1.1 Background

1.1.1 History of procedure

The OSHA Analytical Laboratory received a set of samples requesting the analysis of pirimiphos-methyl and other pesticides. The samples had been collected on OVS-2 tubes. This report describes the analytical method developed.

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

The oral LD₅₀ for rats is 1250 mg/kg. ( Ref. 5.1) The acute dermal LD₅₀ for female rats is greater than 4592 mg/kg. (Ref. 5.2)

1.1.3 Potential workplace exposure

Pirimiphos-methyl is a fast acting and broad-spectrum insecticide. No estimate of worker exposure to pirimiphos-methyl could be found. (Ref. 5.1)

1.1.4 Physical properties (Ref. 5.1 to 5.3)

Molecular weight:	305.37
Molecular formula:	C11H20N3O3PS
CAS number:	29232-93-7
IMIS number:	P309
Specific gravity:	1.157
Vapor pressure:	0.015 Pa (1.1×10-4 mmHg) at 30°C
Solubility:	miscible with most organic solvents; in water, 5 mg/L at 30°C
Chemical name:	O-(2-diethylamino-6-methylpyrimidin-4-yl)O,O-dimethyl phosphorothioate
Synonyms:	Actelic, Actellic, Actellifog, Blex, PP-511, Silosan, Plant Protection PP511, Pyridimine Phosphate
Description:	straw colored liquid
Structure:

1.2 Limit defining parameters

The detection limit of the analytical procedure, including a 15:1 split ratio, is 0.04 ng per injection. This is the amount of analyte which will give a peak whose height is approximately five times the baseline noise.

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., packed with a 140-mg backup section, a 270-mg sampling section of cleaned XAD-2 adsorbent and a 13 mm diameter glass fiber filter. The backup section is retained by two foam plugs and the sampling section is between one foam plug and the glass fiber filter. The glass fiber filter is held next to the sampling section by a polytetrafluoroethylene (PTFE) retainer.

Figure 2.1.2 OVS-2 Sampling Tube

2.2 Reagents

No sampling reagents are required.

2.3 Sampling technique

2.3.1 Immediately before sampling, remove the plastic caps from the OVS-2 tube.

2.3.2 Attach the small end of the tube to the sampling pump with flexible tubing.

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 tube and seal 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 Submit bulk samples for analysis in a separate container.

2.4 Desorption efficiency (glass fiber filter and XAD-2 adsorbent)
 

Six vials each containing a 13-mm glass fiber filter and 270-mg of XAD-2 adsorbent were each liquid spiked on the glass fiber filter with 74.57 μg of pirimiphos-methyl and allowed to dry for 2 hours. These samples were each desorbed with 3 mL of acetonitrile, shaken for 30 min and analyzed as in Section 3. The results are listed in the Table below.

Table 2.4 Desorption Efficiency amount spiked, μg amount found, μg % recovered 74.57 74.57 74.57 74.57 74.57 74.57 69.74 66.56 63.42 65.66 71.57 80.32 93.5 89.3 85.0 88.1 96.0 07.8   93.3

2.5 Retention efficiency

Eighteen OVS-2 tubes were each liquid spiked with 74.57 μg of pirimiphos-methyl on the glass fiber filter. These were allowed to dry and then 240 L of humid air (~80% relative humidity) were drawn through each tube at 1 L/min. Six of the tubes were each desorbed with 3 mL of acetonitrile, shaken for 30 min and then analyzed as in Section 3. The results are listed in the Table below. The remaining samples were stored, 6 in a drawer at ambient temperature and 6 in a freezer.

Table 2.5  Retention Efficiency amount spiked,  μg amount found,  μg % recovered 74.57 74.57 74.57 74.57 74.57 74.57 73.25 67.58 66.17 65.19 75.58 77.21 98.2 90.6 88.7 87.4 100.0 103.5   94.7

2.6 Sample storage

After 4 days of storage, 6 tubes, 3 from the ambient storage group and 3 from the freezer storage group, were each desorbed with 3 mL of acetonitrile, shaken for 30 min and then analyzed as in

Section 3. The remaining tubes were desorbed and analyzed after 7 days of storage. The results are given in the Tables below.

Table 2.6.1 Ambient Storage days  stored amount spiked,  μg amount found,  μg % recovered 4 4 4 7 7 7 74.57 74.57 74.57 74.57 74.57 74.57 69.68 67.76 72.34 71.12 67.66 72.53 93.4 90.9 97.0 95.4 90.7 97.3     of 4 of 7 93.8 94.5

Table 2.6.2 Freezer Storage days stored amount spiked,  μg amount found,   μg % recovered 4 4 4 7 7 7 74.57 74.57 74.57 74.57 74.57 74.57 68.31 74.22 74.00 63.91 68.25 69.10 91.6 99.5 99.2 85.7 91.5 92.7     of 4 of 7 96.8 90.0

2.7 Recommended air volume and sampling rate

2.7.1 The recommended air volume is 120 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 pirimiphos-methyl. Any suspected interference should be reported to the laboratory.

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.

3.1 Apparatus

3.1.1 A balance capable of weighing to the nearest tenth of a milligram. A Mettler HL52 balance was used in this evaluation.

3.1.2 A mechanical shaker.

3.1.3 A GC equipped with an ECD. A Hewlett Packard (HP) 5890 was used in this evaluation.

3.1.4 A GC column capable of separating pirimiphos-methyl from any interferences. A 15 m × 0.32 mm i.d. (1.0 μm film) DB-5 capillary column was used in this evaluation.

3.1.5 An electronic integrator, or some other suitable means for measuring detector response. The Hewlett-Packard 3357 Laboratory Data System was used in this evaluation.

3.1.6 Volumetric flasks and pipets. 

3.1.7 Vials, 2-mL.

3.2 Reagents

3.2.1 Acetonitrile, reagent grade.

3.2.2 Pirimiphos-methyl, reagent grade. A standard obtained from EPA (EPA # 5643, 100% purity) was used in this evaluation.

3.3 Standard preparation

Prepare pirimiphos-methyl stock standards by weighing 10 to 15 mg of pirimiphos-methyl. Transfer the pirimiphos-methyl to separate 10-mL volumetric flasks, and add acetonitrile to the mark. Make working range standards of 0.5 to 50 μg/mL by pipet dilutions of the stock standards with acetonitrile. Store stock and dilute standards in a freezer.

3.4 Sample preparation

3.4.1 Transfer the 13-mm glass fiber filter and the 270-mg sampling section of the tube to a 4-mL vial. Place the first foam plug and the 140-mg section in a separate 4-mL vial. A small glass funnel can be used to facilitate the transfer of the adsorbent. Discard the rear foam plug. Do not discard the glass sampling tube; it can be reused.

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

3.4.3 Shake the vials for 30 minutes on a mechanical shaker.

3.4.4 Transfer the samples to 2-mL vials for use on an HP autosampler.

3.5. Analysis

3.5.1 Instrument conditions

Column:	DB-5, 15 m × 0.32 mm i.d., 1.0-μm film
Injector temperature:	275°C
Column temperature:	220°C
Detector temperature:	300°C
Gas flows:
Column:	4 mL/min hydrogen
ECD make up:	42 mL/min nitrogen
Injection volume:	1.0 μL
Split ratio:	15:1
Retention time:	3.06 min

3.5.2 Chromatogram
 

Figure 3.5.2 Chromatogram of Pirimiphos-methyl

3.6 Interferences (analytical)

3.6.1 Any collected compound having a similar retention time to that of the analyte is a potential interference.

3.6.2 GC conditions may 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, detection on a flame photometeric detector and confirmation by mass spectrometry are additional means of identification.

3.7 Calculations

3.7.1 Construct a calibration curve by plotting detector response versus concentration (μg/mL) of pirimiphos-methyl. 3.7.2 Determine the μg/mL of pirimiphos-methyl in both sections of each sample and blank from the calibration curve. 3.7.3 Blank correct each section by subtracting the μg/mL found in the blank section from the μg/mL found in the sample section and then add the sections together. 3.7.4 Determine the air concentration by using the following formula.

Figure 3.7.1 Calibration Curve

 

mg/m3 =

(mg/mL blank corrected)(desorption volume, mL) (air volume, L)(desorption efficiency, decimal)

3.8 Safety precautions (analytical)

3.8.1 Avoid skin contact and air exposure to pirimiphos-methyl.

3.8.2 Avoid skin contact with all solvents.

3.8.3 Wear safety glasses at all times.

5.1 Farm Chemicals Handbook; Berg, Gordon L. Ed.; Meister: Willoughby, Ohio, 1986; p C6.

5.2 Registry of Toxic Effects of Chemical Substances 1985-86 Edition; U.S. Department of Health and Human Services: Cincinnati, OH, 1987; DHHS(NIOSH) Publication No. 87-114, p 3425.

5.3 Merck Index, 10th ed.; Windholz, Martha ED.; Merck: Rathway, N.J., 1983; p 1082.