1.1 Background

The OSHA Analytical Laboratory received a set of samples for which an analysis of Apron was requested. The air samples had been collected on glass fiber filters at a flow rate of 1 L/min. This report describes the analytical method developed for Apron and a preliminary validation of glass fiber filter as the sampling medium. 

1.2 Toxic effects (This section is for information only and should not be taken as the basis of OSHA policy.)
 
The oral LD₅₀ of Apron is 669 mg/kg in rats. The acute dermal LD₅₀ is >3100 mg/kg for rats. It is relatively non-toxic to fish and wildlife. (Ref. 5.1) 

1.3 Potential workplace exposure (Ref. 5.3)
 
Apron is used as a fungicide in agricultural applications. No estimate of worker exposure during its production, formulation and use as a fungicide could be found. 

1.4 Physical properties (Ref. 5.1 and 5.2)

Chemical name:	N-(2,6-Dimethylphenyl)-N-(methoxyacetyl) -DL-alanine methyl ester
Synonym:	Apron 2E; CG 117; CGA 48988; Metalaxil; Ridomil; Ridomil 2E; Subdue; Subdue 2E; Subdue 5SP; N-(Methoxyacetyl)-N-(2,6-xylyl)-DL-alanine methyl ester
CAS no.:	57837-19-1
Molecular formula:	C15H21NO4
Molecular weight:	279.37
Appearance:	White crystals
Melting point:	71-72°C
Vapor pressure:	2.2×10-6 mmHg at 20°C

 
Structure:     



    

Solubility:	Solubility in water at 20°C: 7.1 g/L. Readily soluble in most organic solvents.
UV scan:

1.5 Detection limit of the analytical procedure

The detection limit of the analytical procedure is 4.3 ng per injection. 

2.1 Apparatus and reagents

2.1.1 A personal sampling pump that can be calibrated to within 5% of the recommended flow rate.
 
2.1.2 Glass fiber filter, 37-mm diameter, Gelman Type A, or equivalent. 

2.1.3 Filter holder for 37-mm filters, Millipore M000037A0, or equivalent.

2.2 Sampling procedure  

Use standard air sampling technique as specified in OSHA Instruction CPL 2-2.20A, Chapter II: Standard Methods for Sampling Air Contaminants. 

2.3 Recommended air volume and sampling rate

2.3.1 The recommended air volume is 60 L. 

2.3.2 The recommended sampling rate is 1 L/min.

2.4 Extraction efficiency

Three glass fiber filters were each spiked with 16.35 µg of Apron. The filters were extracted with 5.0 mL of acetonitrile and analyzed. The average recovery of Apron was 100.4%.

Sample	Apron recovered	Recovery
YC1	16.07 µg	98.3%
YC2	16.60 µg	101.5%
YC3	16.56 µg	101.3%
	Average	= 100.4%

2.5 Retention efficiency

Three glass fiber filters were each spiked with 16.35 µg of Apron. Humid air (50% RH, 183 L @ 1 L/min) was drawn through the filters. The filters were extracted with 5.0 mL of acetonitrile and analyzed. The average recovery of Apron was 97.9%.

Sample	Apron recovered	Recovery
YC7	15.46 µg	94.6%
YC8	16.40 µg	100.3%
YC9	16.13 µg	98.7%
	Average	= 97.9%

2.5 Storage

Three glass fiber filters were each spiked with 16.35 µg of Apron. Humid air (50% RH, 183 min @ 1 L/min) was drawn through the filters. The filters were stored at room temperature for 5 days, extracted with acetonitrile, and analyzed. The average recovery of Apron was 104.9%.

Sample	Apron recovered	Recovery
YC10	17.05 µg	104.3%
YC11	17.05 µg	104.3%
YC12	17.33 µg	106.0%
	Average	= 104.9%

2.6 Interferences
 
There are no known interferences to the sampling procedure.

3.1 Apparatus

3.1.1 High performance liquid chromatograph. 

3.1.2 Alltech C₁₈ column or equivalent. 

3.1.3 UV detector.
 
3.1.4 Stripchart recorder.

3.2 Reagents

3.2.1 Water, HPLC grade.
 
3.2.2 Acetonitrile, HPLC grade.
 
3.2.3 Apron (Ridomil), EPA standard # F701. 

3.3 Standard preparation

Weigh 2 to 4 mg of Apron in a 10-mL volumetric flask. Add acetonitrile to the mark. Dilute with acetonitrile to a suitable working range. 

3.4 Sample preparation

Samples were extracted with 5.0 mL of acetonitrile, 30 minutes on a mechanical shaker.  

3.5 Analysis

3.5.1 Instrument conditions

Column:	Alltech C18
Mobile phase:	60% acetonitrile, 40% water
Detector:	198 nm (primary), 214 nm
Flow rate:	1.0 mL/min
Injection size:	25 µL
Retention time:	7.0 min

3.5.2 Chromatogram

 
Figure 1. HPLC Chromatogram of Apron.

3.6 Interferences

3.6.1 Any collected compound that has the same retention time as Apron and absorbs at 198 and 214 nm is an interference.
 
3.6.2 HPLC parameters may be varied to circumvent most interferences.
 
3.6.3 Retention time alone is not proof of a chemical identity. Confirmation by other means should be sought when possible.

3.7 Calculations

3.7.1 A calibration curve is constructed by plotting standard concentrations versus detector response. 

3.7.2 The concentration of a sample is determined from the calibration curve.

 
Figure 2.  Calibration curve of Apron.
 
3.7.3 The air concentration is determined by the formula: 
 

mg/m3 =	(µg/mL)(5 mL)
	(air volume, L)(extraction efficiency)

 

5.1 Registry of Toxic Effects of Chemical Substances, 1983-84 Supplement, DHHS (NIOSH) Publication No. 86-103, Cincinnati, Ohio, 1986.
 
5.2 Merck Index, Tenth Edition, Merck & Co., Rahway, N.J., 1983.
 
5.3 Farm Chemicals Handbook, Meister Publishing, Willoughby, Ohio, 1981.