Air Quality Monitoring | Water Quality Monitoring

PIDs

Photoionization detectors use an ultraviolet lamp to ionize a gas sample and detect its concentration. The UV lamp ionizes the sample, electrically charging it. The sensor electrodes detect and measure the current. The instrument software translates the detected current into ppm or ppb. Since PIDs ionize only a small fraction of the sample during detection, the sample can be collected from the PID outlet for further analysis. PIDs are typically zeroed in clean air, and calibrated to 100 ppm (parts per million) isobutylene.

PIDs are handheld, portable instruments. Some have belt-clips, and are suitable for personal protection monitoring against most VOCs.

The range of most PIDs is 0 to 10,000 ppm. Some PIDs, the ppbRAE plus for example, have a range of 1 ppb (parts per billion) to 4000 ppm. Readings below 10 ppm display in ppb. PIDs can detect samples in an inert sample matrix without oxygen, such as argon or nitrogen. PIDs will not detect methane, which has an ionization potential of 12.6 eV. PIDs are limited to detecting compounds with ionization energies less than 11.7 eV. They are available with lamps of varying intensities (9.8 eV, 10.6 eV, 11.7 eV) to target certain compounds. The 10.6 eV lamp is the most common.

FIDs

Flame Ionization Detectors use a hydrogen flame to ionize the sample gas and then detect its concentration. Electrons are ejected from the VOC molecules in the hydrogen flame. The electrically charged ions produce a current detected by the sensor electrodes. The FIDs converts this current to a ppm reading on the screen. FIDs are usually calibrated with 100 ppm methane, but calibration concentrations up to 25,000 ppm methane are available. Although the hydrogen flame ionization allows us to detect methane at 12.6eV, it is a destructive method. The sample is burned, preventing collection for later analysis.

FIDs are handheld, but not suitable for personal monitoring. They tend to be larger than PIDs. Since FIDs use a hydrogen flame, the internal tank needs filling after 4 – 8 hours of use.

FIDs, such as the Photovac MicroFID, will detect VOCs in reference to methane from 0 to 50,000 ppm. Oxygen is required to sustain the hydrogen flame; therefore, FIDs will not operate in an inert matrix unless introducing oxygen to the sample stream.

FID / PID combination units

The Thermo TVA-1000 PID/ FID is a combination unit, containing both a PID and FID. It is about the size of a small brief case, with a sensor handle attached to the unit with a sample hose. In situations where a sample contains methane and VOCs, the TVA-1000 will do the job by displaying a VOC only reading, since it cannot detect methane. The FID will detect methane and VOCs. If you take a FID reading with a carbon filter attached to scrub out VOCs, you will get a methane only reading.

Why do PIDs and FIDs read the same gasses differently?

While both units detect VOCs, they do it differently, PIDs with UV light, and FIDs with a hydrogen flame. PIDs are more accurate at the low scale, while FIDs have better linearity throughout their range.

PID order of sensitivity: Aromatics, iodine compounds, olefins, ketones, ethers, amines,sulfur compounds, esters, aldehydes, alcohols, aliphatics, chlorinated aliphatics, ethane, methane (no response)

FID order of sensitivity: Aromatics, long-chain compounds, short-chain compounds (methane), chlorine, bromine and iodine compounds.

PID and FID Information

• The NIOSH Pocket Guide to Chemical Hazards is useful in determining the IP (ionization potential) of many compounds, and ways to detect them.

• Another good resource for IPs and correction factors is RAE Systems tech note 106, Correction Factors, Ionization Energies, and Calibration Characteristics.

Contact your local Pine office for a copy of the Photovac MicroFID or Thermo TVA-1000 response factor lists.

Please call your local Pine office with any questions and thank you for choosing Pine!

Color and Spectral Analysis

Colorimeters measure light absorbed by a sample after a chemical reagent produces a color change. The intensity of absorbed light is directly proportional to the concentration of the compound, therefore colorimeters can accurately measure the concentration of various compounds in the sample. Colorimeters measure light wavelengths in the visible light range. The Hach DR 890 colorimeter has four fixed wavelengths: 420, 520, 560, and 610 nm. Hach colorimeters function with specific compound test kits for relatively quick and accurate analysis. The instruments are pre-programmedwith a variety of test methods which can reduce operator error and simplify analysis.

Spectrophotometers, sometimes referred to as UV-Vis spectrophotometers, also measure the intensity of light passing through a sample. They are used to determine the absorbance of light in a sample, ultimately allowing for the determination of color, concentration, or other pertinent information. Spectrophotometers operate using a broader wavelength range than colorimeters, including UV and visible wavelengths; 190–1100 nm. The broader spectral range increases the number of analytes detected by the instrument to almost twice as many substances as colorimeters with greater accuracy.

In short, a colorimeter provides an overall measure ment of the light absorbed, while a spectrophotometer measures the light absorbed at varying wavelengths.

Tips:

• When choosing between a colorimeter and a spectrophotometer, look at the available tests and ranges to find the appropriate instrument for your job. Although spectrophotometers are more versatile, a colorimeter will often suit your job requirements.

• Review the test procedures you will be using prior to going out to the jobsite. Look at the required reagents and required apparatus sections to ensure you have everything you will need. They are at the end of each test.

• Ensure that the unit’s battery is charged, or has fresh batteries. Some spectrophotometers require AC power, so plan accordingly.

Pine rents the following Hach instruments;

• DR850 Colorimeter
• DR870 Colorimeter
• DR890 Colorimeter
• DR2010 Spectrophotometer
• DR2400  Spectrophotometer
• DR2700  Spectrophotometer
• DR2800  Spectrophotometer
• DR5000 Spectrophotometer

To view a table comparing colorimeters to spectrophotometers please click here

To view the DR 890 Colorimeter tests and ranges please click here

To view the DR 5000 Spectrophotometer test and rangesplease click here

Please call your local Pine office with any questions and thank you for choosing Pine!

First, A lesson in Fluorescence

What is XRF?  Well it is X-Ray Fluorescense of course.  The next obvious question is “What is fluorescence?”.   When high-energy, primary X-ray photons (such as those emitted from the XRF analyzer’s x-ray tube) strike a sample, the electrons of the innermost K or L orbits are displaced and become unstable ions.  Electrons seek stability, therefore this results in an electron from an outer L or M orbit to shift into the vacant space at the inner orbital.  The electron moving from the outer orbital into the inner orbital causes a secondary X-ray photon to be emitted.  This is known as fluorescence. 

Individual elements produce their own characteristic secondary X-rays, which means they fluoresce differently than other elements.  The energy (E) of the emitted fluorescent X-ray photon is determined by the difference in energies between the initial and final orbit of the transitions.  The XRF can then measure these energy signatures and frequencies and determine the concentrations of specific elements and alloys in the sample.  Simple enough, right?

Applications of XRF technology

When an X-Ray Fluoroscope or XRF is used properly it can confirm the absence or presence of specific elemental metals and alloys in soils, paint, and a variety of other materials.  The technology of hand-held XRF and field portable analyzers allows the end user the ability to gather screening level to laboratory grade data at measurable concentrations and detection limits.  Therefore the applications where XRF technology can be applied are tremendous.  Manufacturers of XRF analyzers have developed instruments to benefit a wide variety of market places including many environmental applications.  One benefit to the end user is that the handheld XRF analyzers can be used to analyze samples insitu, or with minimal transportion, alteration, or damage, making them an ideal field tool.

XRF analyzers of the past required the instrument to contain a hazardous radioactive source, requiring extra safety requirements and restrictive regulation.  Modern XRF units do not contain radioactive material.  The instrument generates and emits X-rays only when the X-ray tube is energized and taking readings.  Although the modern, XRF analyzers are much safer than the older models, one must still be aware of the safety requirements.  The instrument still emits X-ray energy and should never be pointed at anyone.  It is important to follow all of the safety recommendations in the operator’s manual.

When using and XRF for environmental applications, it is imprtant to be aware of the accepted methodology for various applications.  It is important to follow the workplan set forth in your scope of services and if the workplan states that work will be performed in accordance with a regulator approved protocol, please make sure you fully understand the methodology.  Below is a list of some of the excepted regulator developed methodologies.

US EPA: Comply with Method 6200 for Metals in Soil; 8 RCRA (Cr, As, Pb, Hg, Se, Ag, Cd, Ba) & Priority Pollutant (Tl, Cu, Ni, Sb, Zn) Metals; CCA in Pressure Treated Woods http://www.epa.gov/waste/hazard/testmethods/sw846/pdfs/6200.pdf

US OSHA: Comply with Methods OSSA1 & OSS1 for Pb in Air Filters & Dust Wipes

US NIOSH: Comply with Method 7702 for Pb in Air Filters

EU RoHS: Screen for RoHS (Restriction of Hazardous Substances) Compliance for Pb, Hg, Cr, Br, and Cd

EU WEEE: Screen for WEEE (Waste Electrical and Electronic Equipment) Directive Identification of RoHS elements, in particular Hg, Cl, and other toxic metals

Understanding X-Rays and XRF Safety

Pine Environmental Services, Inc. does not intend this article to be a substitute for fully comprehending the risks and safety precautions associated with use of XRF analyzers.

X-radiation (composed of X-rays) is a form of electromagnetic radiation.  X-rays have a wavelength of 10 to 0.01 nanometers, with frequencies in the range 30 petahertz to 30 exahertz (30×1015Hz to 30×1018Hz).  X-ray energies are in the range 120 eV to 120 keV and are longer than gamma rays but shorter than UV rays. 

The rem is the traditional unit of dose equivalent.  This describes the energy delivered by X-radiation (indirectly ionizing radiation) for humans.  The SI (International System of Units) counterpart is the sievert (Sv).  One sievert is equal to100 rem.  Because the rem is a relatively large unit, X-rays are typically measured in millirem (mrem), or in microsievert (μSv).

1 rem = 1000 mrem         1 Sv = 100 rem         1 μSv = 1/1000000 Sv         1 mrem = 10 μSv

The average person living in the United States is exposed to approximately 150 mrem annually from background sources alone.  Dental X-rays dosage reports seem to vary significantly.  Depending on the x-ray source, a typical dental X-ray results in an exposure varying from 3 to 900 mrems (30 to 9,000 μSv) with common medical and/or dental x-rays: 20-30 mrem each.  Mammogram exposure is measured between 100-200 mrem, flying in a commercial jet coast to coast (6 hrs.) has exposures between 1-2 mrem, and daily exposure from background radiation measures between 0.3 to 0.5 mrem/day (depends on geographic location)

A single case of XRF analyzer misuse may issue a measured dose between70-250 mrem however, regular misuse, such as taking safety shortcuts, produces radiation exposure that greatly exceeds these typical levels and should be avoided entirely.

XRF Tips

• Familiarize yourself with the XRF analyzer prior to field operation.   This saves time during sampling.

• When using the handheld or field portable XRF analyzers in accordance with USEPA Method 6200, become familiar with procedures outlined in the method to ensure compliance and optimum results.

• Instead of recording readings with only date time and sample number, customize data entry with dropdowns and detailed information about each sample.

• A fully charged XRF battery will last approximately 4 hours (Pine includes 2 batteries with rental).  Pleaese be sure that both batteries are charged before sampling.  Please request an additional battery if you anticipate longer work days.

• Use the soil or paint chip standards to confirm XRF accuracy and comply with QA/QC protocols.

• Be familiar with XRF safety and your state’s XRF safety regulations.

 Link to the NRC: Federal & State Materials & Environmental Management website: http://nrc-stp.ornl.gov/asdirectory.html

Please call your local Pine office with any questions or concerns.

Electrical conductivity is a measure of a water sample’s ability to conduct electricity, and therefore a measure of the water’s ionic activity and content. In a water sample, the higher the concentration of ionic (dissolved) constituents, the higher the conductivity.

Conductivity is usually measured in units of micro Siemens per centimeter (µS/cm) or milliSiemens per centimeter (mS/cm). 1 mS/cm equals 1,000 µS/cm.

Conductivity of the same water changes substantially as its temperature changes. This can have a confounding effect on attempts to compare this feature across different waters, or seasonal changes in this parameter for a particular body of water. When measuring in specific conductance, the conductivity is normalized to temperature of 25°C. This eliminates complication, and allows valuable comparisons at different water temperatures. Read the rest of this entry »

It’s that time of year again…freezing temperatures, snow, ice, and time to store the equipment in a temperature controlled area. Avoid storing or transporting monitoring equipment in cold and freezing conditions. Its just equipment right….Well, waiting for equipment to warm up may lead to time lost in the field and not letting it warm up may lead to improper operation and calibration.

Here are some of the potential consequences to storing your instruments in cold or near freezing environments and tips to avoid potential field issues. Just like people, the instrument will function much better if allowed to warm up and be put to bed in a nice warm environment.

Water Quality Instruments

• Stabilization of temperature will take longer as the instrument is moved form warm to cold environments. Save yourself time by storing your solutions and instruments in a controlled environment if possible. Stabilization of your instruments readings during calibration will occur more readily if the sensors are warm and solutions are at a constant temperature.
• Turbidity vials will break if frozen. Empty sample vials and/or store solutions indoors.
• Before storing water quality instruments, put a moist sponge in the sensor storage container. Do not add water or storage solution, as it could freeze around the sensors. pH probe bulbs will break if ice forms around them.
• Some submersible pumps use water for lubrication. Frozen water in the pump will damage it.
• Batteries do not last as long, and/or may not charge properly when they are cold.

Air Quality Instruments

• Electro-chemical gas sensors take longer to warm up when they are cold.
• Condensation can build inside F.I.Ds, causing the flame to extinguish. The dramatic temperature difference after ignition will cause water droplets to form in the detector chamber.
• Liquid crystal displays (LCDs) become sluggish and difficult to read when frozen.
• Batteries do not last as long, and/or may not charge properly when they are cold.

Please call your local Pine office with any questions or concerns.

Have you ever been on a site where your PID’s output value continues to climb, even in clean air? This is common in high humidity, and after long-term use. 

This occurrence may lead you to ask, “What value should I record as my screening value? Should I submit this soil sample to the lab? Are any of my readings accurate?”

 There are a couple of common causes for false positive readings; either a dirty hydrophobic filter (water trap) or a dirty lamp and detector combined with high humidity.

 Good news, the PID is not broken. Here’s what you need to do.

 1. First, swap the external hydrophobic filter. If the readings remain unstable, continue to step 2.

2. Take the instrument into a low humidity environment with clean ambient air.

3. Make sure the instrument is on and warmed up for at least 5 minutes.

4. Zero the PID in clean air and calibrate with fresh span gas..

5. Loosely cup your hand (clean hand) around the end of the probe.

If the PID indicates a steady increase in readings in excess of 10 ppm after about 15 seconds, then your lamp and sensor may be dirty and need cleaning prior to continued field use. Keep in mind that Methanol is required to clean the lamp and detector in the field and should be performed in accordance with the manufacturer’s recommendations.

6. Call your local Pine office with any questions or concerns. 

For more information on moisture and its impact on PIDs please view the following technical note provided by RAE Systems:

http://www.raesystems.com/~raedocs/App_Tech_Notes/Tech_Notes/TN-163_MiniRAE_2000_Moisture.pdf