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Related Information: Chemical Sampling - Hexylene Glycol


Method no.: PV2101
   
Control no.: T-PV2101-01-8802-CH
   
Matrix Air
   
Target concentration: 25 ppm (125 mg/m3) ACGIH Ceiling TLV
   
Procedure: Samples are collected by drawing a known volume of air through a charcoal tube. Samples are desorbed with a 95:5 solution of methylene chloride:methanol, and analyzed by gas chromatography with a flame ionization detector (GC-FID).
Air volume and sampling rate recommended: 3 liters at 0.2 L/min
   
Status of method: Stopgap method. This method has been only partially evaluated and is presented for information and trial use.
   
Date: February 1988 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 Laboratory recently received samples requesting the analysis for hexylene glycol collected on charcoal tubes. The desorption efficiency was highest using a 95:5 methylene chloride:methanol solution. The other solvents tried and their recoveries at the TLV were CS2 at 66% and 99:1 CS2:DMF at 79.2%. The retention and storage studies remained above 95%.

1.1.2  Potential workplace exposure (Ref 5.1) 

Hexylene glycol is used as a chemical intermediate, as a selective solvent in petroleum refining, as a component of hydraulic fluids, as a solvent for inks, in cosmetics, and as a cement additive. 

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)
 
Oral administration of hexylene glycol causes central nervous system depression. Skin irritation results from direct contact. In studies performed on humans, exposure to 50 ppm for 15 minutes caused slight eye irritation. At an exposure of 100 ppm for 5 minutes there was slight nasal and respiratory discomfort, along with the eye irritation. At an exposure of 1000 ppm for 5 minutes, subjects had various degrees of eye irritation, throat irritation, and respiratory discomfort. The ACGIH recommends a ceiling level of 25 ppm to prevent eye irritation.

1.1.4  Physical properties (Ref 5.2):

Synonyms: 2-methyl-2, 4-pentanediol; pinakon
Compound: compound
Molecular weight: 118.17
Density: 0.924
Boiling point: 198°C
Flash point: 93°C (200°F)
Odor: mild sweetish odor
Color: clear liquid
Molecular formula: C6H14O2
CAS: 107-41-5
IMIS: 1389
RTECS: SA0810000

1.2  Limit defining parameters 

1.2.1  The detection limit of the analytical procedure is 9.24 ng per injection. This is the smallest amount that could be detected under normal operating conditions, using a 1 μL injection volume. 

1.2.2  An overall detection limit based on a 3 L air volume (15 minutes at 0.2 Lpm) and an overall desorption efficiency of 99.9% is 0.6 ppm. All ppm concentrations listed in this procedure are based on a 3 L air volume and a 1 mL desorption 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 compounds at the same time.

1.3.5  Interferences may be avoided by proper selection of column and GC parameters.

1.4  Disadvantages

None known.

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 Charcoal tubes, coconut shell, containing a 100-mg adsorbing section with a 50-mg backup section separated by a 2 mm portion of urethane foam, with a silane-treated glass wool plug before the adsorbing section and a 3-mm 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. and 4 mm I.D., SKC tubes or equivalent. 

2.2  Sampling technique

2.2.1  The ends of the charcoal tube are opened immediately before sampling.
 
2.2.2  Connect the charcoal 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 closest to the pump.

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

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

2.2.6  With each batch of samples, submit at least one blank tube from the same lot of charcoal used for samples. This tube should be subjected 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 mailing container from the samples.

2.3 Desorption efficiency

Six tubes were liquid spiked at each loading of 0.1201 (8.283 ppm), 0.6006 (41.42 ppm), 1.201 (82.83 ppm), and 2.402 mg (165.7 ppm) hexylene glycol. They were allowed to equilibrate overnight at room temperature. They were opened, each section was placed into a separate 2 mL vial, desorbed with 1 mL of the desorbing solution, desorbed for 30 minutes with occasional shaking, and analyzed by GC-FID. The overall average was 99.9% recovered (Table 2.3). 

Table 2.3
Desorption Efficiency


% Recovered

2.402 mg

1.201 mg

0.6006 mg

0.1201 mg

165.7 ppm

82.83 ppm

41.42 ppm

8.283 ppm

Tube #

% Desorption

1
2
3
4
5
6

99.5
98.7
99.8
101
97.7
99.1

104
98.0
99.2
lost
101
101

99.7
99.2
99.8
102
100
98.9

101
99.0
98.4
98.1
99.9
99.4

average

99.3

101

99.9

99.3

overall average

99.9%

standard deviation 1.68

2.4  Retention efficiency

Six tubes were liquid spiked with 1.201 mg (24.85 ppm based on 10 liter air volume or 82.83 ppm based on a 3 liter air volume) hexylene glycol, allowed to equilibrate overnight, and had 10 liters of humid air (91% RH) pulled through them. They were opened, desorbed and analyzed by GC-FID. There was no hexylene glycol found on the backup portions of the tubes (Table 2.4). The retention efficiency averaged 98.7%.

Table 2.4
Retention Efficiency

Tube #

% Recovered
'A'

% Recovered
'B'

Total


1
2
3
4
5
6

97.3
97.3
97.1
97.8
104
98.7

0.0
0.0
0.0
0.0
0.0
0.0

97.3
97.3
97.1
97.8
104
98.7

average

98.7


2.5  Storage

Charcoal tubes were spiked with 1.201 mg (82.83 ppm) hexlene glycol and stored at room temperature until opened and analyzed. The recoveries averaged 97.8% for the 15 days stored (Table 2.5).

Table 2.5

Days Stored

% Recovered


5
5
5
12
12
12
15
15
15

99.5
100
98.8
93.5
95.4
94.2
101
100
98.2

average

97.8


2.6 Precision

Precision was determined by injecting standard solutions six times. The standard solutions used were 0.1201 mg/mL (8.283 ppm), 0.6006 mg/mL (41.42 ppm), 1.201 mg/mL (82.83 ppm), and 2.402 mg/mL (165.7 ppm) hexylene glycol in the desorbing solution, which correspond to approximately 0.3, 1.6, 3.3, and 6.6 the TLV (Table 2.6).

Table 2.6

INJECTION
NUMBER

2.402
mg/mL
165 ppm

1.201
mg/mL
82.8 ppm

0.6006
mg/mL
41.4 ppm

0.1201
mg/mL
8.28 ppm


1
2
3
4
5
6

6256149
6284925
6257428
6368661
6284569
6284803

3173206
3185187
3169345
3146888
3132323
3115201

1317202
1327468
1306625
1336024
1319897
1306397

309848
311433
303459
307956
305946
308072

Average

6289423

3153692

1318936

307786

Standard
Deviation 

41169

26841

11641

2820

CV

0.006546

0.008511

0.008826

0.009162

Pooled CV

0.007523


Pooled CV

A(l), A(2), A(3), A(4)   = # of injections at each level 
CV1, CV2, CV3, CV4 = Coefficients at each level 

2.7  Air volume and sampling rate studied

2.7.1  The air volume studied is three liters.

2.7.2  The sampling rate studied is 0.2 liters per minute

2.8  Interferences

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 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  Gas chromatograph (GC equipped with a flame 
ionization detector.
 
3.1.2  GC column capable of separating the analyte and an internal standard from any interferences. In this study, a 60-m DB-Wax capillary column was used.
 
3.1.3  An electronic integrator or some other suitable method of measuring peak areas.
 
3.1.4  Two milliliter vials with Teflon-lined caps.
 
3.1.5  A 10-μL syringe or other convenient size for sample injection.
 
3.1.6  Pipets for dispensing the desorbing solution. The Glenco 1-mL dispenser was used in this method.

3.1.7  Volumetric flasks - 5 mL and other convenient sizes for preparing standards.

3.2 Reagents

3.2.1 Purified GC grade nitrogen, hydrogen, oxygen, and air.

3.2.2 Methanol, Reagent grade.

3.2.3 Methylene chloride, Reagent grade.

3.2.4 Hexylene glycol, Reagent grade.,

3.2.5 n-Hexanol, Reagent grade (Internal Standards.

3.2.6 The desorbing solvent was a 95:5 mixture of methylene chloride:methanol with 1 μL/mL n-hexanol internal standard.

3.3 Sample preparation 

3.3.1 Sample tubes are opened and the front and back section of each tube are placed in separate 2 mL vials.

3.3.2 Each section is desorbed with 1 mL of the desorbing solvent.
 
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 Standards are prepared by diluting a known quantity of hexylene glycol with the desorbing solvent. A 1 μL/mL hexylene glycol in the desorbing solvent corresponds to 63.73 ppm based on a 3 liter air volume, 1 mL desorption volume, and the 99.9% desorption efficiency.

3.4.2 At least two separate standards should be made.

3.4.3 A third standard at a different concentration should be made to check the linearity of the detector.

3.5 Analysis

3.5.1 Gas chromatograph conditions. 

Flow rates (mL/min) Temperature (°C)
Nitrogen (makeup): 24 Injector: 200°C
Hydrogen (carrier): 2 Detector: 220°C
Air (detector): 240 Column: 120°C for 6 min 10°C/min to 150°C
Hydrogen (detector): 30
Injection size:  1 μL
Elution time:  12.41 min 
Chromatogram: 

Chromatogram

Figure 3.5.1 A standard of 1μL/mL (63.73 ppm) hexylene glycol in the desorbing solvent.

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

3.6  Interferences (analytical)

3.6.1  Possible interferences should be listed on the sample date sheet. Any compound having the general retention time of the analyte or the internal standard used is an interference. GC parameters should be adjusted if necessary so these compounds 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/mL)(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 & 760mmHg) = volume the analyte will occupy at 25°C & 760mmHg

(volume analyte occupies)(106)*
(air volume)
= ppm

*All units must cancel.

3.7.2  The above equations can be consolidated to form the following formula. To calculate the ppm of analyte in the sample based on a 3 liter air sample:

ppm = (g/mL)(DV)(24.46)(106)(g)(mg)
(3 L)(DE)(MW)(1000 mg)(1000 m)

μg/mL = concentration of analyte in sample or standard
24.46 = Molar volume (liters/mole) at 25°C and 760 mmHg
MW = Molecular weight (g/mole)
DV = Desorption volume
3 L = 3 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
 
Vapor generated samples should be prepared to evaluate the collection efficiencies from an atmosphere. 

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. 309.

5.2  Windholz, M., "The Merck Index", Tenth Edition, Merck & Co., Rahway, N.J., 1983, p. 681.