1. Introduction
1.1 Scope
This method describes the collection and analysis of airborne methyl tin mercaptide (MTM). It is applicable for time-weighted average
exposure evaluations. The analysis is based on the technique of graphite furnace atomic absorption.
1.2 Physical and Chemical Properties
Appearance - clear yellow to light amber liquid
Specific gravity - 1.02 (at approx. 250 °C)
Refractive index - 1.5085 (at approx. 250 °C)
% Sn - 11%
Decomposes to form tin oxides and sulfur dioxide
Boiling point - not distillable
2. Range and Detection Limit
2.1 The lower analytical limit for MTM is 0.1 µg/mL.
2.2 This is based on a detection limit of .02 µg/mL for graphite furnace analysis of Sn as MTM in butyl
cellusolve.
3. Precision and Accuracy
3.1 Precision
3.2 Coefficient of Variation
3.3 Recovery
|
S = .020
CV = 0.023
Average mean recovery = .874 |
The above are based on recovery data for eighteen impingers, spiked with MTM in butyl cellusolve at
.5×, 1×, and 2× the PEL based on a 150 liter air volume and 0.1 mg/m3 PEL. Six samples were spiked at each level. Refer to
addendum for data on recovery study.
4. Interferences
Other organotins would interfere if they are soluble in butyl cellusolve.
5. Sampling Procedure
The sample is collected in an impinger containing 15 mL butyl cellusolve at a flow rate of
1 L/min.
The recommended air volume is 150 L.
The impingers are capped, sealed with OSHA tape, labeled, and sent to the laboratory for analysis as soon as possible.
6. Analytical Procedure
6.1 Apparatus
6.1.1 Sample collection
Personal sampling pumps
Impingers as needed
6.1.2 Sample analysis
Atomic absorption spectrophotometer
HGA graphite furnace
Electrodeless discharge lamp for Sn
Laboratory glassware
6.2 Reagents
All reagents should be ACS analyzed reagent grade or better.
6.2.1 Butyl cellusolve (2-Butoxyethanol)
6.2.2 Stock methyl tin mercaptide
6.2.3 Stock tin (1000 ppm), Scientific Products, Fisher or equivalent
6.3 Safety precautions
6.3.1 Use caution when handling butyl cellusolve and organotins. Methyl tin mercaptide is a toxic compound.
Always wear rubber gloves and work in a fume hood. Waste organics should be collected in a suitable marked container and properly
disposed of in the organic laboratory.
6.3.2 Avoid using glassware with chips or sharp edges. Never pipette by mouth.
6.3.3 Before using the graphite furnace, the analyst should read the operator's manual and be familiar with the equipment. Ensure that the furnace tube is properly seated, the contact rings are clean, and that cooling water is circulating. Do not exceed an atomization
temperature of 2750 degrees. Heating or cooling problems could cause the tube to explode on atomization.
Always wear safety glasses and never look at the tube during atomization. Even during normal firing, the intense light is harmful to the eyes.
Be aware of the high current supplied to the furnace through the copper cables; check that the insulating cover is in place over the terminals.
Since toxic substances are vented by the furnace, a fume hood must be in operation over the furnace.
6.3.4 Observe care with respect to harming the equipment. Do not operate an EDL below its recommended wattage. Be certain that the
purge air is circulating when using the background corrector. Do not operate any equipment without first reading its instruction manual.
6.4 Glassware preparation
6.4.1 Clean the 50 mL volumetric flasks by refluxing with 1:1 nitric acid. Thoroughly rinse all glassware with
deionized water, invert, and allow to dry.
6.5 Standard preparation
6.5.1 The procedure is to analyze the tin in methyl tin mercaptide. Prepare a 10 ppm Sn stock solution from two
serial 10-fold dilutions of 1000 ppm stock.
6.5.2 Working standards are prepared from the 10 ppm Sn stock as follows:
Prepared std. |
Std. stock used |
Aliquot |
Dil. vol. |
2.0 ppm |
|
10 ppm |
|
10 mL |
|
50 mL |
1.0 ppm |
|
10 ppm |
|
5 mL |
|
50 mL |
0.2 ppm |
|
1 ppm |
|
10 mL |
|
50 mL |
0.1 ppm |
|
1 ppm |
|
5 mL |
|
50 mL |
0.04 ppm |
|
1 ppm |
|
2 mL |
|
50 mL |
6.6 Sample preparation
Measure the volume of the impinger and record a sample volume. Transfer into sampling cup and analyze directly on graphite furnace.
If off-scale, make all dilutions in butyl cellusolve.
6.7 Analysis
The analysis is done by graphite furnace/AA. The instrumental
parameters for determining Sn in butyl cellusolve are as follows:
Atomic absorption unit:
Sn wavelength |
224.6 nm |
integ. time |
10 sec. |
slit width |
.7 low |
signal |
Pk. Ut. |
mode |
abs. |
BGC |
on |
Furnace parameters:
step |
temperature |
ramp time |
hold time |
internal flow |
dry |
100 °C |
50 s |
40 s |
50 mL/min |
char |
800 °C |
50 s |
20 s
| 50 mL/min |
atomize |
2500 °C |
0 s |
8 s |
30 mL/min |
(with HGA 500, program -10 chart and 0 read in atomization step) |
Chart = 5 mv scale, 20 mm/min
6.7.2 Parameters are adjusted so that the 2.0 ppm standard gives a near full-scale deflection on the chart. The entire
series of standards is run at the beginning and end of the analysis; a standard is also run after every fourth or fifth
sample during the analysis.
6.8 Calculations
6.8.1 The OSHA Auto Colorimetric program is used for the calculations.
6.8.2 Results are reported as mg/m3 Sn.
ADDENDUM I
A recovery study of MTM in 15 mL impinger of butyl cellusolve was
done. 0.240 g MTM was weighed into a 1000 ml volumetric, diluted to volume with butyl
cellusolve, and mixed. Assuming MTM is 11% Sn, this is 26.4 ppm Sn as MTM. From this a 13.2 ppm and a 6.6 ppm standard
are also prepared. Six impingers were spiked at each level = .5×, 1×, and 2× the OSHA PEL based on a 150 liter air volume
and 0.1 mg/m3 OSHA PEL. The spikes were made as follows:
Sample |
Stock std. |
ml. aliquot |
final vol. |
theor. Sn |
0.5×-l |
6.6 ppm |
1.0 mL |
15 mL |
0.44 ppm |
0.5×-2 |
6.6 ppm |
1.0 mL |
15 mL |
0.44 ppm |
0.5×-3 |
6.6 ppm |
1.0 mL |
15 mL |
0.44 ppm |
0.5×-4 |
6.6 ppm |
1.0 mL |
15 mL |
0.44 ppm |
0.5×-5 |
6.6 ppm |
1.0 mL |
15 mL |
0.44 ppm |
0.5×-6 |
6.6 ppm |
1.0 mL |
15 mL |
0.44 ppm |
|
|
|
|
|
1.0×-1 |
13.2 ppm |
1.0 mL |
15 mL |
0.88 ppm |
1.0×-2 |
13.2 ppm |
1.0 mL |
15 mL |
0.88 ppm |
1.0×-3 |
13.2 ppm |
1.0 mL |
15 mL |
0.88 ppm |
1.0×-4 |
13.2 ppm |
1.0 mL |
15 mL |
0.88 ppm |
1.0×-5 |
13.2 ppm |
1.0 mL |
15 mL |
0.88 ppm |
1.0×-6 |
13.2 ppm |
1.0 mL |
15 mL |
0.88 ppm |
|
|
|
|
|
2.0×-1 |
26.4 ppm |
1.0 mL |
15 mL |
1.76 ppm |
2.0×-2 |
26.4 ppm |
1.0 mL |
15 mL |
1.76 ppm |
2.0×-3 |
26.4 ppm |
1.0 mL |
15 mL |
1.76 ppm |
2.0×-4 |
26.4 ppm |
1.0 mL |
15 mL |
1.76 ppm |
2.0×-5 |
26.4 ppm |
1.0 mL |
15 mL |
1.76 ppm |
2.0×-6 |
26.4 ppm |
1.0 mL |
15 mL |
1.76 ppm |
The mean standard deviation and coefficient of variation for the recovery at each level using the OSHA
"Precision and Accuracy Data" program:
Level .5× (OSHA PEL)
µg taken |
µg found |
AMR |
|
0.44 |
0.38 |
0.864 |
N = 6 |
0.44 |
0.40 |
0.909 |
Mean = 0.875 |
0.44 |
0.38 |
0.864 |
Std Dev = 0.019 |
0.44 |
0.38 |
0.864 |
CV1 = 0.022 |
0.44 |
0.39 |
0.886 |
|
0.44 |
0.38 |
0.864 |
|
Level 1× (OSHA PEL)
µg taken |
µg found |
AMR |
|
0.88 |
0.75 |
0.852 |
N = 6 |
0.88 |
0.75 |
0.852 |
Mean = 0.845 |
0.88 |
0.75 |
0.852 |
Std Dev = 0.020 |
0.88 |
0.74 |
0.841 |
CV1 = 0.024 |
0.88 |
0.71 |
0.807 |
|
0.88 |
0.76 |
0.864 |
|
Level 2× (OSHA PEL)
µg taken |
µg found |
AMR |
|
1.76 |
1.57 |
0.892 |
N = 6 |
1.76 |
1.54 |
0.875 |
Mean = 0.901 |
1.76 |
1.56 |
0.886 |
Std Dev = 0.020 |
1.76 |
1.60 |
0.909 |
CV1 = 0.024 |
1.76 |
1.59 |
0.903 |
|
1.76 |
1.65 |
0.938 |
|
|