Numerous methods have been described in the literature for the determination of arsenic both in water and in particulate matrices. Many of these methods essentially employ the same principles, but apply different reagents, concentrations or instrumentation. The most popular techniques for arsenic analyses include hydride generation and AA, ICP-OES or ICP-MS. Although many water labs have these types of spectrometers already, many labs do not. The cost of these types of spectrometers is in the $100-200K price range. Many labs would have to choose the older colorimetric methods but we have developed and modified the PID and GC-PID methods for arsenic in water analysis at ppb levels (1) to work with food and juice. The system cost is a fraction of the $100K spectrometer price.

1. RV Knorr docked at Woods Hole, MA (WHOI)
Jennifer, Jack, Greg and Carrie on board RV Knorr
RV Knorr is known for supporting the WHOI and
French researchers who discovered the wreck of the Driscoll & Cutter with PID-based arsenic GC’s on
1
RMS Titanic in 1985 board the RV Knorr

2. Introduction
• Over one third of the arsenic in the
atmosphere comes from man-made
sources, notably fossil fuel combustion
and copper smelting, while the rest is
from natural sources such as volcanoes
• Arsenic can cause bladder, lung, and
skin cancer in humans (National
Academy of Science 1999)
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3. Arsenic Rule
• Although EPA regulations are set for total As
concentrations in drinking water; the standard is 10 parts
per billion ppb (http://water.epa.gov/lawsregs/rulesregs/sdwa/arsenic/regulations.cfm),
the element can exist in different oxidation states (+V,
+III, -III) and inorganic and organic forms within a given
oxidation state (e.g., As+V as arsenate, AsO43- or
dimethyl arsinate, (CH3)2AsO2 -); these all have different
bioavailability and toxicity (e.g., Sanders, 1979).
• Therefore, the chemical speciation of As in natural waters
can be just as relevant as its total concentration.
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4. Arsenic contamination in food & juice
• Arsenic contamination in foods or juices can
occur from As contaminated water or soil
• A number of techniques have been used for the
determination of As; some of these are quite
complex and expensive as shown in the next slide
• A relatively new technique, photoionization (PID)
has been used since the 1980’s for the analysis of
As compounds in sea water; we will discuss that
technique in this paper
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5. Instrumentation for the
Analysis of Arsenic
Type Detection Limit (ug/L) Cost ($)
ICP-MS 1.4 200,000
ICP-OES 8 80,000
GFAAS 8 80,000
HGAAS 0.5 60,000
ASV 1 30,000
PID 1 12,000
GC-PID 0.075 20,000
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6. Hydride Generation
• The simplest and most common method for converting As
in solution to a measurable species is hydride generation
(formation of AsH3 (g) with Na BH4 as a reducing agent)
and using pH adjustment for speciation.
• As III is converted to arsine using a TRIS-HCl buffer-pH 6.2
with NaBH4 reducing agent in the presence of sulfanilamide
(0.5 mL of a 2% solution) to remove nitrite interference. For
the PID only method and AsH3,as As III, the gas from hydride
generation flows through the PID. The PID has enough
sensitivity so that it does not have to be concentrated.
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7. Hydride generation continued
• The AsH3 is cryogenically trapped, and then determined via
GC with a 2 m Carbopak B-HT packed column (1/8” FEP
Teflon tubing) at 25 °C and PID.
• The results for Hydride generation at 0.5 M HCl and GC/PID
detection produces the concentration of As(III + V) As(V) is
then the difference between the two separate
determinations. The detection limit for inorganic As is 0.075
ug/L and precision at 40 ug/L is better than 5% (relative
standard deviation, RSD) (12). The standard additions
method of calibration can be used to improve the accuracy.
• A chromatogram of a low level (ppb) arsenic sample is
shown in the next slide
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8. Low ppb Levels of AsH3 by GC PID
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9. Photoionization
• The PID uses a 10.6 eV lamp to ionize arsine
(g) generated by reduction with NaBH4. When
AsH3 absorbs a photon, it forms a positive ion
AsH3+ plus an electron (e-).
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10. Photoionization continued
• The positive ions are collected in an ionization
chamber where the bias electrode pushes the
ions to the collection electrode and the
current collected is proportional to the
concentration over a range of 107 from ppb to
%. The schematic of the PID is shown in the
next slide.
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11. PID for Arsenic Species
Schematic of PID Photo PID
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12. Calibration Curve for AsH3- PID
Calibration Curve As in Water- PID
2000
y = 29.427x - 25.018
1500
AsH3 Reading
R2 = 0.9983
1000
500
0
0 10 20 30 40 50 60
-500
ug/L As in water
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13. Comparison of the Precision of Various
Instrumental Techniques for Arsenic
Technique DL (ug/L) RSD %
PN-T-MIP 500 4.8
GF-3F-MP 50 1.8
HG-CT-3F-MIP 0.8 6.7
HG-GFT-3F-MIP 0.4 4.5
HG-PID Driscoll (2006) 1 10
HG-GC-PID Cutter (1991) >0.075 <5%
ICP-MIP- Inductively Coupled
Plasma-Microwave Induced Plasma
PID- Photoionization Detection
GC- Gas Chromatography
HG- Hydride Generation
HG-CT-3F-MIP
PN-T-MIP
GF-3F-MIP- Graphite Furnace
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14. GC PID System for Arsenic
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15. ppb Levels of Organoarsenic
Compounds by GC PID
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16. GC-PID of Multiple Hydrides
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17. As in Food & Juices
• Consumer Reports (1/12) tested 5 brands of juices and found
that 10% had total arsenic levels that exceeded federal drinking-
water standards (10 ppb).
• Dr. Brian Jackson & co-workers at Dartmouth College tested
products sweetened with organic brown rice syrup, including
cereal bars and baby formulas, and found ppb levels of arsenic
that exceeded U.S. standards for bottled water
• The method described in this paper is easily adapted to the
analysis of As in food or juices.
• The advantage of the PID method is that it is easy to use, does
not require a high level of training and has a low capital cost
(see Slide #3)
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18. METHOD FOR ARSENIC IN FOOD AND WATER
•The most dangerous form of arsenic is As III.
•This can be determined using the following procedure:
•An aliquot of the juice or a known weight of a solid is added to the buffer solution.
•As III is converted to arsine using a TRIS-HCl buffer-pH 6.2 with NaBH4 (reducing
agent) in the presence of sulfanilamide (0.5 mL of a 2% solution) to remove nitrite
interference. As III is reduced to AsH3 (g) during the hydride generation .
Nitrogen is used to sweep the AsH3 through the PID. The PID has sufficient
sensitivity so that it does not need to be pre concentrated. As V can also be
determined using the procedure in slide #4.
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19. Summary
• As is an impurity in many soils and water supplies used to
grow fruits in the US and foreign countries. As a result, low
ppb levels of As are often found in many fruit juices and rice
sweeteners.
• PID/hydride generation (HD-PID) is an extremely sensitive,
simple and inexpensive method for analysis of arsenic in
solution with detection limits of 1 ppb without
preconcentration.
• Total As, As III, As V/or organic arsenic compounds can be
detected by varying the pH of the solution as shown in slide
#4.
• The PID method is easily adapted to the measurement of As
in fruit juices or food.
• Other metals that form hydrides can also be determined if
the GC-PID method is used
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20. Arsenic in Food
~a thematic program at #ACSNewOrleans~
245th ACS National Meeting & Exposition Spring 2013 Chemistry of Energy & Food
Organizer: James N. Seiber
April 7-11, 2013, New Orleans, Louisiana
Abstracts Submission Opens August 20, 2012
Arsenic in Food Symposium sponsored by the
Small Chemical Businesses Division of the
American Chemical Society and co-sponsored
by the Environmental Chemistry Division of the
American Chemical Society
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