Troubleshooting and Maintenance of Graphite Furnace AA Systems
Contents
1. Common AA Problems Reported by Customers Sensitivity Sensitivity is worse than it used to be have a new application and can t get the sensitivity need How come can t get the instrument to meet published detection limits Precision Sensitivity is acceptable but precision is terrible High noise Can get the right answers but very noisy signal this is also giving bad precision Accuracy Instrument does not give the right results Poor Sample Throughput The instrument throughput needs to improve Burner blocks too quickly Shooting Feb 2014 Agilent Technologies Causes of Poor Furnace AA Sensitivity Missed injection ervet Aged or damaged tube in use Wrong electrodes fitted Poor optimization esp drying conditions Workhead incorrectly aligned Optimization Optics setting using right wavelength slit No modifier or incorrect modifier used Use of nitrogen as inert gas No acid in solution Standard High blank level aa A Standards prepared amp stored correctly Samples prepared correctly digestion Agilent Technologies Causes of Poor Furnace AA Precision Missed injection Bubble formation in syringe ar Dirty dispensing capillary Using non Agilent graphite tubes Graphite components excessively worn poor electrical contact i Wrong dispensing height Optimization Poor optimization esp drying conditions Missing a cooldown step2. 0 04 0 02 0 00 1000 2000 3000 4000 5000 Number of Firings CCV Concentration ug L a ro o o o Agilent Technologies Agilent Furnace AA Systems Benefits Flexibility amp Superior Furnace Performance Competitor A e Highest furnace sensitivity 2 14 Best Zeeman correction capability lt 2 error at gt 2 Abs b ground e Polynomial interpolation of the background 1 pg L Se 20 pL e 100 120 readings Pd Modifier every second Agilent i M itivit e Best capability to handle pean difficult samples Agilent Technologies Tips to Improve Standard Preparation How are they prepared Ensure purchased standards are still within Use By date Use calibrated pipettes and class A volumetric flasks for dilutions Periodically check accuracy amp reproducibility of your pipettes Use de ionized water Type conductivity gt 18 M cm Lower grades may have contamination e Use serial dilutions for preparing low concentrations from 1 000 ppm stock Please don t do large dilutions gt 1 10 000 in 1 step What concentration are they e Low concentration standards have a finite life Prepare ppb ug L concentration standards daily from high conc stock Prepare low ppm mg L concentration standards weekly How are they stored e Plastic vessels ensure better stability e Stabilize with acid low pH ensures be
3. with the optimum ash and atomise temperatures displayed below The results are plotted on the aar Ash Atomise Measured SRM aj Method Temp C Temp C _Abeorbance SEE ee MiTo 2050 04178 n fat a Ce Gee ie o xc K Te ale le e o T h e 3 7 2180 04185 4 300 2150 0 0972 5 20 0 122 6 200 2100 fea z 2100 0 03 8 sm 2100 nos 3 a 2029 0224 w aw an 021 mo s 2100 0 2370 j2 s 2100 022 Optimun Temperature Ash 63 e Momie aa e Surtace Shape Elliptic Furnace AA System Tips Reducing Sensitivity May be required due to sensitivity of this technique e Switch to an alternate wavelength Select a less sensitive wavelength if available e Reduce sample volume e Use slower ramp rate to atomization Aim to broaden the peak during atomization e Use low gas flow during the atomization step s Agilent Technologies Furnace AA System Tips Factors Influencing Tube Lifetimes Graphite components excessively worn poor electrical contact No tube preconditioning or always using Tube Clean Sample matrix Inert gas used e Argon gives longest life e Nitrogen degrades tube faster due to oxygen presence Temperature program used eran Type of chemical modifiers used ae Joe e Powerful oxidizing agents degrade tube faster ae se Perchloric acid cevconantason 10 Perchlorates cov Absorbance 70 08 Sodium nitrate Q 8 P a v 8 Absorbance 0 06
4. GTA 120 or Agilent 240 280 Series AA Agilent Technologies Summary To Achieve Quality Data e Most instrument failures occur in the sample introduction area Includes e Burner e Spray chamber e Nebulizer All tubing e Drain Assembly Improper maintenance of this area can result in poor data quality e Frequently less experienced analysts can fail to recognize problems resulting in productivity losses e Establishing maintenance procedures can prevent problems Agilent Technologies
5. dure e Is the digest stable or are you seeing any precipitates or a suspension Do you see any potential contamination from either reagents or the digestion equipment e g especially with Si B or Ca Include a Reagent Blank with every sample batch to monitor Agilent Technologies Tips for Cleaning Dirty Optics Monitor the windows regularly Check lamp for fingerprints Check sample compartment windows for build up of film chemical residue Smudges or chemical residue reduces light and increases noise Cleaning the windows Wipe clean with an optical tissue as you would use to clean a camera lens cleaning end windows If necessary use optical tissue moistened with ethanol mom ol workhnea Agilent Technologies Furnace AA Rec Maintenance Schedule Daily e Check the gas delivery pressures amp cylinder contents e Check exhaust system e Check condition of the graphite tube replace as necessary When replacing the tube check the condition of the electrodes e Check dispensing capillary free and syringe e Top up rinse reservoir as required e Clean the workhead around the sample injection hole e Empty waste container Weekly e Check furnace workhead windows clean if necessary Agilent Technologies Overview Key Consumables for AA All instruments HC lamps AA standard solutions Flame AA systems Glass impact beads burner cleaning strips nebulizer comp
6. esp with platforms Gas purity ET E No acid or detergent in rinse memory effects amp sample No acid in solution preparation Incomplete digestion particles in solution Agilent Technologies Causes of High Noise in Furnace AA F rnace Dirty windows in workhead Wworkeag Use of platforms High background levels High absorbance signals EREE Wrong lamp operating current Workhead incorrectly aligned Poor optimization especially the HC lamp Dirty optics Gas purity Standard amp sample Incomplete digestion particles in solution preparation 5 Agilent Technologies Furnace AA System Tips o Y Check optimization each analysis Check monitor the dispensing height Ensure the rinse solution has 10 drops conc HNO 5 drops Triton X 100 Remove residue from the dispensing capillary Check monitor the graphite tube Check the blank reading Clean the workhead regularly Inspect condition of the graphite components Follow analytical recommendations in cookbook Don t Assume system is still optimized Assume dispensing height is the same Use a simple water rinse Start analysis with a dirty capillary tip Start analysis with a tube near the end of it s life Agilent Technologies Furnace AA System Tips Workhead Alignment lt Sa Furnace workhead e Workhead position must be optimized want light beam to pass through centre of graphite tube Align lamp first n
7. o workhead then place workhead in position and align Sample Dispenser settings e Carefully adjust injection depth easy with the furnace camera Light Beam Aligned Through Center of Graphite Tube Furnace AA System Tips Setting Injection Depth Correct dispensing Capillary tip must remain in contact with solution during dispensing Reduce dispensing height if sample spreads due to low surface tension Ensure there is no liquid on the outside of the capillary after dispensing Pipet tip too low Ensure there is no liquid inside the capillary tip after dispensing Pipet tip too high Sample should remain as a drop in the centre of the tube e Agilent Technologies Furnace AA System Tips Tube Conditioning Why condition the tubes before use e Helps remove residual contamination e Gently beds a new tube in Important when determining concentrations near detection limit Also important with some complex matrices e Critical when using modifiers Helps to build up coating inside the tube Improves efficiency of the modifier e Improves reproducibility GTA ETC 60 0N Fumace Video Close i Help Recommended process e Use Tube Condition facility or otherwise fire tube 5 10 times using either reagent blank or representative sample Agilent Technologies Furnace AA System Tips Method Parameters What to Check Furnace parameters e Set appro
8. onents capillary tubing burners etc lonization suppressant buffer solutions With the SIPS dilution system SIPS pump tubing and transfer tubing With an autosampler sample tubes racks probes and transfer tubing Graphite furnace AA systems Graphite tubes Sample vials dispensing capillary and syringe for autosampler Matrix modifiers Vapor generation AA systems Quartz atomization cells Peristaltic pump tubing Connecting tubing Shooting Feb 2014 Agilent Technologies 20 Agilent AA Consumable Kits Part Number 190034100 190065400 190067900 for GTA 120 or 190068000 for GTA 120 Zeeman 190025200 190025400 Description Flame AA operating supplies kit for Mark 7 atomization system SPS 3 Flame Autosampler cece supplies i Graphite Furnace AA operating supplies kits VGA 77 Vapor Generation ine operating supplies i SIPS Flame Dilution een operating supplies i Content Nebulizer venturi capillary kit nebulizer block excl integral nebulizer Glass impact beads Capillary tubing Oring kit Mixing paddles Burer cleaning strips 0 8 mm id inert probe 2 packs grey grey 3 bridged pump tubing 12 pk Connecting tubing drain tubing and capillary tubing Rinse reservoir 10 L 1 pack 16 mm od polypropylene tubes 1000 pk 3 sample racks for 30 mm od tubes 21 positions 1 pack 30 mm od polypropylene sample tubes 500 pk 2 sets graphite elect
9. priate drying temperature and time 2 3 sec uL of solution injected e Optimize ashing temperature using ashing study use SRM optimization e Ensure inner gas flow off just prior to atomization Does the sample sizzle or splatter during the dry stage e Listen for the sound e Use the mirror or furnace video to monitor the sample drying Furnace AA System Tips Method O SRM Wizard SRM Wizard automates furnace A optimization Optimizes absorbance as a function of ashing and atomization temperature Automatically creates a method using recommended conditions Reduces training requirements for new users Optimization results for Pb determination using phosphate modifier otimization SRM Surface Response Methodology Wizard amp Set up the Ash and Atorise start and stop steps temperature and change temperature to create the values for the fumace methods When finished press New a Step Temp C Method Ash Temp Atomise Temp Start Step 4 1 85 i sopste p E 2 s 2 w 2060 Temperature C 400 v o K 2 4 400 4 w 2180 Eang t oo 5 400 5 400 2100 e 400 6 o 2100 Atonise 7 20 7 8 2100 setsi pE E a 8 BH 2100 3 2100 3 40 2029 Sion Sten Bad 10 2100 10 400 aa Temperate t 21m w 1 200 n w 2100 Change 50 w S 0 an SRM Surface Response Methodology x ea are the results for the furnace optimisation test
10. rodes Graphite shroud 5 packs Omega tubes each 10 pk 100 uL syringe for PSD 1 pack of capillary assemblies for PSD 5 pk 1 pack of plastic beakers 5 pk 2 packs 2 mL furnace vials 1000 pk 2 sets tubing and connector kits 2 packs sample pump tubes 12 pk 2 packs reagent pump tubes 12 pk 1 set replacement pump beds 1 replacement AA gas liquid separator 1 Hg Flow Through Cell 1 pk 2 packs hydride absorption cell 2 pk 1 spare AA hydride module 2 ea 500 mL constant pressure vessel 1x 1L diluent bottle 1 x 3 way tee piece assembly 1 Pack SIPS pump tubing 6 pk 1 Pack Pump Bands 10 pk 1 SIPS tubing kit AA Maintenance amp Trouble Shooting Feb 2014 Agilent Technologies 21 Where to Find the Right Consumable Analytical Consumables Agilent Assist Consumables amp Supplies Instrument Sales amp Services 1 800 227 9770 Option 1 1 1 800 227 9770 Option 1 3 www agilent com chem contactus www agilent com chem contactus On Line resources Atomic Absorption Supplies Mark 7 Sample Introduction Spares Z SPECTROSCOPY AA FAQs Macarena ICP OES Parts amp Supplies Portfolio ICP MS Supplies Instrument Parts amp Supplies Atomic Spectroscopy Application Notes Recorded Agilent e Seminars Agilent Quick Reference Guide for AA pub 5990 9476EN Agilent Spectroscopy Supplies Catalogue pub 5991 1060EN Instrument User Manual for Agilent Graphite Tube Atomizer
11. tter stability Agilent Technologies Tips to Reduce Contamination Contamination can come from anything that comes into contact with your sample during storage digestion dilution and analysis e Check reagent purity foe CATE ica ae oY eS Always buy the best reagents 4 Always check the certificate of analysis for Be eters ieee wenn HB elevated levels Seley in F Caution if buying in large quantities Worst case can use contaminated acid for cleaning Ensure still within use by date Reseal immediately after use lie ALL VALUES ARE REPORTED IN PARTS PER TRILLION PPT Other common contamination sources Reagent water Clean glassware Airborne dust in the lab Pipette tips Don t insert pipette tips into your acids Use natural tips colored tips may increase contamination Cu Fe Zn Cd Powdered gloves esp for Zn Agilent Technologies Tips to Improve Accuracy of Results Sample preparation e Is the most appropriate digestion being used e Are all of the analytes being quantitatively and reproducibly extracted and dissolved Many digestions are only partial extracts efficiency will vary with the sample matrix Some volatile analytes may be lost during digestion Confirm by taking a solid certified reference material through your preparation and analysis proce
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