Frequently Asked Questions - radiello® Products
General
What is the purpose of the recommended extra storage tubes?
The extra storage tubes are just proposed for reusable tubes (RAD145 for instance) and for replacing glass tubes that could get broken. If you are in the field and you break a storage tube or lose it, we recommend you carry a few extra empty glass tubes in the field or have them available in the lab.
What are the max/min sampling temperatures for each of the media?
If temperatures deviate significantly from 20-25 °C the results need to be corrected according to the equation provided in the radiello Overview. We have performed product validation experiments in the range of -10 to 40 °C.
Has each media type been tested for interfering components?
The interfering agents, (with the exception of CS2 interference for H2S measurement), are mentioned in the radiello Overview; examples: water vapor for anesthetics, ozone for aldehydes, excess of water vapor for VOCs, etc.
Why are some sampling rates given in mL/min and some are given in ng/ppb-min?
The 2 different units for uptake rate are both mentioned in standards for air quality measurements with diffusive samplers; our preference depends on the way in which the reference concentration was measured. For example, the NO2 sampler was validated by measuring the concentration with a chemiluminescence analyser, measuring in ppb.
Has precision been evaluated for the various media types?
The precision has been evaluated extensively for some sorbents and less extensively for the remaining media. At the very least, we have tested 6 replicates in an exposure test.
Why are 3 blanks recommended for some tests, and 2 for others?
Some media have a higher intrinsic variability, while others do not. Our experience suggests that some media do not require many blanks (e.g. RAD130 for BTEX) while others do (e.g. aldehydes).
It is also important to distinguish between laboratory blank, media blank, and field/transport blank. In general, it is good practice to include one trip blank for each sampling activity - unless one has good control over the overall IH procedure, including shipping of media, sampling, transport, shipping to the lab, etc. The testing lab may avoid performing a replicate lab blank based on manufactured lot number of the passive sampler.
Are there any Desorption Efficiency (D) studies for radiello samplers?
For every radiello sampler, the desorption efficiency (D) is included in the sampling rate, so one does not need to include D in the calculations, because the sampling rate is determined by the amount of analyte recovered (i.e. desorbed) from the exposed cartridges. Furthermore, applying a D factor in the calculations would involve an error (overestimation). We suggest you closely follow the recommended analytical procedure outlined in the radiello Overview.
Is it acceptable to use a solvent other than carbon disulfide (CS2), for example methanol, for solvent desorption?
A simple means for correcting the sampling rate value for the change of solvent would be to determine desoprtion efficiency of VOCs of interest by using carbon disulfide and then by using methanol at the same loading level(s). Then divide the CS2 sampling value by D[CS2], and multiply the result by D[methanol]: you should get the "apparent" sampling rate for desorption by methanol.
Contact our Technical Service group for futher advice about your specific application.
Diffusive Bodies
Can diffusive bodies can be affected from adsorption of solvents when used in high concentration environments; for example, when sampling hexane, xylene and other vapors in high concentration?
We have no data that would permit us to make general recommendation about reusing diffusive bodies after exposure to high solvent concentrations. In IH practice, the diffusive bodies often get dirty after a sampling workshift in high concentration environments. So in most cases they are discarded. On the other hand, in ambient air they can be reused more times but are cleaned before reuse.
What method do you recommend for cleaning the diffusive bodies so they can be reused for sampling?
When exposed outdoors or in a workplace environment, the diffusive body may get dirty from airborne dust. Fine particles (PM10) are especially harmful to yellow diffusive bodies since they can obstruct the pores. On the other hand, diffusive bodies used in ambient air can be reused, but are cleaned before reuse. You can clean them as follows:
(1) Immerse the diffusive bodies in a beaker with a soapy solution (e.g. we usually employ mildly alkaline detergent - used also for laboratory glassware - at 2% in deionised water); then, sonicate for 20 minutes. As the diffusive bodies float in this solution, you could make them sink by putting a weight (such as a small beaker) on them to ensure they remain submerged.
(2) Rinse the diffusive bodies with plenty of water and then with deionized water. Let them finally dry in air.
After four or five washings and reuse, the diffusive bodies should be replaced. Adsorbed dust can penetrate deep within the pores over time, and may not be eleiminated by the above washing procedure.
Can I use solvents or heat the diffusive bodies to clean them?
The diffusive bodies should never be rinsed with solvents, nor heated in an oven. As indicated above, after some exposure cycles, the exact number depending on the concentration of particulate matter found in the environment where they have been exposed, they should be washed by immersion in a soapy solution with sonication. They should be thoroughly rinsed with water and deionised water, then dried in air. (previous question)
What is the difference between the white diffusive body (RAD120) and the blue diffusive body (RAD1201)? Why is the yellow diffusive (RAD1202) body specified for TD sampling?
There is no difference in the porosity between the white and blue diffusive bodies; however, the blue body is recommended for sampling light sensitive compounds or when light sensitive reagents (e.g., DNPH) are used. The yellow diffusive body has a thicker membrane, designed for TD samplers that contain reversible adsorbents with lower capacity.
Is it possible to use a different color diffusive body from what is recommended in the radiello overview for sampling BTEX/VOCs? If so, what effect does it have on the diffusion rate in the calculations provided?
We strongly encourage you to use the diffusive body specified in the method; however, if you are sampling in a high concentration environment it is possible to reduce the diffusion rate by changing from a blue or white diffusive body to the yellow diffusive body which is specified for use with the TD samplers. In order to correct for this change, we recommend you proceed with caution. We suggest to assume a reduction of uptake rate is proportional to the uptake ratio of some VOCs. For example, toluene and ethylbenzene, which have almost complete recoveries both on charcoal (RAD130 - white body) and on Carbograph (RAD145-yellow body), the UR ratios are 2.5 - 2.6; so, one might assume an uptake rate reduction by that factor.
What is the recommended washing schedule for the diffusive bodies?
PM10 Concentration (µg/m³): <30 40 >50
Washing after days of exposure: 45 30 15
Can I use solvents or heat the diffusive bodies to clean them?
The diffusive bodies should never be rinsed with solvents, nor heated in an oven. As indicated above, after some exposure cycles, the exact number, depending on the concentration of particulate matter found in the environment where they have been exposed, they should be washed by immersion in a soapy solution (we usually employ mildly alkaline detergent - used also for laboratory glassware - at 2% in deionised water) with sonication. They should be thoroughly rinsed with water and deionised water, then dried in air.
Estimation procedure for sampling rates of new/unlisted compounds
The calculation of the uptake rate could be a practical way for measuring it, provided that it is adsorbed and desorbed.
The diffusion coefficient D mentioned in page A2, eq. [5] of the radiello Overview is meant for diffusion in air. Actually we do not know D through the diffusive membrane of radiello, i.e. the porous polyethylene of the diffusive body. From another point of view, we have determined that, while the nominal geometrical constant of a typical radiello (like the activated charcoal cartridges with white diffusive body) is 28 cm, the experimental value of this constant is 14.52 cm. The geometrical constant is the ratio under eq. [5], i.e. [(2 p h) / ln (rd/ra)]. We have derived this value calculating it back from the experimental uptake rates and the diffusion coefficient in air (Lugg, Anal. Chem, 40, no. 7 (1968), 1072-1077). So, multiplying D values in air in cm2/sec by the radiello's white diff. body's geometrical constant of 14.52 cm, you can calculate uptake rates for other compounds (provided the suitability of the sorbent for the compound is known).
With RAD145, which is used inside yellow bodies, the diffusion geometry changes. You do not know the geometrical constant, but you can use the ratio of diffusion coefficients: you need to know the D in air of MITC and the one of a compound of thermal desorption radiello's list, e.g. the toluene. Divide the U value of the "known" compound by its diffusion coefficient and you will get the "apparent" geometrical constant. Then multiply by the MITC's diffusion coefficient.
However concerns are still chemical stability and desorption efficiency of the "unknown" compound.
RAD170 for Hydrogen Sulfide
Can I use Sodium Sulfide as the calibration standard?
Do not calibrate using sodium sulfide, since it is unstable. We recommend using RAD171 for the calibration solution. RAD171 is a diluted solution of methylene blue (the reaction product). Follow the instructions in the radiello overview for the dilution protocol. Start by diluting the solution using the ratio 1:50.
When using radiello H2S (RAD170), what are the setup specifications for analysis by spectrophotometry?
Wavelength: 665nm
Slit width: 2nm
Optical Path: 1cm, quartz cell
How is the concentration of hydrogen sulfide derived in µg/mL from the calibration curve?
After recording the absorbance of the samples, we take these values and multiply by 10 (the volume of water used for extraction in mL). This represents the mass (m) of sulfide ion in the sample. (This must be used for proper calculation of the formula, refer to the radiello overview). Adjust the value of QK according to the sampling temperature (Use the formula located in the radiello Overview).
Do I need to perform another correction factor after calibration?
There is no need to perform another correction because the calibration already accounts for it.
Is Desorption Efficiency available for the radiello H2S sampling device?
The desorption efficiency has not be studied directly. The Q value in the calculation accounts for the desorption efficiency because the sampling rate (apparent) by dividing the recovered amount. Therefore we looked at the amount recovered at the end of the process, thus including the desorption efficiency. Thus exposure (concentration per time) by this factor is already included (hidden) within the sampling rate.
Correcting Sampling Rate for the Temperature:
The formula for correcting the sampling value for the temperature depends on the fact that the adsorption process depends on the temperature. The mean temperature must be recorded in Kelvin (K). So Qk (sampling value at temperature K) is calculated by multiplying Q298 (i.e. 0.0096) for the ratio between sampling temperature and 298 elevated to the power 3.8. Concerning temperature correction, the value in ng/ppb min contains the concentration expressed in ppb, which is a unit that is not dependent on the temperature. You have to start with the value of Q298 = 0.096 ng/ppb min, then correct for the actual sampling temperature using the formula: QK= 0.096*(K/298)^3.8 ng/ppb min.
What is the relationship between the sampling rate of 69 mL/min and 0.096 ng/ppb-min?
The value in mL/min was determined as an alternative unit, but the "native" unit of sampling rate is ng/ppb min. It was calculated starting with the value in ng/ppb min,assuming a temperature of 25 °C.
Do I need to convert the final values to the number of sulfide ions?
The final values are expressed as ppb of H2S, even if you put into the formula the amount of sulfide ions. The sampling rate value was calculated in ng S= ions /ppb H2S * min, with no conversion, for convenience of the users.
How is LOQ of 1 ppb determined?
The LOQ of 1 ppb is an estimation based on typical instrumental conditions. Each user should calculate his own LOQ, based on blank variability and/or calibration curve. There are many methods for determining LOQ.
Do you have a method for spiking samples onto the H2S cartridge?
We do not recommend making spike solutions using the RAD171 calibration standard because it contains the reaction product. The concentration of the undiluted solution is 57.25 µg/mL (as sulfide ion). If you have to make the spike solution using methylene blue standard, check the absorbance of the same spikes with diluted water (as for preparing standards). The "BS" should be the same as your fourth standard (0.5725), while the "MDL" should be equal to the first standard. You should have more or less the same values, otherwise it means that the cartridge retains some methylene blue. Be sure to stir well. *Note: we do not use the above spiking procedure for determining the recovery; we determine the overall response of the whole process.
What are the interferences for the Hydrogen Sulfide method?
Carbon disulfide is a potential interferent and the interference rate was assessed to be 0.026 µg/m³ H2S per µg/m³ of CS2
Is there any information available regarding possible side reactions and interference from other compounds (particularly from those compounds that are common in landfill gas—e.g. methane, carbon dioxide, other reduced sulfur compounds/mercaptans/etc.)?
From a theoretical point of view, every compound able of reactting with zinc ion to produce a sulfide can interfere. So we could exclude interference from methane and carbon dioxide, but not other sulfides and mercaptans.
How should samples be stored prior to analysis?
We recommend storing the samples at 4 ºC
What are typical blank values for the cartridge (10 mL water + 0.5 mL of ferric chloride-amine solution)?
Typical blank levels are between 0.010 and 0.015 absorbance units, which correspond to about 0.1 - 0.2 micrograms as H2S.
Has the radiello RAD170 sampler been used for any significant studies within the US?
The RAD170 sampler has been used extensively within the US to detect low levels of hydrogen sulfide in homes that may have been built with "Chinese Drywall".
Another important recent study is referenced below:
J Anim Sci. 2009 Jun;87(6):2124-32. Epub 2009 Feb 27. Leibovich J, Vasconcelos JT, Galyean ML, Effects of corn processing method in diets containing sorghum wet distillers grain plus solubles on performance and carcass characteristics of finishing beef cattle and on in vitro fermentation of diets. Department of Animal and Food Sciences, Texas Tech University, Box 42141, Lubbock 79409, USA.
RAD145 for BTEX/VOCs
Will the RAD145 adsorbing cartridges fit my thermal desorption instrument?
The RAD145 cartridges will fit into any thermal desorption instrument accepting ¼ in. (6.35 mm) x 3.5 in. (89 mm) tubes such as Markes, PerkinElmer, DANI, OI Analytical and Shimadzu Instruments.
We need to sample low concentrations of VOCs. What is the best approach for conditioning the RAD145 sampler?
The RAD145 cartridges are conditioned before they are packed in order to lower the background of benzene, toluene and other potential contaminants to a few nanograms. The best approach for minimizing the background for the measurement of low concentrations is to condition the cartridges again individually, before exposure. This can be done by means of a dedicated apparatatus (18-port) or by thermal desorbers - like Turbo Matrix from PerkinElmer - which can be programmed for tube heating cycles. We recommend you follow your instrument manufacturer's instructions for conditioning.
Can customers purchase empty cartridges and pack them with the adsorbent of their choice?
Empty cartridges are not available for sale.
What determines sampling rate for a compound? Is it adsorbent, diffusive body or both?
The sampling rate for RAD145 inside the yellow membrane RAD1202 is determined by the combination of the adsorbent and of the diffusive body, which is thicker than the standard bodies (white and blue), in order to reduce sampling rate (SR). and preventing competition of heavier compounds on lighter compounds (e.g.benzene) onto the adsorbent surface.
Sometimes when I open the RAD145 cartridge packaging, I notice fines of Carbograph 4. Will they damage my instrument?
Carbograph 4, contained inside SS net cartridges of RAD145, is a very fragile material. The presence of a small amount of fine powder outside the net cannot be avoided. The cartridges are vibrated to eliminate much of the fine powder that could escape from the net; but all subsequent treatment and handling steps (introduction in glass tubes, packaging, storage, transportation, etc.) may create additional fines. That small an amount of fine powder is not a problem for thermodesorbers - the ATD400 or TurboMatrix desorbers run thousands of desorbing cycles with Carbograph 4 radiello cartridges per year, without clogging problems. Perform regular maintenance of the TD's inlet filters, which catch the fine powder during tube desorption. We also recommend the use of gloves when handling the cartridge (any radiello cartridge) in order to avoid any potential contamination.
What determines the recommended exposure times listed in the radiello overview? Why can some compounds be sampled for up to 14 days, while for others, only 7 day sampling is recommended?
The sampling rates values listed for RAD145 are determined for two possible exposure durations (7-day and 14-day). Lighter compounds, like benzene, show a slight decrease in sampling rate with time (from 7 to 14 days), while other compounds behave differently. That is why two sets of sampling rates are listed. If no Sampling Rate is listed for 14 days, it means that we have no validation data. Of course, it is important to use the sampling rate value that matches the exposure duration.
Have any studies been documented that compare canister methods with radiello diffusive samplers?
We do not have comparison studies with Summa Canisters, however, your Analytical Test Lab may have performed their own internal studies. Please consult with them for more information.
Are there any studies where results from sampling with axial diffusion caps have been compared to results obtained with radiello diffusive samplers?
ICSM has presented in 2006, a review of some comparative studies involving radiello and pumped sampling or radiello, pumped sampling and axial diffusive samplers (tetrachloroethylene, benzene, toluene, xylenes,
cite link to radiello Literature : http://www.radiello.com/english/inter_en.htm
Can RAD145 be used for sampling the VOCs TCE and PCE (trichloroethylene and tetrachloroethylene)? Are validation studies available?
Yes. As far as validation studies are concerned, ICSM was involved since 2001 in the preparation and implementation of the Observatory of Indoor Air Quality in France. We did a validation study for measuring VOCs in indoor air, by means of RAD145/RAD1202, based upon 7-day samplings; then we participated also in the data collection phase, involving more than 500 measurements throughout the years 2003-2005. Among the compounds measured for 7-day exposure, TCE and PCE were included, along with 14 more VOCs. The description of the survey, carried out by CSTB (a french public organisation charged with the setup and management of the Observatory http://www/www.pngr-interieur.org) is available online: http://www/www.pngr-interieur.org/observatory.aspx?IDPage=5
Can the sampling time be extended to 3-4 weeks for the RAD145 Sampler?
It is likely that sampling rates will decrease by exposing RAD145 to sampling durations of 3 or 4 weeks. For longer term sampling, we suggest using the RAD130 for BTEX/VOCs.
In the Sampling Rate Values Table in the radiello overview for the RAD145, what does "Linear Up to µg/m³-min" (column 4) represent?
The upper linearity limit represents the upper validation point for that individual compound. For example when referring to n-hexane in the table, it means that diffusive sampling was validated onto RAD145 up to an exposure of 420,000 µg/m³ x min, i.e. about 42 µg/m³ by 7 days (10,000 min). That figure is related to the mass uptake onto the cartridge. It is the maximum mass uptake measured during validation. It is useful to determine the maximum concentration that you can apply for a defined exposure time, or the maximum exposure time for a defined concentration level.
Knowing the "Linear Up to µg/m³-min" value, how do I calculate if I have enough mass on the cartridge?
If one wants to evaluate if you have enough on the cartridge, multiply the expected concentration (µg/m³) by the uptake rate (mL/min) by the time (min) and divide by 1,000,000. You will get the expected amount in micrograms. This is the way of calculating the uptake.
How does radiello compare to other thermal diffusive samplers such as a single-bed PerkinElmer tube (RAD145)?
With thermal desorption, the gain ratio is even higher: for benzene (as an example) the uptake rate on RAD145 is 27 mL/min vs. about 0.5 mL/min of PE ATD tube. In this case, the analyst who is familiar with PE tubes should increase the split ratio when using radiello.
Is it possible to sample for vinyl chloride with RAD130 or RAD145?
Vinyl chloride is a difficult compound to sample due to its volatility, we have not performed any sampling rate studies at this time.
How can uptake rates being calculated for compounds where no sampling rate is given?
For RAD145/1202 the most practical method to estimate the uptake rate is the one you show below, based on the ratio do D values.
Possible to simply calculate the Q (individual) by: Q (individual) = Q (known)/ D (known) * D (Compound).
But this model is based on the hypothesis that the compound for which you want to calculate UR and the "known" compound are chemically similar, i.e. we must trust that they have both a 100% desorption efficiency, that they do not decompose during desorption step, that they do not show significant dependency on exposure time, and so on. In a word, they have both to behave ideally in the diffusive sampling system. Calculated valus will have an uncertainty, that is not known with out practical proof studies.
So, the above calculation model can be applied only with caution, when we are sure that the target compounds behave ideally and are neither too much volatile nor too heavy.
RAD130 for BTEX/VOCs
Is it acceptable to use a different solvent than carbon disulfide (CS2), such as methanol for solvent desorption?
In principle, yes; but since the sampling rate also incorporates the desorption efficiency, it needs to be corrected. A simple means to correct the sampling rate value for the change of solvent would be to determine desoprtion efficiency of the VOCs of interest by using carbon disulfide and then by using methanol at the same loading level. Next, divide the CS2 sampling value by D[CS2], and multiply the result by D[methanol]: you should get the "apparent" sampling rate for desorption by methanol.
Is it possible to sample for vinyl chloride with RAD130 or RAD145?
Vinyl chloride is a difficult compound to sample, we have not performed any sampling rate studies at this time.
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