<< Back to Sampling and Analytical Methods

For problems with accessibility in using figures and illustrations 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.


Related Information: Chemical Sampling - Methyl Formate


Method number: PV2041
 
Matrix: Air
 
Target Concentration: 100 ppm (246 mg/m3) OSHA permissible exposure limit (PEL).
 
Procedure: Samples are collected by drawing known volumes of air through Anasorb 747 sampling tube (6-mm i.d. glass tube, the front section contains 400 mg and the back 200 mg of sorbent). Samples are desorbed with a 90:10 (v/v) methyl alcohol/dimethylformamide solution and analyzed by gas chromatography (GC) using a flame ionization detector (FID).
 
Recommended air volume
and sampling rate:

3 L at 0.05 L/min
 
Detection limit of the overall procedure (based on the recommended air volume and the analytical detection limit): 1.16 ppm (2.84 mg/m3)
 
Special requirements: Ship the samples cold after sampling to the laboratory and analyzed immediately.
 
Status of method: Partially evaluated method. This method has been partially evaluated and is presented for information and trial use only.
 
April 1992 (final) Chemist: Ing-Fong Chan
Organic Service Branch II
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 develop a sampling and analytical procedure for methyl formate at the OSHA PEL 100 ppm (Ref. 5.1.).

1.1.2. Toxic effects (This section is for information only and should not be taken as the basis of OSHA policy.)

Inhalation of vapor produces nasal and conjunctival irritation, retching, narcosis, and death from pulmonary effects (Ref. 5.2., 5.3. and 5.4.).

1.1.3. Potential workplace exposure

Methyl formate has been employed as a fumigant and larvicide, as well as a solvent for cellulose acetate and in organic synthesis. (Ref. 5.2., 5.3. and 5.4.). No data is available on the extent of work place exposure.

1.1.4. Physical properties (Ref. 5.2., 5.3. and 5.4.)


CAS number: 107-31-3
IMIS number: 1770
Molecular weight: 60.05
Molecular formula: C2H4O2
Density: 0.987 at 20°C
Boiling point: 31.5°C at 101.3 kPa (760 mmHg)
Solubility: soluble in about 3.3 parts water
miscible with alcohol and ether
Chemical name: methyl formate
Synonyms: methyl methanoate
formic acid methyl ester
Appearance: colorless liquid with an agreeable odor
Structure: HCOOCH3

1.2. Limit defining parameters

The detection limit of the analytical procedure, including a 2.7:1 split ratio, is 3.16 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. A sample is 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. A sample is collected with 6-mm i.d. × 8-mm o.d. glass sampling tube packed with two sections of Anasorb 747 separated by a 2-mm portion of urethane foam. The sampling section contains 400 mg and the back section contains 200 mg of Anasorb 747. The sorbent is held in place with a glass wool plug at the front and a foam plug at the end of the sorbent bed. The sampling tubes are commercially available from SKC.

2.2. Reagents

No sampling reagents are required.

2.3. Sampling technique

2.3.1. Immediately before sampling, break off the ends of the sampling tube. All tubes should be from the same lot.

2.3.2. Attach the sampling tube to the sampling pump with flexible tubing. Position the tube so that sampled air first passes through the 400-mg section.

2.3.3. Attach the tube vertically in the employee's breathing zone in such a manner that it does not impede work performance.

2.3.4. After sampling for the appropriate time, remove the sample tube and seal it with plastic caps.

2.3.5. Wrap each sample end-to-end with an OSHA seal (Form 21).

2.3.6. Record the air volume for each sample and list any possible interferences.

2.3.7. Submit at least one blank for each set of samples. Handle the blank in the same manner as the samples, except no air is drawn through it.

2.3.8. Ship the samples cold after sampling to the laboratory and analyzed immediately.

2.3.9. Submit bulk samples for analysis in a separate container. Do not ship bulk samples with air samples.

2.4. Desorption efficiency

Twelve vials, each containing 400-mg portion of Anasorb 747, were divided into four groups of three vials each. Vials of the first and the second groups were liquid spiked with 1.2 and 3.8 µL of 10% methyl formate in methyl alcohol, respectively. Vials of the other two groups, were liquid spiked with 1.6 and 3.2 µL of 50% methyl formate in methyl alcohol, respectively. These amount represent 0.15×, 0.5×, 1.0×, and 2.0× the target concentration. The vials were stored overnight in a refrigerator (0°C), desorbed with 3.0 mL of the desorbing solution, and analyzed as in Section 3. The average desorption efficiency was 95.7%. The results are listed in Table 2.4.

Table 2.4.
Desorption Efficiency


Sample #
Amount
Spiked, µg
Amount
Found, µg
%
Recovered

D1
D2
D3
115
115
115
115
112
115
100.0
97.4
100.0
Average of 0.15× PEL = 99.1%

D4
D5
D6
366
366
366
343
343
347
93.7
93.7
94.8
Average of 0.5× PEL = 94.0%

D7
D8
D9
770
770
770
717
729
742
93.1
94.7
96.4
Average of 1× PEL = 94.7%

D10
D11
D12
D13
1540
1540
1540
Blank
1427
1474
1494
0
92.7
95.7
97.0
0.0
Average of 2× PEL = 95.1%

2.5. Retention efficiency

Four Anasorb 747 tubes were each liquid spiked with 1.6 µL (1× PEL) of 50% methyl formate in methyl alcohol. These were allowed to equilibrate for 2 hours and then 3 L of humid air (~80% relative humidity) were drawn through each tube at 0.05 L/min. Then the tubes were desorbed with 3.0 mL of desorbing solution, and then analyzed as in Section 3. The results are listed in Table 2.5.

Table 2.5.
Retention Efficiency


Sample #
Amount
Spiked, µg
Amount
Found, µg
%
Recovered

R1
R2
R3
R4
770
770
770
770
711
724
770
748
92.3
94.0
100.0
97.1
Average = 95.9%

2.6. Sample storage

Nine Anasorb 747 tubes were each liquid spiked with 1.6 µL (1× PEL) of 50% methyl formate in methyl alcohol. These were allowed to equilibrate for 2 hours and then 3 L of humid air (~80% relative humidity) were drawn through each tube at 0.05 L/min. The nine tubes were divided into three groups of three tubes each. The first group was stored in a drawer at ambient temperature, the second group was stored in a refrigerator (0°C) and the third group was stored in a freezer (-5°C). After seven days they were extracted and analyzed as in Section 3. No analytes were observed in backup section. The results are given in Tables 2.6.1., 2.6.2. and 2.6.3..

Table 2.6.1.
Ambient Storage

Days
Stored
Amount
Spiked, µg
Amount
Found, µg
%
Recovered

7
7
7
770
770
770
95
143
91
12.3
18.6
11.8

Average = 14.2%


Table 2.6.2.
Refrigerator Storage

Days
Stored
Amount
Spiked, µg
Amount
Found, µg
%
Recovered

7
7
7
770
770
770
615
640
633
79.9
83.1
82.2

Average = 81.7%


Table 2.6.3.
Freezer Storage

Days
Stored
Amount
Spiked, µg
Amount
Found, µg
%
Recovered

7
7
7
770
770
770
623
642
649
80.9
83.4
84.3

Average = 82.9%

2.7. Recommended air volume and sampling rate

2.7.1. The recommended air volume is 3 L.

2.7.2. The recommended flow rate is 0.05 L/min.

2.8. Interferences (sampling)

It is not known if any compounds will interfere with the collection of methyl formate. Any suspected interferences should be reported to the laboratory with submitted samples.

2.9. Safety precautions (sampling)

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 GC equipped with an FID. A Hewlett-Packard 5890 Gas Chromatograph equipped with a 7673A Autosampler and an FID was used in this evaluation.

3.1.2. A GC column capable of separating methyl formate from any interferences. A 60 m × 0.32 mm i.d. (1.0 µm film) STABILWAX capillary column was used in this evaluation.

3.1.3. An electronic integrator or some other suitable means to measure detector response. A Waters 860 Networking Computer System was used in this evaluation.

3.1.4. Volumetric flasks, pipets, and syringes for preparing standards, making dilutions and performing injections.

3.1.5. Vials, 2-mL, and 4-mL, with PTFE-lined caps.

3.1.6. Mechanical shaker.

3.2. Reagents

3.2.1. Methyl formate. Methyl formate, 97.5+% purity, was obtained from Eastman Chemical Company.

3.2.2. Methyl alcohol. The methyl alcohol used in this evaluation was purchased from Fisher Scientific.

3.2.3. Dimethylformamide (DMF). The DMF was purchased from Burdick and Jackson.

3.2.4. Desorbing solution, 90/10 (v/v) methyl alcohol and DMF.

3.3. Standard preparation

Prepare standards at concentrations of 1 µL, 2 µL and 4 µL of methyl formate per milliliter of desorbing solution. Standards must be used the day they are prepared.

3.4. Sample preparation

3.4.1. Transfer the 400-mg section of the sampling tube to a 4-mL vial. Place the 200-mg backup section in a separate 4-mL vial.

3.4.2. Add 3.0 mL of desorbing solultion to each vial and seal with a Teflon-lined cap.

3.4.3. Shake the vials on a mechanical shaker for an hour.

3.5. Analysis

3.5.1. Instrument conditions

Column: STABILWAX, 60 m × 0.32 mm i.d., 1.0 µm film
Injector temperature: 150°C
Detector temperature: 200°C
Column temperature: 50°C (initial temp)
Temperature program: hold initial temp. 5 min, increase temp. at 10°C/min to 190°C, hold final temp. 2 min
Gas flow rates:
    column:
    septum purge:
    FID:
    FID:
    FID:
2.0 mL/min (hydrogen)
7.5 mL/min (hydrogen)
32 mL/min (hydrogen)
34 mL/min (nitrogen)
400 mL/min (air)
Injection volume: 1 µL
Split ratio: 2.7:1
Retention time: 5.4 min (methyl formate)
8.7 min (methyl alcohol)
18.9 min (DMF)

3.5.2. Chromatogram (Figure 1.)

3.5.3. Measure detector response using a suitable method such as electronic integration.

3.6. Interferences (analytical)

3.6.1. Any collected compound which produces an FID response and has a similar retention time as methyl formate is a potential interference.

3.6.2. GC conditions may generally be varied to circumvent interferences.

3.6.3. Retention time on a single column is not proof of chemical identity. Analysis by an alternate GC column, high performance liquid chromatography (HPLC) and confirmation by mass spectrometry are additional means of identification.

3.7. Calculations

3.7.1. An external standard (ESTD) calibration method is used. A calibration curve may be constructed by plotting concentration of analyte per sample versus response of standard concentration (µg/mL) of methyl formate. Bracket the samples with freshly prepared analytical standards over a range of concentrations.

3.7.2. Determine the µg/mL of methyl formate in both sections of each sample and blank from the calibration curve. If methyl formate is found on the backup section, it is added to the amount found on the front section. Blank corrections should be performed before adding the results together.

3.7.3. Determine the air concentration by using the following formula.

mg/m3 = (µg/mL, blank corrected) × (desorption volume, mL)
(air volume, L) × (desorption efficiency, decimal)
ppm = (mg/m)(24.46)
(60.05)
where 24.46
60.05
=
=
molar volume (liters) at 101.3 kPa (760 mmHg) and 25°C
molecular weight of methyl formate

3.8. Safety precautions (analytical)

3.8.1. Avoid skin contact and air exposure to methyl formate.

3.8.2. Avoid skin contact with all solvents.

3.8.3. Wear safety glasses in laboratory.

4. Recommendation for Further Study

This method should be fully validated.

chromatogram of methyl formate at 1.0× target level
Figure 1. Chromatogram of methyl formate at 1.0× target level.

5. References

5.1. "Code of Federal Regulations", 29 CFR 1910.1000, Table Z-1-A. Limits for Air Contaminants, U.S. Government Printing Office, Washington, D.C., 1990.

5.2. Documentation of the Threshold Limit Values and Biological Exposure Indices, American Conference of Governmental Industrial Hygienist INC., 5th ed., 1986; p 397.

5.3. Sitting, M., Handbook of Toxic and Hazardous Chemicals, Noyes Publications, Park Ridge, N.J., 1981; p 453.

5.4. Windholz, M., Budavari, S., Blumetti, RF., and Otterbein, E., The Merck Index, 10th ed., Merck & CO., Inc., Rahway, N.J., 1983; p 870.