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 #6 #9 #7 #8 #3 #2 #1 #5 #4 Before After Peak Peak Peak Before After No. Width Width Area Area Type Normal #1 0.014 0.102 288 6213 TBB #2 0.020 0.111 559 2922 TBB #3 0.022 738 BB #4 0.026 0.024 585 227 BV #5 0.025 267 VB #1 #6 0.029 0.030 1231 543 BB #2 #7 0.035 0.036 1010 396 BB #8 0.030 1041 BV #6 #7 #9 #4 #9 0.031 0.031 1195 478 BB Problem FID Problem #2 #1 #9 #2 #5 #7 #4 #3 #8 #6 Before After Peak Peak Peak Before After No. Width Width Area Area Type Normal #1 0.014 0.031 288 259 BB #2 0.020 0.020 559 503 BB #3 0.022 0.022 738 664 BB #4 0.026 0.026 585 526 BV #5 0.025 0.024 267 240 VB #6 0.029 0.028 1231 1170 BB #9 #6 #7 #1 #8 #5 #2 #4 #3 #7 0.035 0.034 1010 909 BB #8 0.030 0.030 1041 936 BV #9 0.031 0.030 1195 1075 BB Problem Agilent 7890 FID Jets Adaptable FID Jets Jet Type Part# Jet Tip ID 0.29 mm Capillary 19244-80560 0.011 in. 0.47 mm Packed 18710-20119 0.018 in. 0.79 mm Paced Wide Bore 18789-80070 0.030 in. 0.47 mm High Temp G1531-80620 0.018 in. Capillary-Optimized FID Jets Jet Type Part# Jet Tip ID 0.29 mm Capillary G1531-80560 0.011 in. 0.47 mm High Temp G1531-80620 0.018 in. Agilent 7890 FID Setup – Column Installation General Rule: Push to tip of Jet then withdraw 1 mm. Capillary Optimized FID Adaptable FID 0 mm 0 mm 10 10 20 20 30 48mm 30 40 68mm 40 1mm 50 50 60 70 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. Yes Still No Noisy? Check/Clean/Replace: Check/Clean/Replace: •Interconnect/collector connection. •Filters, traps, gases. •Collector and insulators. •FID jet. •Detector interconnect. •Column and connections. •Detector board. •Inlet and consumables. 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? Agilent 7890 Thermal Conductivity Detector 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 Thermal Conductivity Basics The TCD is a nondestructive, When the carrier gas is contaminated concentration sensing detector. by sample , the cooling effect of A heated filament is cooled by the gas changes. The difference in the flow of carrier gas . cooling is used to generate the detector signal. Flow Flow The TCD will respond to any substance different from the carrier gas as long as its concentration is sufficiently high enough. 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. TCD Normal Flow Ratio 20 mL/min Filament Col + MUG Filament 30 mL/min Reference + Sample Reference Reading 10 mL/min Ref Reading 20 mL/min Reference 20 mL/min Col + MUG 30 mL/min 30 mL/min Reference 20 mL/min 20 mL/min Reference Column + MUG Column + MUG Signal (+ polarity) = Sample - Reference TCD Problem #1 #6 #3 #8 #2 #9 #7 #4 #5 #1 Before After Peak Peak Peak Before After No. Width Width Area Area Type Normal #1 0.030 0.028 1920 1643 BB #2 0.033 0.031 4279 3215 BB #3 0.028 0.027 4503 3803 BB #4 0.033 0.031 3380 3043 BV #5 VB 0.026 0.023 2109 1810 #8 #3 #6 #6 0.038 0.036 7233 6528 BB #2 #9 #7 #7 0.044 0.040 4386 3551 BV #4 #5 #1 #8 0.046 0.043 6898 6124 VB #9 0.050 0.049 6817 6252 BB Problem Choosing Reference Flow Rate Ratioof Ref flow to Column MUG + 3.5 3 2.5 2 1.5 1 0.5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 Column + Makeup flow (mL/min) Column + MUG Flow = 10 mL/min Ref flow = 2.3 X 10 = 23 mL/min Agilent 7890 TCD EPC Flow Diagram Agilent 7890 TCD EPC Module Reference Gas Line Switching Valve Make Up Gas Line Agilent 7890 TCD Filament Drive – ΔT Sensor 500 D T 50C 400 Response Filament 300 Temp C 200 DT135C 100 100 200 300 400 100 200 300 400 Detector Temp (body temp) C Detector response versus detector temperature. Filament Temperature versus Block Temperature. 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 Benchtop GC 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. 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.