Presented at the Spring 2015 National Meeting of the American Chemical Society in Denver, CO on March 23, 2015 on the Analytical Chemistry Division program track. Presentation overview: We used a sensitive but nonspecific photoionization detector (PID) with a 10.6eV lamp to measure mercury, which has an ionization potential of 10.43eV. The PID responds to both mercury and VOC’s so the VOC’s have to be removed to make the technique specific for mercury. The chemistry of the gold/mercury amalgam makes this method specific for mercury and eliminates interferences from VOC’s. This technique also concentrates the sample making the method sensitive to sub ppb levels.

1. Separation of mercury from VOC’s andSeparation of mercury from VOC’s and
selective detection using gold filmselective detection using gold film
amalgamation and photoionizationamalgamation and photoionization
Dr. Jack N. Driscoll & Jennifer Maclachlan
PID Analyzers, LLC
Sandwich, MA 02563
ACS Spring National Meeting, Denver, CO
Paper # ANYL 15
March 23, 2015
1Advances in Analytical Separations

2. We used a sensitive but nonspecific photoionization
detector (PID) with a 10.6eV lamp to measure mercury,
which has an ionization potential of 10.43eV.
The PID responds to both mercury and VOC’s so the
VOC’s have to be removed to make the technique
specific for mercury.
The chemistry of the gold/mercury amalgam makes this
method specific for mercury and eliminates interferences
from VOC’s.
This technique also concentrates the sample making the
method sensitive to sub ppb levels.
Advances in Analytical Separations 2
OverviewOverview

3. IntroductionIntroduction
• Hgo
has long been detected by non specific
techniques such as UV absorbance (253.7 nm).
Fluorescence is also a popular non specific
technique for Hgo
• The reaction of mercury vapor (Hgo
) with gold
(Au) is used to concentrate the Hg while
removing any potential interferences
• The free mercury is desorbed from the amalgam
by rapidly heating to 500o
C
• This amalgamation reaction turns non specific Hg
methods into specific ones.
3Advances in Analytical Separations

4. Introduction (cont.)Introduction (cont.)
• Photoionization (PID) is a technique that has been used
primarily for ppb detection of VOC’s.
• We report here, for the first timeWe report here, for the first time, that Hgthat Hg00
with its ionizationwith its ionization
potential (IP) of 10.4 eV can be detected at low ppb levelspotential (IP) of 10.4 eV can be detected at low ppb levels
(using the gold pre concentrator) with the 10.6 eV lamp in our(using the gold pre concentrator) with the 10.6 eV lamp in our
PID.PID.
• A known volume of air containing Hgo
is passed over a gold
substrate at ambient temperatures to form an amalgam
(Au/Hg). An ambient nitrogen flow purges and removes VOC’s
and water. The gold substrate is rapidly heated to 500o
C to
desorb only mercury vaporspecifically into the PID
• We will describe our work on the detection of ppb levels of
Hg in air & water in this presentation.
4Advances in Analytical Separations

5. Photoionization ProcessPhotoionization Process
R + hν => R+
+ e-
Where:
R is any molecule with an Ionization Potential 10.6 eV
or less.
Hg IP = 10.4 eVHg IP = 10.4 eV
hν is a high energy photon (10.6 eV)
The R+
ions are collected in an ionization chamber
adjacent to the UV lamp; the current is proportional to
concentration over a range of 10⁷.
So it has a very wide dynamic range.
5Advances in Analytical Separations

6. Photoionization DetectorPhotoionization Detector
PID Schematic & Photo Compounds Detected
• Hgo
, & As, Pb, Fe, Cd…
Hydrides
• Aromatics, Alkenes, Alkanes
>C4+
• Hydrogen sulfide, ammonia
• Any compound with an
ionization potential <10.7
eV
6Advances in Analytical Separations

7. List of Ionization PotentialsList of Ionization Potentials
Name Formula Ionization Potential (eV)
Methane CH4 12.48
Oxygen O2 12.08
Water H2O 12.59
Arsine AsH3 10.5
Phosphine PH3 10.1
Mercury Hgo
10.4
Benzene C6H6 9.24
Toluene C7H8 8.82
O-Xylene C8H10 8.56
Ethylene C2H4 10.15
Hydrogen telluride H2Te 9.14
Germane GeH4 10.53
Advances in Analytical Separations 7

8. Applications of the GC/PID-Applications of the GC/PID-HC AnalysisHC Analysis
• First commercial PID was introduced by HNU Systems (Driscoll) at Pittcon
1976 in Cleveland. The detector was described as being 50x more
sensitive than the FID for aromatic HC
• 1978- EPA method 602 for aromatics in drinking water recommended the
HNU Model PI52 since it was the only PID commercially available
• Drinking water- EPA 602b, 502.3, 506,
• Solid waste- EPA SW846. 8021, 8260,
• Soil –OSW 8021B, EMMI 1997, OSW 8020B,
• Solid waste- 1996B, OSW 5021
• Air- TO3, TO14
• OSHA- Tetra ethyl lead, Ethylene oxide
• PID/FID ratios for HC identification- basis of >40 state & EPA methods for
gasoline hydrocarbon samples instead of dual column confirmation
• SINCE 1976 the primary application for the PID has been HC Analysis
8Advances in Analytical Separations

9. Air and Water Hg MethodsAir and Water Hg Methods
• Hg- Air
– Collect, pre concentrate (Au/Hg amalgam), and
make sample specific for Hgmake sample specific for Hgo
then flash heat to
the PID for detection
• Hg- Water
– Hg using H+
/NaBH4 to reduce Hg+2
to Hgo
– Analysis collection with Au/Hg amalgam & then
thermal desorption with PID detection
9Advances in Analytical Separations

10. Mercury in AirMercury in Air
• Ambient air sampling usually involves looking for
low levels (0.5 to 5 ng/m3
) of mercury (typical
sampling times can range from 5 to 30 min.
• For workplace air sampling, the levels are
typically higher (0-50 µg/m3
or0-6 ppb) and prone
to sudden fluctuations. Shorter sampling times
can be used with an increased sampling
frequency. We’re working with these levels in
this paper.
10Advances in Analytical Separations

11. Air Sample Collection SystemAir Sample Collection System
Description
• Sample collection is
via a metering
pump for a specific
period of time. As
seen in the next
slide, the detection
limit by PID is
approximately at
the OSHA PEL so
sample
concentration is
necessary. We use a
gold film pre
concentrator.
Collection
11Advances in Analytical Separations

12. Hg in NHg in N22 Detection by PIDDetection by PID
100 ppb Hg direct injection Description
• A Hgo
permeation tube (at
50o
C) was purged with a
constant flow of nitrogen
and directed into the PID.
The results are shown in
the figure on the left. The
response to Hgo
is quite
strong and reproducible.
The detection limit for Hgo
is < 10 ppb for direct
injection of 1 cc of Hgo
in N2.
Note this would not be
specific if VOC’s were
present.
12Advances in Analytical Separations

13. 12.5 ppb Hg w/gold pre concentrator12.5 ppb Hg w/gold pre concentrator
Description
• Here, the Hg o
permeation
tube at 20o
C is run
through the gold pre
concentrator (GPC) for 2
minutes, wait for 30
seconds to establish a
baseline, then flash heat
to 500o
C and introduce
the sample to the PID.
The detection limit here is
about 100 ppt Hgo
and
this GPC ensures that it is
specific for Hgo
. This is
sufficient for the OSHA
limit but a much larger
sample would be needed
for ambient air.
Chromatogram
13Advances in Analytical Separations

14. Conversion fromConversion from µg/mg/m33
to ppb or pptto ppb or ppt
• Hg values are frequently quoted in units of
mg/m3
to convert to ppm/ppb/ppt see below:
MW Hg= 200.59 g/mole
ppb = ug/m3
x 24.45/ MW
ppb= µg/m3
x 0.12
ppt= ng/m3
x 0.12
14Advances in Analytical Separations

15. WhatWhat MetalsMetals have been Analyzed by GC/PID?have been Analyzed by GC/PID?
• Vien 1988 arsenic, selenium, tin and antimony (as hydrides) in natural
waters
• Yamamoto 1992 As, Sb in natural waters
• Cutter 1991, 2006 As, Sb; in natural waters
• Haque 2007 As, in natural waters
• Mergemeyer- no GC-just single element-
Analysis has been by Hydride generation (with strong acidic reducing agents)-
generally with the metalloids using a liquid N2 trap/concentrator- These
methods were not very popular and produced fewer than 7 papers in the
last 25 years. This very sensitive method has been underutilized.
Driscoll & Maclachlan described a more sensitive GC/PID methoda more sensitive GC/PID method at
ACS/NOLA (2013) for As in Juices at sub ppb levels. No liquid nitrogen was
needed to concentrate the sample. We also described HG/GC/PID
methods for Pb, Cd & FePb, Cd & Fe at ACS in SF (2014).
Now we can add HgNow we can add Hgo
with gold pre concentration/PID to the list of metals that
can be detected specifically at sub ppb levels
15Advances in Analytical Separations

16. Jack and Jennifer at the 2013 R&D 100 AwardsJack and Jennifer at the 2013 R&D 100 Awards
in Orlando, FL: Arsenic in Food & Water Analyzerin Orlando, FL: Arsenic in Food & Water Analyzer
Advances in Analytical Separations 16

17. Also presented at this meeting in Denver:Also presented at this meeting in Denver:
Arsenic in drinking water samplesArsenic in drinking water samples
from Bangladeshfrom Bangladesh
• CHED: Division of Chemical Education
• 293 - Apparatus for ultratrace detection of arsenic in drinking water by hydride
generation gas chromatography with photoionization detection
• View Session Detail
Author Block: William Borgeson1
, Seth Frisbie1
, Jack Driscoll2
1
Chemistry & Biochemistry, Norwich University, Brooklyn, New York, United
States; 1
Chemistry & Biochemistry, Norwich University, Brooklyn, New York,
United States; 2
PID Analyzers, LLC, Sandwich, Massachusetts, United States
• Abstract:The hydride generation technique is a common method to determine
trace amounts of arsenic in drinking water. This method produces a considerable
amount of pressure which would be unsafe if carried out in a normal closed glass
reaction vessel. A stainless steel reaction vessel was machined which could handle
the pressure generated in the hydride generation technique as well as provide an
oxygen free environment to reduce interferences. A sample loop was also
constructed to reduce systematic error and ensure a uniform sample introduction
into the gas chromatograph. A very sensitive photoionization detector was used. A
calibration curve was then constructed to determine the dynamic range of the
instrument. This instrument was validated by the analysis of highly characterized
drinking water samples from Bangladesh.
Advances in Analytical Separations 17

18. Apparatus for ultratrace detection of arsenic in drinking
water by hydride generation gas chromatography with
photoionization detection at #ACS Denver 2015
Advances in Analytical Separations 18

19. A New Method for the Analysis of ppb Levels ofA New Method for the Analysis of ppb Levels of
Mercury in Air and WaterMercury in Air and Water
• At Pittcon 2015 in New Orleans, we reported for theeported for the
first timefirst time, that Hgthat Hg00
with its ionization potential (IP) ofwith its ionization potential (IP) of
10.43 eV can be detected at low ppb levels with the10.43 eV can be detected at low ppb levels with the
10.6 eV lamp in our PID via GC/PID.10.6 eV lamp in our PID via GC/PID.
• Instead of Au/Hg amalgam, we chose NIOSH method
6009 for collection(on a Hopcalite® tube) &
concentration of a Hg air sample followed by
dissolution in Nitric/HCl, followed by reduction with
NaBH4 and specific analysis by GC/PID.
• Our work with the detection of ppb levels of Hg in air
& water were presented.
Advances in Analytical Separations 19

20. Cold Vapor Mercury AnalysisCold Vapor Mercury Analysis
One of the most popular methods for Hg
analysis involves the conversion of Hg salts to
Hg vapor using an strong acidic reducing agent
such as Sn/HCl or NaBH4/HCl as shown below:
3H2O+ 2NaBH4 => 8H. + 2H3BO3
8H. + Hg+2
=> Hgo
+ 3 H2
Atomic absorption or Atomic fluorescence are
common detectors for this analysis. Now GC/PID
is also available for this analysis
20Advances in Analytical Separations

21. Mercury Generator for WaterMercury Generator for Water
Description
• 25 ml of an aqueous sample
containing ppb level of Hg salt is
pipeted into the sparging vessel.
• Add 1 ml of concentrated HCl and
screw the top on tight. Start the
nitrogen purge at 50 cc/min and
continue for 3-4 min.
• Start the teflon stirring bar, then
add 1 cc of 4% NaBH4 with a
syringe via the septum.
• Inject a number of samples via the
10 port valve. At low levels, it will
take 10-13min to collect all the Hgo
• EPA drinking water standard for Hg0
is 2 ppb
Hydride Generator
21Advances in Analytical Separations

22. HG Generation & Detection by Au-Hg/PIDHG Generation & Detection by Au-Hg/PID
22Advances in Analytical Separations

23. Hg Analysis for Water SamplesHg Analysis for Water Samples
Hydride generation
• The Hgo
from the sparger
is collected on a gold pre
concentrator
continuously at a
flowrate of 50 cc/min for
a period of 10-12
minutes. Then purged
with nitrogen for 3
minutes to remove water
vapor or VOC’s and finally
flash heated to 500o
C to
release Hgo
for the PID to
detect. A typical analysis
is shown in the Fig. to the
right
Hg concentration
23Advances in Analytical Separations

24. Hg Analyzer for Air and WaterHg Analyzer for Air and Water
Advances in Analytical Separations 24

25. Comparison of HGAAS & HG/PIDComparison of HGAAS & HG/PID
HG/AAS
• Cleans up sample
• Concentrates the sample
• Uses a Hg lamp/uv
absorption
• Detection limits in low or
sub ppb
• Sample concentrated
using Au amalgam (gold
pre concentrator
HG/PID
• Cleans up the sample
• Reduces the Hg salt to elemental
Hgo
that the PID can detect
• Major improvements in PID
sensitivity and optimization,
reduces the detection limit to <
100 ppt
• Air sample is concentrated using
gold preconcentrator
• Water samples are concentrated
using hydride generation and a
gold pre concentrator
• PID is 10-50 times more sensitive
than AAS 25Advances in Analytical Separations

26. ConclusionsConclusions
• Mercury (IP= 10.4 eV) is detected with sub ppb
sensitivity by the PID (10.6 eV lamp) with gold pre
concentration (first time reported).
• Mercury vapor in the air can be collected and pre
concentrated using a gold substrate. Hg detection
levels down to ppt are achievable by PID.
• Mercury in water can be detected by PID or with
improved specificity by gold pre concentration after
reduction with NaBH4 (hydride reduction) Part per
trillion levels of Hg can be detected.
• This new method of analysis for Hg has significant
potential for measuring ppt levels of Hg (specifically)
in air, water and food analysis.
26Advances in Analytical Separations

27. Connect with us!Connect with us!
27
@pidguy @pidgirl
www.hnu.com
www.facebook.com/pidanalyzers
www.twitter.com/pidguy
www.twitter.com/pidgirl
www.analyzersource.blogspot.com
www.linkedin.com/in/johnjackdriscoll
www.linkedin.com/in/jenniferlmaclachlan
Advances in Analytical Separations