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Diethanolamine

Related Information: Chemical Sampling - Diethanolamine
Method number: PV2018
 
Matrix: Air
 
Target concentration: 3 ppm (15 mg/cu m) ACGIH TWA TLV
 
Procedure: Samples are collected by drawing a known volume of air through sampling tubes containing XAD-2 resin coated with 10% 1-naphthylisothiocyanate (NITC) by weight. Samples are analyzed by desorbing the adsorbent with dimethylformamide and quantitating the amine derivative by high performance liquid chromatography (HPLC) using ultraviolet detection.
 
Air volume and
sampling rate studied:

10 L at 0.1 L/min
 
Status of method: Stopgap method. This method has been only partially evaluated and is presented for information and trial use.
 
Date: November, 1987 Chemist: Mary E. Eide



Solvents Branch
OSHA Analytical Laboratory
Salt Lake City, Utah



1. General Discussion
1.1. Background
1.1.1. History of procedure

The OSHA lab has been recommending the collection of diethanolamine with 0.1 N sulfuric acid bubblers. Direct analysis of the diethanolamine is difficult due to the peak shape and carryover problems. An adsorbent tube makes the collection easier for the industrial hygienist, and derivatization of the diethanolamine would improve the chromatography. Sampling tubes containing XAD-2 resin coated with 10% NITC by weight provided derivatization. The derivative desorbed well, was retained and showed no effects upon storage.

1.1.2. Potential workplace exposure (Ref 5.1)

Diethanolamine is an adsorbent for acidic gases. It is used as an intermediate in the manufacture of resins and plasticizers. Diethanolamine acts as a detergent in paints, cutting oils, shampoos, and other cleaners.

1.1.3. Toxic Effects (This section is for information purposes and should not be taken as the basis for OSHA policy.)(Ref. 5.1)

The recommended TLV for diethanolamine is the same as for ethanolamine due to similar skin effects, though diethanolamine has been shown to be less toxic in oral exposures. The LD50 in rats and guinea pigs for oral exposure is 2 g/kg. The skin exposure at 500 mg in a 24 hour period to the skin of rabbits resulted in mild damage. Exposure to the eye of rabbits at a level of 750 ug in a 24 hour caused severe damage.

1.1.4. Physical properties (Ref 5.2):

Compound: Structural Formula

Synonyms: bis(2-hydroxyethyl)amine;
diolamine;
2,2'-iminodiethanol;
2,2'-dihydroxydiethylamine

Molecular weight: 105.4

Density: 1.0966

Freezing point: 28°C

Odor: ammoniacal

Color: clear liquid

Molecular formula: C4H11NO2

CAS: 111-42-2

IMIS: D129

RTECS: KL2975000
1.2. Limit defining parameters
1.2.1. The detection limit of the analytical procedure is 1 ng, with a 15 uL injection volume. This is the smallest amount which could be detected under normal operating conditions.

1.2.2. The overall detection limit is 0.04 ppm based on a 10 liter air volume.
1.3. Advantages
1.3.1. The sampling procedure is convenient.

1.3.2. The analytical method is reproducible and sensitive.

1.3.3. Reanalysis of samples is possible.

1.3.4. It may be possible to analyze other amines at the same time.

1.3.5. Interferences may be avoided by proper selection of column and LC parameters.
1.4. Disadvantages

Sampling tubes are not commercially available, and must be obtained from the laboratory.
2. Sampling procedure
2.1. Apparatus
2.1.1. A calibrated personal sampling pump, the flow of which can be determined within ± 5% at the recommended flow.

2.1.2. Sampling tubes containing XAD-2 resin coated with 10% NITC by weight. A sampling tube consists of two sections of coated XAD-2 resin separated by a glass wool plug. The front section contains 80 mg coated sorbent and the backup section 40 mg. The sections are held in place with Teflon wool plugs in a glass tube 4 mm ID × 70 mm length.

The adsorbent is prepared by coating commercially purified 16/50 mesh XAD-2 (Supelco) with 10% NITC by weight using methylene chloride as a solvent. The solvent is removed by rotary evaporation (Ref 5.3)

2.1.3. Lengths of flexible tubing are needed to connect the sampling tubes to the sampling pumps.
2.2. Sampling technique
2.2.1. The ends of the sample tube are opened immediately before sampling.

2.2.2. Connect the sample tube to the sampling pump with flexible tubing.

2.2.3. Tubes should be placed in a vertical position to minimize channeling, with the smaller section towards the pump.

2.2.4. Air being sampled should not pass through any hose or tubing before entering the sampling tube.

2.2.5. Seal the sampling tube with plastic caps immediately after sampling. Seal each sample lengthwise with OSHA Form-21.

2.2.6. With each batch of samples, submit at least one blank tube from the same lot used for air samples. This tube should be subjected to exactly the same handling as the samples (break ends, seal, & transport) except that no air is drawn through it.

2.2.7. Transport the samples (and corresponding paperwork) to the lab for analysis.

2.2.8. Bulks submitted for analysis must be shipped in a separate container from the samples.
2.3. Desorption efficiency
2.3.1. A loading of 134.7 ug corresponds to 6.26 ppm based on a 10 liter air volume and a 2 mL desorption volume.

2.3.2. Sampling tubes were spiked with 269.4, 134.7, 67.35, and 13.47 ug diethanolamine. They were allowed to equilibrate at room temperature overnight. They were opened, each section placed in a 4 mL vial, and 2 mL of dimethylformamide was added. They were allowed to desorb for 30 minutes with occasional shaking, then analyzed by HPLC. The desorption efficiency averaged 100% (Table 1).

Table 1
Desorption efficiency
Tube# % Recovered
269.4 ug
% Recovered
134.7 ug
% Recovered
67.35 ug
% Recovered
13.47 ug

1
2
3
4
5
6

average
103
101
103
104
101
100

102
104
104
104
104
104
105

104
102
     96.3
     94.3
     95.9
     95.2
     98.9

     97.1
99.8
99.8
97.5
98.9
97.6
97.0

98.4

overall average 100
standard deviation ± 3.33

2.4. Retention efficiency
2.4.1. Sampling tubes were spiked with 269.4 ug diethanolamine, and 10 liters of humid air (93% RH) were drawn through them. They were desorbed and analyzed by HPLC. There was little or no diethanolamine found on the backup portions of the sampling tubes (Table 2).

Table 2
Retention Efficiency
Tube # % Recovered 'A' % Recovered 'B' % Total

1
2
3
4
5
6

average
     99.9
101
     92.6
101
     97.7
     99.4

     98.8
0   
0   
0.4
0.4
0.3
0.6
     99.9
101
     92.6
101
     98.0
100

2.5. Storage
2.5.1. Sampling tubes were spiked with 134.7 ug diethanolamine and stored at room temperature until they were desorbed and analyzed. The recoveries remained above 92.5% for the 16 day storage period (Table 3).

Table 3
Storage Study
Day % Recovered

  4
  4
  4
  8
  8
  8
16
16
16
     99.6
105
104
     99.6
101
     98.0
101
     97.3
     92.5

2.6. Precision
2.6.1. Precision was calculated using the area counts from six injections of each standard at concentrations of 7.0, 70, and 140 ug/ml ethanolamine (based on a 10 liter air volume these concentrations correspond to 0.325, 3.25, and 6.5 ppm)(Table 4).

Table 4
Precision
Injection
number
7.0 ug/mL
0.325 ppm
70.47 ug/mL
3.25 ppm
140 ug/mL
6.5 ppm

1
2
3
4
5
6
546480
528418
518930
510596
511803
517226
5401085
5650258
5553324
5251672
5440720
5233302
12541460
11950484
11966070
12048538
11971644
12164448

average 522242 5421727 12107107

standard
deviation
± 13464 ± 164167 ± 227224

CV 0.02578 0.03028 0.01877

Pooled CV 0.1077



CV (Coefficient of Variable) =  standard devation

average
Pooled CV =


A1(CV1)2 + A2(CV2)2 + A3(CV3)2 + A4(CV4)2

A1 + A2 + A3 + A4


A(1), A(2),A(3),A(4) = # of injections at each level
CVl, CV2, CV3, CV4 = Coefficients at each level
2.7. Air volume and sampling rate studied
2.7.1. The air volume studied was 10 liters.

2.7.2. The sampling rate studied was 0.1 liters per minute.
2.8. Interferences (sampling)
2.8.1. Compounds which can react with the derivatizing reagent may decrease the capacity for the analyte.

2.8.2. Suspected interferences should be listed on sample data sheets.
2.9. Safety precautions
2.9.1. Sampling equipment should be placed on an employee in a manner that does not interfere with work performance or safety.

2.9.2. Safety glasses should be worn at all times.

2.9.3. Follow all safety practices that apply to the workplace being sampled.
3. Analytical method
3.1. Apparatus
3.1.1. Liquid chromatograph equipped with an ultraviolet detector capable of detecting 254 and 280 nm. The response is most sensitive at 254 nm. For this study a Waters M-6000A pump was used with a Waters 440 Absorbance Detector.

3.1.2. LC column capable of separating the analyte from any interferences. A 10u Radial CN, 10 cm × 8 mm ID, was used for this study.

3.1.3. An electronic integrator or some other suitable method of measuring peak areas.

3.1.4. Four milliliter vials with Teflon-lined caps for sample desorption.

3.1.5. A 20 uL syringe or other convenient size for sample injection, or an autosampler that can inject 15 uL. Injections were made with a Waters WISP 710 automatic sample injection module in this study.

3.1.6. A dispenser or pipet capable of delivering 2.0 mL dimethylformamide.

3.1.7. Volumetric flasks and pipets for preparing standards.

3.1.8. An analytical balance capable of weighing to the nearest 0.01 mg.
3.2 Reagents
3.2.1. Diethanolamine, reagent grade

3.2.2. Dimethylformamide (DMF), HPLC grade

3.2.3. 1-Naphthylisothiocyanate (NITC), reagent grade

3.2.4. Isooctane, HPLC grade

3.2.5. Isopropanol, HPLC grade
3.3. Sample preparation
3.3.1. Sample tubes are opened and the front and back section of each tube are placed in separate 4 mL vials.

3.3.2. Each section is desorbed with 2 mL DMF.

3.3.3. The vials are sealed immediately and allowed to desorb for 30 minutes with occasional shaking.
3.4. Standard preparation
3.4.1. Stock standards are prepared by diluting a known quantity of diethanolamine with a solution of NITC in DMF. The molecular weight of NITC is 185.25, and the molecular weight of diethanolamine is 105.14. One molecule of the derivative is formed from one molecule of diethanolamine and one molecule of NITC. Excess NITC is added to insure that all of the diethanolamine is reacted. For example, a stock standard containing 2.694 mg/10 mL diethanolamine in DMF should contain at least 4.747 mg NITC, so 5 mg NITC was added to ensure that all the diethanolamine reacted.

3.4.2. At least two seperate stock standards should be made.

3.4.3. Dilutions of these stock standards are made over the range of the samples, down to the level of the detection limit. At least four working standards should be prepared, so that a curve of concentration versus response can be plotted. Samples should be bracketed with working standards.

3.4.4. Standards and/or samples should not be placed in an ultrasonic, as it will decompose the derivative.
3.5. Analysis
3.5.1. Liquid chromatograph conditions.

Column: 10u Radial CN, 10 cm × 8 mm ID

Mobile Phase: Isooctane/isopropanol 80/20 at 1mL/min

Injection size: 15 uL

Detector: UV at 254 nm

Chromatogram: (See Figure 1)

Retention time: 15.7 min


3.5.2. Peak areas are measured by an integrator or other suitable means.

3.5.3. A calibration curve is constructed by plotting detector response of standard injections versus ug of diethanolamine.
3.6. Interferences (analytical)
3.6.1. Any compound having the general retention time of the analyte is an interference. Possible interferences should be listed on the sample data sheet. LC parameters should be adjusted if necessary so these interferences will pose no problems.

3.6.2. Retention time data on a single column is not considered proof of chemical identity. Samples over the target concentration should be confirmed by GC/Mass Spec or other suitable means.
3.7. Calculations
3.7.1. 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.

3.7.2. The above formulas can be consolidated to make the following formula. To calculate the ppm of analyte in the sample based on a 10 liter air sample, and a 1 mL desorbing solution:

(µg/mL)(DV)(24.45)(106)
(10 L)(DE)(MW)
× (g)
(1000 mg)
× (mg)
(1000 µg)
= ppm


ug/mL = concentration of analyte in sample or standard
24.45 = Molar volume (liters/mole) at 25 °C and 760 mm Hg.
MW = Molecular weight (g/mole)
2 mL = Desorption volume
10 L = 10 liter air sample
DE = Desorption efficiency


3.7.3. This calculation is done for each section of the sampling tube and the results added together.
3.8. Safety precautions
3.8.1. All handling of solvents should be done in a hood.

3.8.2. Avoid skin contact with all solvents.

3.8.3. Wear safety glasses at all times.
4. Recommendations for further study

Collection efficiencies need to be studied.

For problems with accessibility in using figures please contact the SLTC at (801) 233-4900.
Figure 1. Standard of 134.7 ug/mL diethanolamine with NITC in DMF.


5. References
5.1. "Documentation of the Threshold Limit Values and Biological Exposure Indices", Fifth Edition, American Conference of Governmental Industrial Hygienists Inc., Cincinnati, OH, 1986, p.197.

5.2. Weast, R.C., "Handbook of Chemistry and Physics", 67th Edition, CRC Press Inc., Boca Raton FL, 1986, p. C244.

5.3. Elskamp, C., Method 60, "Ethylenediamine, diethylenetriamine, and triethylenetetramine", Organic Methods Evaluation Branch, OSHA Analytical Laboratory, 1986.