Model 2537A Training Course Validation of Low Readings Rev: Nov 2003

Traditional Wisdom Using traditional methodology: Using traditional methodology: Six to 24 hour integrated samples Six to 24 hour integrated samples Gold coated sand/beads often failed (usually after many desorptions) Gold coated sand/beads often failed (usually after many desorptions) Main symptom of a failure was low readings Main symptom of a failure was low readings Therefore, low readings (< 1 ng/m 3 ) were routinely discarded Therefore, low readings (< 1 ng/m 3 ) were routinely discarded Inevitable conclusion was: Inevitable conclusion was: Background mercury levels were always >1 ng/m 3 Background mercury levels were always >1 ng/m 3

What the 2537A Reveals Values vary considerably more than expected Values vary considerably more than expected Unexpected low values found Unexpected low values found Different mechanisms thought to be responsible Different mechanisms thought to be responsible Occasional periods of cartridge passivation observed Occasional periods of cartridge passivation observed

Characteristics of Passivation Arctic & Marine Passivation: Arctic & Marine Passivation: Builds up slowly after weeks of operation Builds up slowly after weeks of operation Temporarily cured by a calibration cycle, ie: exposure to zero air cleans up cartridges Temporarily cured by a calibration cycle, ie: exposure to zero air cleans up cartridges Affects one cartridge before the other, resulting in sawtooth or bi-modal values Affects one cartridge before the other, resulting in sawtooth or bi-modal values Often totally cured by increasing cartridge heating Often totally cured by increasing cartridge heating

Why Bi-modality ? Cartridges have thousands of times the surface area theoretically required to capture the mercury Cartridges have thousands of times the surface area theoretically required to capture the mercury 20 cm 2 approx surface area 20 cm 2 approx surface area Gold has 1 ug/cm 2 mercury absorption capacity Gold has 1 ug/cm 2 mercury absorption capacity Typical loadings: 50 pg ( 8 ng/m 3, 7.5 l samples ) Typical loadings: 50 pg ( 8 ng/m 3, 7.5 l samples ) Cartridges only fail when 99+% of surface area is passivated Cartridges only fail when 99+% of surface area is passivated Very unlikely that this failure point is reached on both cartridges simultaneously Very unlikely that this failure point is reached on both cartridges simultaneously

Data Validation Techniques After the Fact: Graphical Examination of Data After the Fact: Graphical Examination of Data Check for obvious bi-modality Check for obvious bi-modality Plot A & B cartridge responses separately Plot A & B cartridge responses separately Perform A/B cartridge plot Perform A/B cartridge plot During Monitoring: Standard Additions During Monitoring: Standard Additions Automatic using internal perm source: Model 1120 Automatic using internal perm source: Model 1120 Manual, using injection source: Model 2505 Manual, using injection source: Model 2505

Example of Passivation

Passivation – Time Zoom

Separate A & B Plots

A Divided by B Plot

Manual Validation of Readings Can perform manual injections (using Model 2505 or equivalent) into: Can perform manual injections (using Model 2505 or equivalent) into: Injection port on 2537A Injection port on 2537A Tests analyzer passivation Tests analyzer passivation Sample probe while sampling ambient air Sample probe while sampling ambient air Tests for passivation & sample line losses Tests for passivation & sample line losses Closed system sample line test Closed system sample line test Performs complete sample line validation Performs complete sample line validation

Sample Line Validation

Outdoor Sample Head

Automated Standard Additions Use Model 1120 controller to activate internal perm source periodically Use Model 1120 controller to activate internal perm source periodically Injection is performed late in monitoring cycle Injection is performed late in monitoring cycle Use odd number of cycles so that A & B cartridges are tested alternately Use odd number of cycles so that A & B cartridges are tested alternately Either a second 2537A or the readings immediately before & after the spike are used for background correction Either a second 2537A or the readings immediately before & after the spike are used for background correction

Unusual Data The following graph shows unusual data The following graph shows unusual data This data would not have been believed in previous years This data would not have been believed in previous years We know that this dataset is correct We know that this dataset is correct Two analyzers independently obtained the same results Two analyzers independently obtained the same results The Model 1120 standard additions were good ( Instrument S/N: 007 ) The Model 1120 standard additions were good ( Instrument S/N: 007 )

Actual Arctic Data

Remedial Action – Heat Level Improve power to analyzer Improve power to analyzer Higher, constant mains voltage (no sag!) Higher, constant mains voltage (no sag!) 115 VAC or 230 VAC minimum, 50–60 Hz 115 VAC or 230 VAC minimum, 50–60 Hz Sine waveform preferred Sine waveform preferred Ensure cartridge heaters are getting hot enough Ensure cartridge heaters are getting hot enough Increase heat time to (typically) 32 sec Increase heat time to (typically) 32 sec Ensure cartridge heater terminal screws are tight Ensure cartridge heater terminal screws are tight Position heaters properly over cartridges Position heaters properly over cartridges Replace heaters Replace heaters

Remedial Action - Cleaning Clean Cartridges Clean Cartridges Air burn procedure Air burn procedure Rinse with reagents / solvents Rinse with reagents / solvents 10% nitric acid, aqua regia 10% nitric acid, aqua regia DI water DI water iso-octane iso-octane methanol methanol Soda lime trap on inlet Soda lime trap on inlet

End – Low Readings Section