handling difficult samples in karl fischer analysis

Handling Difficult Samples in Karl Fischer Analysis

Background

• Analysis of moisture is becoming increasingly important to many different industries

• Many of these reasons require not only a precise, but also accurate reading

• For years, most moisture analyses have been conducted on a semi-quantitative or even qualitative level

Questions about how much water? Karl Fischer analysis is the answer.• Karl Fischer (KF) titrations have been the gold standard for water

analysis since 1935

• The KF titration provides a reliable and robust way to directly analyze for water in a sample

• Many other techniques exist for indirect analysis of water in a sample, but KF titration is the best way to calibrate this other methodology

• KF is rapid, well characterized, and the recognized standard for water analysis in many solids, liquids and semi-solids

CH3OH + SO2 + RN → (RNH)SO3CH3 H2O + I2 + (RNH)SO3CH3 + 2 RN → (RNH)SO4CH3 + 2 (RNH)I

Measurement range

% range ppm range

Volumetric KF titration Coulometric KF titration

Volumetric KF titration

Direct addition of reagents by burette to

sample in methanol

Typical volumetric KF titrator

Coulometric KF titration

In situ generation of iodine by electrical means

Typical coulometric KF titrator

Most KF systems I see can only handle one sample at a time!

Coulometric KF

Volumetric KF

Karl Fischer reaction

CH3OH + SO2 + RN (RNH)SO3CH3 H2O + I2 + (RNH)SO3CH3 + 2 RN (RNH)SO4CH3 + 2 (RNH)I

Hydroxide, Carbonate

Reducing agent

Oxidant

Silanol

Acid Acid / Base

Ketone / Aldehyde Aldehyde

Side reactions

• Acids

• Bases

• Aldehydes and ketones

• Carbonates, hydroxydes and oxides

• Silanol / Siloxane

• Strong reducing agents

• Strong oxidizing agents

KF titration curve

Fast release of waterSlow release of water

~130 s ~290 s

How do we mitigate side reactions, poor water release and gaseous samples?

• Adjust pH with buffers• Use specialized reagents for

aldehydes and ketones• Use different sample preparation

What if my sample comes in a container that looks like this?

KF Gas Analyzer

• For determining water in:

• Propane• Propene• LPG• LNG• Butane• Butene• Butadiene• Dimethyl ether• Ethylene oxide• Methylene chloride• Ethylene chloride• Vinyl chloride• Chlorofluorocarbons

• Analyzes gases and liquefied gases from sample cylinders!

Mass Flow ↙ Controller

← Oil Filter

Heater →

Precision← ControlValve

↙ Coulometer

Sample Inlet→

Nitrogen Inlet→

KF Gas Analyzer

Reproducibility

Results of 360 measurements of LPG (3 g per measurement) within 84 h, mean value: 26,5 µg/g ± 0,8 µg/g

y = -0,005x + 27,389

0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350

number of measurements

wat

er c

on

ten

t [µ

g/g

]

80°C / constant sample flow

50°C / constantsample flow

50°C / fluctuating sample flow

What if my sample is solid or liquid and needs a lot of preparation?

Gas extraction

1. Samples soluble in KF reagent

2. Samples that release water in KF compatible solubility promoters

direct titration gas extraction

1. Samples that are not soluble in KF reagent

2. Samples that cause side reactions

liquid extraction

1. Samples that release water in organic liquids

Principle of the Metrohm oven technique

Dry carrier gas is used to

transport evaporated humidity

into titration vessel

Universal to nearly all samples

Principle of the Metrohm oven technique

Metrohm developed the orginal

headspace analysis for Karl Fischer

titration

Advantages of using a KF Oven

• Nearly all KF analyses can utilize oven• Very economical

• Much smaller reagent use• Much more effective use of time

• Efficient• Automation to handle many samples without human

interaction• No need to clean vessel after just a few analyses

• Wide variety of applications• Nearly all KF samples can be adapted to oven

technique

Gas extraction (oven method)

• Step 1: (use empty vial)

- Heat up KF oven

- Start gas flow

- Titrate cell to dryness

• Step 2: (use empty vial)

- Determine blank value

• Step 3:

- Put sample vial into the oven

- Heat up sample and transfer released water with carrier

gas to KF cell

Gas extraction (oven method)

Sample: Motor oil

• Oven, 160°C, N2

Content: ~ 390 ppm

• Direct measurement

Content: ~ 960 ppmlong determination time

curve with side reaction

Headspace KF analysis

• Wonderful technique for most sample types• Until recently, Metrohm sample changers would

only accommodate a 6 mL headspace vial• Now Metrohm can adapt our 874 USB KF Oven

Sample Processor to fit many of the most common vials

How do you adapt a sample to KF Ovens?• Choose a temperature

• Classic method• Multiple samples with different temperatures• Choose best temperature for most stable and

reproducible moisture evolution• Optimize for speed

• Gradient Method• One sample over a range of temperatures

• Choose a carrier gas• Choose air, nitrogen or argon depending on the

thermal stability and combustibility of the sample

Example data: method development Classic method of temperature determination

• Steroidal compoundTemp. Air

sourceExtraction

TimeWater

ContentDecompositi

on?1 150 Air 300 0.04% Yes2 160 Air 300 4.44% Yes3 170 Air 300 6.60% Yes4 200 Air 300 6.91% Yes5 150 N2 300 0.14% Yes6 155 N2 300 0.98% Yes7 135 N2 1800 0.04% No8 140 N2 900 0.06% No

Temperature gradient

• What oven temperature is optimal for an unknown

sample?

• Find the ideal temperature running a temperature

gradient with the KF OVen

• Looking for a temperature that will accelerate

water extraction but not pyrolyze the sample • Pyrolysis or combustion leads to erroneously high results

Example data from temperature gradient analysis

• Sample of mixed sugars and buffers• Lyophilized Sample• Ran 50 – 180ºC in 30 minutes

Example data from temperature gradient analysis

• Chose temperature of 95 degrees• Analysis was slightly more than 7

minutes• This only took 1 gradient sample and one

sample to confirm• Without gradient, this takes up to 7

samples

Example data: method development Gas determination

• Steroidal compound

Air carrier gas at high temperatureEvidence of decomposition

Nitrogen carrier gas at low temperatureStable extraction

Headspace Karl Fischer moisture analysis in your vial • The 874 uses Metrohm’s

exclusive KF Oven technology for unsurpassed moisture results

• The 874 is perfect for your lyophilized samples because Metrohm USA will customize the 874 to fit your sample vial!

• Because only water vapor is analyzed, reagent costs are greatly reduced

• Holds up to 36 samples depending on rack configuration

Metrohm NIRSystemsPositive vibration

Reagent-free Moisture Analysis

Dr. Hari Narayanan Product Manager NIRS

Metrohm USA

Techniques for moisture analysis

Metrohm expands its portfolio to include Near Infrared Spectroscopy!

<<Green Chemistry>>

Designed by FOSSPowered by Metrohm

Techniques for moisture analysis

Why NIR for moisture analysis

• Requires no sample preparation• Non-destructive• Fast, accurate and precise• Multi component analysis• No solvent procurement or disposal• Low-cost analysis• Easy to use and maintain• Remote sampling via fiber optics

Secondary technique: requires primary method for calibration development

• Stretching

• Bending

symmetrical asymmetrical

scissoring rocking wagging twisting

NIR Spectroscopy

• 780nm to 2500nm• Overtones and Combination Bands

• Based on absorption in the Near Infrared region of the spectrum

• It provides both chemical and physical information

• Primarily sensitive to organic compounds

• O-H, C-H, N-H bonds absorb strongly in NIR

NIR spectroscopy

NIR spectrum

Combination

1st Overtone

2nd Overtone

3rd Overtone

NIR spectrum of water

Transmission spectrum of waterPathlength ~ 3 mm

Sampling in NIR

Samples Types

Reflectance: Solids, Granules, Powders…Trans-Reflectance: Pastes, Syrups…Transmission: Liquids, Films, Oils…Diffuse Transmission: Tablets, Softgels…

Analysis Types• Identification• Qualification• Quantification• Trend analysis – Determination of

Change• Process monitoring and Control

Identification & Qualification

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

1100 1300 1500 1700 1900 2100 2300 2500

Wavelength (nm)

Ab

so

rba

nc

e (

Lo

g 1

/R)

anhydrous lactose

lactose monohydrate

Water Bands

Run Samples

as Standards

in NIR

Analyze Samples

by Primary Method

Calibration and

Validation

Routine Analysis by NIR

Right Sampling ModuleSample

Presentation

Collection Paramete

r

Accuracy of Primary

method influences

NIR Method

Chemometric

Software

Method Maintena

nce

Quantitative Moisture analysis

Instrumentation Pre-dispersive

Post-Dispersive: Scanning and PDA

XDS Monochromator

Hot-swappable modules

Metrohm NIRSystems Family

Lab

NIRS XDSAnalyzer

NIRS XDS RapidCont

ent Analyzer (RCA)

NIRS XDS

RapidContent

Analyzer – Solids

NIRS XDS MultiVialAnalyzer

NIRS XDS

MasterLab

Analyzer

NIRS XDS SmartProb

eAnalyzer

NIRS XDS

Interactance

OptiProbe Analyzer

NIRS XDS Transmissio

nOptiPr

obe Analyz

er

NIRS XDS RapidLiquid Analyzer

(RLA)

NIRS DS2500Analyzer

Process

NIRS Analyzer PRO

NIRS Analyzer PRODirectLight/NonContact

NIRS Analyzer PROContactReflection

NIRS Analyzer PROFiberSystem

NIRS XDS Process Analyzer

NIRS XDS Process

Analyzer – SingleFiber SinglePoint

NIRS XDS Process

Analyzer – SingleFibe

r 4 Channels

NIRS XDS

Process Analyz

er – SingleFiber 9 Channe

ls

NIRS XDS Process

Analyzer – Microbundle SinglePoint

NIRS XDS Process

Analyzer – Microbund

le 4 Channels

NIRS XDS

Process Analyz

er – Microbundle 9 Channe

ls

NIRS XDS Process

Analyzer – DirectLight/NonContact

NIR Applications

• Pharmaceuticals• Chemicals• Petrochemicals• Polymers• Paper and Pulp• Textiles• Cosmetics• And more…

Moisture in polymer pellets

The water content of expandable polystyrene is determined according to Karl Fischer

The sample is first dissolved in p-xylene to extract the water

Then methanol is added to precipitate the sample

The water is determined in the supernatant solution by coulometric titration

Moisture in polymer pellets

NIRS DS2500 Analyzer: Sample Rotation

Moisture in polymer pellets

Moisture in polymer pellets

• MLR• R2 = 0.9988 • SEC = 0.5413

Lab Moisture %

NIR

Pre

dict

ed M

oist

ure

% NIR Advantage

• Speed and Simplicity• Reduce laboratory analysis • Provide increased process

performance • Quality assurance monitoring

Moisture in solvent and recovery streams

NIRS XDS RapidLiquid Analyzer

Moisture in solvent mixture

Moisture in solvent mixture

PLS: Factor 3 Correlation: 0.9998SEC: 0.1939

• Save Time & Money• NIR can be off-line, at-

line, or on-line

• NIR can measure Solvent components and moisture in single run

Inline Process NIRgranulator drying analysis

• Single-pot granulator dryer

• Probe in contact with powder

• Provides real-time process analysis and control

Granulator drying analysis

• Blend of lactose and starch granulated with 1.5% water and 8% methanol

• Granulation was dried with heat and vacuum

• NIR probe monitored drying in-process• NIR prediction models developed for water

and methanol

NIRS XDS Process Analyzer

Granulator drying spectra

1800 1850 1900 1950 2000-0.020

-0.016

-0.012

-0.008

-0.004

0.000

0.004

0.008

0.012

Granulator drying moisture analysis

Four factor PLS from 1800-2084nm R2= 0.99; SEC=0.022; SECV=0.024

Granulator drying moisture trend

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

5:16:48 5:24:00 5:31:12 5:38:24 5:45:36 5:52:48 6:00:00 6:07:12 6:14:24 6:21:36

Moi

stur

e %

Time

Blend #4 Moisture % vs Time

Granulator drying methanol analysis

Four factor PLS :1800-2084nm; R2=0.99; SEC=0.184; SECV=0.193

Granulator drying methanol trend

0

1

2

3

4

5

6

7

8

9

5:16:48 5:24:00 5:31:12 5:38:24 5:45:36 5:52:48 6:00:00 6:07:12

MeO

H %

Time

Blend # 4 MeOH % vs Time

Moisture analysis in a fluid bed dryer

Sampling

• Fluid bed dryer charged with lactose and MCC

• Spectra collected every 50 seconds

• LOD sample taken every 5 minutes

View of spoon probe

Spectra of dryer samples

Prediction model

2 Factors PLS1100 nm – 1650 nm,SEC = 0.7358 %, R2 = 0.9519.

Validation Example

SEP = 0.204 %

Trend chart of fluid bed

0 5 10 15 20 25 30 35 40 450

2

4

6

8

10

12

Time minutes

Moi

stur

e %

Moisture in lyophilized material

KFCalibrationValidation

NIRRoutine Samples

NIR instrumentation

• NIRS XDS Rapid Content Analyzer• Scan range

400–2500 nm• 32 scans/spectrum

Experimental design

• Lyophilized product• Contained in ~ 30 mL serum vials• Average cake weight is 1.6 g• Acceptable moisture limit is NMT 2 %

• Calibration sample set• 46 samples used to prepare training and test sets

• Near-IR analysis• Spectra of calibration samples collected in triplicate

• Primary analyses• Regression equations developed using data from

volumetric Karl Fischer titration

Raw NIR absorbance spectra

Calibration for low residual moisture

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

NIR

Pre

dict

ed (

% m

oist

ure)

Karl Fischer (% moisture)

NIR Predicted % Moisture = 0.806 - 19.411 A"

A"1844 nm

2124 nm

SEP = 0.119 R = 0.992

Comparison of NIR and LOD methods

LOD values were, on average, lower than NIR results by 0.20 ± 0.17 % H2O.

Conclusion

• NIR is well suited for analysis of residual moisture in lyophilized products

• Samples can be easily altered to provide calibration sets with varying amounts of moisture

• Regression equations should be optimized for the specific moisture range of interest

• The speed of the technique allows large sample sets to be analyzed, enabling NIR to be used either as a diagnostic or inspection tool

• Combined KF Thermoprep with NIR allows the quick calibration and validation

Summary• Combined Titration and NIR

• Calibration and Validation• Routine application

• Accuracy and calibration stability• Methods from lab to process • Flexible and customized sampling accessories• Rugged instrumentation• Continual technical and application support

Thank You