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radiello® Diffusive Air Sampling Application - Volatile Organic Compounds (VOCs) Chemically Desorbed With CS2

radiello Components Used:

White diffusive body Product No. RAD120
Supporting plate Product No. RAD121
Vertical adapter Product No. RAD122 (optional)
Adsorbing cartridge Product No. RAD130

Or: radiello-ready-to-use Product No. RAD1231

Principle

Cartridge RAD130 is a stainless steel net cylinder, with 100 mesh grid opening and 5.8 mm diameter, packed with 530 ± 30 mg of activated charcoal with particle size 35-50 mesh. Volatile organic compounds are trapped by adsorption and recovered by carbon disulfide displacement, analysis is performed by FID gas chromatography.

Sampling Rates

The table below lists sampling rate values at 298 K (25 °C) and 1013 hPa, experimentally measured in a standard atmosphere chamber. For other compounds, whose diffusion coefficient1 is known, sampling rate can be calculated according to equation 5, taking into account that white diffusive body and RAD130 cartridge give the geometric constant of radiello the value of 14.145 ± 0.110 cm. Several experiments performed in the standard atmosphere chamber demonstrate that the calculated sampling rates seldom deviate by more than ± 10% from the experimentally measured values.

Effect of Temperature, Humidity, and Wind Speed

Sampling rates varies from the value at 298 K on the effect of temperature (in Kelvin) as expressed by the following equation

where QK is the sampling rate at the temperature K and Q298 is the reference value at 298 K. This produces a variation of ± 5% for 10 °C variation (upwards or downwards) from 25 °C.

Sampling rate is invariant with humidity in the range 15-90% and with wind speed between 0.1 and 10 m·s-1.

1Lugg G.A.: Diffusion Coefficients of Some Organic and Other Vapours in Air. Anal. Chem. 40-7:1072-1077 (1968).

 

Sampling Rate Values Q at 25 °C (298 K)

  Q298 linearity range uncertainty at 2σ  
Compound ml·min-1 μg·m-3·min % notes
acetone 77 10,000-600·106 7.0 a
acetonitrile 73 10,000-6·106 8.2 b
acrylonitrile 75 1,000-50·106 2.2  
benzyl alcohol 37 1,000-800·106 6.5  
amyl acetate 52 1,000-800·106 3.4  
benzene 80 500-500·106 1.8  
bromochloromethane 70 50,000-1,000·106 1.4  
butanol 74 1,000-500·106 5.0  
sec-butanol 64 1,000-300·106 5.2  
tert-butanol 62 1,000-300·106 5.5  
butyl acetate 60 1,000-1,000·106 3.0  
2-butoxyethanol 56 1,000-100·106 5.7  
2-butoxyethyl acetate 41 1,000-100·106 5.5  
carbon tetrachloride 67 100,000-60·106 9.0  
cyclohexane 54 500-500·106 4.5  
cyclohexanone 68 5,000-120·106 4.2  
cyclohexanol 54 5,000-120·106 4.5  
chlorobenzene 68 1,000-1,000·106 3.6  
chloroform 75 100,000-60·106 9.7 a
n-decane 43 500-1,000·106 1.1  
diaceton alcohol 43 500-1,000·106 4.5  
1,4-dichlorobenzene 51 1,000-1,000·106 7.7  
1,2-dichloroethane 77 1,000-500·106 8.2  
1,2-dichloropropane 66 500-250·106 4.5  
dichloromethane 90 500-60·106 8.7  
N,N-dimetylformamide 82 1,000-200·106 14.5 c
1,4-dioxane 68 1,000-600·106 5.5  
n-dodecane 8 1,000-1,000·106 4.7  
n-heptane 58 5,000-1,500·106 3.0  
n-hexane 66 1,000-1,000·106 2.5  
1-hexanol 52 5,000-120·106 5.5  
ethanol 102 10,000-500·106 7.5 a-b
diethyl ether 78 5,000-500·106 12.0 a
ethyl acetate 78 1,000-1,000·106 1.5  
ethylbenzene 68 1,000-1,000·106 2.4  
2-ethyl-1-hexanol 43 5,000-500·106 10.1  
2-ethoxyethanol 55 500-50·106 6.7 b
2-ethoxyethyl acetate 54 10,000-100·106 2.5  
ethyl-tert-butyl ether (ETBE) 61 500-200·106 3.0  
isobutanol 77 1,000-300·106 2.5  
isobutyl acetate 63 1,000-1,000·106 5.2  
isooctane 55 500-1,000·106 3.2  
isopropanol 52 10,000-400·106 12.0 b
isopropyl acetate 66 1,000-1,000·106 9.9  
isopropylbenzene 58 1,000-1,000·106 2.7  
limonene 43 1,000-1,000·106 10.0  
methanol 125 10,000-250·106 9.2 a-b
methyl acetate 80 1,000-1,000·106 12.0  
methyl-ter-butyl ether (MTBE) 65 500-200·106 2.5  
methylcyclohexane 66 1,000-1,000·106 6.5  
methylcyclopentane 70 1,000-1,000·106 2.5  
methylethylketone 79 1,000-500·106 1.6  
methylisobutylketone 67 1,000-250·106 8.7  
methyl metacrylate 68 1,000-500·106 2.5  
2-methylpentane 70 1,000-1,000·106 2.5  
3-methylpentane 70 1,000-1,000·106 2.5  
2-methoxyethanol 35 5,000-100·106 11.0 b
2-methoxyethyl acetate 56 2,000-100·106 3.0  
1-methoxy-2-propanol 55 1,000-350·106 6.0  
1-methoxy-2-propyl acetate 60 2,000-350·106 6.2  
naphthalene 25 1,000-1,000·106 7.0  
n-nonane 48 1,000-1,000·106 5.4  
n-octane 53 500-1,000·106 3.2  
pentane 74 1,000-1,000·106 1.9  
α-pinene 53 1,000-1,000·106 7.0  
propyl acetate 65 500-1,000·106 7.5  
propylbenzene 57 1,000-1,000·106 2.9  
styrene 61 1,000-500·106 3.0  
tetrachloroethylene 59 10,000-500·106 2.5  
tetrahydrofuran 74 2,000-250·106 11.0 b
toluene 74 500-1,000·106 1.5  
1,1,1-trichloroethane 62 5,000-1,000·106 5.5  
trichloroethylene 69 5,000-1,000·106 2.4  
1,2,4-trimethylbenzene 50 500-1,000·106 6.6  
n-undecane 24 1,000-1,000·106 10.0  
m-xylene 70 500-1,000·106 2.5  
o-xylene 65 500-1,000·106 2.5  
p-xylene 70 500-1,000·106 2.5  

Notes:
a = weakly adsorbed compound. If its concentration is higher than the TLV for the workplace environments it may be partially displaced by other compounds that are more strongly trapped if their concentration is also high. If this is the case, it is advisable to reduce sampling time under 8 hours.

b = prolonged exposure of charcoal cartridges at relative average humidity higher than 80% causes adsorption of up to 100 mg of water. Water does not interfere with adsorption mechanisms but is displaced by carbon disulfide and gives raise to a separate layer. Some very water soluble polar compounds will distribute between the two solvents, thus provoking an underestimation of the actual air concentration since only the carbon disulfide is injected in the gas chromatograph. When the concentration of polar compounds has to be determined, the calibration curve should be prepared by spiking 50 μl of water in each tube containing the cartridge and the 2 ml of carbon disulfide standard solution (see Analysis).

c = better reproducibility obtained by use of methanol as extraction solvent instead of carbon disulfide.

Calculations

The listed sampling rate values already take into account for the desorption efficiency with carbon disulfide. The average concentration over the exposure time interval is therefore calculated from the mass of analyte found onto the cartridge and exposure time without introducing any corrective factor, apart from corrections due to average temperature different from 25 °C.

Average concentration over the whole exposure time is calculated according to the following expression

where:
m = mass of analyte in μg
t = exposure time in minutes

 

Limit of Quantitation

The limit of quantitation depends on the instrumentation and on the analytical conditions. The minimum revealable environmental concentration can be estimated on the basis of the equation on page D1, where m is the minimum revealable mass, experimentally measured for each compound. Under the analytical conditions described on page D4, the limit of quantitation for 7 days exposure usually ranges from 0.05 to 1 μg·m-3, depending on the compound.

Exposure

Cartridge RAD130 has a very large loading capacity: about 80 mg, corresponding to an overall VOCs concentration of 3,000-3,500 mg·m-3 sampled for 8 hours or 70,000-80,000 μg·m-3 sampled for 14 days. Neverthless, if the quantified overall adsorbed mass should be near 80 mg, sampling rate could have deviated from linearity. If this is the case, it is advisable to repeat the sampling experiment reducing exposure time.

Workplace Environment
In workplace environments complex mixtures of airborne solvent vapours are often found at concentrations of 2,000-3,000 mg·m-3. The outstanding adsorbing capacity of RAD130 cartridges allows you to sample them for the whole working shift of 8 hours. On the other hand, the very high values of sampling rates for a variety of compounds allow you to perform accurate concentration measurements even after very short exposures. For example, 15 minutes are enough to measure 0.1 mg·m-3 of benzene.

radiello can therefore be employed to evaluate both TWA and STEL concentrations.

Other Indoor Sampling Experiments and Outdoor Campaigns
High sampling rates of radiello ensure very low limits of detection also for short exposure time intervals. For example, you may measure benzene concentrations as low as 2 μg·m-3 with an error not exceeding 4% after 8 hours of exposure. If radiello is exposed for 7 days, limit of quantitation becomes 0.1 μg·m-3.

Generally speaking, we suggest exposure time duration ranging from 8 hours to 30 days, the ideal value being 7 days.

 

Storage

The activated charcoal cartridges have undergone a complex conditioning process that ensures an outstanding chromatographic blank level, never exceeding three times the instrumental noise of a FID detector at the lowest attenuation.
Kept in a cool place and away from volatile organic compounds, the cartridges maintain unchanging blank level and adsorbing capacity for at least two years. Expiry date and lot number are printed onto the plastic bag wrapping each cartridge: its integrity stands as warranty seal.

After exposure the cartridges, well capped and kept in a cool and solvent-free place, maintain their content unalterated for at least six months.

Analysis

Extraction
Introduce 2 ml of CS2 and 100 μl of internal standard solution directly in the radiello glass tube without drawing out the cartridge. Always use class A volumetric pipettes or dispensers. Stir from time to time for 30 minutes. If analysis is not performed soon after, draw out the cartridge and discard it.

Calibration
Outdoor Environment Sampling
If benzene, toluene, ethylbenzene and xylenes (BTEX) have to be analyzed, prepare three or four standard solutions in CS2 having decreasing concentrations of the analytes in the following ranges (in mg·l-1):
 

benzene 0.04-17.6 ethylbenzene 0.04-17.7
toluene 0.09-34.8 m-xylene 0.04-17.2
o-xylene 0.04-17.6 p-xylene 0.04-17.2

It is advisable to proceed via consecutive dilutions, starting for example from a stock solution containing 1 ml of each compound in 100 ml. Always use class A volumetric glassware. Introduce 2 ml of each standard solution, along with 100 μl of internal standard, onto a blank RAD130 cartridge in its glass tube.

IMPORTANT
Always use high purity grade CS2, for example Product No. 84713 or Aldrich Product No. 34,227-0

BE CAREFUL
Even refrigerated, CS2 permeates the tube plastic cap: its volume decreases by 4-5% a day. If the internal standard
has been added, it is only matter of unpleasant odour...

Analysis of Unknown Samples

Identify the sample that has been exposed for the longest time or at the highest expected concentration. Introduce 2 ml of CS2 but do not add the internal standard, stir and let the sample stand for 30 minutes. Without discarding the cartridge, inject the CS2 solution in the gas chromatograph with FID detector (see below), identify the compounds appearing in the chromatogram and make an estimation of the order of magnitude of their concentrations.

Prepare a CS2 solution of the identified compounds with doubled concentration with respect to the sample. Dilute this solution in order to obtain standard solutions of concentration respectively about 0.1, 0.5 and 1 times the concentration estimated in the sample. Introduce 2 ml of each standard solution onto a blank RAD130 cartridge in its glass tube, along with the chosen internal standard solution.

The chosen internal standard should have a retention time that does not interfere with other compounds in the chromatogram. Compatibly with this requirements, we suggest to employ a solution of 2-fluorotoluene (e.g. Product No. F1,532-3 or Product No. 47520) in CS2 with concentration of 100 μl·l-1 for outdoor samples and 2 ml·l-1 for workplace samples.

Add 2 ml of CS2 and the internal standard to all of the samples, stir, let the samples stand for 30 minutes and discard the cartridges prior to the analysis.

USER TIP
For a very accurate calibration we offer the preloaded cartridges RAD405 (outdoor environment) and RAD406 (workplace environment).

Instrumental Analysis (advised)

Capillary Gas Chromatography With FID Detection

Outdoor environment samples: 100% dimethylpolysiloxane column 50m x 0.2mm, film thickness 0.5 μm; (e.g.
Petrocol DH 50.2, Product No. 24133-U) split injection of 2 μl; split ratio 25:1; nitrogen carrier gas at constant pressure of 20 psi; injector temperature 240 °C; oven initial temperature 35 °C for 5 minutes, 5 °C/min up to 90 °C, maintain for 3 minutes, 10 °C/min up to 220 °C, final isotherm for 5 minutes.

Chromatogram of Urban Outdoor Sample


Workplace samples: 100% dimethylpolysiloxane column 0.2 mm·50 m, film 0.5 μm; split injection of 3 μl, split ratio 100:1; carrier N2 at constant pressure of 20 psi; injector temperature 240 °C; oven initial temperature 50 °C for 5 minutes, 5 °C/min up to 80 °C, 15 °C/min up to 135 °C, 20 °C/min up to 220 °C, final isotherm 10 minutes. Total time: 29 minutes. The retention times for several compounds analyzed under the described conditions are listed below.

FID Chromatogram of Workplace Sample

 

Compound Retention Time
(minutes)
  Compound Retention Time
(minutes)
methanol 4.834   propyl acetate 11.868
ethanol 5.34   n-eptane 12.068
acetone 5.712   1-ethoxy-2-propanol 12.775
isopropanol 5.835   methylcyclohexane 12.912
pentane 6.121   methylisobutylketone 13.258
methyl acetate 6.346   isobutyl acetate 14.005
dichloromethane 6.405   toluene 14.055
2-methylpentane 7.559   butyl acetate 15.279
methylethylketone 7.719   n-octane 15.435
3-methylpentane 7.941   tetrachloroethylene 15.601
ethyl acetate 8.331   diaceton alcohol 15.915
n-hexane 8.402   1-methoxy-2-propyl acetate 16.609
isobutanol 8.763   ethylbenzene 16.997
methylcyclopentane 9.35   m+p-xylene 17.241
1,1,1-trichloroethane 9.636   cyclohexanone 17.436
butanol 9.956   cyclohexanol 17.436
isopropyl acetate 9.978   styrene 17.716
benzene 10.203   o-xylene 17.832
1-methoxy-2-propanol 10.424   2-buthoxyethanol 17.88
cyclohexane 10.58   n-nonane 18.186
1,2-dichloropropane 11.285   α-pinene 19.129
trichloroethylene 11.625   n-decane 20.334
isooctane 11.667   n-undecane 22.142
2-ethoxyethanol 11.831      

 

USER TIP
If you perform several analyses, a barcode reader will greatly improve productivity in your laboratory and will also minimize the possibility of errors in the copying of sample labels.

Please contact us to help you in the implementation of the reader.

We have also developed software solutions for the analytical data processing and automated production of analysis reports.

What makes the RAD130 cartridge incomparable?

The container is made of stainless steel cloth AISI 316 with 100 mesh grid opening. It is electric welded with no supply of foreign materials. It has tolerance of ± 0.05 mm diameter and of ± 0.1 mm length.

The cartridge is packed with vegetal activated charcoal with a very large adsorbing surface. Its exceptionally low blank is obtained by conditioning it in a nitrogen stream fluidised bed at 450 °C for 16 hours. The fluidised bed technique does not only guarantee the thorough purification of adsorbing material but also performs an accurate selection of its granulometry, by ventilation separations of the fraction under 50 mesh and over 35 mesh.


The Container & Contents

The container is made of stainless steel cloth AISI 316 with 100 mesh grid opening. It is electric welded with no supply of foreign materials. It has tolerance of ± 0.05 mm diameter and of ± 0.1 mm length.

The cartridge is packed with vegetal activated charcoal with a very large adsorbing surface. Its exceptionally low blank is obtained by conditioning it in a nitrogen stream fluidised bed at 450 °C for 16 hours. The fluidised bed technique does not only guarantee the thorough purification of adsorbing material but also performs an accurate selection of its granulometry, by ventilation separations of the fraction under 50 mesh and over 35 mesh.


The Production

The cartridge is filled up with charcoal by a very complex automated apparatus that was designed and realised in our laboratory. It avoids any contamination of the adsorbing material during the delicate process of cartridge production and ensures a very accurate dosing of the material itself, providing a variability of less than 2% of the weight of the activated charcoal among the cartridges.


The Quality Control

Each cartridge batch undergoes statistical quality control of the blank level. If amounts higher than 20 ng of each of the BTEX compounds are found, the entire lot is discarded.


The Sampling Rate Measurements

The sampling rate is measured in a standard atmosphere chamber unique in Italy (and one of the few found all over Europe) that allows the dynamic generation of high flows of controlled concentration gas mixtures from 1 μg·m-3 to 1,000 mg·m-3 (dynamic range from 1 to 106) of each investigated compound alone or mixed with others. The chamber allows temperature control from -20 to 60 °C, relative humidity control from 5% to 100% and air speed variation from 0.1 to 10 m·s-1.

All of the gas flows are measured as mass flows and have therefore the properties of primary standards. All of the operating parameters (gas flows, temperature, relative humidity, ...) are recorded and the records are available along with the certification documents.

Materials

     
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