Evaluating Applications of Field Spectroscopy Devices to Fingerprint Commonly Used Construction Materials (2013)

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67 A p p e n d i x d Field Operation Manual for portable Attenuated Total Reflectance Fourier Transform infrared Spectroscopy 1. Scope and Overview 1.1 This manual covers the use of field-portable attenuated total reflectance Fourier transform infrared (ATR-FTIR) spec- troscopy for on-site characterization of construction materials. 1.2 Field-portable ATR-FTIR is a useful technique for on-site characterization of materials with little or no sample prepara- tion. An ATR-FTIR spectrometer measures the infrared spectrum of a material, which can be used to identify or quan- tify the compounds present in a material, or both. 1.3 Given the variety of ATR-FTIR spectrometers available, this guide is not a sufficient substitute for the instruction manual issued by the manufacturer. 2. Apparatus 2.1 Portable ATR-FTIR Spectrometer—Portable ATR-FTIR spectrometers are designed to be compact, battery-powered units that can be easily transported to field sites. The main components of the spectrometer include housing for the laser source and optics, and a sampling plate. The sampling plate contains an optically dense crystal called an internal reflection element (IRE) on which the material is placed during measurements. 2.2 Accessories—A laptop computer with measurement software is typically required to perform measurements. A recharge- able battery pack will be required to power the spectrometer on site, as well as a crossover cable to interface the spec- trometer and the computer. 3. Sampling 3.1 Use precaution to ensure that sample selection is random and that measurements are an accurate representation of the true composition of the entire quantity of material in question. 4. Potential Interferences 4.1 Poor Sample Contact—Inadequate contact of a sample with the IRE will result in a noisy spectrum with bands of low intensity, if any. Recall that an ATR spectrum is the result of the interaction between the sample and the IR radiation Field Operation Manuals

68 that protrudes a very small distance (on the order of microns) above the IRE; thus close contact of the sample with the IRE is required to obtain a high-quality spectrum. This can present a challenge when testing solids and powders. Many modern spectrometers have addressed this issue by incorporating a clamp mechanism that applies pressure on the sample. 4.2 Residue on the IRE—Potential spectral interference may arise from an unclean IRE surface, which may be attributable to residue from a previously tested sample, a leftover quantity of the chemical used to clean the IRE, or even fingerprints. Therefore it is necessary to ensure that the IRE is sufficiently clean before measurements. Rapidly evaporating solvents such as acetone and ethanol are typically used as cleaning agents. Modern spectroscopy programs often include func- tions for determining if the IRE is sufficiently clean. 4.3 Spectral Overlap—ATR spectra represent contributions from all detectable compounds present in the sample, creating the potential for spectral overlap, in which case the IR bands of interest may be obscured. This is a common occurrence in samples that contain water, which strongly absorbs IR radiation. Often in such cases, subtraction of the interfering spectrum (e.g., a spectrum of pure water) can isolate the IR bands from the compound of interest. 5. Procedure 5.1 Follow the instructions for device start-up as described in the instruction manual of the spectrometer. Make sure that the proper environmental operating requirements, such as ambient temperature and humidity, are met. For example, on a hot and humid day, the ambient temperature may exceed the recommended limit set by the manufacturer. 5.2 Select values for resolution and number of scans to be averaged per measurement. Typically, 24 scans are collected at resolution of 4 cm-1. 5.3 Collect a background spectrum (i.e., a spectrum of the bare IRE). The software uses this spectrum to eliminate atmo- spheric contributions and produce the sample spectrum. 5.4 Place a portion of the material onto the sampling plate such that sufficient coverage of the IRE is achieved. Take note of the following nuances associated with different sample types (in order of increasing difficulty): 5.4.1 Liquids—Place enough of the liquid sample on the sampling plate to cover the IRE using a pipette, or a spatula for more viscous samples. Use caution to avoid spillage, which can damage components of the spectrometer and the computer. 5.4.2 Particulate Solids—After covering the IRE with the powdered material, use the pressure clamp (if available) to hold the sample in place and maintain close contact the IRE. 5.4.3 Bulk Solids/Mixes—Materials containing larger particles, such as aggregates, asphalt mixtures, and coatings on larger particles, require more effort to achieve good IRE contact and obtain meaningful results because of their bulkiness and inherent nonuniformity. Portions of the sample with flat surfaces should be selected for measure- ment, and the pressure clamp should be used. The number of samples may need to be increased to obtain an accurate representation of the bulk material. 5.5 Collect a sample spectrum with the same measurement parameters (number of scans and resolutions) used for the background spectrum. Perform multiple measurements as need (e.g., to obtain a less noisy average spectrum or to evaluate changes in sample composition over time). 5.6 Evaluate the quality of the spectrum by visual inspection (e.g., to determine if IRE contact was sufficient) and perform an additional measurement, if needed, starting from Step 5.3.

69 5.7 Perform spectral processing as needed. Such tasks can be completed on most spectroscopy programs and typically include baseline subtraction, conversion of ATR units to absorbance units, and atmospheric correction, which involves removal of bands associated with water vapor and carbon dioxide. 5.8 The resulting spectra can then be used for quantitative analysis or to fingerprint the material with the aid of a spectral database, or both. Field Operation Manual for Field-portable x-Ray Fluorescence Spectroscopy 1. Scope and Overview 1.1 This manual covers the use of field portable X-ray fluorescence (XRF) spectroscopy for on-site characterization of con- struction materials. 1.2 Field-portable XRF is a quick and inexpensive technique for on-site elemental analysis with little to no sample prepara- tion. XRF spectrometry is based on the characteristic energies of elements, of which the intensities are measured by a detector and translated into elemental concentrations. 1.3 Despite having a common scientific basis, the specific method of operation varies among the multitude of field-portable XRF devices available on the market, and thus this guide is not a sufficient substitute for the instruction manual issued by the manufacturer. 2. Safety 2.1 XRF spectrometers produce ionizing radiation, which can damage biological tissue. Thus, necessary precautions must be followed to ensure safety and minimize exposure. 2.2 XRF spectrometers should be used only by trained operators in accordance with the instructions issued by the manu- facturer and applicable occupational safety regulations. 2.3 Engineered safety features, such as trigger locking mechanisms and sample proximity sensors, are specific to the device. Consult the technical manual supplied by the manufacturer for device-specific safety practices and operating instructions. 2.4 The dangers involved with X-ray devices, and mitigation thereof, are well documented and, as such, this manual is not intended to be a reference to all the hazards associated with X-ray devices. 3. Apparatus 3.1 Portable XRF Spectrometer—This is typically designed as a handheld device that is easily transported to and from field sites and measurement locations therein. The detectable elements depend on the instrument and manufacturer. Typical accessories include batteries, charging adapters, and a personal digital assistant (PDA) installed with the necessary measurement software. 3.2 Sampling Containers—Containers should be selected based on manufacturer recommendations. These are required when the material of interest must be sampled before analysis (i.e., for ex situ XRF measurements). 3.3 X-Ray Transparent Tape or Film—The sample containers should be covered by an X-ray transparent tape or film, such that X-rays can penetrate the sample in close proximity without damaging the instrument.

70 4. Sampling 4.1 Use precaution to ensure that sample selection is random and that measurements are an accurate representation of the true composition of the entire quantity of material in question. 5. Potential Interferences 5.1 Moisture Effects—Caution must be exercised when analyzing and comparing XRF results obtained for materials that have variable moisture content. For example, a drying paint layer or freshly mixed cement may experience dilution effects that skew the results towards lower and higher relative concentrations when wetter or dryer, respectively. 5.2 Sample Preparation—Steps should be taken to ensure that samples are uniform, homogenous, and randomly sampled, such that the results obtained are representative of the bulk of the material. 5.3 Spectral Overlap—When interpreting XRF results, one must be aware of potential overlap of signals from different ele- ments with similar characteristic energies. This phenomenon is well documented and is likely addressed by the manufacturer. 5.4 Penetration Depth—If the sample is thinner than the depth of X-ray penetration, the results will include contribution from the substrate. 6. Procedure 6.1 Follow the instructions for device start-up and calibration as described by the manufacturer. Typically, calibration is performed using a standardization material (e.g., Alloy 316) after a specified instrument warm-up period. Most devices have a digital screen or PDA that will prompt the user to perform the specific calibration method for internal standardization. 6.2 For in situ measurements, gently apply the XRF device directly to a clean, uniform surface, such that it is flush against the device. For ex situ measurements, place a uniform, homogenized, and representative amount of the material into the sample container and cover with X-ray transparent film. 6.3 Perform the measurement in accordance with the operating instructions for the device. Typically, data are collected on a continuously averaged basis for 1 to 2 minutes. 6.4 Repeat as necessary to obtain a sufficient sample size. 6.5 Quality assurance can be addressed by periodically restandardizing the instrument, verifying the internal calibration by measuring a known standard, and performing a blank measurement. If necessary and possible, collect a sample for laboratory analysis to verify measurement accuracy or identify possible matrix effects, or both.