CYCLOHEXYLAMINE
Method number: |
PV2016 |
|
Matrix: |
Air |
|
Target concentration: |
10 ppm (41 mg/m3) (ACGIH TWA PEL) |
|
Procedure: |
Samples are collected by drawing a known volume of air
through a 10% phosphoric acid coated XAD-7 tube. Samples are desorbed
with 1 mL of 1:1 solution of methanol:deionized water for ½ hour with
shaking, then 0.5 mL of the sample is removed and added to 0.5 mL of
1:4 solution of 1.0 N NaOH:methanol and analyzed by gas chromatography
using a flame ionization detector (GC-FID). An alternate desorbing
solvent is 1 mL of 0.888 N NH4OH in methanol on a shaker for
30 minutes then analysis by GC-FID. |
|
Recommended air volume and sampling rate: |
10 L at 0.1 L/min (maximum 20 liters at a flow rate of 0.2 L/min) |
|
Reliable quantitation limit: |
0.04 ppm (0.16 mg/m3) |
|
Status of method: |
Partially Evaluated Method. This method has been subjected to established
evaluation procedures, and is presented for information and trial use. |
|
Date: November, 1993 Revised: February, 1994 |
Chemist: Mary E. Eide |
Organic Service Branch I
OSHA Salt Lake Technical Center
Salt Lake City, UT 84165-0200
1. General Discussion
1.1 Background
1.1.1 History
The partially validated NIOSH method 221 for aliphatic amines suggests
cyclohexylamine can be collected on silica gel tubes, but no validation
studies have been performed. (Ref. 5.1) Silica gel tubes adsorb water
readily, and there was some dilution of the sample when humid air was
drawn through the tubes due to the adsorbed water, making recoveries
appear lower. A media which was not affected by the humidity was
desired. XAD-7 tubes were explored initially, but there was 6.7%
breakthrough when 20 liters of humid air (87% RH) was drawn through
them. The 10% phosphoric acid coated XAD-7 tubes were then tried and
found to have desorption, retention, and storage recoveries above 95%.
Desorption with a 1:4 solution of 1.0 N NaOH:water was initially tried
and found to give 96% recovery, but something on the XAD-7 resin, or
the resin itself, appeared to react with the NaOH causing a sticky
residue to build up in the syringe on the autosampler, despite using a
solvent wash. To avoid this problem, desorption with 1:1 water:methanol
was used (30 minutes of shaking was necessary), then 0.5 mL was removed
from the resin and neutralized with 0.5 mL of 1:4 solution of 1.0 N
NaOH:methanol before analysis. After this study was completed, a new
desorbing solvent was found. Samples desorbed with 0.888 N
NH4OH in methanol gave an overall desorption of 97.0% without
the stickiness in the autosampler syringe. This generates ammonia,
which may become an interference on some columns.
1.1.2 Toxic effects (This section is for information only and should
not be taken as the basis of OSHA policy.) (Ref. 5.2 and 5.3)
Cyclohexylamine is moderately toxic and intensely irritating to the
skin, and may cause sensitization. Human subjects exposed to 125 mg
using skin patch tests over 48 hours showed a severe reaction. Workers,
wearing personal protective equipment, exposed to 4-10 ppm cyclohexylamine
showed no ill effects. Cyclohexylamine has been reported to cause human
mutation in sperm. Symptoms of exposure are lightheadedness, drowsiness,
anxiety and apprehension, nausea, slurred speech, vomiting, and pupillary
dilation.
1.1.3 Workplace exposure (Ref. 5.2 and 5.4)
Cyclohexylamine is used in synthesis, manufacture of insecticides,
plasticizers, rubber chemicals, dyestuffs, emulsifying agents, and
dry cleaning soaps, in acid gas adsorbents, and as a corrosion inhibitor
in boiler feed water.
1.1.4 Physical properties and other descriptive information (Ref. 5.3 and 5.4)
Synonyms: |
Aminocyclohexane; Aminohexahydrobenzene; Cyclohexanamine; Hexahydroaniline |
CAS number: |
108-91-8 |
IMIS: |
0842 |
RTECS: |
GX0700000; 28789 |
DOT: |
UN 2357 (flammable liquid and corrosive) |
Molecular weight: |
99.20 |
Flash point: |
31°C (88°F)(cc) |
Boiling point: |
134.5°C |
Melting point: |
-17.7°C |
Odor: |
strong fishy or amine odor |
Color: |
clear to light yellow |
Autoignition temperature: |
293°C (560°F) |
Density: |
0.8647 |
Molecular formula: |
C6H13N |
Structural formula: |
|
The analyte air concentrations throughout this method are based on the
recommended sampling and analytical parameters of 10 liters and a
desorption volume of 1 mL. Air concentrations listed in ppm are
referenced to 25°C and 101.3 kPa (760 mmHg).
1.2 Limit defining parameters
1.2.1 Detection limit of the overall procedure (DLOP)
The detection limit of the overall procedure is 0.5 µg per sample (0.01
ppm or 0.05 mg/m3). This is the amount of analyte spiked on
the sampler that will give a response that is significantly different
from the background response of a sampler blank.
The DLOP is defined as the concentration of analyte that gives a
response (YDLOP) that is significantly different (three
standard deviations (SDBR)) from the background response
(YBR).
YDLOP - YBR = 3(SDBR)
The direct measurement of YBR and SDBR in
chromatographic methods is typically inconvenient, and difficult
because YBR is usually extremely low. Estimates of these
parameters can be made with data obtained from the analysis
of a series of samples whose responses are in the vicinity of the
background response. The regression curve obtained for a plot of
instrument response versus concentration of analyte will usually be
linear. Assuming SDBR and the precision of data
about the curve are similar, the standard error of estimate (SEE) for
the regression curve can be substituted for SDBR in the above
equation. The following calculations derive a formula for the DLOP:
Yobs |
= |
observed response |
Yest |
= |
estimated response from regression curve |
n |
= |
total no. of data points |
k |
= |
2 for a linear regression curve |
At point YDLOP on the regression curve
YDLOP = A(DLOP) +YBR
A = analytical sensitivity (slope)
therefore
Substituting 3(SEE) + YBR for YDLOP gives
Table 1.2.1 Detection Limit of the Overall Procedure
|
mass per sample |
area counts |
(µg) |
(µV-s) |
|
0 |
0 |
1.038 |
634 |
2.076 |
1094 |
3.114 |
1514 |
4.152 |
2207 |
5.19 |
2761 |
6.228 |
3313 |
7.266 |
3894 |
8.304 |
4595 |
9.342 |
5000 |
10.38 |
5549 |
|
Figure 1.2.1. Plot of data to determine the DLOP/RQL.
1.2.2 The reliable quantitation limit is 1.5 µg per sample (0.04 ppm).
This is the amount of analyte spiked on a sampler that will give a
signal that is considered the lower limit for precise quantitative measurements.
The RQL is considered the lower limit for precise quantitative
measurements. It is determined from the regression line data obtained
for the calculation of the DLOP (Section 1.2.1), providing at least 75%
of the analyte is recovered. The RQL is defined as the concentration
of analyte that gives a response (YRQL) such that
YRQL - YBR = 10(SDBR)
therefore
Figure 1.2.3. Chromatogram of the RQL.
2. Sampling Procedure
2.1 Apparatus
2.1.1 Samples are collected using a personal sampling pump calibrated, with the sampling device attached, to within ±5% of the recommended flow rate.
2.1.2 Samples are collected on 10% phosphoric acid coated XAD-7 tubes,
lot 540, containing 80 mg adsorbing section with a 40 mg backup section
separated by a 2 mm portion of urethane foam, with a silanized glass
wool plug before the adsorbing section and a 3mm plug of urethane foam
at the back of the backup section. The ends are flame sealed and the
glass tube containing the adsorbent is 7 cm long, with a 6 mm O.D., SKC tubes or equivalent.
2.2 Technique
2.2.1 Immediately before sampling, break off the ends of the sampling tube. All tubes should be from the same lot.
2.2.2 Attach the sampling tube to the pump with flexible tubing. It is desirable to utilize sampling
tube holders which have a protective cover to shield the employee from the sharp, jagged end of
the sampling tube. Position the tube so that sampled air passes through the reference, larger, section of the tube first.
2.2.3 Air being sampled should not pass through any hose or tubing before entering the sampling tube.
2.2.4 Attach the sampler vertically with the reference, larger, section
pointing downward, in the worker's breathing zone, and positioned so it does not impede work performance or safety.
2.2.5 After sampling for the appropriate time, remove the sample and seal the tube with plastic
end caps. Wrap each sample end-to-end with a Form OSHA-21 seal.
2.2.6 Submit at least one blank sample with each set of samples. Handle
the blank sampler in the same manner as the other samples except draw no air through it.
2.2.7 Record sample volumes (in liters of air) for each sample, along with any potential interferences.
2.2.8 Ship any bulk samples separate from the air samples.
2.2.9 Submit the samples to the laboratory for analysis as soon as possible after sampling. If
delay is unavoidable, store the samples in a refrigerator.
2.3 Desorption efficiency
2.3.1 The desorption efficiencies (DE) of cyclohexylamine were
determined by liquid-spiking the sampling tubes with 43.2 (1.07), 216
(5.33), 432 (10.7), and 865 µg (21.3 ppm) cyclohexylamine. These
samples were stored overnight at ambient temperature and then desorbed
with 1 mL of 1:1 solution of deionized water:methanol for
30 minutes on the shaker. An aliquot of 0.5 mL of each sample was
removed and added to 0.5 mL of 1:4 solution of 1.0 N NaOH:methanol and
analyzed by GC-FID. The average desorption efficiency over the studied range was 95.9%.
Table 2.3.1 Desorption Efficiency of Cyclohexylamine
|
|
43.2 µg |
216 |
432 |
865 |
|
µg |
µg |
µg |
|
DE(%) |
97.2 |
95.6 |
96.7 |
94.0 |
|
lost |
96.6 |
97.7 |
95.2 |
|
96.7 |
95.5 |
94.5 |
93.4 |
|
94.9 |
94.1 |
96.1 |
95.6 |
|
97.5 |
93.6 |
96.4 |
98.0 |
|
94.7 |
96.7 |
96.2 |
98.4 |
mean |
96.2 |
95.4 |
96.3 |
95.8 |
overall average |
95.9 |
|
standard deviation |
±1.42 |
|
|
2.3.2 The desorption efficiencies (DE) of cyclohexylamine were
determined by liquid-spiking the sampling tubes with 43.2 (1.07), 216
(5.33), 432 (10.7), and 865 µg (21.3 ppm) cyclohexylamine. These samples
were stored overnight at ambient temperature and then desorbed with 1
mL of 0.888 N NH4OH in methanol for 30 minutes on the shaker,
and analyzed by GC-FID. The average desorption efficiency over the
studied range was 97.0%.
Table 2.3.2 Desorption Efficiency using 0.888 N NH4OH in Methanol
|
|
43.2 µg |
216 |
432 |
865 |
|
µg |
µg |
µg |
|
DE(%) |
97.4 |
98.3 |
97.7 |
95.7 |
|
98.1 |
95.4 |
98.7 |
97.1 |
|
94.0 |
99.0 |
97.0 |
96.6 |
|
96.6 |
97.7 |
96.3 |
96.9 |
|
95.8 |
98.8 |
97.4 |
96.8 |
|
96.9 |
97.6 |
95.8 |
96.0 |
mean |
96.5 |
97.8 |
97.2 |
96.5 |
overall average |
97.0 |
|
standard deviation |
±1.19 |
|
|
2.4 Retention efficiency
The sampling tubes were spiked with 865 µg (21.3 ppm) cyclohexylamine,
allowed to equilibrate overnight at room temperature, and then had 20
L humid air (87% RH at 23°C) pulled through them at 0.2 Lpm. They were
opened, desorbed, and analyzed by GC-FID. The results were desorption
corrected. The retention efficiency averaged 99.1%. There was no
cyclohexylamine found on the backup portions of the tubes.
Table 2.4 Retention Efficiency of Cyclohexylamine
|
Tube # |
A section |
B section |
total |
|
recovery (%) |
recovery (%) |
recovery (%) |
|
1 |
97.9 |
0.0 |
97.9 |
2 |
96.9 |
0.0 |
96.9 |
3 |
99.2 |
0.0 |
99.2 |
4 |
102 |
0.0 |
102 |
5 |
98.9 |
0.0 |
98.9 |
6 |
99.4 |
0.0 |
99.4 |
mean |
|
99.1 |
|
2.5 Sample storage
The front sections of six sampling tubes were each spiked with 432 µg
(10.7 ppm) of cyclohexylamine. Six more tubes had 10 liters of humid
air (83% RH at 23°C) drawn through them before they were spiked with
432 µg (10.7 ppm) of cyclohexylamine. They were sealed and stored at
room temperature. Three dry samples and three humid air samples were
analyzed after 7 days and the remaining three samples of each after
14 days. The amounts recovered, corrected for desorption efficiency,
indicate good storage stability for the time period studied.
Table 2.5 Storage Test for Cyclohexylamine
|
Dry Samples |
| |
Humid Air Samples |
|
time |
recovery |
| |
time |
recovery |
(days) |
(%) |
| |
(days) |
(%) |
|
7 |
101 |
| |
7 |
100 |
7 |
99.6 |
| |
7 |
100 |
7 |
98.5 |
| |
7 |
101 |
14 |
100 |
| |
14 |
98.1 |
14 |
99.3 |
| |
14 |
100 |
14 |
101 |
| |
14 |
100 |
mean |
98.8 |
| |
mean |
99.8 |
|
2.6 Precision
The precision was calculated using the area counts from six injections
of each standard at concentrations of 21.6, 108, 216, and 432 µg/mL
cyclohexylamine in the desorbing solution.
Table 2.6 Cyclohexylamine Precision Study
|
injection # |
21.6 |
108 |
216 |
432 |
|
µg/mL |
µg/mL |
µg/mL |
µg/mL |
|
1 |
10986 |
44698 |
84534 |
182682 |
2 |
11166 |
45444 |
82640 |
184770 |
3 |
10954 |
44654 |
81126 |
182416 |
4 |
10866 |
45826 |
78582 |
183678 |
5 |
10760 |
47110 |
78290 |
182946 |
6 |
10754 |
46176 |
77620 |
181338 |
mean |
10914 |
45651 |
80465 |
182972 |
standard deviation |
± 156 |
936 |
2760 |
1166 |
|
2.7 Recommended air volume and sampling rate.
Based on the data collected in this evaluation, 10 L air samples should
be collected at a sampling rate of 0.1 L/min.
2.8 Interferences
2.8.1 It is not known if any compounds will severely interfere with the
collection of cyclohexylamine on the sampling tubes. In general, the
presence of other contaminant vapors in the air will reduce the
capacity of 10% phosphoric acid coated XAD-7 tubes to collect
cyclohexylamine.
2.8.2 Suspected interferences should be reported to the laboratory
with submitted samples.
2.9 Safety precautions (sampling)
2.9.1 The sampling equipment should be attached to the worker in such a manner that it will not interfere with work performance or safety.
2.9.2 All safety practices that apply to the work area being sampled should be followed.
2.9.3 Protective eye wear should be worn when breaking the ends of the glass sampling tubes.
3. Analytical Procedure
3.1 Apparatus
3.1.1 The instrument used in this study was a gas chromatograph equipped with a flame ionization detector, specifically a Hewlett Packard model 5890.
3.1.2 A GC column capable of separating the analyte from any interferences. The column used in this study was a 60 meter Stabilwax
DB, 1.0 µ film thickness, 0.32 mm i.d.
3.1.3 An electronic integrator or some suitable method of measuring peak areas.
3.1.4 Two milliliter vials with TeflonTM-lined caps.
3.1.5 A 10µL syringe or other convenient size for sample injection.
3.1.6 Pipets for dispensing the desorbing solution.
3.1.7 Volumetric flasks - 10 mL and other convenient sizes for preparing standards.
3.2 Reagents
3.2.1 GC grade nitrogen, hydrogen, and air.
3.2.2 Cyclohexylamine, Reagent grade
3.2.3 Deionized water
3.2.4 Methanol, HPLC grade
3.2.5 Sodium hydroxide, Reagent grade
3.2.6 Ammonium hydroxide, concentrated, Reagent grade
3.2.7 Desorbing solution of 1:1 methanol:deionized water is neutralized with a solution of 1:4 of 1.0 N NaOH:methanol.
3.2.8 An alternate desorbing solution, which requires no further neutralization is a solution of 0.888 N ammonium hydroxide in methanol,
is prepared by placing 3 mL of the concentrated ammonium hydroxide in 50 mL methanol.
3.3 Standard preparation
3.3.1 At least two separate stock standards are prepared by diluting a known quantity of cyclohexylamine with 1:4 solution of water:methanol pH adjusted to 7.
3.3.2 Dilutions of the stock standards should be prepared to bracket the
range of the samples. The standards used in this study ranged from 1 to 864 µg/mL.
3.4 Sample preparation
3.4.1 Sample tubes are opened and the front and back section of each tube are placed in separate 2 mL vials.
3.4.2 Each section is desorbed with 1 mL of 1:1 solution of water:methanol.
3.4.3 The vials are sealed immediately and allowed to desorb for 30 minutes with constant shaking.
3.4.4 A 0.5 mL aliquot of each sample is removed, being careful to leave the media behind, placed into a 2 mL vial, and 0.5 mL of 1:4 solution of
1.0 N NaOH:methanol is added to neutralize the sample. The vial is sealed and shaken briefly to mix well, and then analyzed.
3.4.5 An alternate desorbing solution, which requires no further
neutralization, is a solution of 0.888 N ammonium hydroxide in methanol.
After the contents of the tubes are placed in separate 2 mL vials, they
are desorbed with 1 mL of this solution and placed on a shaker for 30 minutes.
3.5 Analysis
3.5.1 Gas chromatograph conditions.
Injection size: |
1 µL |
|
Flow rates (mL/min) |
|
Nitrogen (make-up): |
30 |
|
Hydrogen(carrier): |
2 |
|
Hydrogen(detector): |
60 |
|
Air: |
450 |
|
Temperatures (°C) |
|
Injector: |
180 |
|
Detector: |
220 |
|
Column: |
70° for 2 min then 10°/min to 150° for 3 min |
|
Figure 3.5.1 Chromatogram of the target concentration.
Figure 3.5.2 Calibration curve for cyclohexylamine based on standards presented in 2.6.
3.5.2 Peak area are measured by an integrator or other suitable means.
3.6 Interferences (analytical)
3.6.1 Any compound that produces a response and has a similar retention
time as the analyte is a potential interference. If any potential
interferences were reported, they should be considered before samples
are desorbed. Generally, chromatographic conditions can be altered to
separate an interference from the analyte.
3.6.2 When necessary, the identity or purity of an analyte peak may be
confirmed by GC-Mass spec or by another analytical procedure.
3.7 Calculations
3.7.1 The instrument was calibrated with a standard of 216 µg/mL
cyclohexylamine in the desorbing solution. The linearity of the
calibration was checked with a standards over the range of 1 to 864 µg/mL.
3.7.2 If the calibration is non-linear, two or more standard at different
concentrations must be analyzed, bracketing the samples, so a calibration
curve can be plotted and sample values obtained.
3.7.3 To calculate the concentration of analyte in the air sample the
following formulas are used:
(µg/m) (desorption volume) (desorption efficiency) |
= mass of analyte in sample |
(mass of analyte in sample) molecular weight |
= number of moles of analyte |
(number of moles of analyte) |
(molar volume at 25°C & 760mm) |
= |
volume the analyte will occupy at 25°C & 760mm |
(volume analyte occupies) (106)* (air volume) |
= ppm |
* All units must cancel.
3.7.4 The above equations can be consolidated to the following formula.
(µg/mL)(DV)(24.45)(106) (10 L)(DE)(MW) |
× |
(g) (1000 mg) |
× |
(mg) (1000 µg) |
= ppm |
µg/mL | = | concentration of analyte in sample or standard |
24.45 | = | Molar volume (liters/mole) at 25 ° and 760 mm Hg. |
Mw | = | Molecular weight (g/mole) |
DV | = | Desorption volume |
10 L | = | 10 liter air sample |
DE | = | Desorption efficiency |
3.7.5 This calculation is done for each section of the sampling tube and
the results added together.
3.8 Safety precautions
3.8.1 Avoid skin contact and inhalation of all chemicals.
3.8.2 Wear safety glasses, gloves and a lab coat at all times while in
the laboratory areas.
4. Recommendations for Further Study
Collection studies need to be performed.
5. References
5.1 "NIOSH Manual of Analytical Methods", U.S. Department of Health,
Education, and Welfare, Public Health Service, Center for Disease
Control, National Institute for Occupational Safety and Health, Second
Edition, Vol. 1, Method 221.
5.2 Lewis, R., "Hawley's Condensed Chemical Dictionary", Twelfth Edition, Van Nostrand Reinhold Co., New York, 1993, p. 338.
5.3 Windholz, M., "The Merck Index", Eleventh Edition, Merck & Co., Rahway N.J., 1989, p. 427.
5.4 "Documentation of the Threshold Limit Values and Biological Exposure Indices",
Fifth Edition, American Conference of Governmental Industrial Hygienists Inc., Cincinnati, OH, 1986, p.161.
|