2-BUTOXYETHANOL (BUTYL CELLOSOLVE) 2-BUTOXYETHYL
ACETATE (BUTYL CELLOSOLVE ACETATE)
Method no.: |
83 |
|
Matrix: |
Air |
|
Procedure: |
Samples are collected by drawing air through standard
size coconut shell charcoal tubes. The charcoal is desorbed with a
95/5 (v/v) methylene chloride/methanol solution and the desorbate is
analyzed by gas chromatography using a flame ionization
detector. |
|
Recommended air volume and sampling rate: |
48 L at 0.1 L/min |
|
|
|
2-butoxyethanol |
2-butoxyethyl acetate |
|
Target concentration: |
5 ppm (24 mg/m3) |
5 ppm (33 mg/m3) |
|
Reliable quantitation limit: |
31 ppb (150 µg/m3) |
24 ppb (157 µg/m3) |
|
Standard error of estimate at target
concentration: (Section 4.7.) |
5.2% |
5.5% |
|
|
|
Special requirement: |
Samples for 2-butoxyethyl acetate should
be stored at 0°C or colder to reduce hydrolysis. Reduced temperature
shipment of samples to the laboratory is not necessary. |
|
Status of method: |
Evaluated method. This method has been subjected to
the established evaluation procedures of the Organic Methods
Evaluation Branch. |
|
Date: May 1990 |
Chemist: Carl J.
Elskamp |
Organic Methods Evaluation Branch OSHA Analytical
Laboratory Salt Lake City, Utah
1. General Discussion
1.1. Background
1.1.1. History
Methodologies to determine airborne concentrations of
2-methoxyethanol (methyl Cellosolve),
2-methoxyethyl acetate (methyl Cellosolve acetate),
2-ethoxyethanol (Cellosolve), and
2-ethoxyethyl acetate (Cellosolve acetate) have
previously been evaluated by the OSHA Laboratory at two different
target concentrations. (OSHA Method 53, Ref. 5.1. and OSHA Method
79, Ref. 5.2.) These two methods were based on work done by NIOSH
where samples are collected by drawing air through coconut shell
charcoal and are analyzed by GC after desorption of the charcoal
with 95/5 (v/v) methylene chloride/methanol. (Ref. 5.3.) The NIOSH
method also included an evaluation of
2-butoxyethanol at a range of 124 to 490
mg/m3 for 10-L air samples.
NIOSH has no evaluated method for 2-butoxyethyl
acetate.
OSHA has adopted a PEL of 25 ppm for 2-butoxyethanol
(Ref. 5.4.) and currently has no PEL for 2-butoxyethyl
acetate. NIOSH is considering issuing recommendations to lower the
PEL for 2-butoxyethanol and to establish a PEL at about
the same recommended concentration for 2-butoxyethyl
acetate, thus a target concentration of 5 ppm was chosen for both
analytes in this evaluation. A number of modifications were made to
OSHA Method 79 for this evaluation. Although an
RTx-Volatiles (Restek Corp.) capillary column is
acceptable for analysis of 2-butoxyethanol, there was
less peak-tailing when a Nukol (Supelco, Inc.)
capillary column was used. There is no significant
peak-tailing for 2-butoxyethyl acetate on
either of these columns. In OSHA Method 79, solid anhydrous
magnesium sulfate was added to the desorption vials for
2-methoxyethanol and 2-ethoxyethanol
samples to improve desorption efficiency. This was found to be
unnecessary for 2-butoxyethanol samples.
To ascertain the validity of this method at higher
concentrations, the collection efficiency of charcoal sampling tubes
was confirmed at 50 ppm for each analyte. The stability and
desorption efficiency of the analytes should not be affected at
these higher loadings.
1.1.2. Toxic effects (This section is for information only and
should not be taken as the basis of OSHA policy.)
The effects of overexposure to 2-butoxyethanol and
2-butoxyethyl acetate are similar. Inhalation of vapors
may be irritating to the respiratory tract and may cause nausea,
headaches, vomiting, dizziness, drowsiness, and unconsciousness. The
liquid is readily absorbed through the skin and may cause irritation
to the skin and eyes. Ingestion may cause nausea, vomiting,
headaches, dizziness, and gastrointestinal irritation. Chronic
overexposure may damage the kidneys, liver and blood. (Ref. 5.5.)
1.1.3. Workplace exposure
2-Butoxyethanol is used as a solvent for nitrocellulose, natural
and synthetic resins, soluble oils, lacquers, varnishes and enamels.
It is also used in textile dyeing and printing, in the treatment of
leather, in the production of plasticizers, as a stabilizer in metal
cleaners and household cleaners, and in hydraulic fluids,
insecticides, herbicides and rust removers. (Ref. 5.6.)
2-Butoxyethyl acetate is used as a high-boiling solvent for
nitrocellulose lacquers, epoxy resins, and multicolor lacquers. It
is also used as a film coalescing aid for polyvinyl acetate latex.
(Ref. 5.7.)
1.1.4. Physical properties (Ref. 5.6. unless otherwise noted)
chemical formula:
2-butoxyethanol:
CH3CH2CH2CH2OCH2CH2OH
2-butoxyethyl acetate:
CH3CH2CH2CH2OCH2CH2OOCCH3
|
2-butoxyethanol |
2-butoxyethyl
acetate |
CAS no.: |
111-76-2 |
112-07-2 |
mol wt: |
118.17 |
160.21 |
bp at 101.3 kPa, °C: |
171.2 |
192 |
appearance: |
colorless liquid |
colorless liquid |
sp gr at 20/20°C: |
0.9022 (Ref. 5.8.) |
0.9422 |
vp at 20°C, Pa: |
101 |
33-40 |
vapor density, air=1: flash point, °C |
4.1 |
5.5 |
open cup: (Ref. 5.8.) |
69.4 |
87.8 |
closed cup: (Ref. 5.8.) |
60.0 |
73.9 |
autoignition temp.,°C: |
244 |
340 |
odor: |
mild |
pleasant, sweet, fruity |
odor threshold, ppm: |
approx. 0.4 |
0.1 (absolute perception limit) 0.35-0.48
(recognition) |
explosive limits, % lower:
upper: |
1.1 10.1 |
0.88 8.54 |
solubility: |
soluble in water, alcohol, ether |
moderately soluble (1 g per 100 g at 20°C) in water,
soluble in hydrocarbons and other organic
solvents |
synonyms and trade names:
2-butoxyethanol:
ethylene glycol monobutyl ether; ethylene glycol
n-butyl ether; butyl Cellosolve
2-butoxyethyl acetate:
ethylene giycol monobutyl ether acetate;
2-butoxyethanol acetate; acetic acid,
2-butoxyethyl ester; ethylene glycol butyl ether
acetate; Ektasolve EB Acetate; butyl Cellosolve acetate
The analyte air concentrations throughout this method are
based on the recommended sampling and analytical parameters. Air
concentrations listed in ppm and ppb are referenced to 25°C and
101.3 kPa (760 mmHg). |
1.2. Limit defining parameters
1.2.1. Detection limit of the analytical procedure
The detection limits of the analytical procedure are 0.12 and
0.13 ng per injection (1.0-µL injection with a 58:1
split) for 2-butoxyethanol and
2-butoxyethyl acetate respectively. These are the
amounts of each analyte that will give peaks with heights
approximately 5 times the height of baseline noise. (Section 4.1.)
1.2.2. Detection limit of the overall procedure
The detection limits of the overall procedure are 7.22 and 7.54
µg per sample for 2-butoxyethanol and
2-butoxyethyl acetate respectively. These are the
amounts of each analyte spiked on the sampling device that allow
recovery of amounts of each analyte equivalent to the detection
limits of the analytical procedure. These detection limits
correspond to air concentrations of 31 ppb (150
µg/m3) and 24 ppb (157
µg/m3) for 2-butoxyethanol
and 2-butoxyethyl acetate respectively. (Section 4.2.)
1.2.3. Reliable quantitation limit
The reliable quantitation limits are the same as the detection
limits of the overall procedure because the desorption efficiencies
are essentially 100% at these levels. These are the smallest amounts
of each analyte that can be quantitated within the requirements of
recoveries of at least 75% and precisions (±1.96 SD) of ±25% or
better. (Section 4.3.)
The reliable quantitation limits and detection limits
reported in the method are based upon optimization of the GC
for the smallest possible amounts of each analyte. When the
target concentration of an analyte is exceptionally higher
than these limits, they may not be attainable at the routine
operating parameters. |
1.2.4. Instrument response to the analyte
The instrument response over the concentration ranges of 0.5 to 2
times the target concentrations is linear for both analytes.
(Section 4.4.)
1.2.5. Recovery
The recovery of 2-butoxyethanol and 2-butoxyethyl
acetate from samples used in a 15-day storage test
remained above 98 and 86% respectively when the samples were stored
at ambient temperatures. (Section 4.5., from regression lines shown
in Figures 4.5.1.2.
and 4.5.2.2.)
1.2.6. Precision (analytical procedure)
The pooled coefficients of variation obtained from replicate
injections of analytical standards at 0.5, 1 and 2 times the target
concentrations are 0.004 and 0.002 for 2-butoxyethanol
and 2-butoxyethyl acetate respectively. (Section 4.6.)
1.2.7. Precision (overall procedure)
The precisions at the 95% confidence level for the ambient
temperature 15-day storage tests are ±10.1 and ±10.8%
for 2-butoxyethanol and 2-butoxyethyl
acetate respectively. These include an additional ±5% for pump
error. The overall procedure must provide results at the target
concentration that are ±25% or better at the 95% confidence level.
(Section 4.7.)
1.2.8. Reproducibility
Six samples for each analyte collected from controlled test
atmospheres and a draft copy of this procedure were given to a
chemist unassociated with this evaluation. The samples were analyzed
after 8 days of refrigerated storage. No individual sample result
deviated from its theoretical value by more than the precision
reported in Section 1.2.7. (Section 4.8.)
1.3. Advantages
1.3.1. Charcoal tubes provide a convenient method for sampling.
1.3.2. The analysis is rapid, sensitive, and precise.
1.4. Disadvantage
It may not be possible to quantitate certain co-collected solvent
vapors using this method because most other common solvents which are
collected on charcoal are normally analyzed after desorption with
carbon disulfide and may exhibit unacceptably low desorption
efficiencies when 95/5 (v/v) methylene chloride/methanol is used.
2. Sampling Procedure
2.1. Apparatus
2.1.1. Samples are collected using a personal sampling pump
calibrated to within ±5% of the recommended flow rate with a
sampling tube in line.
2.1.2. Samples are collected with solid sorbent sampling tubes
containing coconut shell charcoal. Each tube consists of two
sections of charcoal separated by a urethane foam plug. The front
section contains 100 mg of charcoal and the back section, 50 mg. The
sections are held in place with glass wool plugs in a glass tube
4-mm i.d. × 70-mm length. For this
evaluation, SKC Inc. charcoal tubes (Catalog Number
226-01, Lot 120) were used.
2.2. Reagents
None required
2.3. Technique
2.3.1. Immediately before sampling, break off the ends of the
charcoal tube. All tubes should be from the same lot.
2.3.2. Connect the sampling tube to the sampling pump with
flexible tubing. It is desirable to utilize sampling tube holders
that have protective covers to shield the employee from the sharp,
jagged end of the sampling tube. Position the tube so that sampled
air passes through the 100-mg section first.
2.3.3. Air being sampled should not pass through any hose or
tubing before entering the sampling tube.
2.3.4. To avoid channeling, place the sampling tube vertically in
the employee's breathing zone.
2.3.5. After sampling, seal the tubes immediately with plastic
caps and wrap lengthwise with OSHA Form 21.
2.3.6. Submit at least one blank sampling tube with each sample
set. Blanks should be handled in the same manner as samples, except
no air is drawn through them.
2.3.7. Record sample volumes (in liters of air) for each sample,
along with a list of any other solvents being used in the sampling
area.
2.3.8. Ship any bulk sample(s) in a container separate from the
air samples.
2.4. Sampler capacity
Sampler capacity is determined by measuring how much air can be
sampled before breakthrough of analyte occurs, i.e., the sampler
capacity is exceeded. Individual breakthrough studies were performed
on each of the analytes by monitoring the effluent from sampling tubes
containing only the 100-mg section of charcoal while
sampling at 0.1 L/min from atmospheres containing 50 ppm analyte. The
atmospheres were at approximately 80% relative humidity and
20-25°C. No breakthrough was detected in any of the
studies after sampling for more than 8 h (>48 L).
2.5. Desorption efficiency
2.5.1. The average desorption efficiencies of 2-butoxyethanol
and 2-butoxyethyl acetate from SKC Inc. Lot 120
charcoal are 99.0 and 101.5% respectively over the range of 0.5 to 2
times the target concentrations. (Section 4.9.)
2.5.2. Desorbed samples remain stable for at least 24 h. (Section
4.10.)
2.5.3. Desorption efficiencies should be periodically confirmed
because they may change slightly due to variations in charcoal and
operator technique.
2.6. Recommended air volume and sampling rate
2.6.1. For TWA samples, the recommended air volume is 48 L
collected at 0.1 L/min (8-h samples).
2.6.2. For short-term samples, the recommended air volume is 15 L
collected at 1.0 L/min (15-min samples).
2.6.3. When short-term samples are required, the reliable
quantitation limits become larger. For example, the reliable
quantitation limit is 99 ppb (478 µg/m3)
for 2-butoxyethanol when 15 L is sampled.
2.7. Interferences (sampling)
2.7.1. It is not known if any compound(s) will severely
interfere with the collection of the two analytes on charcoal. In
general, the presence of other solvent vapors in the air will reduce
the capacity of charcoal to collect the analytes.
2.7.2. Other solvents used in the sampling area should be
reported to the laboratory as potential interferences.
2.8. Safety precautions (sampling)
2.8.1. Attach the sampling equipment to the employee so that it
will not interfere with work performance or safety. Use sampling
tube holders with protective covers if possible.
2.8.2. Wear eye protection when breaking the ends of the charcoal
tubes.
2.8.3. Follow all safety procedures that apply to the work area
being sampled.
3. Analytical Procedure
3.1. Apparatus
3.1.1. A GC equipped with a flame ionization detector. For this
evaluation, a Hewlett-Packard 5890 Series II Gas
Chromatograph equipped with a 7673A Automatic Sampler was used.
3.1.2. A GC column capable of separating the analyte of interest
from the desorption solvent, internal standard and any
interferences. A 30-m × 0.25-mm i.d.
(0.25-µm film), fused silica Nukol column (Catalog
Number 2-4107M, Supelco, Inc., Bellefonte, PA) was used
in this evaluation.
3.1.3. An electronic integrator or some other suitable means of
measuring peak areas or heights. A Waters 860 Networking Computer
System was used in this evaluation.
3.1.4. Two-milliliter vials with Teflon-lined caps.
3.1.5. A dispenser capable of delivering 1.0 mL to prepare
standards and samples. If a dispenser is not available, a
1.0-mL volumetric pipet may be used.
3.1.6. Syringes of various sizes for preparation of standards.
3.1.7. Volumetric flasks and pipets to dilute the pure analytes
in preparation of standards.
3.2. Reagents
3.2.1. 2-Butoxyethanol and 2-butoxyethyl acetate,
reagent grade. Aldrich Lot 01604KT 2-butoxyethanol and
Lot 01106KP 2-butoxyethyl acetate were used in this
evaluation.
3.2.2. Methylene chloride, chromatographic grade. American
Burdick and Jackson Lot AQ553 was used in this evaluation.
3.2.3. Methanol, chromatographic grade. American Burdick and
Jackson Lot AW106 was used in this evaluation.
3.2.5. A suitable internal standard, reagent grade. Aldrich Lot
01601HT 2-ethyl-1-hexanol was used in this evaluation.
3.2.6. The desorption solvent consists of methylene
chloride/methanol, 95/5 (v/v) containing an internal standard at a
concentration of 1.5 mL/L.
3.2.7. GC grade nitrogen, air, and hydrogen.
3.3. Standard preparation
3.3.1. Prepare concentrated stock standards by diluting the pure
analytes with methylene chloride. Prepare working standards by
injecting microliter amounts of concentrated stock standards into
vials containing 1.0 mL of desorption solvent delivered from the
same dispenser used to desorb samples. For example, to prepare a
stock standard of 2-butoxyethanol, dilute 3.0 mL of
pure 2-butoxyethanol (sp gr = 0.9022) to 10.0 mL with
methylene chloride. This stock solution would contain 270.7 µg/µL. A
working standard of 1137 µg/sample is prepared by injecting 4.2 µL
of this stock into a vial containing 1.0 mL of desorption solvent.
3.3.2. Bracket sample concentrations with working standard
concentrations. If samples fall outside of the concentration range
of prepared standards, prepare and analyze additional standards to
ascertain the linearity of response.
3.4. Sample preparation
3.4.1. Transfer each section of the samples to separate vials.
Discard the glass tubes and plugs.
3.4.2. Add 1.0 mL of desorption solvent to each vial using the
same dispenser as used for preparation of standards.
3.4.3. Immediately cap the vials and shake them periodically for
about 30 min before analysis.
3.5. Analysis
3.5.1. GC conditions
column: |
30-m × 0.25-mm i.d. fused silica, Nukol,
0.25-µm film |
|
injection volume: |
1.0 µL (with a 58:1 split) |
|
zone temperatures: |
column- injector- detector- |
90°C 150°C 200°C |
|
gas flows: |
hydrogen (carrier)- nitrogen (makeup)-
hydrogen (flame)- air- |
1.7 mL/min (83 kPa head pressure) 20 mL/min 65
mL/min 315 mL/min |
|
retention times: |
2-butoxyethanol- 2-butoxyethyl
acetate- (2-ethyl-l-hexanol- |
7.55 min 9.75 min 11.5 min) |
|
chromatogram: |
Section 4.11. |
3.5.2. Peak areas (or heights) are measured by an integrator or
other suitable means.
3.5.3. An internal standard (ISTD) calibration method is used.
Calibration curves are prepared by plotting micrograms of analyte
per sample versus ISTD-corrected response of standard
injections. Sample concentrations must be bracketed by standards.
3.6. Interferences (analytical)
3.6.1. Any compound that produces a flame ionization detector
response and has a similar retention time as the analyte or internal
standard is a potential interference. Any potential interferences
reported to the laboratory by the industrial hygienist should be
considered before samples are desorbed.
3.6.2. GC parameters (i.e. column and column temperature) may be
changed to possibly circumvent interferences.
3.6.3. Retention time on a single column is not considered proof
of chemical identity. Analyte identity should be confirmed by
GC/mass spectrometer if possible.
3.7. Calculations
The analyte concentration for samples is obtained from the
appropriate calibration curve in terms of micrograms per sample,
uncorrected for desorption efficiency. The air concentration is
calculated using the following formulae. The back (50-mg)
section is analyzed primarily to determine if there was any
breakthrough from the front (100-mg) section during
sampling. If a significant amount of analyte is found on the back
section (e.g., greater than 25% of the amount found on the front
section), this fact should be reported with sample results. If any
analyte is found on the back section, it is added to the amount found
on the front section.
This total amount is then corrected by subtracting the total amount
(if any) found on the blank.
mg/m3 = |
(micrograms of analyte per sample, blank
corrected)
(liters of air sampled) (desorption
efficiency) |
ppm = |
(mg/m3)
(24.46)
(molecular weight of analyte) |
where 24.46 = molar volume (L) at 250°C and 101.3 kPa
(760 mmHg)
molecular weight = |
118.17 for 2-butoxyethanol 160.21 for
2-butoxyethyl acetate |
3.8. Safety precautions (analytical)
3.8.1. Avoid skin contact and inhalation of all chemicals.
3.8.2. Restrict the use of all chemicals to a fume hood when
possible.
3.8.3. Wear safety glasses and a lab coat at all times while in
the lab area.
4. Backup Data
4.1. Detection limit of the analytical procedure
The injection size listed in the analytical procedure (1.0 µL with
a 58:1 split) was used in the determination of the detection limits of
the analytical procedure. The detection limits of 0.12 and 0.13 ng
were determined by making injections of 7.22 and 7.54 ng/µL standards
for 2-butoxyethanol and 2-butoxyethyl
acetate respectively. These amounts were judged to produce peaks with
heights approximately 5 times the baseline noise. A chromatogram of
such an injection is shown in Figure
4.1.
4.2. Detection limit of the overall procedure
Six samples for each analyte were prepared by injecting 7.22 µg of
2-butoxyethanol and 7.54 µg of 2-butoxyethyl
acetate into the 100-mg section of charcoal tubes. The
detection limits of the overall procedure correspond to air
concentrations of 31 ppb (150 µg/m3) and 24
ppb (157 µg/m3) for
2-butoxyethanol and 2-butoxyethyl acetate
respectively. The results are given in Tables 4.2.1. and 4.2.2.
Table 4.2.1. Detection Limit of Overall
Procedure for 2-Butoxyethanol
|
sample no. |
µg spiked |
µg recovered |
|
1 |
7.22 |
6.87 |
2 |
7.22 |
7.03 |
3 |
7.22 |
7.49 |
4 |
7.22 |
7.36 |
5 |
7.22 |
6.98 |
6 |
7.22 |
7.16 |
|
Table 4.2.2 Detection Limit of Overall Procedure for
2-Butoxyethyl Acetate
|
sample no. |
µg spiked |
µg recovered |
|
1 |
7.54 |
8.57 |
2 |
7.54 |
8.51 |
3 |
7.54 |
7.76 |
4 |
7.54 |
7.58 |
5 |
7.54 |
7.72 |
6 |
7.54 |
7.34 |
|
4.3. Reliable quantitation limit
The reliable quantitation limits were determined by analyzing
charcoal tubes spiked with loadings equivalent to the detection limits
of the analytical procedure. Samples were prepared by injecting 7.22
µg of 2-butoxyethanol and 7.54 µg of
2-butoxyethyl acetate into the 100-mg
section of charcoal tubes. These amounts correspond to air
concentrations of 31 ppb (150 µg/m3) and 24
ppb (157 µg/m3) for
2-butoxyethanol and 2-butoxyethyl acetate
respectively. The results are given in Tables 4.3.1. and 4.3.2.
Table 4.3.1. Reliable Ouantitation Limit for
2-Butoxyethanol (Based on samples and data of Table
4.2.1.)
|
sample no. |
percent recovered |
statistics |
|
1 |
95.2 |
= |
99.0 |
2 |
97.4 |
3 |
103.7 |
4 |
101.9 |
SD = |
3.25 |
5 |
96.7 |
Precision = |
(1.96)(±3.25) |
6 |
99.2 |
= |
±6.37 |
|
Table 4.3.2. Reliable Ouantitation Limit for
2-Butoxyethyl Acetate (Based on samples and data of
Table 4.2.2.)
|
sample no. |
percent recovered |
statistics |
|
1 |
113.7 |
= |
105.0 |
2 |
112.9 |
3 |
102.9 |
4 |
100.5 |
SD = |
6.74 |
5 |
102.4 |
Precision = |
(1.96)(±6.76) |
6 |
97.3 |
= |
±13.2 |
|
4.4. Instrument response to the analyte
The instrument response to the analytes over the range of 0.5 to 2
times the target concentrations was determined from multiple
injections of analytical standards. These data are given in Tables
4.4.1. and 4.4.2. and Figures 4.4.1. and 4.4.2. The response is linear
for both analytes with slopes (in ISTD-corrected area
counts per micrograms of analyte per sample) of 226.3 and 219.6 for
2-butoxyethanol and 2-butoxyethyl acetate
respectively.
Table 4.4.1. Instrument Response to
2-Butoxyethanol
|
× target conc. µg/sample ppm |
0.5× 568.9 2.45 |
1× 1138 4.91 |
2× 2276 9.81 |
|
area counts |
130013 |
265338 |
511143 |
|
130843 |
264851 |
511543 |
130236 |
266530 |
510113 |
130759 |
264206 |
507834 |
130483 |
266271 |
508070 |
130198 |
265353 |
514955 |
|
![mean](../mean.gif) |
130422 |
265425 |
510610 |
|
Table 4.4.2. Instrument Response to
2-Butoxyethyl Acetate
|
× target conc. µg/sample ppm |
0.5× 791.3 2.52 |
1× 1583 5.03 |
2× 3165 10.07 |
|
area counts |
174117 |
355187 |
690704 |
|
174715 |
355740 |
688825 |
173817 |
355966 |
690567 |
173654 |
355907 |
690419 |
173498 |
355731 |
693114 |
173516 |
354933 |
692883 |
|
![mean](../mean.gif) |
173886 |
355577 |
691085 |
|
4.5. Storage test
Storage samples are normally generated by sampling the recommended
air volume at the recommended sampling rate from test atmospheres at
80% relative humidity containing the analyte at the target
concentration. Because this would require generation of
8-h samples, in the interest of time, samples. were
generated by sampling from atmospheres containing the analytes at
about 4 times the target concentrations for 60 min at 0.2 L/min (12-L
samples). For each set of 36 samples for each analyte, six samples
were analyzed immediately after generation, fifteen were stored in a
refrigerator at 0°C and fifteen were stored in a closed drawer at
ambient temperatures of 20-28°C. Six samples, three from
refrigerated and three from ambient storage, were analyzed at
intervals over a period of fifteen days. The results are given in
Tables 4.5.1. and 4.5.2. and shown graphically in Figures 4.5.1.1.,
4.5.1.2.,
4.5.2.1.
and 4.5.2.2.
The loss of analyte on the 2-butoxyethyl acetate samples
was due to hydrolysis of the ester to 2-butoxyethanol and
acetic acid. This was supported by the fact that amounts of
2-butoxyethanol were found on these samples which
corresponded to the loss of 2-butoxyethyl acetate. The
loss of analyte in this study after 15 days was about 3% for
refrigerated storage and about 10% for ambient storage. If possible,
stored 2-butoxyethyl acetate samples should be
refrigerated to reduce hydrolysis.
Table 4.5.1. Storage Test for
2-Butoxyethanol
|
storage time |
|
% recovery |
(days) |
|
(refrigerated) |
|
(ambient) |
|
0 |
|
98.5 |
96.9 |
98.0 |
|
98.5 |
96.9 |
98.0 |
0 |
97.7 |
98.2 |
98.4 |
97.7 |
98.2 |
98.4 |
2 |
99.7 |
99.7 |
99.2 |
99.5 |
98.9 |
99.7 |
6 |
97.9 |
98.3 |
99.0 |
97.5 |
98.2 |
99.0 |
8 |
95.5 |
96.0 |
96.2 |
95.2 |
96.4 |
96.3 |
13 |
100.3 |
100.2 |
100.8 |
98.4 |
99.4 |
100.0 |
15 |
99.1 |
99.0 |
100.0 |
98.2 |
99.6 |
98.2 |
|
Table 4.5.2. Storage Test for
2-Butoxyethyl Acetate
|
storage time |
|
% recovery |
(days) |
|
(refrigerated) |
|
(ambient) |
|
0 |
|
99.2 |
98.6 |
98.9 |
|
99.2 |
98.6 |
98.9 |
0 |
97.7 |
94.0 |
99.4 |
97.7 |
94.0 |
99.4 |
2 |
98.6 |
96.4 |
98.6 |
93.2 |
96.5 |
95.8 |
6 |
97.5 |
97.1 |
97.9 |
91.6 |
86.7 |
92.4 |
8 |
96.0 |
96.5 |
97.7 |
89.3 |
90.1 |
90.9 |
13 |
97.4 |
95.1 |
97.1 |
88.2 |
85.2 |
90.0 |
15 |
97.2 |
93.1 |
96.8 |
87.0 |
89.7 |
89.1 |
|
4.6. Precision (analytical procedure)
The precision of the analytical procedure for each analyte is the
pooled coefficient of variation determined from replicate injections
of standards. The precision of the analytical procedure for each
analyte is given in Tables 4.6.1. and 4.6.2. These tables are based on
the data presented in Section 4.4.
Table 4.6.1. Precision of the Analytical Procedure
for 2-Butoxyethanol (Based on Table 4.4.1.)
|
× target conc. µg/sample ppm |
0.5× 568.9 2.45 |
1× 1138 4.91 |
2× 2276 9.81 |
|
SD (area counts) |
330.6 |
867.7 |
2624 |
CV |
0.0025 |
0.0033 |
0.0051 |
|
= 0.004 |
|
Table 4.6.2. Precision of the Analytical Procedure
for 2-Butoxyethyl Acetate (Based on Table
4.4.2.)
|
× target conc. µg/sample ppm |
0.5× 791.3 2.52 |
1× 1583 5.03 |
2× 3165 10.07 |
|
SD (area counts) |
466.2 |
418.9 |
1632 |
CV |
0.0027 |
0.0012 |
0.0024 |
|
= 0.002 |
|
4.7. Precision (overall procedure)
The precision of the overall procedure is determined from the
storage data. The determination of the standard error of estimate
(SEE) for a regression line plotted through the graphed storage data
allows the inclusion of storage time as one of the factors affecting
overall precision. The SEE is similar to the standard deviation,
except it is a measure of dispersion of data about a regression line
instead of about a mean. It is determined with the following equation:
where |
n = k =
k = |
total no. of data points 2 for linear regression 3 for
quadratic regression |
|
Yobs =
Yest =
|
observed % recovery at a given time estimated % recovery
from the regression line at the same given time
|
An additional 5% for pump error is added to the SEE by the addition
of variances. The SEEs are 5.2% and 5.5% for
2-butoxyethanol and 2-butoxyethyl acetate
respectively. The precision of the overall procedure is the precision
at the 95% confidence level, which is obtained by multiplying the SEE
(with pump error included) by 1.96 (the z-statistic from
the standard normal distribution at the 95% confidence level). The 95%
confidence intervals are drawn about their respective regression lines
in the storage graphs. The precisions of the overall procedure are
±10.1% and ±10.8% for 2-butoxyethanol and
2-butoxyethyl acetate respectively. The SEE and precision
of the overall procedure for each analyte were obtained from Figures
4.5.1.2.
and 4.5.2.2.
for 2-butoxyethanol and 2-butoxyethyl
acetate respectively.
4.8. Reproducibility
Six samples for each analyte, collected from controlled test
atmospheres (at about 80% R.H., 24-28°C,
86-88 kPa) containing the analytes at about 4 times the
target concentrations, were analyzed by a chemist unassociated with
this evaluation. The samples were generated by drawing the test
atmospheres through sampling tubes for 60 min at approximately 0.2
L/min. The samples were stored in a refrigerator for 8 days before
being analyzed. The results are presented in Tables 4.8.1. and 4.8.2.
Table 4.8.1. Reproducibility for
2-Butoxyethanol
|
sample no. |
µg found |
µg expected |
% found |
% deviation |
|
1 |
1008 |
1090 |
92.5 |
-7.5 |
2 |
992.6 |
1073 |
92.5 |
-7.5 |
3 |
994.5 |
1073 |
92.7 |
-7.3 |
4 |
993.2 |
1063 |
93.4 |
-6.6 |
5 |
1007 |
1091 |
92.3 |
-7.7 |
6 |
1036 |
1104 |
93.8 |
-6.2 |
|
Table 4.8.1. Reproducibility for
2-Butoxyethyl Acetate
|
sample no. |
µg found |
µg expected |
% found |
% deviation |
|
1 |
1347 |
1396 |
96.5 |
-3.5 |
2 |
1337 |
1372 |
97.4 |
-2.6 |
3 |
1315 |
1371 |
95.9 |
-4.1 |
4 |
1318 |
1361 |
96.8 |
-3.2 |
5 |
1364 |
1373 |
99.3 |
-0.7 |
6 |
1380 |
1414 |
97.6 |
-2.4 |
|
4.9. Desorption efficiency
The desorption efficiency for each analyte was determined by
injecting microliter amounts of stock standards onto the front section
of charcoal tubes. Eighteen samples were prepared, six samples for
each concentration level listed in the following table.
Table 4.9. Desorption Efficiency Data
|
analyte |
2-butoxyethanol
|
|
2-butoxyethyl acetate
|
× target concn |
0.5× |
1× |
2× |
|
0.5× |
1× |
2× |
µg/sample |
568.9 |
1138 |
2276 |
|
791.3 |
1583 |
3165 |
ppm |
2.45 |
4.91 |
9.81 |
|
2.52 |
5.03 |
10.07 |
|
desorption |
99.0 |
99.4 |
99.9 |
|
101.6 |
100.6 |
102.2 |
efficiency, % |
98.7 |
99.1 |
99.1 |
|
101.6 |
101.7 |
101.8 |
|
100.4 |
98.5 |
98.4 |
|
101.9 |
101.4 |
101.3 |
99.2 |
98.9 |
99.0 |
|
101.5 |
101.2 |
102.2 |
98.5 |
98.0 |
99.2 |
|
101.4 |
100.9 |
101.7 |
99.1 |
98.2 |
99.3 |
|
101.1 |
100.9 |
102.4 |
|
![mean](../mean.gif) |
99.2 |
98.7 |
99.2 |
|
101.5 |
101.1 |
101.9 |
|
![mean](../mean.gif) |
99.0 |
|
101.5 |
|
4.10. Stability of desorbed samples
The stability of desorbed samples was checked by reanalyzing the
target concentration samples from Section 4.9. one day later using
fresh standards. The sample vials were resealed with new septa after
the original analyses and were allowed to stand at room temperature
until reanalyzed. The results are given in Table 4.10.
Table 4.10. Stability of Desorbed Samples at the
Target Concentration
|
|
% desorption after 24 h |
sample no. |
2-butoxyethanol |
2-butoxyethyl acetate |
|
1 |
101.8 |
103.4 |
2 |
102.7 |
103.8 |
3 |
102.7 |
103.8 |
4 |
101.7 |
103.8 |
5 |
101.0 |
103.6 |
6 |
100.7 |
103.4 |
|
![mean](../mean.gif) |
101.8 |
103.6 |
|
4.11. Chromatograms
A chromatogram of the two analytes is shown in Figure 4.11.
The chromatogram is from an injection of a standard equivalent to a
48-L air sample at the target concentrations.
![graph](org83fig4.gif) Figure 4.1. Detection limit
chromatogram. Key: (1) 2-butoxyethanol, (2) 2-butoxyethyl
acetate, (3)2-ethyl-l-hexanol.
![graph](org83fig5.gif) Figure 4.4.1. Instrument
response to 2-butoxyethanol.
![graph](org83fig6.gif) Figure 4.4.2. Instrument
response to 2-butoxyethyl acetate.
![graph](org83fig7.gif) Figure 4.5.1.1.
2-Butoxyethanol refrigerated storage smaples.
![graph](org83fig8.gif) Figure 4.5.1.2.
2-Butoxyethanol ambient storage samples.
![graph](org83fig9.gif) Figure 4.5.2.1.
2-Butoxyethyl acetate refrigerated storage samples.
![graph](org83fig10.gif) Figure 4.5.2.2.
2-Butoxyethyl acetate ambient storage samples.
![graph](org83fig11.gif) Figure 4.11. Chromatogram
of a standard at the target concentrations. Key: (1)
2-butoxyethanol, (2) 2-butoxyethyl acetate,
(3)2-ethyl-l-hexanol.
5. References
5.1. "OSHA Analytical Methods Manual" U.S. Department of Labor,
Occupational Safety and Health Administration; OSHA Analytical
Laboratory: Salt Lake City, UT, 1985; Method 53; American Conference
of Governmental Industrial Hygienists (ACGIH): Cincinnati, OH, ISBN:
0-936712-66-X.
5.2. Elskamp, C.J. "OSHA Method 79; 2-Methoxyethanol,
2-Methoxyethyl Acetate, 2-Ethoxyethanol, and
2-Ethoxyethyl Acetate", OSHA Analytical Laboratory,
unpublished, Salt Lake City, UT 84165, January, 1990.
5.3. "NIOSH Manual of Analytical Methods", 3rd ed.; U.S. Department
of Health and Human Services, Public Health Service, Centers for
Disease Control, National Institute for Occupational Safety and
Health, Division of Physical Sciences and Engineering; Cincinnati, OH,
1984, Method 1403, DHHS (NIOSH) Publ. No. 84-100.
5.4. "Air Contaminants - Permissible Exposure Limits", Code of
Federal Regulations, Title 29; 1910.1000, U.S. Department of Labor,
OSHA; Washington, DC, 1989, DOL (OSHA) Publ. No. OSHA 3112.
5.5. J.T. Baker Chemical Co.: Material Safety Data Sheets (MSDS)
for 2-butoxyethanol and 2-butoxyethyl
acetate, Jan. 1989.
5.6. ChemInfo Database on CCINFO CD-ROM disc 89-2, Canadian Centre
for Occupational Health and Safety, Hamilton, Ontario.
5.7. "Hawley's Condensed Chemical Dictionary" 11th ed.; Sax, N.I.,
Lewis, R.J., Eds.; Van Nostrand Reinhold, New York, 1987.
5.8. Brown, E.S. et al. In "Kirk-Othmer Encyclopedia of Chemical
Technology" 3rd ed.; Grayson, M., Ed.; John Wiley & Sons, New
York, 1980, Vol. 11, pp 933-956.
|