2.1 Apparatus

2.1.1. 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. OVS-2 tubes, which are specially made 13-mm, o.d. glass tubes that are tapered to 6-mm o.d. They 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 poly- tetrafluoroethylene (PTFE) retainer.

Figure 2.1.2. 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.

2.3.2 Attach the sampler vertically (large end down) in the worker's breathing zone in such a manner that it does not impede work performance.

2.3.3 After sampling for the appropriate time, remove the sampling device and seal the tube with plastic end caps.

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

2.3.5 Submit at least one blank with each set of samples. Handle the blank the same as the other samples but do not draw air through it.

2.3.6 Submit any bulk samples in a separate container. Do not ship them with the air samples.

2.4 Extraction and desorption efficiencies

2.4.1 Glass fiber filter

Six 13-mm glass fiber filters were placed in separate 4-mL vials. Five of these filters were each liquid spiked with 28 µL of a 5.345 mg/mL solution of methomyl in acetonitrile. These six vials were sealed with PTFE-lined septa and stored overnight in a drawer at room temperature. They were then extracted with 2.0 mL of acetonitrile and analyzed as in Section 3.5.
 

Table 2.4.1
Glass Fiber Filter Extraction Study
Filter #	Amount Spiked	Amount Recovered	% Recovery
F1	149.66 µg	147.56 µg	98.6
F2	149.66 µg	148.91 µg	99.5
F3	149.66 µg	149.66 µg	100.0
F4	149.66 µg	148.91 µg	99.5
F5	149.66 µg	141.13 µg	94.3
F6	00.00 µg	00.00 µg	Blank
	Average recovery is 98.4%

2.4.2 XAD-2 adsorbent 

An amount of XAD-2 adsorbent equal to the sampling section (270 mg) of an OVS-2 tube was placed in each of six 4-mL vials which were then sealed with PTFE-lined septa. Five of these vials were then each liquid spiked with 28 µL of a 5.345 mg/mL solution of methomyl in acetonitrile by injecting the solution onto the adsorbent through the septum. After replacing the punctured septa, these vials were allowed to equilibrate overnight in a drawer at room temperature. They were then desorbed with 2.0 mL of acetonitrile and analyzed as in Section 3.5. 
 

Table 2.4.2
XAD-2 Adsorbent Desorption Study
Adsorbent #	Amount spiked	Amount recovered	% Recovery
AD1	149.66 µg	149.96 µg	98.2
AD2	149.66 µg	148.61 µg	99.3
AD3	149.66 µg	147.56 µg	98.6
AD4	149.66 µg	147.56 µg	98.6
AD5	149.66 µg	148.01 µg	98.9
AD6	0.00 µg	0.00 µg	Blank
	Average recover is 98.7%

2.5 Retention efficiency

Six OVS-2 tubes were each liquid spiked with 28 µL of a 5.345 mg/mL solution of methomyl in acetonitrile by spiking the glass fiber filter. These tubes were then sealed with plastic end caps and placed in a drawer at room temperature. After overnight storage, 60 liters of humid air (approximately 70% relative humidity) were drawn through each tube. Three of these tubes, along with a blank tube, were then desorbed and analyzed as in Section 3. No methomyl was recovered from the backup section of these tubes. 
 

Table 2.5
Retention Efficiency Study
Tube #	Amount spiked	Amount recovered	% Recovery
RET1	149.66 µg	146.22 µg	97.7
RET2	149.66 µg	162.23 µg	108.4
RET3	149.66 µg	153.70 µg	102.7
RET4	0.00 µg	0.00 µg	Blank
Average recovery is 102.9%

2.6 Sample storage

The remaining three spiked tubes from Section 2.5 (and a blank tube) were stored for a total of 7 days in a-drawer at room temperature. They were then desorbed and analyzed as in Section 3. No methomyl was recovered from the backup section of these tubes.
 

Table 2.6
Storage Study
Tube #	Amount spiked	Amount recovered	% Recovery
ST1	149.66 µg	partial sample loss
ST2	149.66 µg	138.88 µg	92.8
ST3	149.66 µg	148.91 µg	99.5
ST4	0.00 µg	0.00 µg	Blank
Average recovery (excluding ST1) is 96.2%

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 (sampling)

It is not known if any compounds will interfere with the collection of methomyl. 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.