<<< Back to Sampling and Analytical Methods |
Printing Instructions |
For problems with accessibility in using figures, illustrations and PDFs in this method, please contact
the SLTC at (801) 233-4900. These procedures were designed and tested for internal use by OSHA personnel.
Mention of any company name or commercial product does not constitute endorsement by OSHA. |
Benomyl
Related Information: Chemical Sampling -
Benomyl (Total Dust),
Benomyl (Respirable Fraction)
|
Method no.: |
PV2107 |
|
|
Control no.: |
T-PV2107-01-8804-CH |
|
|
Matrix: |
Air |
|
|
Target Concentration: |
10 mg/m3 (ACGIH TLV) |
|
|
Procedure: |
Samples are collected by drawing known volumesof air through OSHA versatile sampler (OVS-2) tubes, containing a glass fiber filter and two sections of XAD-2 adsorbent. Samples are extracted with acetonitrile (ACN) and analyzed by high performance liquid chromatography (HPLC) using an ultraviolet (UV) detector. |
|
|
Recommended air volume and sampling rate: |
60 L at 1.0 L/min |
|
|
Detection limit of the overall procedure (based on the recommended air volume): |
0.05 mg/m3 |
|
|
Status of method: |
Stopgap method. This method has been only partially evaluated and is presented for information and trial use. |
|
|
April, 1988 |
David B. Armitage |
|
|
Methods Development Team
Industrial Hygiene Chemistry Division
OSHA Salt Lake Technical Center
Sandy UT 84070-6406 |
1. General Discussion
1.1 Background
1.1.1 History of procedure
This evaluation was undertaken to determine the effectiveness of the OVS-2 tube
as a sampling device for benomyl. It follows the procedure developed for carbaryl.
(Ref. 5.1)
The literature indicates that benomyl decomposes in many organic solvents to
give carbendazim and n-butyl isocyanate (BIC). It is possible to analyze for benomyl
in organic solvents, but this calls for the addition of BIC at 100D times the level
of benomyl encountered to force the equilibrium back to the undecomposed benomyl. Due
to this decomposition the analytical method developed in this evaluation is for
carbendazim (however, the analyte is referred to as benomyl throughout this evaluation).
It follows a method developed by Zweig and Gao. (Ref. 5.2)
1.1.2 Toxic effects (This section is for information only and should not
be taken as the basis of OSHA policy).
The acute oral LD50 for rats is >10,000 mg/kg. The acute skin
absorption LD50 for rabbits is >10,000 mg/kg. (Ref. 5.3)
A low order of chronic toxicity has been found in several studies. The
results of these studies as well as the original references can be found
in the ACGIH documentation volume. (Ref. 5.3)
Due to its low toxicity the ACGIH has given benomyl a 10 mg/m3 TLV.
1.1.3 Potential workplace exposure
No estimate of worker exposure to benomyl could be found. Benomyl is used
as a systemic fungicide. (Ref. 5.4)
1.1.4 Physical properties (Ref. 5.3-5.5)
Molecular weight: |
290.32 |
Molecular formula: |
C14H18N4O3 |
CAS #: |
17804-35-2 |
Melting point: |
decomposes |
Vapor Pressure: |
negligible |
Appearance: |
white crystalline solid |
Solubility: |
insoluble in water and oil soluble in acetone,
alcohol, dimethyl formamide, chloroform, and xylene |
Synonyms: |
Benex, Benlate, Tersan 1991 |
Chemical name: |
Methyl 1-(butylcarbamoyl)- 2-benzimidazolecarbamate |
Structure: |
|
UV maxima (in ACN) (i.e., values are for carbendazim): |
286 nm and 244 nm |
1.2 Limit defining parameters
The detection limit of the analytical procedure is 10 ng per injection. This is
the amount of analyte which will give a peak whose height is approximately five
times the baseline noise.
2. Sampling procedure
2.1 Apparatus
2.1.1 Samples are collected by using a personal sampling pump that can be
calibrated to within ±5% of the recommended flow rate with the sampling device in line.
2.1.2 Samples are collected with OVS-2 tubes, which are specially made 13-mm
o.d. glass tubes that are tapered to 6-mm o.d. These tubes are packed with a 140-mg
backup section and a 270-mg sampling section of cleaned XAD-2. The backup section is
retained by two foam plugs and the sampling section is between one foam plug and a
13-mm diameter glass fiber filter. The glass fiber filter is held next to the sampling
section by a polytetrafluoroethylene (PTFE) retainer.
Figure 1. OVS-2 Sampling Device
2.2 Reagents
No sampling reagents are required.
2.3 Sampling technique
2.3.1 Attach the small end of the OVS-2 sampling tube to the sampling pump
with flexible, plastic tubing such that the large, front section of the sampling
tube is exposed directly to the atmosphere. Do not place any tubing in front of the
sampler. Attach the sampler vertically (large end down) in the worker's breathing zone
in such a manner that it does not impede work performance.
2.3.2 After sampling for the appropriate time, remove the sampling device and seal the tube with plastic end caps.
2.3.3 Wrap each sample end-to-end with an OSHA seal (Form 21).
2.3.4 Submit at least one blank with each set of samples. Handle the blanks the same as the other samples except draw no air through them.
2.3.5 Submit any bulk samples in a separate container. Do not ship them with the air samples.
2.4 Extraction efficiency
2.4.1 Glass fiber filter
Five 13-mm glass fiber filters were each liquid spikedwith 50 µL of an 838 µg/mL
solution of benomyl in methanol. These five filters, along with an unspiked filter,
were place in separate 4-mL vials and allowed to sit overnight at room temperature.
They were then extracted with 3.0 mL of acetonitrile.
Table 2.4.1 Glass Fiber Filter Extraction Study
Filter # |
Amount Spiked |
Amount Recovered |
% Recovery |
AD1 |
41.90 µg |
42.08 µg |
100.4 |
AD2 |
41.90 µg |
40.60 µg |
96.9 |
AD3 |
41.90 µg |
43.35 µg |
103.5 |
AD4 |
41.90 µg |
41.71 µg |
99.6 |
AD5 |
41.90 µg |
41.64 µg |
99.4 |
AD6 |
0.00 µg |
0.00 µg |
blank |
|
Average Recovery is 100.0 % |
2.4.2 XAD-2 adsorbent
An amount of XAD-2 adsorbent equal to the A section (270 mg) of an OVS-2 tube
was placed in each of five 4-mL vials which were then sealed with PTFE lined septa.
The adsorbent in each vial was then liquid spiked with 50 µL of an 838 µL/mL
solution of benomyl in methanol by injecting the solution onto the adsorbent
through the septum. These vials were then allowed to equilibrate overnight in
a drawer at room temperature. They were then desorbed with 3.0 mL of acetonitrile.
Table 2.4.2 XAD-2 Adsorbent Desorption Study
Adsorbent# |
Amount Spiked |
Amount Recovered |
% Recovery |
AD1 |
41.90 µg |
39.13 µg |
93.4 |
AD2 |
41.90 µg |
39.55 µg |
94.4 |
AD3 |
41.90 µg |
40.05 µg |
95.6 |
AD4 |
41.90 µg |
40.70 µg |
97.1 |
AD5 |
41.90 µg |
41.22 µg |
98.4 |
AD6 |
0.00 µg |
0.00 µg |
Blank |
|
Average Recovery is 95.8% |
2.4.3 OVS-2 tubes
Nine OVS-2 tubes were each liquid spiked with 50 µL of an 838 µg/mL
solution of benomyl in methanol by spiking the glass fiber filter. The tubes
were sealed and stored overnight in a drawer at room temperature. A blank tube
was also stored with the nine above. Three of the spiked tubes and the blank were
then extracted as in Section 3.4.
Table 2.4.3 OVS-2 tube Extraction Study
Tube # |
Amount spiked |
Amount recovered |
% Recovery |
OVS 1 |
41.90 µg |
41.74 µg |
99.6 |
OVS 2 |
41.90 µg |
41.93 µg |
100.1 |
OVS 3 |
41.90 µg |
42.47 µg |
101.4 |
OVS BL |
0.00 µg |
0.00 µg |
Blank |
|
Average recovery is 100.4 % |
2.5 Retention efficiency
The remaining six OVS-2 tubes each had
60 liters if humid air (65% relative humidity) drawn through them. Three
of these tubes were extracted as in Section 3.4 and analyzed
immediately. The remaining three tubes were returned to the drawer for
the storage study.
Table 2.5 Retention Efficiency Study
Tube # |
Amount spiked |
Amount recovered |
% Recovery |
OVS 4 |
41.90 µg |
42.75 µg |
102.0 |
OVS 5 |
41.90 µg |
43.66 µg |
104.2 |
OVS 6 |
41.90 µg |
42.57 µg |
101.2 |
|
Average recovery is 101.5 % |
2.6 Sample Storage
The remaining three spiked tubes from
section 2.5 above were stored for a total of 7 days in a drawer at room
temperature. They were then extracted as in Section 3.4.
Table 2.6 Storage Study
Tube # |
Amount spiked |
Amount recovered |
% Recovery |
OVS 7 |
41.90 µg |
40.76 µg |
97.3 |
OVS 8 |
41.90 µg |
40.76 µg |
97.3 |
OVS 9 |
41.90 µg |
41.51 µg |
99.1 |
|
Average recovery is 97.9 % |
2.7 Recommended air volume and sampling rate
2.7.1 The recommended air volume is 60 L.
2.7.2 The recommended flow rate is 1.0 L/min.
2.8 Interferences
It is not known if any compounds will interfere with the collection
of benomyl. Suspected interferences should be reported to the laboratory
with submitted samples.
2.9 Safety precautions
2.9.1 Attach the sampling equipment in such a manner that it will
not interfere with work performance or employee safety.
2.9.2 Follow all safety practices that apply to the work area being sampled.
3. Analytical procedure
3.1 Apparatus
3.1.1 A high performance liquid chromatograph equipped with a UV detector,
and manual or automatic injector. A Waters 510 pump, Waters 710B autosampler,
and Waters 490E UV detector were used in this evaluation.
3.1.2 An HPLC column capable of separating benomyl from any
interferences. A 25-cm × 4.6-mm i.d. Chromasil 5 micron C18 column
was used in this evaluation.
3.1.3 An electronic integrator or other suitable means of measuring
detector response. A Hewlett-Packard 3357 data system was used in this
evaluation.
3.1.4 Vials, 4-mL glass with PTFE-lined septa.
3.1.5 Volumetric flasks, pipets, and syringes for preparing
standards, making dilutions, and performing injections.
3.2 Reagents
3.2.1 HPLC grade ACN.
3.2.2 HPLC grade water. A Millipore Milli-Q system was used to
prepare the water in this evaluation.
3.2.3 Benomyl, 99+% (EPA).
3.3 Standard preparation
Prepare stock standard solutions by adding acetonitrile to
pre-weighed amounts of benomyl. Prepare working range standard solutions
by diluting stock solutions with acetonitrile. Store stock and dilute
standards in a freezer.
Place aliquots of the working range standards in 4-mL vials and
handle them along with the samples.
Note: A benomyl in methanol standard was used for spiking in the
extraction, retention, and storage tests because benomyl is more soluble
in methanol than acetonitrile. Methanol was not used for sample
extraction because the literature indicates quicker and more complete
decomposition of benomyl in acetonitrile.(Ref. 5.2)
3.4 Sample preparation
3.4.1 Transfer the 13-mm glass fiber filter and the 270-mg section
of the sampling tube to a 4-mL vial. Place the first foam plug and the
140-mg section in a separate vial. A small glass funnel can be used to
facilitate the transfer of the adsorbent. Discard the rear foam plug.
No not discard the glass sampling tube; it can be reused after it has
been cleaned with surfactant or suitable solvent.
3.4.2 Add 3.0 mL of ACN to each vial.
3.4.3 Seal the vials the PTFE-lined septa and allow them to extract
for one half hour. Shake the vials by hand periodically during this
extraction time. Place the vials in a 45ºC water bath for an
additional half hour to ensure complete decomposition of benomyl
to carbendazim.
3.5 Analysis
3.5.1 Instrument conditions
Column: |
25-cm × 4.6-mm i.d. Chromasil 5 micron C18 |
Mobile Phase: |
70% acetonitrile / 30% water |
Flow rate: |
1 mL/min |
UV detector: |
244 and 286 nm |
Retention time: |
3.5 minutes (carbendazim) |
Injection volume: |
10 µL |
3.5.2 Chromatogram
Figure 2. Chromatogram of Carbendazim (note the small benomyl peak,
benomyl not completely decomposed)
3.6 Interferences
3.6.1 Any compound having a similar retention time to the analyte
is a potential interference. Generally, chromatographic conditions can
be altered to separate an interference from the analyte.
3.6.2 Retention time on a single column is not proof of chemical identity.
Analysis by an alternative HPLC column, detection at another
wavelength, comparison of absorbance response ratios, and confirmation
by mass spectrometry are additional means of identification.
3.7 Calculations
3.7.1 A calibration curve is constructed by plotting detector
response versus standard concentration.
3.7.2 The concentration of benomyl in a sample is determined from the calibration curve. If
benomyl is found on the backup section, it is added to the amount
found on the front section. Blank corrections for each section should
be performed before adding the results together.
3.7.3 The air concentration is then determined by the following formula.
mg/m2 |
= |
(mg/mL in sample)(desorption volume, mL) |
|
(air volume, L)(desorption efficiency, decimal) |
3.8 Safety Precautions
3.8.1 Avoid exposure to all standards.
3.8.2 Avoid exposure to all solvents.
3.8.3 Wear safety glasses at all times.
4. Recommendations for further study
An HPLC column which gives better chromatographic results should be
used for the analysis of benomyl in the future. One such column is a 25-cm × 4.6-mm
i.d. Chromegabond 5 micron TMS (see the n-butyl isocyanate
in the presence of benomyl stopgap)(Ref. 5.6) This method should be
fully validated.
5. References
5.1 Burright, D., Method #63, "Carbaryl (Sevin)", OSHA
Analytical Laboratory, unpublished, 1987.
5.2 Zweig, G. and R. Gao. Anal. Chem. 55:1448-51 (1983).
5.3 "Documentation of the Threshold Limit Values and Biological
Exposure Indices, American Conference of Governmental Industrial
Hygenists Inc., fifth edition, 1986.
5.4 "Farm Chemicals Handbook", Meister Publishing Co.,
1985.
5.5 Windholz, M., Ed. "Merck Index", 10th ed.; Merck and
Co., Rahway, NJ, 1983.
5.6 Armitage, D.B., Stopgap, "Benomyl with n-Butyl Isocyanate",
OSHA Analytical Laboratory, unpublished, 1988.
|
|
|