|
MALEIC ANHYDRIDE
| Method no.: |
25 |
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| Matrix: |
Air |
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| Target concentration: |
1 mg/m3 (OSHA PEL) |
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| Procedure: |
Collection and derivatization on a sampling
train consisting of two adsorption tubes connected in series.
The first tube contains XAD-2 coated with p-anisidine and the
second tube contains untreated XAD-2. The anisidine-maleic anhydride
derivative is desorbed with methanol and analyzed by reverse phase
HPLC with a UV detector. |
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Recommended air volume
and sampling rate: |
20 L at 0.1 L/min |
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| Reliable quantitation limit: |
0.005 mg/m3 |
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Standard error of estimate
at the target concentration:
(Section 4.7.) |
7.6% |
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| Special requirements: |
p-Anisidine coated sorbent tubes should be shielded
from sunlight at all times. The recommended sampling rate should not
be exceeded. |
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| Status of method: |
An air sampling and analytical method that has
been evaluated according to the criteria established
by the Organic Methods Evaluation Branch. |
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| Date: February 1981 |
Chemists: Keith Motley
Tom Plummer
|
Carcinogen/Pesticides Branch
OSHA Analytical Laboratory
Salt Lake City, Utah
1. General Discussion
1.1. Background
1.1.1. History
The procedure for determining maleic anhydride air
concentrations which employs isopropanol impingers encounters
a serious interference with the presence of maleic acid.
The monoisopropyl ester of maleic acid was previously
considered to be formed solely from the reaction of maleic
anhydride with isopropanol and hence was the compound
considered to exclusively represent the concentration of
maleic anhydride. It can be shown, however, that maleic
acid also reacts with isopropanol to form this ester in
significant quantities. Further, the maleic acid itself
may be either of ambient origin or formed from the
hydrolysis of maleic anhydride utilizing trace amounts of water
in the isopropanol impingers. In view of the myriad of
equilibria and unknown factors involved, the use of
isopropanol impingers for the quantitative determination of
maleic anhydride is found to be lacking in both specificity
and accuracy. (Section 4.8.)
During the past several months, attempts have been made at
this lab to selectively derivatize maleic anhydride in the
presence of maleic acid. Among the derivatizing agents
tried were triphenyl phosphine, various Diels-Alder reagents
such as cyclopentadiene and 1,3-diphenyl isobenzofuran,
imidazoles and thiazoles. All of the above fell
short of the desired goal due either to stability problems
or the inability to chromatograph and analyze the
resultant derivative. p-Anisidine, however, serves as an
excellent analytical derivatizing agent for maleic anhydride
due to: 1) its ability to react with the anhydride in
high yield (Figure l.l.l.), 2) the ease with which the
derivative is chromatographed and, 3) the convenience of
collection on solid sorbent tubes rather than liquid
impingers (Ref. 5.1.).
The collection and analysis of maleic anhydride using
p-anisidine on solid sorbent tubes was therefore examined
and the results presented in the method that follows.
1.1.2. Toxicology (This section is for information only and
should not be taken as the basis for OSHA policy).
Maleic anhydride is a severe irritant to the eyes, skin
and respiratory tract which can, upon exposure, produce
intense burning sensations in the eyes and throat with
coughing and vomiting. Among workers repeatedly exposed
to 5-10 mg/m3, toxic effects included ulceration of nasal
mucous membranes, chronic bronchitis, and in some cases,
asthma. Other potential effects of exposure are
dermatitis, pulmonary edema, respiratory sensitization, skin
sensitization, photophobia and double vision. (Ref. 5.2.)
1.1.3. Uses where exposure may occur
Most maleic anhydride now produced in the United States is
obtained from the catalytic oxidation of either benzene or
butene. An exception is the isolation of maleic anhydride
as a by-product in the production of phthalic anhydride.
Approximately 50% of the maleic anhydride produced is used
in the manufacture of polyester resins. The remaining
maleic anhydride is used in the preparation of fumaric
acid, agricultural pesticides, alkyd resins and
miscellaneous chemical products. No literature data indicating the
number of workers potentially exposed to maleic anhydride
were found. (Ref. 5.3.)
1.1.4. Physical properties
Maleic Anhydride (Ref. 5.6.)
| molecular weight: |
98.06 |
| melting point: |
53°C |
| boiling point: |
202°C |
| vapor pressure: |
1 mm Hg at 44.0°C |
| structure: |
Figure 1.1.4. |
| synonyms: |
2,5-furandione, toxilic anhydride, cis butenedioic anhydride. |
Maleic Anhydride - p-Anisidine Derivative (experimental)
| molecular weight: |
221.21 |
| melting point: |
184°C |
| boiling point: |
unknown |
| appearance: |
yellow-green powder or crystals |
| structure: |
Figure 1.1.4. |
1.2. Limit defining parameters
1.2.1. Detection limit of the analytical procedure
The detection limit of the analytical procedure is 2.4 ng
of maleic anhydride per injection. This is the amount of
maleic anhydride necessary to produce a derivative peak
whose height is approximately five times the baseline
noise height. (Section 4.1.)
1.2.2. Detection limit of the overall procedure
The detection limit of the overall procedure is 97 ng of
maleic anhydride per sample or 0.005 mg/m3 based on the
recommended air volume of 20 L. This is the amount of
maleic anhydride spiked on the sampling device as the
maleic anhydride - p-anisidine derivative which allows
recovery of an amount of that derivative equivalent to the
detection limit of the analytical procedure. (Section
4.2.)
1.2.3. Reliable quantitation limit
The reliable quantitation limit is 97 ng of maleic anhydride
per sample or 0.005 mg/m3 based on the recommended
air volume. This is the smallest amount of maleic anhydride
which can be quantitated within the requirements of
75% recovery and 95% confidence limits of less than ±25%.
(Section 4.2.)
1.2.4. Sensitivity
The sensitivity of the analytical procedure over a
concentration range representing 0.5 to 2 times the PEL based on
the recommended air volume is 2019 area units/ng of maleic
anhydride detected as the derivative. The sensitivity is
determined by the slope of the calibration curve. (Section
4.4.)
1.2.5. Recovery
The recovery of analyte from the sorbent tubes must be
greater than 75%. The average recovery over the range of
0.5 to 2 times the PEL is 96%. (Section 4.6.)
1.2.6. Precision of the analytical method
The pooled coefficient of variation obtained from replicate
determinations of analytical standards at 0.5, 1, and
2 times the PEL is 0.0095. (Section 4.3.)
1.2.7. Precision of the overall procedure
The overall procedure must provide results that are ±25%
or better at the 95% confidence level. The precision at
the 95% confidence level for the 15-day storage test is
±15.9%. This figure includes an additional ±5% for sampling
error. (Section 4.7.)
1.3. Advantages
1.3.1. The major advantage is the quantitative recovery of maleic
anhydride as the derivative without interferences from
maleic acid or degradation of the highly unstable and
reactive anhydride.
1.3.2. The sampling apparatus is compact, easy to use, and has no
liquid spill potential.
1.3.3.
The analytical procedure is straight-forward and reproducible
with detection limits well below the PEL value.
1.4. Disadvantages
1.4.1. The derivatization tube contains p-anisidine, which is
listed in some journals as a suspected carcinogen. This
necessitates a backup XAD-2 tube in the sampling train to
collect any p-anisidine lost from the first tube.
p-Ansidine is known to collect on XAD-2 tubes (Ref. 5.4.).
1.4.2. The capacity of the treated sorbent tube is limited but
should give quantitative recovery up to 4 times the PEL at
the recommended air volume.
2. Sampling Procedure
2.1. Apparatus
2.1.1. XAD-2 sorbent tubes coated with 500 µg of p-anisidine.
Instructions for the preparation of these tubes are
presented in Section 4.9.
2.1.2. Untreated XAD-2 sorbent tube used as an in-series backup
to the p-anisidine coated tube.
2.1.3. An air sampling pump with a flow rate which can be
calibrated to within ±5% of the recommended 0.1-L/min flow
rate while the sampler is in line.
2.2. Reagents
None required.
2.3. Sampling technique
2.3.1. The air sampling train is composed of one treated XAD-2
tube followed by an untreated XAD-2 tube in series. The
tubes are connected with a modified end cap which has had
the closed portion cut off. The "B" section of the treated
tube should be followed by the "A" section of the untreated
tube. (Figure 4.5.)
2.3.2. Connect the sampling train to the sampling pump with a
piece of flexible tubing. Cover each tube with masking
tape or other material to prevent exposure to sunlight.
2.3.3. The air sampler should be placed in a vertical position to
minimize channeling.
2.3.4. Sampled air should pass directly into the sampling train
without use of extraneous tubing.
2.3.5. Immediately after sampling, separate the air sampling
train into its component tubes, identify each tube as
treated or untreated tube and seal each tube with plastic
end caps. Also, wrap each sample end to end with official
OSHA seals.
2.3.6. With each batch of samples, submit at least one blank
p-anisidine treated tube from the same lot used for
samples. This tube should be subjected to the same treatment
and handling as the samples except that no air is drawn
through it.
2.3.7. The presence of phthalic or trimellitic anhydride in the
sampling area must be reported to the lab.
2.3.8. Transport the samples and paperwork to the lab for analysis.
2.3.9. Sampling tubes are stable for at least 30 days if shielded
from light and stored in a freezer.
2.4. Breakthrough (Breakthrough for the purposes of this study will be
defined as the presence of the maleic anhydride derivative on the
"B" section of the treated sorbent tube).
2.4.1. Vapor generation system
A vapor generation system for maleic anhydride was
constructed by filling an empty silanized sorbent tube with
glass wool and placing it in front of the treated XAD-2
tube. A chloroform solution of maleic anhydride was
injected onto the glass wool and quantitatively leached off
by drawing dry air through the system. This gave
experimental control over both the quantity of maleic anhydride
and the flow rate while eliminating the possible hydrolysis
of maleic anhydride before contact is made with the
treated tube. (Section 4.5.)
2.4.2. Laboratory experiments consisted of the following: 1)
drawing 60 L of humid air through the treated sorbent tube
to simulate a humid sampling atmosphere, 2) transferring
the tube to the dry air vapor generator and introducing a
known quantity of maleic anhydride, and 3) subsequently
passing more humid air through the sampling system. It is
this volume of humid air which is presented in the third
column of Table 4.5.2.
2.4.3. Breakthrough of the maleic anhydride from the "A" section
to the "B" section of the tube is primarily a function of
the flow rate at which the derivative will all form on the
"A" section and secondarily a function of the air volume
at which migration of the derivative will take place. At
0.1 L/min, all of the derivative will be formed on the "A"
section and up to 150 L of humid air could be pulled without
appreciable migration. A 20-L air volume at 0.1 L/min
falls well within the parameters of providing a sensitive
detection limit , quantitative recovery of maleic anhydride
and a practical sampling period of 200 min. This study
used an amount of maleic anhydride approximately equal to
2 times the PEL based on the recommended air volume. (Section 4.5.)
2.5. Desorption efficiency
The average desorption efficiency from p-anisidine treated XAD-2
tubes with 9.5, 19.1, and 41.5 µg of maleic anhydride injected as
the p-anisidine derivative was 96.2%. The spiked tubes represent
a range from 0.48 mg/m3 to 2.08 mg/m3 based on the recommended air
volume. (Section 4.6.)
2.6. Recommended air volume and sampling rate
2.6.1. The recommended air volume is 20 L.
2.6.2. The recommended sampling rate is 0.1 L/min.
2.7. Interferences (sampling)
Generic anhydrides present in the sampled atmosphere will react
with the p-anisidine and thereby reduce the amount available for
the derivatization of maleic anhydride. Hence, both phthalic and
trimellitic anhydride should be considered as potential sampling
interferences.
2.8. Safety precautions (sampling)
2.8.1. Observe due care when working with the sharp ends of the
air sampler.
2.8.2. Attach the sampling equipment to the worker in such a
manner that it will not interfere with work performance.
2.8.3. Assure that the untreated XAD-2 backup tube is securely in
place to collect any p-anisidine lost from the treated
tube.
2.8.4. Follow all safety practices that apply to the work area
being sampled.
3. Analytical Method
3.1. Apparatus
3.1.1. A High Performance Liquid Chromatograph interfaced to a UV
absorbance detector.
3.1.2. A reverse phase C18 liquid chromatographic column.
3.1.3. An electronic integrator or other suitable method to measure
peak magnitude.
3.1.4. An analytical balance.
3.1.5. 2-mL vials with Teflon-lined caps.
3.1.6. Syringes, 50-µL for sample injections.
3.1.7. Pipets of convenient sizes for diluting standards and a
1-mL pipet or dispenser for the desorbing solvent.
3.1.8. Volumetric flasks of convenient sizes for diluting standards.
3.1.9. Shaking device for desorption of samples.
3.2. Reagents
3.2.1. p-Anisidine, reagent grade.
3.2.2. Maleic anhydride, reagent grade.
3.2.3. Methyl alcohol, chromatographic grade.
3.2.4. Water, LC grade.
3.2.5. Phosphoric acid.
3.2.6. Chloroform, chromatographic grade.
3.3. Sample preparation
3.3.1. The status of the OSHA seal on each sample is noted and
recorded as intact, broken, or none.
3.3.2. The field and laboratory numbers are checked against those
on the sample identification sheets.
3.3.3. The "A" and "B" sections of the treated sorbent tube
should be transferred to separate 2-mL vials. The front
glass wool plug should be included with the "A" section
and great care should be exercised with the sorbent beads
closest to the front of the tube as this is where the
maleic anhydride derivative concentration will be greatest.
3.3.4. To each vial, add 1.0 mL of methanol and seal immediately
with Teflon-lined caps.
3.3.5. The vials should be shaken vigorously for 60 min.
3.4. Standard preparation
3.4.1. Neat standard preparation is accomplished by dissolving
stoichiometric quantities of p-anisidine and maleic
anhydride in separate solutions of chloroform and then
combining the two solutions. The derivative will precipitate
as a yellow solid. After washing the solid several times
with chloroform to remove excess p-anisidine and maleic
anhydride, evaporate the chloroform using a vacuum or
under a nitrogen gas stream and use the solid as neat
standard.
3.4.2. Weigh out the derivative into a volumetric such that the
concentration of the stock solution is no more than 1
mg/mL after addition of methanol. Sonication, shaking
and/or warming this standard may facilitate the
derivative's dissolution in the methanol. Dilute to the working
range with methanol. A derivative solution of 45.1
µg/mL is equivalent to a maleic anhydride air concentration
of 1.0 mg/m3 for a 20-L air sample desorbed with 1 mL
of methanol. This amount is uncorrected for the desorption
efficiency.
3.4.3. Standards are stored in dark bottles under refrigeration.
3.5. Analysis
3.5.1.
| LC conditions - |
Waters M-6000A HPLC Pump |
| column: |
Nucleosil C18 (25 cm × 4.6 mm) |
| eluent: |
50% MeOH, 50% H2O, 0.1% phosphoric acid |
| flow: |
1.5 mL/min |
| pressure: |
2600 psi |
| injection volume: |
25 µL |
| elution time: |
6.5 min |
3.5.2.
| Detector conditions - |
Waters 440 Dual Wavelength
Absorbance Detector |
| wavelength: |
313 nm primary, 254 nm secondary |
| attenuation: |
vary as per need. |
3.5.3. Chromatogram (Figure 4.3.)
3.5.4. Peak magnitude is measured by electronic integration or
other suitable means.
3.5.5. An external standard procedure is used to prepare a
calibration curve from the analysis of at least six different
standards diluted from two separate weighings.
3.5.6. Bracket the samples with analytical standards.
3.6. Interferences (analytical)
3.6.1. Any collected compound that has the same LC retention time
as the derivative and exhibits a UV absorbance at 313 nm
is an interference.
3.6.2. LC parameters may be changed to circumvent most interferences.
3.6.3. Retention time alone is not proof of a chemical identity.
Samples should be confirmed by GC/MS or other suitable
means when required.
3.7. Calculations
3.7.1. The integrator value in area units for each standard is
plotted against its concentration in µg/mL and a
calibration curve using the best straight line through the
points obtained.
3.7.2. The concentration values in µg/mL for both "A" and "B"
sections of the treated XAD-2 tube are determined from the
calibration curve, added together and corrected for the
desorption efficiency.
3.7.3. The air concentration of maleic anhydride (MA) for a sample
is calculated by the following equation:
mg/m3 = (A)(B)(C)/D
| where |
A |
= |
µg/mL derivative from Section 3.7.2. |
|
B |
= |
desorption volume in mL |
|
C |
= |
molecular weight ratio maleic
anhydride/derivative = 0.443 |
|
D |
= |
sample air volume in liters |
3.8. Safety precautions (analytical)
3.8.1. Maleic anhydride is an extremely dangerous irritant with a
high vapor pressure that readily sublimes at room temperature.
Avoid all skin contact and use only in a well
ventilated area.
3.8.2. p-Anisidine is a suspected carcinogen. Avoid all skin
contact with both the chemical and the treated sorbent
beads. Use in a well ventilated area.
3.8.3. Confine the use of solvents to a fume hood.
3.8.4. Wear safety glasses in all laboratory areas.
4. Backup Data
4.1. Detection limit
A 0.22 mg/mL derivative standard is prepared by injecting 4.0 µL
of a 55.10 µg/mL derivative standard into 1.0 mL of MeOH.
Twenty-five microliters of this standard injected 5 times gave the
following values. Peak heights were used because integration was
poor at this level. A typical chromatogram can be seen in Figure
4.1.
Table 4.1.
Detection Limit Data
|
| peak height (cm) |
statistics |
|
| 0.54 |
|
| 0.54 |
 |
= |
0.586 |
| 0.62 |
SD |
= |
0.049 |
| 0.58 |
CV |
= |
0.084 |
| 0.65 |
|
|
4.2. Reliable quantitation limit
Exactly 4.0 µL of a 55.10 µg/mL standard of the derivative was
injected onto five p-anisidine treated XAD-2 tubes and allowed to
stand capped overnight. Desorption in 1 mL of MeOH, shaking for 1 h
and analysis by injecting 25 µL into HPLC apparatus produced the
following results.
Table 4.2.
Reliable Quantitation Limit Data
|
| peak height |
% recovered |
|
| (cm) |
(0.586 cm = 100%) |
statistics |
|
| 0.50 |
85.3 |
|
| 0.49 |
83.6 |
|
|
= |
93.1 |
| 0.58 |
98.9 |
|
SD |
= |
7.93 |
| 0.58 |
98.9 |
±1.96 |
SD |
= |
±15.5 |
| 0.58 |
98.9 |
|
|
4.3. Precision
The data in Table 4.3. represent replicate 25-µL injections of
three standard solutions. The concentrations of the standards
were 9.53 19.05 and 41.50 µg/mL maleic anhydride as the p-anisidine
derivative. These values would approximate 0.5, 1, and 2
times the PEL at the recommended air volume. A typical integration
by the HP 3354 Laboratory Data System is shown in Figure 4.3.
Table 4.3.
Precision of the Analytical Method
|
| × target concentration |
0.5× |
1× |
2× |
| µg MA |
9.53 |
19.05 |
41.50 |
| µg adduct formed |
21.48 |
42.96 |
93.59 |
|
| area counts |
501687 |
1030920 |
2045560 |
|
507853 |
1036560 |
2062770 |
|
507141 |
1017060 |
2064960 |
|
503126 |
1054290 |
2072360 |
|
|
|
|
|
504952 |
1034707 |
2064556 |
| SD |
3035 |
15410 |
12075 |
| CV |
0.0060 |
0.0149 |
0.0058 |
|
|
|
|
 = 0.0095 |
|
|
4.4. Sensitivity
A calibration curve is shown in Figure 4.4. using data from Table
4.3. The slope of the curve indicates the sensitivity of the
method over the range of 0.5 to 2 times the PEL based on the
recommended air volume.
4.5. Breakthrough
4.5.1. The data in Table 4.5.1. represent the vapor generation
unit's efficiency at producing maleic anhydride vapors at
quantitative levels. Ten microliters of a 1905 µg/mL
maleic anhydride standard was injected onto the glass wool
tube and then dry air was pulled through the system.
Table 4.5.1.
Vapor Generation System Efficiency
|
|
air volume (L) |
% recovered |
|
dry air |
as derivative |
| tube no. |
at 0.2 L/min |
from treated tube |
|
| 1 |
2 |
98 |
| 2 |
3 |
100 |
| 3 |
5 |
96 |
| 4 |
4 |
100 |
| 5 |
4 |
96 |
| 6 |
4 |
100 |
|
4.5.2. The data in Table 4.5.2. represent areas obtained from "A"
and "B" sections of treated tubes using different flow
rates for the vapor generation. The percent B figure is
indicative of breakthrough being flow related.
Table 4.5.2.
Variation of Sampler Flow Rates During Vapor Generation
|
|
vapor generation |
|
|
|
3-L vol. dry air |
humid air |
% found |
| number |
flow rate (L/min) |
volume (L) |
on "B" section |
|
| 1 |
0.2 |
60 |
2.6 |
| 2 |
0.2 |
60 |
2.3 |
| 3 |
0.1 |
60 |
0.08 |
| 4 |
0.1 |
60 |
0.06 |
| 5 |
0.1 |
150 |
0.15 |
|
4.6. Desorption
Samples representing maleic anhydride concentrations of 0.49, 0.98
and 1.95 mg/m3, based on a 20-L air volume and a 1-mL desorption
volume, were prepared by injecting 4, 8, and 16 µL of a MeOH
solution of derivative, whose concentration was 5510 µg/mL, onto
p-anisidine treated tubes. The samples were stored for 24 h and
analyzed.
Table 4.6.
Desorption Efficiency Data
|
| mg/m3 |
0.49 |
0.98 |
1.95 |
|
| desorption |
89.78 |
100.00 |
99.62 |
| efficiency, |
92.63 |
100.13 |
100.10 |
| % |
94.57 |
99.46 |
99.10 |
|
92.94 |
97.83 |
97.48 |
|
87.61 |
98.02 |
92.71 |
|
|
|
|
|
92.14 |
99.09 |
97.43 |
|
|
|
|
| = 96.22 |
|
4.7. Storage
Storage samples were prepared by injecting 8 µL of a 55.10 mg/mL
standard of the derivative onto 36 treated XAD-2 tubes. This
value approximates the PEL level for maleic anhydride based on the
recommended air volume. The data in Table 4.7. represent the
recovery of derivative from treated XAD-2 tubes stored at the
ambient temperature (approximately 23°C) and at reduced
temperature (approximately 5°C). A graphical representation can be
found in Figures 4.7.1. and 4.7.2.
Table 4.7.
Storage Tests
|
| storage time |
% recovery |
| (days) |
(refrigerated) |
|
(ambient) |
|
| 0 |
94.0 |
94.0 |
98.0 |
|
99.0 |
95.0 |
96.0 |
| 3 |
94.0 |
93.0 |
96.0 |
|
95.0 |
92.0 |
86.0 |
| 7 |
78.0 |
83.0 |
95.0 |
|
100.0 |
88.0 |
94.0 |
| 10 |
99.0 |
99.0 |
99.0 |
|
99.0 |
93.0 |
91.0 |
| 14 |
92.0 |
99.0 |
93.0 |
|
98.0 |
87.0 |
94.0 |
| 15 |
92.0 |
98.0 |
94.0 |
|
101.0 |
102.0 |
89.0 |
|
4.8. The data in Table 4.8. represent the esterification of maleic acid
in isopropanol under various conditions. A 0.5-mL aliquot of a
222 ng/µL solution of maleic acid in isopropanol was added to each
of 8 vials containing 4.5 mL of isopropanol with the pH adjusted
as follows:
1) 3 vials adjusted to pH 1.8 with H2SO4
2) 3 vials left neutral
3) 2 vials adjusted to pH 13.0 with KOH
All vials were subjected to a temperature of 41°C over a 36-h
period and analyzed for the monoisopropyl ester of maleic acid by
HPLC. Results are shown in Table 4.8. Note that the ester was
previously believed to have been formed only from maleic anhydride
in isopropanol. A significant doubt could be raised as to the
validity of maleic anhydride air concentration results determined
in this manner.
Table 4.8.
Esterification of Maleic Acid in IPA Under Various Conditions
|
|
|
% maleic acid |
|
|
esterified |
| vial no. |
pH condition |
(vs. 22.2 ng/µL std) |
|
| 1 |
acid |
12.2 |
| 2 |
acid |
12.4 |
| 3 |
acid |
13.3 |
| 4 |
neutral |
2.7 |
| 5 |
neutral |
3.0 |
| 6 |
neutral |
3.3 |
| 7 |
basic |
1.6 |
| 8 |
basic |
1.6 |
|
4.9. Preparation of p-Anisidine coated XAD-2 tubes
4.9.1. Reagents
Methylene chloride, chromatographic grade.
p-Anisidine. Prepare a solution containing 2 mg/mL
p-anisidine in methylene chloride. Store in a dark bottle and
refrigerate.
XAD-2 sorbent tubes; 7-cm length, 6-mm o.d., 80-mg front,
40-mg back. SKC catalog no. 226-30.
4.9.2. Preparation
The tubes are prepared by breaking both ends of untreated
XAD-2 tubes open and adding 250 µL of the p-Anisidine/methylene chloride solution to the tube. Both sections of
the tube should be uniformly wetted by the solution. The
methylene chloride is evaporated under a reduced
atmosphere, the tubes are capped and stored in a freezer.
Figure 1.1.1. Derivatization reaction between maleic anhydride and
p-anisidine.
Figure 1.1.4. Structure of maleic anhydride and of the p-anisidine derivative of maleic anhydride.
Figure 4.1. Detection limit of the analytical procedure.
Figure 4.3. A typical chromatogram for the p-anisidine derivative of maleic anhydride.
Figure 4.4. Calibration curve.
Figure 4.5. Vapor generation and sampling system for maleic anhydride.
Figure 4.7.1 Ambient temperature storage test.
Figure 4.7.2. Refrigerated temperature storage test.
5. References
5.1. March, J.: "Advanced Organic Chemistry: Reactions, Mechanisms and
Structure", p. 336. McGraw-Hill, New York (1968).
5.2. Proctor, N., Hughes, J.: "Chemical Hazards of the Workplace", p.
318, J.B. Lippincott Company, Philadelphia (1978).
5.3. SRI International: "1980 Directory of Chemical Procedures United
States of America", pp. 680-681, SRI International, Menlo Park, CA
(1980).
5.4. U.S. Department of HEW, 1977. "NIOSH Manual of Analytical
Methods", 2nd Edition, Vol. 5 Method No. S163, Anisidine (o,p isomers).
5.5. Sax, N.I.: "Dangerous Properties of Industrial Materials", p. 883
Van Nostrand Reinhold Company, New York (1975).
5.6. "The Merck Index", Ninth Edition, p. 5540, Merck & Company, Inc.
Rahway, N.J.
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