Post on 17-Dec-2015
December 2012
Analysis of Drinking Water Using LIBS
Applied Research Associates, Inc. Proprietary Information
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To Be Covered
LIBS Overview Advantages Methods of Analysis Direct Analysis Pre-concentration Prior to LIBS Analysis PMACS 1000 (for pre-concentration) Summary
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How does LIBS work?
LIBS is a form of atomic emission spectroscopy
• Laser pulse creates a spark on the sample material
• Light emissions are collected and input into a spectrometer
• Processor is used to compare the emissions with our database
• Analysis results listed in seconds to minutes depending on sample complexity
Laser spark on soil
3-5 mm
laser
receiver
plasma on sample The Laser Plasma
Hotter than the sun’s surface
Plasma lasts ~20 µs
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LIBS Instrument Configurations are Application Specific
SPECTROGRAPH
LASERMIRROR
LENS
SAMPLE
DETECTOR
FIBEROPTIC
COMPUTER
0
5000
10000
15000
20000
25000
200 300 400 500 600 700 800 900 1000
wavelength (nm)
inte
nsity
(cou
nts)
General LIBS Set-up
Table top ARA built food prototype: distinguishes E. Coli from Salmonella
LIBS Instruments • Customized for the application• Lab and production line deployment• Size, cost, complexity determined by the application
LIBS spectrum analyzed to ID pathogens
LVSB. anthracis
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Advantages of LIBS for Water Analysis
Rapid analysis for targeted species (<5 min for comprehensive analysis).
Simultaneous detection of all targeted species (eliminates separate tests for individual targets)
No chemical agents or consumables required in contrast to current reagent based methods.
Field deployable LIBS instrument through the use of compact and rugged components available commercially-off-the-shelf.
Automated analysis of all targets through instrument control and analysis software.
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Methods of Analysis
Without Pre-concentration of sample using LIBS• Useful when contaminant concentrations are high enough (103 – 109 cells/mL)• Samples could be dried on slides or a direct sampling method could be developed.
Pre-concentration of samples prior to LIBS testing• Useful when contaminant concentration are very low
Without Pre-concentration
With Pre-concentration
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Direct Analysis Pathogens and other contaminants can be detected in a variety of water matrices
by creating chemometric differentiation models for analysis of LIBS spectra and deploying models in an analysis algorithm specifically designed for the detection application.
Recent study of LIBS detection capability in tap water indicates detection is possible in many types of water for concentrations ranging ≥ 103 cells/mL
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Example of Analysis Algorithm for E. coli, Salmonella, and E. faecalis in Tap water
Blank slide or Other? Blank Slide
Tap Water Flow
Tap water or Other? Tap water
E. coli or Other? E. coli
Salmonella or E.
faecalis?Salmonella
E. faecalis
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Differentiation of uncontaminated Tap Water
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Differentiation of E. coli in Tap Water
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Differentiation of Salmonella from E. faecalis in Tap Water
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Pre-concentration prior to LIBS Analysis of Sample
Collect and pre-concentrate particles and organisms in 200 mL volume of aqueous suspension using the PMACS 1000 IntelliSense DesignTM flow system
Collect particles and organisms in the aqueous suspension on a filter substrate
Collect metal ions from the aqueous suspension on ion exchange membrane filters (e.g. 3M Empore® Extraction Disks; 3M Corp. St. Paul, MN).
Interrogate particles, organisms, and metals ions collected on filters using laser spark.
Spark scanned along surface
R.C. Chinni, D.A. Cremers, and R.A. Multari, “Analysis of material collected on swipes using Laser-Induced Breakdown Spectroscopy (LIBS),” Applied Optics, Vol. 49, Issue 13, pp. C143-C152 (2010).
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The unit as currently configured has dimensions 36x12x12 inches and a flow rate of 4 L/min. A typical concentration factor is x1000.
PMACS 1000
The device is shown in use at the Dunedin, FL water utility for groundwater collection of indicator organisms.
• Kearns, E.A., S. Magana, and D.V. Lim. 2008. “Automated concentration and recovery of microorganisms from drinking water using dead-end ultrafiltration,” J. Appl. Microbiol. 105:432-442.
• Leskinen, S.D. and D.V. Lim. 2008. “Rapid ultrafiltration concentration and biosensor detection of enterococci from large volumes of Florida recreational water,” Appl. Environ. Microbiol. 74:4792-4798.
Could be used for pre-concentration if necessary.
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Collection using the PMACS 1000
Closed
Backflushrecovery: pushing buffer in direction opposite to test fluid
(1) Filtration of several liters of drinking water supply (4 L/min. flow rate)
(2) Backflush to collect targeted materials on filters
Hollow fibers
Filter membrane
Closed
Filtered water either discarded or routed back to
supply at a location distant from intake to
filter
Supply
Diagram showing flow from a water supply through the PMACS unit to concentrate particles and organisms (metal ions collected on filter ).
Diagram showing flow during the Backflush to collect particles and organisms on a filter ( ).
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Differentiation of E. coli post pre-concentration
-6
-4
-2
0
2
4
6
8
10
12
Clas
sifica
tion
Valu
e
E.coli Contamination
Tampa Water Tap Concentrate
Albuquerque Tap Water (unconcentrated)
Each Point is the Average of 5 Measurements(5 seconds data collection per point)
-6
-4
-2
0
2
4
6
8
10
12
Clas
sifica
tion
Valu
e Tampa Water Tap Concentrate
Albuquerque Tap Water (unconcentrated)
E.coli in Tap Concentrate (CFU/mL)
Each Point is the Average of 40 Measurements(40 seconds data collection per point)
E.coli Contamination
10
10 2
10 3
10 4
10 5
10 6
10 7
10 8
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Summary ARA has demonstrated the ability to differentiate contaminates in water
matrices using LIBS• Multiple studies using samples provided by the University of South Florida
Basic Detection Blind Study (100%) Detection Limit Study (direct detection limit ~103 cells/mL) Study of LIBS post pre-concentration of sample (10 cells/mL demonstrated)
LIBS for water analysis could be used in real time to• Differentiate “good” from bad water• Monitor for specific contaminations in water• Flag changes in water composition
Advantages of using LIBS:• Fast• Simultaneous analysis of multiple parameters is easily possible• Results can be obtained on-site, in real time