Figure 3.11 Raman Spectroscopy

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1 Instrumentation 381 Figure 3.11 An example of portable FTIR instrumentation is the HazMatID Ranger (www. smithsdetection.com). (Image courtesy of Smiths Detection.) Raman Spectroscopy Instruments using Raman spectroscopy (Figure 3.12) use an infrared laser to excite target molecules, which return a small portion of inelastically scattered light to the detector. The inelastically scattered light exhibits a quantum decrease in frequency. The scattering is influenced by several types of movement within the molecular bond. Atom-to-atom bonds are unique and are influenced in turn by neighboring atoms or functional groups. A pattern of all the inelastic scattering of the laser consisting of wave shift and intensity is processed into a spectrum that in turn is compared to a library. Some software is capable of matching several spectra from the library to determine mixtures. Mixture analysis is particularly useful for products that may vary the concentration of ingredients, for contaminated samples and for pure compounds that may have degraded over time. Raman spectroscopy results can be affected by temperature, interfering radiation, the ability to induce strong polarization of the electron cloud around a bond, and absorption of the IR frequency rather than scattering. Large molecules tend to present more complex spectra. The most intense Raman scattering is observed from electron clouds that can be vibrationally distorted in a symmetrical manner, making Raman spectroscopy sensitive to these compounds. In comparison, infrared absorption is most intense when asymmetrical vibration is present. When the two technologies are used in a complementary manner, analysis is enhanced.

2 382 Field Confirmation Testing for Suspicious Substances Figure 3.12 An example of a Raman spectrometer is the Ahura Scientific FirstDefender (www. ahurascientific.com). Raman spectroscopy is preferred over IR spectroscopy when analyzing organic components in aqueous solution. IR spectroscopy detects water, and the water peak can obscure other organic peaks. Raman spectroscopy is a poor detector of water and thus increases selectivity in aqueous solutions. Some Raman instruments can detect through most glass, translucent plastic, and thin paper. Hydrocarbon compounds containing double bonds return a strong Raman signal. Strongly polar compounds (e.g., water, methanol), most metals and elements, and dark objects that absorb laser energy return a weak Raman signal. Proteins and other laserfluorescent molecules are poorly detected due to noise in the signal that obscures the analyte peaks. Field measurements made with Raman instrumentation will differ from controlled laboratory results, from which the library reference spectra are built. Unless the instrument software concludes a highly confident result, a no match message may be displayed after analysis. When this occurs, a second level of analysis is required by a spectroscopist. Figure 3.13 shows a report with a no match result and a spectrum that contains strong peaks. Spectral analysis through reach back support in the context of other field tests and observations can provide confirmation of identification or functional groups of a suspicious compound. Table 3.3 displays peak ranges and intensity by functional groups, and Table 3.4 displays groups and intensity by peak ranges. These tables may be used to confirm the presence of functional groups in a sample; however, the tables do not consider all possibilities, especially in the context of variables that may occur in field testing. These tables do not

3 Instrumentation 383 No Match AhuraScientific FirstDefender FD2889 No match found in the library. Despite strong molecular signal, the system could not reliably identify this material. Contact Ahura ( ) for spectral analysis assistance. Mode: Power Setting: Laser Status: CCD Status: Lamp Status: Calibration: Last Checked: Scan Warnings: None Auto, Vial Holder High Pass Pass Pass Pass 5/28/ :43 AM All results should be verified using other methods or techniques Scan 500 Session003 - Scan Raman Shift (cm 1 ) /18/ :25 PM Figure 3.13 A report generated by the Ahura Scientific FirstDefender containing Raman spectrum data. replace the skill of a spectroscopist. Manufacturers provide reach back support and access to a spectroscopist. Consult the manufacturer to determine if these tables can be applied to an individual model of Raman instrumentation. Modern portable instruments integrate reach back support for first responders and other users. A review by a spectroscopist provides a strong, second tier of analysis beyond that offered by an extensive library and computing power resident in the instrument. The following actual reach back support account provided by Ahura Scientific illustrates the value added by a spectroscopist. This case involved the discovery and subsequent attempt to confirm a substance as containing nitrate as well as other possible explosive compounds. Thank you for using Ahura Scientific s reach back service. While I can not make a conclusive identification of the material under question, I believe the information I can provide will be of use to you. You described the material as a pea green liquid in a plastic bottle. As we discussed over the phone, the data you collected are suggestive that a nitrate containing material is present. The on-board analysis you collected in the field reported a mixture of mercury(i) nitrate, sulfuric acid, and several other nitrate containing entities. While this mixture solution does explain many of the features in the data, several of these items are not readily available so it is germane to question the results. Based on my examination of the data, I believe the particular nitrate present in the sample is ammonium nitrate. An overlay of the unknown data and a spectrum for ammonium nitrate are shown below (Figure 3.14).

4 384 Field Confirmation Testing for Suspicious Substances Table 3.3 Single Vibration and Group Frequencies of Peaks Commonly Identified by Raman Scattering Listed by Group Group Approximate Wave Number Range (cm 1 ) Intensity =CH Strong Acid chloride Moderate Alcohol Weak Aldehyde Weak Aldehyde Weak Aldehyde Moderate Aliphatic azo Moderate Aliphatic ester Moderate Alkyne Strong Alkyne Very weak Amide Moderate Amide Strong Amine Moderate Anhydride Moderate Aromatic azo Very strong Aromatic C-H Strong Aromatic nitrile Moderate Aromatic ring Moderate Aromatic rings Strong Aromatic/hetero ring Strong Azide Moderate C=C Very strong C=N Very strong C=S Strong C=S Strong Carboxylate salt Moderate Carboxylic acid Moderate Carboxylic acid dimer Weak C-Br Strong C-C aliphatic chain Strong C-C aliphatic chains Moderate C-CH Strong C-CH Weak C-Cl Strong C-F Strong CH=CH Strong CH Strong CH Weak CH Strong CH Weak C-I Strong C-O-C Weak C-S Strong

5 Instrumentation 385 Table 3.3 Single Vibration and Group Frequencies of Peaks Commonly Identified by Raman Scattering Listed by Group (continued) Group Approximate Wave Number Range (cm 1 ) Intensity Diazonium salt Moderate Ester Moderate Isocyanate Very weak Isonitrile Moderate Isothiocyanate Moderate Ketone Moderate Lactone Moderate Lattice vibrations Strong N-CH Weak Nitrile Moderate Nitro Moderate Nitro Very strong O-CH Weak OH Weak P-H Very weak Phenol Weak Se-Se Strong Si-H Moderate Si-O-C Weak Si-O-C Weak Si-O-Si Strong Si-O-Si Weak S-S Strong Sulfonamide Moderate Sulfone Moderate Sulfonic acid Very weak Sulfonic acid Very weak Thiocyanate Very weak Thiol Strong Urethane Moderate Xmetal-O Strong Source: Adapted from Smith, E., and Dent, G. Modern Raman Spectroscopy: A Practical Approach, John Wiley & Sons, Ltd., West Sussex, England, May As you can see from the plot above, ammonium nitrate corresponds well to the spectral features in the unknown at 718 cm 1 and 1048 cm 1. The remainder of the spectrum does not contain many Raman peaks, suggesting that whatever other component is present is a very simple molecule with only a few covalent bonds. When ammonium nitrate is used as an explosive material, it is most often mixed with some sort of fuel such as kerosene. These materials have many more bonds resulting in complex spectra, so they can be ruled out as being present. Outside of applications in explosives, ammonium nitrate is most often used as a fertilizer. Many fertilizer mixtures, including liquid fertilizers, contain ammonium nitrate mixed with one or more other simple materials such as urea, potassium sulfate, etc. Whereas I can not

6 386 Field Confirmation Testing for Suspicious Substances Table 3.4 Single Vibration and Group Frequencies of Peaks Commonly Identified by Raman Scattering Listed by Wavenumber Approximate Wavenumber Range (cm 1 ) Group Intensity Lattice vibrations Strong Xmetal-O Strong C-C aliphatic chain Strong Se-Se Strong S-S Strong Si-O-Si Strong C-I Strong C-Br Strong C-Cl Strong C=S Strong C-C aliphatic chains Moderate C-S Strong C-F Strong C-O-C Weak Carboxylic acid dimer Weak Aromatic rings Strong Si-O-C Weak Si-O-Si Weak C=S Strong Sulfonic acid Very weak Sulfonamide Moderate Sulfone Moderate Si-O-C Weak Sulfonic acid Very weak Carboxylate salt Moderate Nitro Very strong C-CH 3 Weak Aromatic azo Very strong CH 2 Weak CH 3 Weak Aromatic ring Moderate Nitro Moderate Aliphatic azo Moderate Aromatic/hetero ring Strong Amide Strong Ketone Moderate Carboxylic acid Moderate C=C Very strong C=N Very strong Urethane Moderate Aldehyde Moderate Ester Moderate Aliphatic ester Moderate Lactone Moderate

7 Instrumentation 387 Table 3.4 Single Vibration and Group Frequencies of Peaks Commonly Identified by Raman Scattering Listed by Wavenumber (continued) Approximate Wavenumber Range (cm 1 ) Group Intensity Anhydride Moderate Acid chloride Moderate Isothiocyanate Moderate Alkyne Strong Si-H Moderate Isonitrile Moderate Thiocyanate Very weak Azide Moderate Aromatic nitrile Moderate Diazonium salt Moderate Nitrile Moderate Isocyanate Very weak P-H Very weak Thiol Strong Aldehyde Weak N-CH 3 Weak CH 2 Strong Aldehyde Weak O-CH 3 Weak C-CH 3 Strong Aromatic C-H Strong OH Weak CH 2 Strong CH=CH Strong =CH 2 Strong Amide Moderate Amine Moderate Phenol Weak Alcohol Weak Alkyne Very weak Source: Adapted from Smith, E., and Dent, G. Modern Raman Spectroscopy: A Practical Approach, John Wiley & Sons, Ltd., West Sussex, England, May provide a definitive identification of the second component, the simplicity of the data and the location of the peaks are consistent with sulfate containing molecules (also likely why the onboard mixture analysis suggested that sulfuric acid was present). As such, I would speculate that the unknown is likely a fertilizer composed of ammonium nitrate and some sort of sulfate containing molecule. Whereas I believe the data is most consistent with sulfate containing materials, it is also possible that a phosphate containing material is present. As always, we remind users that FirstDefender is not a trace detection tool. The findings provided here should always be verified with other tools at your disposal. If I can answer any further questions, please let me know. Always consider any test and related analysis as a resource to be used by first responders and other field workers in conjunction with other situational analysis. Those responsible

8 388 Field Confirmation Testing for Suspicious Substances Unknown Spectrum Ammonium Nitrate Reference Raman Shift Δ(cm 1 ) Figure 3.14 Spectra returned in spectroscopist s report. for response are wise to determine a course of action that considers all information and not just the results of a single test. X-Ray Fluorescence X-ray fluorescence (XRF) analyzers use x-rays to irradiate a sample and excite the electrons of metals and other compounds. The electrons will emit x-rays of differing wavelength (fluoresce) when returning to a normal state. An XRF instrument (Figure 3.15) detects the pattern of fluorescence and identifies elements. XRF can generally detect elements with an atomic number of 16 (sulfur) through 94 (plutonium). Practically, the detection ability of the instrument depends on the element used to generate x-rays. In general, XRF instruments use one or more of the following x-ray generating sources: Cobalt-57 for the detection of lead Iron-55 for the detection of calcium, chromium, potassium, sulfur, titanium, and vanadium Cadmium-109 for the detection of arsenic, chromium, cobalt, copper, iron, lead, manganese, mercury, molybdenum, nickel, plutonium, rubidium, selenium, strontium, uranium, vanadium, zinc, and zirconium Americium-241 for the detection of antimony, barium, cadmium, silver, and tin XRF is used to detect solid and concentrated liquid forms of (although water interferes with): Aluminum Antimony

9 Instrumentation 389 Figure 3.15 An example of a portable XRF instrument is the NITON XL3t ( com/niton). (Image courtesy of Thermo Fisher Scientific.) Arsenic Barium Bromine Cadmium Chromium Cobalt Copper Iron Lead Magnesium Manganese Mercury Nickel Phosphorus Rubidium Selenium Silicon

10 390 Field Confirmation Testing for Suspicious Substances Silver Thallium Tin Titanium Tungsten Zinc Zirconium Sensitivity varies by model and analyte. Typically, XRF can detect 20 to 100 ppm of most analytes. Chromium detection is less sensitive, usually in the 200 to 900 ppm range. The NITON 700 Series reliably detects 15 ppm arsenic in soil for test times of 30 to 60 seconds after sample preparation. The XRF analyzer measures the metal content of the sample over a surface area of about 1 cm 2 to a depth of about 2 mm. Water content greater than about 20% can interfere; drying may be necessary. Pooled water definitely interferes. The most accurate field readings are obtained by drying the sample and then uniformly grinding to about 100 microns before analysis. Some metals will interfere with the detection of other metals in mixtures. For example, iron will absorb x-ray fluorescence from copper, but will increase detection from chromium. Radioisotope Detection Instrumentation is necessary for field confirmation of radioactive material. A few of the basic sensors and associated instrumentation are presented here. A basic understanding of radioisotope detection is necessary to perform field confirmation tests on suspicious material. Commercialized instruments often blend sensor types and processing equipment to meet a certain market niche, and complete coverage of all combinations is too lengthy to be presented here. The Department of Homeland Security has funded an evaluation of field radiation detection instruments. Results of Test and Evaluation of Commercially Available Survey Meters for the Department of Homeland Security; Results of Test and Evaluation of Commercially Available Personal Alarming Radiation Detectors and Pagers for the Department of Homeland Security; and Results of Test and Evaluation of Commercially Available Radionuclide Identifiers for the Department of Homeland Security are good resources. The guides assess commercially available equipment as tested against standards of the National Institute of Standards and Technology (NIST). Access to these documents is limited to first responders and other officials. They are posted at the SAVER web site ( Geiger-Mueller Tube A Geiger-Mueller (GM) tube detects alpha, beta, and gamma ionizing radiation across most, but not all, energy ranges. A GM tube contains one of several possible inert gases to which a high voltage is applied when the unit is powered on. When certain ionizing radiation passes through the tube, an electrical pulse is generated. The pulse is modified by the