerations of Quantitative Analysis§ Some methods are considered semi-quantitative:

§ Difficult to obtain calibration samples with reliable concentration values§ Reference method only gives approximate values

§ Sample to sample variability§ Actual samples can differ from calibration samples§ For example: For soot measurements, particle size may vary§ For example: When measuring fuel, fuel composition may vary between locations

§ Interferences§ Other oil sample constituents and parameters can interfere with the measurement

Interferences§ Parameters with the same functional group will absorb at the same frequency,

interfering with one another§ e.g. Water and Glycol

Water

Ethylene Glycol

Absorbance

Wavenumber (cm-1)

O-H O-H

Interferences from the Base Oil§ The base oil or new oil additives may also interfere with the measurement of some

parameters, especially in the “fingerprint” region.

0.05

0.15

0.25

0.35

0.45

0.55

0.65

0.75

Absorbance

600 800 1000 1200 1400 1600 1800

Wavenumber (cm-1)

Oxidation

Antiwear

Base OilHydraulic Oil

FuelSulfate

Fingerprint Region

Oil Additives

Spectral Subtraction

§ Spectral subtraction is used to subtract out the interferences from the base oil and additives

§ The contaminants, degradation by-products and additive depletion can be visualized and analyzed more easily

Used Oil Spectrum

0.5

1.0

Absorbance

New Reference Oil Spectrum

0.5

1.0

Difference Spectrum

0.5

1.0

1000 1500 2000 2500 3000 3500

Wavenumber (cm-1)

Water

Soot OxidationSulfation

Antiwear

Considerations of Spectral Subtraction§ There are several considerations to take into account when using the spectral subtraction

method:

§ New (reference) oil may not always be available

§ Batch to batch variation in both base oil and formulation for same oil brand§ Need correct reference

§ Oil changes lead to dilution and/or carryover§ Reference no longer good

§ Topping up with another batch or different brand§ Again, reference is no longer good

Contamination/Blending with Different Oils§ FTIR is also very useful for determining significant changes in oil chemistry§ e.g. PAO mixed with an ester- or polyalkylglycol- (PAG) based oi

0.0

0.4

0.8

1.2

1.6

2.0

2.4

Absorbance

1000 1500 2000 2500 3000 3500 Wavenumber (cm-1)

EsterPAG

Parameter Frequency (cm-1) Traditional MethodOxidation 1710 Acid number (AN) titrationNitration 1630 NoneSulfation 1150 Base Number (BN) titrationDiesel Fuel 810 Flash Point, Gas Chromatography

Gasoline 750 Flash Point, GCWater 3420 Karl FisherGlycol 1080,1040, 880 Colorimetry, GCSoot 2000 ThermogravimetricAntiwear 980 Elemental Analysis (Zn etc.)(T)BN 1516,1152 BN by titration

Common Oil Parameters by FTIR

ASTM Standards for oil analysis§ American Society for Testing and Materials (now ASTM International) defines standard

methods and practices for over 12,000 measurement methods for metals, petroleum, construction, environmental and many more.

§ Seen by Industry as THE STANDARD that all measurements should be made in accordance with.

§ ASTM have several published standards and work is ongoing to define more:§ 1 Standard practice (E2412) which defines a total of 12 trend parameters for 3 types of

lubricating oils; Petroleum based, Extreme Pressure (EP) fluids and Synthetic Polyol Esters.

§ 5 Standard methods – Oxidation (D7414), Nitration (7624), Phosphate Antiwear (D7412), Sulphation (D7415), Oxidation in transmission oils (D7214)

§ Proposed methods (WIP) – Acid Number, Base Number, Water Content

ASTM Lubricant Practices & Methods§ D7418-07 Standard Practice for Set-Up and Operation of Fourier Transform Infrared (FTIR)

Spectrometers for In-Service Oil Condition Monitoring.§ E2412-10 Standard Practice for Condition Monitoring of in-service Lubricants by Trend Analysis

Using Fourier Transform Infrared (FT-IR) Spectrometry.§ D7214-07a Standard Test Method for Determination of the Oxidation of Used Lubricants by FT-IR

Using Peak Area Increase Calculation. § D7414-09 Standard Test Method for Condition Monitoring of Oxidation in In-Service Petroleum

and Hydrocarbon Based Lubricants by Trend Analysis Using Fourier Transform Infrared (FT-IR) Spectrometry.

§ D7412-09 Standard Test Method for Condition Monitoring of Phosphate Antiwear Additives in In-Service Petroleum and Hydrocarbon Based Lubricants by Trend Analysis Using Fourier Transform Infrared (FT-IR) Spectrometry.

§ D7415-09 Standard Test Method for Condition Monitoring of Sulfate By-Products in In-Service Petroleum and Hydrocarbon Based Lubricants by Trend Analysis Using Fourier Transform Infrared (FT-IR) Spectrometry.

§ D7624-10 Standard Test Method for Condition Monitoring of Nitration in In-Service Petroleum and Hydrocarbon Based Lubricants by Trend Analysis Using Fourier Transform Infrared (FT-IR) Spectrometry.

Field vs. Lab testing§ Lab testing:

§ Lab testing can offer increased number of alternative tests on oil samples (e.g XRF)

§ Expert advice may be offered on analysis§ Time taken to ship samples from remote locations can be long§ Ongoing cost per sample sent

§ Field Testing:§ Immediate results available so action can be taken fast, before major

problems arise§ No/Low ongoing costs after initial capital outlay§ Some user intelligence required to set up parameters for alarm warning

levels etc§ Subset of full lab tests available

Non ASTM compliant field instruments

Lab instruments unsuitable for the field

Parker Kittiwake FTIR3 Oil AnalyserASTM Compliant, field deployable, all in a small, portable instrument

§ Simple to use§ Software pre-loaded onto Netbook§ Multiple equipment records§ Trending of multiple parameters§ Multiple users

Multiple equipment types

Results Screen – Spectral Mode

Historical data records on equipment

Time trending of parameters

What will the FTIR3 Measure§ Sulphation – TO ASTM D7415-09§ Oxidation – To ASTM D7414-09§ Nitration – To ASTM D7624-10§ Phosphate Antiwear – To ASTM D7412-09§ E2412:

• Soot Water • Diesel• Fuel Contamination• Ethyl Glycol Coolant• Antioxidant depletion

§ Future published ASTM methods can be readily added to the instrument.

§ Customer specific methods can be developed and also added to the instrument.

Advantages and Limitations§ Advantages of FTIR spectroscopy in oil analysis:

§ Rapid analysis with no extensive sample preparation§ Can give information on multiple parameters simultaneously§ Provides quantitative and qualitative data§ Accurate and repeatable results

§ Limitations of FTIR spectroscopy in oil analysis:

§ Different base oils and additives can interfere with the measurement of different parameters

§ For spectral subtraction, sometimes it can be difficult to find a suitable reference oil

§ Difficulty measuring some components that are less than 0.1% w/w§ No elemental analysis

In Summary….§ FTIR provides a quick and accurate test method to measure multiple parameters

on in service oils§ Advances in recent years have allowed reduced size, field deployable devices to

be developed§ ASTM ratification of test Methods is an ongoing process, providing end users with

confidence in reliable and repeatable measurement techniques and results§ More ASTM agreed methods are on the way for additional parameters§ Field deployable, ASTM compliant devices are now available

Any questions?