r-TERT-BUTYLPHENOL

Organic Service Branch I 
OSHA Salt Lake Technical Center
Salt Lake City, UT 84115-1802

1. General Discussion

   1.1 Background

   1.1.1 History of procedure 

   The OSHA Technical Center has received many  requests for a sampling and analytical procedure for r-tert-butylphenol (PTBP). OSHA method 32 recommends collection of phenol and cresol on XAD-7 tubes and desorption with methanol (Ref. 5.1). PTBP is related to these compounds, so this means of collection and analysis was tried and found to be successful. The desorption, retention and storage studies all had good recoveries. 

   1.1.2 Potential workplace exposure (Ref. 5.2) 

   PTBP is used as a plasticizer for cellulose acetate, intermediate for antioxidants, in oil soluble phenolic resins, as pour-point  depressors, as emulsion breakers for petroleum oils and some plastics, as an intermediate in the manufacture of varnish and lacquer resins, and as a soap antioxidant.

   1.1.3 Toxic Effects (This section is for information purposes and should not be taken as the basis for OSHA policy.)(Ref. 5.3) 

   PTBP is a skin, eye, and mucous membrane  irritant. It can cause skin burns, eye damage, and pulmonary edema. 

   1.1.4 Physical properties (Ref. 5.3):

   Compound:

   

    

   Physical properties

   Synonyms:	4-tert-Butylphenol; Butylphen;
   	4-(1,1-Dimethylethyl)phenol;
   	UCAR butylphenol 4-T
   Molecular weight:	150.21
   Melting point:	98° C
   Boiling point:	237° C
   Flash point:	107 ° C (225 ° F) (closed cup)
   Odor:	phenolic
   Color:	white crystals
   Molecular formula:	C10H140
   CAS:	98-54-4
   IMIS:	B109
   RTECS:	SJ8925000; 56585
   DOT:	UN2229

   1.2 Limit defining parameters 

   1.2.1 The detection limit of the analytical procedure is 1 µg PTBP. This is the smallest amount that could be detected under normal operating conditions. 

   1.2.2 The overall detection limit is 0.008 ppm. (All ppm amounts in this study are based on a 20 liter air volume.) 

   1.3 Advantages 

   1.3.1The 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 XAD-7 tubes containing 15/50 mesh XAD-7 with a 100 mg adsorbing section with a 50 mg backup section separated by a silanized glass wool plug, with a silanized glass wool plug before and after the adsorbing sections. The ends are flame sealed and the glass tube containing the adsorbent is 8 cm  long, with a 8 mm O.D. and 6 mm I.D., SKC tubes or equivalent. 

   2.2 Sampling technique 

   2.2.1 Open the ends of the XAD-7 tubes immediately before sampling. 

   2.2.2 Connect XAD-7 tubes to the sampling pump with flexible tubing. 

   2.2.3 Place the tubes 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 XAD-7 tubes. 

   2.2.5 Seal the XAD-7 tubes 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 used for 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 other samples.  

   2.3 Desorption efficiency 

   Six tubes were spiked at loadings of 60.9 µg (0.496 ppm), 304 µg (2.47 ppm), and 609 µg (4.96 ppm) PTBP. They were allowed to equilibrate overnight at room temperature. 

   They were opened, each section placed into a separate 2 mL vial, desorbed with 1 mL of the desorbing solution for 30 minutes with occasional shaking, and analyzed by GC-FID. The overall average was 94.7%.(Table 1) 

   Table 1
   Desorption Efficiency

   Tube#	% Recovered
   	60.9 µg	304 µg	609 µg
   1	96.2	95.5	93.6
   2	94.3	94.9	94.0
   3	96.1	93.9	93.4
   4	94.2	95.5	94.5
   5	95.5	93.9	93.4
   6	95.9	95.4	94.2
   average	95.4	94.9	93.9
   overall average	94.7
   standard deviation	± 0.944

   2.4 Retention efficiency 

   Six tubes were liquid spiked with 609 µg (4.96 ppm) PTBP, allowed to equilibrate overnight, and then had 20 liters humid air (89% RH) pulled through them. They were  opened, desorbed and analyzed by GC-FID. The retention efficiency averaged 99.1%. There was no PTBP found on the backup portions of the tubes. The values are desorption corrected. (Table 2) 

   Table 2
   Retention Efficiency

   Tube #	% Recovered	% Recovered	Total
   	'A'	'B'
   1	101	0.0	101
   2	101	0.0	101
   3	99.0	0.0	99.0
   4	101	0.0	101
   5	97.0	0.0	97.0
   6	95.8	0.0	95.8
   		average	99.1

   2.5 Storage 

   Tubes were spiked with 609 µg (4.96 ppm) PTBP and stored at room temperature until opened and analyzed. Since PTBP may decompose in light, half of the tubes were stored under room light, and half were stored in  darkness. The samples were found to be stable under both conditions. Results were corrected for desorption efficiency. The recoveries averaged 99.0% for the 14 days stored.(Table 3) 

   Table 3
   Storage Study

   Day	% Recovered light	% Recovered dark
   7	101	101
   7	96.8	101
   7	lost	102
   14	101	96.8
   14	97.0	97.8
   14	98.4	96.6
   overall average	99.0

   2.6 Precision 

   The precision was calculated using the area counts from six injections of each standard at concentrations of 60.9, 304, 609, and 1218 µg/mL PTBP in the desorbing solution. The pooled coefficient of variation was 0.00593. (Table 4) 

   Table 4
   Precision Study

   Injection Number	60.9 µg/mL	304 µg/mL	609 µg/mL	1218 µg/mL
   1	19812	97430	195843	395475
   2	19483	97777	196784	399977
   3	19667	97690	195049	396600
   4	19724	97320	195991	399840
   5	19657	96079	195486	399173
   6	19896	96842	194083	399790
   Average	19707	97190	195539	398476
   Standard Deviation	± 142	636	918	1942
   CV	0.00721	0.00654	0.00469	0.00487
   Pooled CV	0.00593

   where:

   

   A(1),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 20 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 a manner that does not interfere with work performance or safety. 

   2.9.2 Safety glasses should be worn at all times in designated areas. 

   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 equipped with a flame  ionization detector. A HP5890 gas chromatograph was used in this study. 

   3.1.2 GC column capable of separating the analyte and  an internal standard from any interferences. The column used in this study was a 30 meter DB-225 capillary column, 0.25 µm df, 0.32 mm I.D. An alternate column is a 60 meter DB-1 capillary column, 1.0 µm df, 0.32 mm I.D.  

   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, and air.

   3.2.2 r-tert-Butylphenol, Reagent grade

   3.2.3 Methanol, HPLC grade 

   3.2.4 Dimethyl formamide, Reagent grade 

   3.2.5 Desorbing solution is methanol with 1 µL/mL  dimethyl formamide used as 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, and the front glass wool was placed in the vial containing the front section.  

   3.3.2. Each section is desorbed with 1 mL of the desorbing solution. 

   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 PTBP with the desorbing solution. 

   3.4.2 At least two separate stock standards should be made. Dilutions of the stock standards are made to bracket the samples. The standards used in  this study ranged

   3.5 Analysis 

   3.5.1 Gas chromatograph conditions using a DB-225 capillary column. 

   Gas chromatograph conditions using a DB-225 capillary column

   Flow rates (mL/min)		Temperature (°C)
   Nitrogen(makeup) :	30	Injector :	240
   Hydrogen(carrier):	1.5	Detector :	240
   Air :	450	Column :	110°C - 1 min
   Hydrogen(detector):	30		4°C/min-160°C
   Injection size :	1 µL
   Elution time :	9.39 min
   Chromatogram :	(See Figure 1)

   3.5.2 Gas chromatograph conditions using a DB-1 capillary column.  

   Gas chromatograph conditions using a DB-1 capillary column

   Flow rates (mL/min)		Temperature (°C)
   Nitrogen(makeup) :	30	Injector :	200
   Hydrogen(carrier):	1.5	Detector :	240
   Air :	450	Column :	80°C - 0 min
   Hydrogen(detector):	30		10°C/min-220°C
   Injection size :	1 µL
   Elution time :	14.87 min
   Chromatogram :	(See Figure 2)

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

   3.6 Interferences (analytical) 

   3.6.1. Any compound having the general retention time of the analyte or the internal standard used is an interference. Possible interferences should be listed on the sample data sheet. GC 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. A curve with area counts versus concentration is calculated from the calibration standards. 

   3.7.2. The area counts for the samples are plotted with the calibration curve to obtain the concentration of PTBP in solution. 

   3.7.3. To calculate the concentration of analyte in the air sample the following formulas are used: 

   

   3.7.4. The above equations can be consolidated to form  the following formula. To calculate the ppm of analyte in the sample based on a 20 liter air sample: 

    

   µg/mL  24.45 MW DV 20 L DE

   = = = = = =

   concentration of analyte in sample or standard Molar volume (liters/mole) at 25°C and 760 mm Hg.  Molecular weight (g/mole) Desorption volume 20 liter air sample 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. All handling of solvents should be done in a hood.

   3.8.2. Avoid skin contact with all chemicals. 

   3.8.3. Wear safety glasses, gloves and a lab coat at all  times in laboratory areas.

4. Recommendations for further study

   Collection studies need to be performed. 

   

   Figure 1. An analytical standard of 609 ug p-tert-butylphenol in methanol with 1 VL/mL dimethyl formamide internal standard analyzed on a DB-225 capillary column. 

   

   Figure 2. An analytical standard of 609 µg p-tert-butylphenol in methanol with 1 PL/mL dimethyl formamide internal standard analyzed on a DB-1 capillary column. 
   
   

5. References

   5.1 Cummins, K., Method 32, "Phenol and Cresol", Organic Methods Evaluation Branch, OSHA Salt Lake Technical Center, 1986. 

   5.2 Windholz, M., "The Merck Index", Eleventh Edition, Merck & Co., Rahway N.J., 1989, p. 241. 

   5.3 Sax, N., Lewis, R., "Hawley's Condensed Chemical Dictionary", Eleventh Edition, Van Nostrand Reinhold Co., New York, 1987, p. 190.