Troubleshooting Tips & Tricks for your GC Analyzer & … · Troubleshooting Tips & Tricks for your...
Transcript of Troubleshooting Tips & Tricks for your GC Analyzer & … · Troubleshooting Tips & Tricks for your...
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
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 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
What are Valves?
Valves are mechanical devices used to switch gas streams.
They are the pneumatic equivalent to the electrical switch.
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.
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!
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).
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
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.