troubleshooting tips & tricks for your gc analyzer & … · troubleshooting tips &...

74
Troubleshooting Tips & Tricks for your GC Analyzer & CFT Application 7890 Detectors October 29, 2014 1

Upload: votuong

Post on 26-Aug-2018

265 views

Category:

Documents


0 download

TRANSCRIPT

Troubleshooting Tips & Tricks for your GC Analyzer & CFT Application

7890 Detectors

October 29, 2014

1

Detector Types

Flame Ionization Detector (FID)

Thermal Conductivity Detector (TCD)

Electron Capture Detector (µECD)

Nitrogen-Phosphorous Detector (NPD)

Flame Photometric Detector (FPD)

Photo Ionization Detector (PID)

Electrolytic Conductivity Detector (ELCD)

Infrared Detector (IRD)

Mass Selective Detector (MSD) Items in red covered in this course

Agilent 7890 FID Theory of Operation

H2 – Air Flame Sample is burned in flame. Charged Ions produced. Ions attracted to collector. Collector current converted to output via Electrometer.

FID Problem #1 N

orm

al

#9#8#7#6

#5#4

#3#2#1

Prob

lem #9#7#6#4

#2#1

TBB

TBB

BB

BV

VB

BB

BB

BV

BB

#1

#2

#3

#4

#5

#6

#7

#8

#9

0.014

0.020

0.022

0.026

0.025

0.029

0.035

0.030

0.031

288

559

738

585

267

1231

1010

1041

1195

0.102

0.111

0.024

0.030

0.036

0.031

6213

2922

227

543

396

478

TypePeakNo.

BeforeArea

BeforePeakWidth

AfterPeakWidth

AfterArea

FID Problem #2

BB#1 0.014 2880.031 259

BB#2 0.020 5590.020 503

BB#3 0.022 7380.022 664

BV#4 0.026 5850.026 526

VB#5 0.025 2670.024 240

BB#6 0.029 12310.028 1170

BB#7 0.035 10100.034 909

BV#8 0.030 10410.030 936

BB#9 0.031 11950.030 1075

TypePeakNo.

BeforeArea

BeforePeakWidth

AfterPeak Width

AfterArea

#9#8#7#6#5#4#3#2#1

Nor

mal

#9#8#7#6#5#4#3#2#1

Prob

lem

Agilent 7890 FID Jets

Capillary-Optimized FID Jets Jet Type Part# Jet Tip ID

Capillary G1531-80560 0.29 mm 0.011 in.

High Temp G1531-80620 0.47 mm 0.018 in.

Adaptable FID Jets Jet Type Part# Jet Tip ID

Capillary 19244-80560 0.29 mm 0.011 in.

Packed 18710-20119 0.47 mm 0.018 in.

Paced Wide Bore 18789-80070 0.79 mm 0.030 in.

High Temp G1531-80620 0.47 mm 0.018 in.

Agilent 7890 FID Setup – Column Installation

mm

010

2030

4050

mm

010

2030

4050

6070

48mm68mm 1mm

General Rule: Push to tip of Jet then withdraw 1 mm.

Capillary Optimized FID

Adaptable FID

Exploded Parts View of the FID

Agilent 7890 FID EPC Flow Module

FID EPC Module

Agilent 7890 Flame Ionization Detector

Typical Problems

• Flame blowing out or not lighting

• Spiking

• Low Sensitivity

• Noise

• Drift

Solving FID Lighting Problems

Check detector parameter settings (keyboard). • Flows • Flame on • Detector on • Lit offset

Check jet. Check igniter. Check column connections. Check gas supply pressures. Check solvent and injection size.

Solving FID Noise Problems Turn off

H2 and Air.

StillNoisy?

Check/Clean/Replace:•Filters, traps, gases.•FID jet.•Column and connections.•Inlet and consumables.

Check/Clean/Replace:•Interconnect/collector connection.•Collector and insulators.•Detector interconnect.•Detector board.

NoYes

Electrical Problem. Contamination Problem.

Routine FID Maintenance Monitor the background signal. Check pressures/flows. Clean or replace the jet. Inspect the igniter assembly. Clean the collector assembly. Remove, trim and reinstall column.

Agilent 7890 Flame Lighting Problems

Check the following:

Measure flows.

Clean/replace jet.

Are column and fittings tight?

Do we have supply gases?

Is detector on?

Thermal Conductivity Values of Common Gases/Solvents

Compound Relative Thermal Conductivity

Carbon Tetrachloride 0.05

Benzene 0.11

Hexane 0.12

Argon 0.12

Methanol 0.13

Nitrogen 0.17

Helium 1.00

Hydrogen 1.28

Thermal Conductivity Relative to Helium

Agilent 7890 Thermal Conductivity Detector

Thermal Conductivity Basics When the carrier gas is contaminated by sample , the cooling effect of the gas changes. The difference in cooling is used to generate the detector signal.

The TCD is a nondestructive, concentration sensing detector. A heated filament is cooled by the flow of carrier gas .

The TCD will respond to any substance different from the carrier gas as long as its concentration is sufficiently high enough.

Flow

Flow

Agilent 7890 TCD 5 Hertz Pneumatic Switching

COLUMN flow enters the center of three ports. REFERENCE flow is directed to either one of the outside ports into the detector cell. The port entered is determined by the SWITCHING SOLENOID. AUXILIARY, or makeup, flow passes along the outside of the column and merges with the column flow prior to entering the detector’s center port.

Signal (+ polarity) = Sample - Reference

20 mL/min Column + MUG

30 mL/min Reference

Filament

Filament

30 mL/min Reference 20 mL/min

Column + MUG

20 mL/min Reference

20 mL/min Col + MUG + 10 mL/min Ref

20 mL/min Col + MUG

30 mL/min Reference Reference

Reading Sample Reading

TCD Normal Flow Ratio

TCD Problem #1

BB #1 0.030 1920 0.028 1643 BB #2 0.033 4279 0.031 3215 BB #3 0.028 4503 0.027 3803 BV #4 0.033 3380 0.031 3043 VB #5 0.026 2109 0.023 1810 BB #6 0.038 7233 0.036 6528 BV #7 0.044 4386 0.040 3551 VB #8 0.046 6898 0.043 6124 BB #9 0.050 6817 0.049 6252

Type Peak No.

Before Area

Before Peak Width

After Peak Width

After Area

#9 #8

#7

#6

#5

#4

#3

#2

#1

Nor

mal

#9 #8

#7

#6

#5

#4

#3

#2

#1

Prob

lem

Choosing Reference Flow Rate

Column + MUG Flow = 10 mL/min Ref flow = 2.3 X 10 = 23 mL/min

Column + Makeup flow (mL/min)

Ratio of R

ef flow to C

olumn + M

UG

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 0.5

1

1.5

2

2.5

3

3.5

Agilent 7890 TCD EPC Flow Diagram

Agilent 7890 TCD EPC Module

Switching Valve

Make Up Gas Line

Reference Gas Line

Agilent 7890 TCD Filament Drive – ΔT Sensor

Filament Temp C

Detector Temp (body temp) C

500

400

300

200

100

Response

100 200 300 400

D T 50C

D T135C

Detector response versus detector temperature. Filament Temperature versus Block Temperature.

100 200 300 400

TCD Typical Problems Drifting or wandering baseline • Normal in temperature programmed analysis • Check heaters/sensors. • Remove contamination by thermal cleaning the detector.

Low sensitivity • Check gas flows. • Check column installation. • Contamination – thermal clean the detector.

Elevated background signal or increased noise level • Contamination – thermal clean

Conditions that prevent the detector from operating • Temperature set below 100°C • Broken or shorted filament • Reference gas flow set to 0

Valves

What are Valves?

Valves are mechanical devices used to switch gas streams.

They are the pneumatic equivalent to the electrical switch.

4 Port LSV with Internal Sample Volume

Gas Tight Syringe versus Gas Valve Injection

Typical values for valve injection reproducibility is <0.5% RSD.

Typical values for manual gas tight syringe injection reproducibility is <5.0% RSD.

Multiple valves can be filled in series with a gas sample.

Manual syringe can only fill 1 injector port.

Note for small sample volumes (<2mL) can only use gas tight syringe.

Injection with Gas Sampling Valves

Loop of known volume switched into carrier gas stream.

Factors that affect the amount of sample transferred onto the column:

• PV=nRT

- Temp = temperature of valve box - R = ideal gas constant - V= volume of sample loop

Pressure is proportional to the amount of mole of gas within sample loop.

How Are Gas Samples Injected?

Gas sampling valves are the most common way of sampling a gas and are used in almost all cases on bench top GC’s.

Almost all gas sampling valves installed on GC’s are produced by VICI™. Spare valve parts can be ordered directly from VICI if required.

www.vici.com

Gas tight syringes can also be used for injection but they are not as reproducible and are more cumbersome.

In This Section, We Will Discuss: Valve rotor replacement

Problems associated with valve GCs

Dealing with water vapor

Backflushing

Reconditioning mol sieve columns

Nafion driers

Genie membrane filter

Trace sulfur gases

SCD potential problems

Other problem compounds

Gas Sample Valves

Liquid Sample Valves

Valve Timing

Valve Rotor Replacement

Number of ports ID letter toward 3 Port 2 4 Port 3 6 Port 4 8 Port 5 10 Port 6

Problems Associated with Valve GC’s

-Moisture is far more important when you are using columns who performance will drop dramatically with moisture absorption.

-Many valved GC’s will have at least 1 x Molecular Sieve column installed so water handling is very important.

-The system should be designed to restrict moisture from reaching these columns from the sample (there are rare exceptions to this).

-Carrier gas is typically at volume of at least 1000 times that of the sample throughout the period of day so it’s dryness is absolutely critical (indicating moisture filters must be used).

- In many cases the sample is not visible before it is connected to the GC so contamination of GSV lines with liquid or metal particles (especially the later) can cause immediate damage.

-Use an inline filter wherever possible to minimize sample impact to system.

Dealing with Water Vapor

Water can be chromatographed and analyzed but this is not recommended. • Problems with preparation of accurate standards

• Poor peak shape

• Memory effects

• On non polar columns it appears as very broad peak which can interfere

with other components (RT can shift dramatically too) It is possible to analyze on polar columns.

Benchtop GC

Dealing with Water Vapor (cont.)

PROBLEMS

If sample gas stream is saturated with moisture then condensation can occur on cold internal tubing surfaces and cause loss of analytes and other more serious problems. Absorbed onto Molecular Sieve columns deactivating them, thus less retention and separation of components. Absorbed onto Alumina columns with resulting shifting in RT’s.

Backflushing

In many cases it is possible to backflush water from the sample to Vent.

This option is available on either the Micro GC or Bench top GC unit.

Backflushing of water is only possible if analytical compound elutes before C3, as water will typically elute between C2 and C3 on most columns.

CP-Sil 5 C

B

µ-TCD µ-TCD µ-TCD µ-TCD

injector

Sample in

Backflush Micro GC

Backflushing - Bench Top Unit

0.5m Hayesep N columns used for backflush of water.

Loss of Resolution Due to H2O Absorption

Reconditioning Molecular Sieve Columns Molecular Sieve columns can be reconditioned. • Bench top GC

- heat Molecular Sieve column to 300°C for a minimum of 4 hours.

• Micro GC - heat 180°C, pressure 45psi O/N minimum

NOTE: • Remove any other columns from GC oven not suited to temperature, replace

with empty ss column.

• Must turn off TCD filaments and ensure carrier gas is dry during reconditioning.

Removing Water Vapor

There are many ways to remove moisture from your samples prior to analysis.

Condensing - run sample through cooler with collecting coil.

Desiccants - may alter conc. of other analytes)

Nafion Dryer - a good solution but can result in the loss of some amount of some polar analytes such as methanol.

Nafion Dryers

• Wet feed gas in

• Dry purge gas, typically at min of 10x sample flow in opposite direction

• Dry feed gas to analyzer http://www.permapure.com/

Nafion Dryers

• Nafion is a special extremely hydroscopic membrane type material.

• Allows easy removal of moisture with little if any alternation to sample.

• Highly recommended for Micro GC applications.

• Also useful for bench top.

Genie Membrane Filter • Protects the analyzer from damage and contamination

• Fully inert membrane technology

• Proven and widely accepted filtering technique

• Removes liquids from gas samples

• Removes particles from gas samples

• No interference with sample composition

• Compliant for BTU calorific value applications

• Suitable for PPB, PPM and percentage level analysis

• Standard Swagelok™ connections

• High and low flow membranes

• Stainless Steel, Polypropylene and Kynar housing

• Standard Viton housing seal

Genie Model 170

Removes droplets – only required for µGC

Moisture from Sample or Carrier Gas

Remember moisture from carrier gas is far more susceptible to cause problems with columns and BF will not remove. On a Micro GC, typical column flow 2mL/min. Typical sample Introduction volume is 200nL. If you inject one sample every 5 min(s) total sample volume introduced, 2400nL. In 1 hour you have 120 mL of carrier gas through your column, so the moisture content of your carrier gas is 50,000 times more important than your sample gas. Always use a carrier gas filter with certain types of packed columns.

Trace Sulfur Gases Low level sulfur analysis requires the following: •Inert surfaces at every point.

•Accurate standard(s) • Shelf lifetime is limited due to reactivity of sulfur components (consider Dynacalibrators).

•Agilent uses Hastelloy C Valves with all sample path material including the detector in Ultimetal.

•Use the most inert stationary phase where possible, CP-Sil5CB.

Trace Sulfur Gases

•H2S, SO2, COS are the most reactive components, with CH3SH, EtSH and on being increasingly less reactive.

•RSD’s for reproducibility typically 3-5% for H2S, SO2 and COS, 5-10% for SO2 maybe 1-3% for other sulfur components.

Percent Level Sulfur Determination

High levels of sulfur species >0.1% should not be analyzed on a FPD due to linear range issues but instead on a TCD.

Use a small loop size to limit impact on corrosive sulfur species generated by reaction of sulfur components with moisture on filaments in TCD.

Dry sample stream if it contains appreciable amounts of moisture and sulfur species such as SO2, H2S, etc.

SCD Potential Problems

•High maintenance detector, vacuum pump, ozone generator etc.

•Ceramic tubes can easily become contaminated and need replacement.

• indication through loss of sensitivity,

• thick film methyl silicone columns can cause this if heated to higher temperatures

Other Problem Compounds

•Chlorine

•Ammonia, if not to be analyzed can be removed using an acid solution with a pH indicator present.

•Special columns designed for ammonia analysis. • Volamine or Chromosorb 103

•No ammonia analysis by µGC.

Sample Introduction Systems (Problems)

Bench Top

• Gas Sampling Valve • Liquid Sampling Valve • Injector Port

Micro GC

• Specific injection technique

Gas Sampling valves Valve cores are rated for different temperature ranges.

• Ambient - 175°C • 100-300°C • ambient to 225°C (valcon E)

Do not overheat or they will no longer function correctly!

Gas Sampling Valves-6 Port

Valves - WCGW

•Valve core damaged due to overheating. •Valve core scratched- gives leaks. • Use Inline filters to stop this occurring

•Valve core or channels blocked. •Loop blocked •Leaks at fittings although this is unlikely. •Always use correct Valco ferrules and nuts.

Replace valve core and body as one unit, carry a spare if at all possible.

Valves- WCGW

Actuators may not turn • Insufficient gas pressure or not on, require 60psi

Actuators may not be aligned correctly • incorrect removal from valve

Wrong angle actuator • check degree turn • Agilent actuators versus other actuators

Micro Electric Actuators

Liquid Sampling Valves

Fixed volume - internal groove -1µl

Liquid must be under pressure to remain in liquid phase.

Easily blocked - use filters to remove particles before the sample inlet.

Use apparatus as described (drawing) for ensuring liquefied gas remains in liquid state.

Sample Introduction Devices Gas (Refinery gas, Natural gas)

• Pressure • 1015 PSI for Natural gas • Up to 290 PSI for Refinery gas

Sample treatment

Controlled pressure reduction

Why • Max 45 PSI sample inlet pressure for bench GCs and max 15 PSI

for the 490 Micro-GC Controlled sample flush flow. • Constant sample pressure prior injection. • Pressure reduction cools down the sample.

• Cold spots • Retention outside the GC • Sample discrimination

GASIFIER

Sample Introduction Devices

Sample treatment

Liquid

Gas

1% gas in sample volume is 0.004% of composition

1% liquid in sample volume is 250% of composition

Liquefied gas (LPG) • Pressure • Temperature

Inject as Gas or as Liquid?

Preferably as a Liquid !

Sample treatment

Inject as a Liquid How ?

SAMPLE OUT TO VENT

SAMPLE IN

Carrier Gas HIGH GAS

PRESSURE IN

TESCOM REGULATOR

RESTRICTION

SAMPLE BUMB

PR

Pressure station

Sample Introduction Devices Liquefied gas (LPG)

• Pressure • Temperature

Sample Introduction Devices

Use fully filled bombs

C3=50.0 C4=50.0

Propane and Butane Mixture in a 1 liter bottle

C3=49.9 C4=50.1

100 ml gas

C3=49.3 C4=50.7

500 ml gas

C3=47.0 C4=53.0

800 ml gas

Else sample discrimination

What about Valve Timing? •Valve timing is either set at the factory if it is SP1 solution or setup in the field typically by an Agilent engineer. SP1’s have detailed manuals for setting up valve timing.

•Valve timing should not require adjustment and original settings should be recorded and kept with the instrument at all times.

•If new columns are purchased they either need to be preconditioned or conditioned on site prior to being set up within the instrument (typically 20C below max temperature for at least 4 hours).

Prior to Injection

Natural Gas Analyzer (SP1 7890-0042)

Natural Gas Analyzer (SP1 7890-0042) Injection

Natural Gas Analyzer (SP1 7890-0042) Elution of Hydrocarbons

Natural Gas Analyzer (SP1 7890-0042) Elution of Permanent Gasses

Typical NGA Chromatogram (SP1 7890-0042)

Page 67

Configuration: • 3-valve/4-column (packed column)/TCD Sample type: • Natural gas and similar gaseous mixtures

Natural Gas Analyzer (SP1 7890-0192) Configuration: • 3-valve/4-column (packed column)/TCD Sample type: • Natural gas and similar gaseous mixtures

SP2 Wasson Tiger Program

Operation Conditions and Catalyst Check

Typical operation temperature is 400°C with 20mL/min of H2 being added post column, pre catalyst

You can check Catalyst functionality by having a standard with known amounts of CH4, CO and CO2

Typically conversion efficiency is >70% so peak areas for the same concentration of CH4, CO and CO2 should be around the same size

Linearity of Methanizer

•DL is approx. 200 ppb using a 0.5 mL sample loop and linear to approx. 10%.

•Large loops (up to 2mL) will result in a lower DL limit but also a lower max. concentration.

•TCD and Methanizer / FID may be used in combination to detect sub ppm levels of these gases as well as high % levels.

Catalyst Poisoning and Practical Tips

•Very small amounts of H2S, SF6 and most other sulfur gases cause immediate and complete deactivation of the catalyst, Regeneration is not possible.

•It is uncertain as to whether large concentrations of O2 can have a negative impact on the catalyst. For this reason it is best to avoid sending large concentrations of O2 to the catalyst.

Catalyst Poisoning and Practical Tips

•Unsaturated hydrocarbons such as pure ethylene cause immediate, but partial, degradation of the catalyst as evidenced by slight tailing of CO and CO2 peaks.

•Any catalyst that is suspected of being poisoned should be replaced and no attempt made to regenerate the material.

Questions?

October 29, 2014

74