1,1-DICHLORO-1-FLUOROETHANE (Freon 141b)
1,1,2-TRICHLORO-1,2,2-TRIFLUOROETHANE (Freon 113)

2. Sampling Procedure

2.1 Apparatus

2.1.1 Samples are collected using a personal sampling pump calibrated, with the sampling device attached, within ±5% at the recommended flow rate.

2.1.2 Samples are collected with two 7-cm × 4-mm i.d. × 6-mm o.d. glass sampling tubes, each packed with two sections of (150/75 mg) Anasorb CMS, connected in series. The sections are held in place with a glass wool plug and two urethane foam plugs. For this evaluation, commercially prepared sampling tubes were purchased from SKC, Inc. (catalog no. 226-121).

2.2 Reagents

None required.

2.3 Technique

2.3.1 Immediately before sampling, break off the ends of both sampling tubes. All tubes should be from the same lot. Connect the outlet end of one tube to the inlet end of the other tube with a 1-in. length of ³/₁₆-in. i.d. silicone rubber tubing. Ensure that the connection is secure and that the broken ends of the tubes just touch each other. Be careful not to cut the silicone tubing with the sharp ends of the sampling tubes.

2.3.2 Attach the sampling device to the sampling pump with flexible, non-crimping 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 tubes so that the sampled air first passes through the inlet of the sampling device.

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

2.3.4 To avoid channeling, attach the sampler vertically with the inlet pointing downward, in the worker's breathing zone. Position the sampler so it does not impede work performance or safety.

2.3.5 After sampling for the appropriate time, immediately remove the sampling device, separate the tubes and seal them with plastic end caps.

2.3.6 Wrap each tube end-to-end with an OSHA-21 form.

2.3.7 Submit at least one blank sample with each set of samples. Handle the blank sampling tube in the same manner as the other samples, except draw no air through it.

2.3.8 Record sample air volumes (in liters) for each sample, along with any potential interferences.

2.3.9 Ship any bulk sample(s) in a container separate from the air samples.

2.3.10 Submit the samples to the laboratory for analysis as soon as possible after sampling. If delay is unavoidable, store the samples at reduced temperature.

2.4 Sampler capacity

Sampler capacity is determined by measuring how much air can be sampled before the analyte breaks through the sampler, i.e., the sampler capacity is exceeded. Breakthrough is considered to occur when the effluent from the sampler contains a concentration of analyte that is 5% of the upstream concentration (5% breakthrough). Testing for breakthrough was performed by using a GC/FID to monitor the effluent from sampling tubes, each containing 225-mg of Anasorb CMS. Dynamically generated test atmospheres, which were about two times the target concentration of each analyte, were used for the capacity tests. The samples were collected at 50 mL/min and the relative humidity was about 75% at 25 °C. The 5% breakthrough air volumes were calculated from the data of duplicate determinations and are 8.66 and 3.88 L for Freon 141b and Freon 113, respectively. (Section 4.9) A goal of this procedure was to develop a common sampling device with a common sampling time for all five studied Freons. 1,1,1,2-Tetrafluoroethane had the shortest sampling time and that was the limiting factor in selecting the 20-min sampling time.

2.5 Desorption efficiency

2.5.1 The average desorption efficiencies for Freon 141b and Freon 113 from Anasorb CMS over the range of 0.5 to 2.0 times the target concentrations (TC) are 99.6% and 100.3%, respectively. (Section 4.10)

2.5.2 The desorption efficiencies at 0.05, 0.1 and 0.2 times the target concentrations (TC) were found to be very good and are listed below. (Section 4.10)

Table 2.5.2
Desorption Efficiencies at
0.05 to 0.2 times TC, %

TC	Freon 141b	Freon 113
0.05×	98.3	98.4
0.1×	99.0	98.8
0.2×	100.5	98.9

2.5.3 Desorbed samples remain stable for at least 24 h.

2.6 Recommended air volume and sampling rate

2.6.1 For long-term samples, collect 1.0 L at 50 mL/min for 20 min.

2.6.2 For short-term samples, collect 0.75 L at 50 mL/min for15 min.

2.6.3 When short-term samples are collected, the air concentration equivalent to the reliable quantitation limit becomes larger. For example, the reliable quantitation limits are 3.6 ppm (17 mg/m³) and 4.1 ppm (32 mg/m³) for Freon 141b and Freon 113, respectively, when 0.75 L is sampled.

2.7 Interferences (sampling)

2.7.1 It is not known if any compounds will severely interfere with the collection of Freon 141b or Freon 113 on Anasorb CMS. In general, the presence of other contaminant vapors in the air will reduce the capacity of Anasorb CMS to collect both analytes.

2.7.3 Suspected interferences should be reported to the laboratory with submitted samples.

2.8 Safety precautions (sampling)

2.8.1 The sampling equipment should be attached to the worker in such a manner that it will not interfere with work performance or safety.

2.8.2 All safety practices that apply to the work area being sampled should be followed.

2.8.3 Protective eyewear should be worn when breaking off the ends of the glass sampling tubes.

3. Analytical Procedure

3.1 Apparatus

3.1.1 Gas chromatograph equipped with an FID. For this evaluation, a Hewlett-Packard 5890 Series II Gas Chromatograph equipped with a 7673A Automatic Sampler was used. A Forma Scientific Model 2006 refrigerated circulator was used to cool the sample tray of the HP 7673A to 10 °C to minimize evaporation.

3.1.2 A GC column capable of separating the analyte of interest from the desorbing solvent, internal standard and any interferences. A 60-m × 0.32-mm i.d. fused silica DB-624 column with a 1.8-µm d_f (J&W Scientific, Folsom, CA) was used in this evaluation.

3.1.3 An electronic integrator or some other suitable means of measuring peak areas. A Waters 860 Networking Computer System and an HP GC ChemStation were used in this evaluation.

3.1.4 Two- and four-milliliter vials with polytetrafluoroethylene-lined caps. Seven-milliliter scintillation vials with polytetrafluoroethylene-lined caps.

3.1.5 Three-fourths milliliter autosampler vials (8-mm × 30-mm) from Kimble Glass (catalog no. 60831D-830).

3.1.6 A dispenser capable of delivering 4.0 mL of desorbing solvent to prepare standards and samples. If a dispenser is not available, a 4.0-mL volumetric pipette may be used.

3.2 Reagents

3.2.1 1,1-Dichloro-1-fluoroethane (Freon 141b), reagent grade or better. The Freon 141b, 97%, used in this evaluation was purchased from PCR, Inc. (Gainesville, FL).

3.2.2 1,1,2-Trichloro-1,2,2-trifluoroethane (Freon 113), reagent grade or better. The Freon 113, distilled in glass, used in this evaluation was purchased from Burdick & Jackson Laboratories, Inc. (Muskegon, MI).

3.2.3 Carbon disulfide (CS₂), reagent grade or better. The CS₂, 99.9+% - low benzene, used in this evaluation was purchased from Aldrich Chemical (Milwaukee, WI).

3.2.4 A suitable internal standard, reagent grade. The benzene, 99.94%, used in this evaluation was purchased from EM Science (Gibbstown, NJ).

3.2.5 Desorbing solvent. The desorbing solvent contains 200 µL of benzene per 1 L of CS₂.

3.2.6 GC grade nitrogen, air, and hydrogen.

3.3 Standard preparation

3.3.1 Prepare concentrated stock standard of Freon 141b and Freon 113 in CS₂. Prepare working analytical standards by injecting microliter amounts of concentrated stock standards into 4-mL vials containing 4.0 mL of desorbing solvent delivered from the same dispenser used to desorb samples. Transfer the standard solution to 2-mL autosampler vials, if necessary. For example, to prepare a target level standard of Freon 141b, inject 20 µL of a stock solution containing 246 mg/mL of Freon 141b in CS₂ into 4 mL of desorbing solvent.

3.3.2 Bracket sample concentrations with working standard concentrations. If samples fall outside the concentration range of prepared standards, prepare and analyze additional standards or dilute the sample.

3.4 Sample preparation

3.4.1 Remove the plastic end caps from the sample tube and carefully transfer both sections of the adsorbent (225 mg) to a 0.75-mL vial. Do not place any markings or tape on the 0.75 mL vial because it will be placed in the desorbing solvent. Discard the glass tube, urethane foam plugs and glass wool plug. Place the 225 mg of adsorbent from the back-up tube in a separate 0.75 mL vial.

3.4.2 Add 4.0 mL of desorbing solvent to each 7-mL scintillation vial using the same dispenser as used for preparation of standards.

3.4.3 Insert the 0.75-mL vial into the 7-mL vial and immediately seal the 7-mL vial with a polytetrafluoroethylene-lined cap.

3.4.4 Shake the vial vigorously by hand several times while keeping the vial horizontally during the next 60 min. This will permit the solvent inside the small vial to mix with the solvent in the larger vial. Do not use a mechanical shaker to agitate the sample. The adsorbent beads will cause the small vial to become stuck in the neck of the larger vial and the result will be inadequate desorption.

3.4.5 Transfer the sample solution to a 2-mL autosampler vial, if necessary.

3.5 Analysis

3.1 Analytical conditions

 

GC conditions
zone temperatures:	35 °C (column) 250 °C (injector) 300 °C (detector)
run time:	15 min
column gas flow:	2.5 mL/min (hydrogen)
septum purge:	1.5 mL/min (hydrogen)
injection size:	1.0 µL (10.2:1 split)
column:	60-m × 0.32-mm i.d. capillary DB-624 (df = 1.8 µm)
retention times:	6.03 min (Freon 141b) 6.55 min (Freon 113) 10.03 min (benzene)
FID conditions
hydrogen flow:	34 mL/min
air flow:	450 mL/min
makeup flow:	33 mL/min (nitrogen)
	Figure 3.5.1. Chromatogram of Freon 141b and Freon 113 at the target concentration. 1 - Freon 141b, 2 - Freon 113, 3 - CS2, 4 - benzene.

3.2 An internal standard (ISTD) calibration method is used. A calibration curve can be constructed by plotting micrograms of analyte per sample versus ISTD-corrected response of standard injections. Bracket the samples with freshly prepared analytical standards over a range of concentrations.

3.6 Interferences (analytical)

3.6.1 Any compound that produces an FID response and has a similar retention time as the analytes or internal standard is a potential interference. If any potential interferences were reported, they should be considered before the samples are desorbed.

3.6.2 Generally, chromatographic conditions can be altered to separate an interference from the analyte.

3.6.3 When necessary, the identity or purity of an analyte peak may be confirmed with additional analytical data. (Section 4.11)

3.7 Calculations

The amount of analyte per sampler is obtained from the appropriate calibration curve in terms of micrograms per sample, uncorrected for desorption efficiency. The back tube is analyzed primarily to determine if there was any breakthrough from the front tube during sampling. If a significant amount of analyte is found on the back tube (e.g., greater than 25% of the amount found on the front tube), this fact should be reported with the sample results. If any analyte is found on the back tube, it is added to the amount on the front tube. This amount is then corrected by subtracting the total amount (if any) found on the blank. The air concentration is calculated using the following formulae.

mg/m3  =

(micrograms of analyte per sample)   (liters of air sampled)(desorption efficiency)

ppm  =

(mg/m3)(24.46)   (molecular weight of analyte)

 

where

molar volume at 25 °C and 101.3 kPa (760 mmHg) is 24.46 molecular weight of Freon 141b is 116.95 molecular weight of Freon 113 is 187.38

3.8 Safety precautions (analytical)

3.8.1 Adhere to the rules set down in your Chemical Hygiene Plan.

3.8.2 Avoid skin contact and inhalation of all chemicals.

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

4. Backup Data

4.1 Determination of detection limits

Y_DL - Y_BR = 3(SD_BR)

Detection limits, in general, are defined as the amount (or concentration) of analyte that gives a response (Y_DL) that is significantly different [three standard deviations (SD_BR)] from the background response (Y_BR).

The measurement of Y_BR and SD_BR in chromatographic methods is typically inconvenient and difficult because Y_BR is usually extremely low. Estimates of these parameters can be made with data obtained from the analysis of a series of analytical standards or 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 SD_BR and the precision of the data about curve are similar, the standard error of estimate (SEE) for the regression curve can be substituted for SD_BR in the above equation. The following calculations derive a formula for DL:

 

where

Yobs is observed response Yest is estimated response from regression curve n is total number of data points k is 2 for linear regression curve

At point Y_DL on the regression curve

Y_DL = A(DL) + Y_BR

where A is analytical sensitivity (slope)

therefore

DL =	(YDL - YBR) A

Substituting 3(SEE) + Y_BR for Y_DL gives

DL =

3(SEE) A

4.2 Detection limit of the analytical procedure (DLAP)

The DLAP is measured as the mass of analyte actually introduced into the chromatographic column. Ten analytical standards were prepared in equal descending increments with the highest standard containing 19.2 and 30.7 µg/mL of Freon 141b and Freon 113, respectively. This is the concentration that would produce a peak approximately 10 times the baseline noise of a reagent blank near the elution time of the analyte. These standards, and the reagent blank, were analyzed with the recommended analytical parameters (1-µL injection with a 10.2:1 split), and the data obtained were used to determine the required parameters (A and SEE) for the calculation of the DLAP.

Table 4.2.1. DLAP Data for Freon 141b A = 186 SEE = 7.16 concentration (µg/mL) mass on column (ng) area counts (µV-s) 0 1.92 3.85 5.77 7.69 9.61 11.5 13.5 15.4 17.3 19.2 0 0.188 0.377 0.565 0.754 0.942 1.13 1.32 1.51 1.70 1.89 0 16 50 89 124 160 194 231 258 303 348

Figure 4.2.1. Plot of the data from Table 4.2.1 to determine the DLAP of Freon 141b, DLAP = 0.12 ng.

Table 4.2.2. DLAP Data for Freon 113 A = 112 SEE = 9.87 concentration (µg/mL) mass on column (ng) area counts (µV-s) 0 3.07 6.14 9.21 12.3 15.4 18.4 21.5 24.6 27.6 30.7 0 0.301 0.602 0.903 1.20 1.50 1.81 2.11 2.41 2.71 3.01 0 16 43 96 137 165 184 216 256 302 330 Figure 4.2.2. Plot of the data from Table 4.2.2 to determine the DLAP of Freon 113, DLAP = 0.26 ng.

The DLOP is measured as mass per sample and expressed as equivalent air concentration, based on the recommended sampling parameters. Ten samplers were spiked with equal descending increments of analyte, such that the highest sampler loading was 76.9 and 123 µg/sample of Freon 141b and Freon 113, respectively. This is the amount, when spiked on a sampler, that would produce a peak approximately 10 times the baseline noise for a sample blank. These spiked samplers, plus a sample blank, were analyzed with the recommended analytical parameters, and the data obtained used to calculate the required parameters (A and SEE) for the calculation of the DLOP. For Freon 141b, the values of 4.12 and 44 were obtained for A and SEE, respectively and the DLOP was calculated to be 4.0 µg per sample (0.84 ppm or 4.0 mg/m³). For Freon 113, the values of 2.33 and 62 were obtained for A and SEE, respectively and the DLOP was calculated to be 7.2 µg per sample (0.94 ppm or 7.2 mg/m³).

Table 4.3.1. DLOP Data for Freon 141b mass per sample (µg) area counts (µV-s) 0 7.69 15.4 23.1 30.8 38.5 46.1 53.8 61.5 69.2 76.9 0 23 55 90 120 156 185 226 252 270 314		Figure 4.3.1. Plot of the data from Table 4.2.1 to determine the DLOP of Freon 141b on Anasorb CMS, (SEE = 5.44).
Table 4.3.2. DLOP Data for Freon 113 mass per sample (µg) area counts (µV-s) 0 12.3 24.6 36.8 49.1 61.4 73.7 86.0 98.2 111 123 0 19 54 77 112 135 159 189 218 261 284		Figure 4.3.2. Plot of the data from Table 4.2.1 to determine the DLOP of Freon 113 on Anasorb CMS, (SEE = 5.62).

4.4 Reliable quantitation limit (RQL)

The RQL is considered the lower limit for precise quantitative measurements. It is determined from the regression line parameters obtained for the calculations of the DLOP (Section 4.3), providing at least 75% of the analyte is recovered. The RQL is defined as the amount of analyte that gives a response (YRQL) such that YRQL - YBR = 10(SDBR) therefore RQL = 10(SEE) A

Figure 4.4. Chromatogram of the RQL for both analytes on Anasorb CMS. 1 = Freon 141b, 2 = Freon 113, 3 = CS2, 4 = interference.

The RQL for each analyte was calculated and is listed above. The recovery of the analyte near the RQL was 99.5% and 96.3% for Freon 141b and Freon 113, respectively.

The precision of the analytical procedure is measured as the pooled relative standard deviation (RSD_P). Relative standard deviations are determined from six replicate injections of analyte standards at 0.5, 0.75, 1, 1.5 and 2 times the target concentration. After assuring that the RSDs satisfy the Cochran test for homogeneity at the 95% confidence level, RSD_P was calculated to be 0.93% and 0.45% for Freon 141b and Freon 113, respectively.

Table 4.5.1
Instrument Response to Freon 141b

× target concn (µg/mL)	0.5× 615	0.75× 923	1× 1230	1.5× 1845	2× 2460
area counts (mV-s) SD RSD (%)	157.23 157.22 159.56 160.15 156.29 156.31 157.79 1.375 0.871	235.20 229.84 230.53 226.62 229.93 225.81 229.66 2.293 0.999	295.72 297.38 296.14 296.65 300.30 302.17 298.06 2.117 0.710	441.19 448.19 437.30 451.01 444.80 440.63 443.85 4.147 0.934	574.19 573.49 571.21 590.26 585.16 581.85 579.36 6.396 1.104

Table 4.5.2
Instrument Response to Freon 113

× target concn (µg/mL)	0.5× 981	0.75× 1472	1× 1963	1.5× 2944	2× 3925
area counts (mV-s) SD RSD (%)	117.04 118.30 119.16 118.39 118.97 119.72 118.60 0.686 0.579	175.15 174.88 173.80 176.22 177.26 175.66 175.49 0.885 0.504	234.08 231.15 231.67 230.90 231.56 233.42 232.13 1.082 0.466	341.46 341.14 345.79 343.27 342.88 343.47 343.00 1.175 0.343	453.08 455.29 454.31 457.94 454.54 452.17 454.56 4.372 0.302

The Cochran test for homogeneity:

The critical value of the g-statistic, at the 95% confidence level, for five variances, each associated with six observations is 0.5065. The g-statistics are 0.2801 and 0.3301 for Freon 141b and Freon 113, respectively. Because the g-statistic does not exceed this value, the RSDs can be considered equal and they can be pooled (RSD_P) to give an estimated RSD for the concentration range studied.

4.6 Precision (overall procedure)

The precision of the overall procedure is determined from the storage data in Section 4.7. The determination of the standard error of estimate (SEE_R) for a regression line plotted through the graphed storage data allows the inclusion of storage time as one of the factors affecting overall precision. The SEE_R is similar to the standard deviation, except it is a measure of the dispersion of data about a regression line instead of about a mean. It is determined with the following equation:

An additional 5% for pump error (SP) is added to the SEE_R by the addition of variances to obtain the total standard error of the estimate.

The precision at the 95% confidence level is obtained by multiplying the standard error of estimate (with pump error included) by 1.96 (the z-statistic from the standard normal distribution at the 95% confidence level). The 95% confidence intervals are drawn about their respective regression lines in the storage graphs, as shown in Figures 4.7.1.1 through 4.7.2.2. The precisions of the overall procedure and the associated figures are listed below.

4.7 Storage test

Storage samples were generated by sampling from a controlled test atmosphere containing 3400 mg/m³ of Freon 141b, about 0.7 times the 1000-ppm target concentration. Anasorb CMS tubes were used to sample for 20 min at 50 mL/min, the relative humidity was about 80% at 22 °C. Thirty-six storage samples were prepared. Six samples were analyzed immediately after generation, fifteen tubes were stored at reduced temperature (4 °C) and the other fifteen were stored in a closed drawer at ambient temperature (about 22 °C). At 2-4 day intervals, three samples were selected from each of the two sets and analyzed.

Figure 4.7.1.1. Ambient storage test for Freon 141b.

Figure 4.7.1.2. Refrigerated storage test for Freon 141b.

4.7.2 Freon 113

Storage samples were generated by sampling from a controlled test atmosphere containing 6700 mg/m³ of Freon 113, about 0.9 times the 1000-ppm target concentration. Anasorb CMS tubes were used to sample for 20 min at 50 mL/min, the relative humidity was about 80% at 22 °C. Thirty-six storage samples were prepared. Six samples were analyzed immediately after generation, fifteen tubes were stored at reduced temperature (4 °C) and the other fifteen were stored in a closed drawer at ambient temperature (about 22 °C). At 3-5 day intervals, three samples were selected from each of the two sets and analyzed.

Figure 4.7.2.1. Ambient storage test for Freon 113.

Figure 4.7.2.2. Refrigerated storage test for Freon 113.

Six samples for each analyte were prepared by drawing humid air through the sampling tube for 20 min at 50 mL/min. The samplers were then liquid-spiked with an aliquot of a solution containing one of the Freons. The samples were submitted, along with a draft copy of this procedure, to an OSHA Salt Lake Technical Center service branch. The samples were analyzed after being stored for 15 days at 4 °C. Sample results were corrected for desorption efficiency. No sample result for Freon 141b or Freon 113 had a deviation greater than the precision of the overall procedure determined in Section 4.6.

4.9 Sampler capacity

The sampling capacity of a sampling tube containing 225 mg of Anasorb CMS was tested by sampling from a dynamically generated test atmosphere of Freon 141b (9560 mg/m³ or 1999 ppm) or Freon 113 (15300 mg/m³ or 1998 ppm). The samples were collected at 50 mL/min and the relative humidity was about 75% at 25 °C. A GC with a gas sampling valve was placed in-line behind the 225-mg front test section. The valve was rotated to measure the amount of Freon passing through the sampler at the time of rotation. The 5% breakthrough air volume was determined to be 8.66 and 3.88 L for Freon 141b and Freon 113, respectively.

Table 4.9.1 Capacity of Freon 141b on Anasorb CMS first test second test air volume (L) breakthrough (%) air volume (L) breakthrough (%) 7.30 7.55 7.80 8.05 8.30 8.55 8.80 9.05 9.30 0 0 0.27 0.48 1.5  2.7  5.9  10.5  16.7  7.54 7.80 8.05 8.3  8.55 8.80 9.05 9.3  0 0 0.36 1.0  2.9  6.7  12.1 18.4

Figure 4.9.1. Five percent breakthrough air volume for Feon 141b on Anasorb CMS.

Table 4.9.2 Capacity of Freon 113 on Anasorb CMS first test second test air volume (L) breakthrough (%) air volume (L) breakthrough (%) 3.24 3.44 3.64 3.85 4.05 4.25 4.65 0 0 1.1 3.3 6.7 11.1 17.7 3.05 3.25 3.46 3.66 3.86 4.06 4.26 4.47 0 0 0.60 2.0 4.4 8.8 14.0 19.6

Figure 4.9.1. Five percent breakthrough air volume for Feon 113 on Anasorb CMS.

4.10 Desorption efficiency and stability of desorbed samples

4.10.1 Freon 141b

The desorption efficiencies (DE) of Freon 141b were determined by liquid-spiking 225-mg of Anasorb CMS in a vial with amounts equivalent to 0.05 to 2 times the 1000-ppm target concentration. These samples were stored overnight at ambient temperature and then desorbed and analyzed. The average desorption efficiency over the working range of 0.5 to 2 times the target concentration is 99.6%.

Table 4.10.1.1
Desorption Efficiency of Freon 141b from Anasorb CMS

× target concn (µg/sample)	0.05× 246	0.1× 492	0.2× 984	0.5× 2460	1.0× 4920	2.0× 9840
DE (%)	98.0 99.6 98.8 97.1 99.6 96.6 98.3	98.5 97.8 97.9 99.3 99.2 101.4   99.0	100.3   99.0 103.0   99.6 100.7 100.4 100.5	98.2 97.1 96.7 95.2 96.4 100.7   97.4	99.3 103.3 101.9 101.3 101.6   96.7 100.7	99.2   99.9 102.3 102.2 100.4   99.8 100.6

The stability of desorbed samples was investigated by reanalyzing the target concentration samples 24 h after initial analysis. After the original analysis was performed, three vials were recapped with new septa while the remaining three retained their punctured septa. The samples vials were stored in the refrigerated sampling tray (10 °C) for the GC injector. The samples were reanalyzed with fresh standards. The average percent change was +1.6% for samples that were resealed with new septa, and - 0.3% for those that retained their punctured septa.

Table 4.10.1.2
Stability of Desorbed Samples for Freon 141b from Anasorb CMS

punctured septa replaced			punctured septa retained
initial DE (%)	DE after one day (%)	difference	initial DE (%)	DE after one day (%)	difference
99.3 103.3 101.9 101.5	102.6 105.2 101.6 (averages) 103.1	+3.3 +1.9 - 0.3 +1.6	101.3   101.6   96.7 99.9	98.5 99.1 101.2   (averages) 99.6	- 2.8 - 2.5 +4.5 - 0.3

The desorption efficiencies (DE) of Freon 113 were determined by liquid-spiking 225-mg of Anasorb CMS in a vial with amounts equivalent to 0.05 to 2 times the 1000-ppm target concentration. These samples were stored overnight at ambient temperature and then desorbed and analyzed. The average desorption efficiency over the working range of 0.5 to 2 times the target concentration is 100.3%.

Table 4.10.2.1
Desorption Efficiency of Freon 113 from Anasorb CMS

× target concn (µg/sample)	0.05× 243.1	0.1× 486.2	0.2× 972.4	0.5× 2431	1.0× 4862	2.0× 9724
DE (%)	97.9 98.9 98.8 99.7 97.6 97.6 98.4	100.2   98.7 98.5 98.5 98.6 98.2 98.8	98.4 98.5 99.0 99.2 99.5 99.0 98.9	99.5 100.3 100.6   99.6 100.3   99.5 100.0	99.5 100.6 100.7 100.4 100.7 101.3 100.5	99.8 101.0   99.8 101.4 100.2 100.4 100.4

The stability of desorbed samples was investigated by reanalyzing the target concentration samples 24 h after initial analysis. After the original analysis was performed, three vials were recapped with new septa while the remaining three retained their punctured septa. The samples vials were stored in the refrigerated sampling tray (10 °C) for the GC injector. The samples were reanalyzed with fresh standards. The average percent change was - 0.9% for samples that were resealed with new septa, and - 0.9% for those that retained their punctured septa.

4.11 Qualitative analysis

Freon 141b and Freon 113 can be easily separated and identified by GC/MS. Mass spectra were obtained from an HP5973 Mass Selective Detector interfaced to an HP6890 GC.

Figure 4.11.1. Mass spectrum of Freon 141b.

Figure 4.11.2. Mass spectrum of Freon 113.

5. References

5.1 NIOSH Manual of Analytical Methods, Eller, P.M., Ed, 4^th ed., US Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, Division of Physical Science and Engineering, Cincinnati, OH, DHHS (NIOSH) Publication No. 94-113, 1994; Method 1018. (Back to Text)

5.2 NIOSH Manual of Analytical Methods, Eller, P.M., Ed, 4^th ed., US Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, Division of Physical Science and Engineering, Cincinnati, OH, DHHS (NIOSH) Publication No. 94-113, 1994; Method 1020. (Back to Text)

5.3 NIOSH Manual of Analytical Methods, Eller, P.M., Ed, 4^th ed., US Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, Division of Physical Science and Engineering, Cincinnati, OH, DHHS (NIOSH) Publication No. 94-113, 1994; Method 1006. (Back to text)

5.4 OSHA Computerized Information System Database, Chemical Sampling Information, Salt Lake Technical Center, Occupational Safety and Health Administration, Salt Lake City, UT, Sept 1998. (Back to text)

5.5 Occupational Health Guidelines for Chemical Substances, NIOSH/OSHA, DHHS (NIOSH) Publ No. 81-123, Jan 1981. (Back to text)

5.6 Material Safety Data Sheet: 1,1-Dichloro-1-fluoroethane, PCR, Inc., Gainesville, FL, Nov 1992. (Back to text)

5.7 Documentation of the Threshold limits Values and Biological Exposures Indices, 6^th ed., American Conference of Governmental Industrial Hygienists, Inc.: Cincinnati, OH, 1991, Vol. III, pp. 1631-1635. (Back to text)

5.8 Hileman, B.; A Chilling Battle. Chem. Eng. News, 1998, 76(31), 33-34. (Back to text)

5.9 Material Safety Data Sheet; Trichlorotrifluoroethane, DuPont Canada, Inc., Mississauga, Ontario, Jan 1998. (Back to text)