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Hydrogen Peroxide
Method number: 1019
Version: 1.
Target concentration: 1.0 ppm (1.4 mg/m^3 )
OSHA PEL: 1.0 ppm (1.4 mg/m^3 ) ACGIH TLV: 1.0 ppm (1.4 mg/m^3 ) vapor or mist
Procedure: Samples are collected by drawing workplace air through two 25-mm quartz filters, coated with titanium oxysulfate, using personal sampling pumps. Samples are extracted with 10 mL of 1 M H 2 SO 4 and analyzed by spectrophotometry.
Recommended sampling time and sampling rate: TWA: 240 min at 1 L/min (240 L) 120 min at 2 L/min (240 L) for vapor and mist short term: 15 min at 2 L/min (30 L)
Reliable quantitation limit: TWA: 36.6 ppb (50.8 μg/m^3 ) short-term: 292 ppb (407 μg/m^3 )
Standard error of estimate at the target concentration: 5.8%
Special requirements: Samples should be protected from light during shipping and storage. Other chemicals used in the area sampled should be reported to the laboratory and the potential impact on analysis should be considered.
Status of method: Fully validated method. This method has been subjected to the established evaluation procedures of the Methods Development Team.
January 2016 Michael Simmons
Methods Development Team Industrial Hygiene Chemistry Division OSHA Salt Lake Technical Center Sandy UT 84070-
- General Discussion
For assistance with accessibility problems in using figures and illustrations presented in this method, please contact OSHA Salt Lake Technical Center (SLTC) at (801) 233-4900. These procedures were designed and tested for internal use by OSHA personnel. Mention of any company name or commercial product does not constitute endorsement by OSHA.
1.1 Background
1.1.1 History
In 1977 OSHA issued Method VI-6 for the sampling and analysis of hydrogen peroxide.^1 When using Method VI-6 samples are collected with a midget fritted glass bubbler containing a titanium oxysulfate collection solution and analyzed by spectrophotometry. OSHA next issued ID-126-SG, with samples collected using a midget fritted glass bubbler containing a titanium oxysulfate collection solution and analyzed by differential pulse polarography. 2
In 2000, Christensen et al. demonstrated the use of glass fiber filters impregnated with titanium tetrachloride, with analysis by spectrophotometry, for the sampling of hydrogen peroxide.^3 Hecht et al. then modified the sampler using quartz filters soaked with a solution of titanium oxysulfate in sulfuric acid.^4 Quartz filters coated with titanium oxysulfate are now commercially available and are validated in this method as a replacement to the fritted glass bubbler method.
1.1.2 Toxic effects (This section is for information only and should not be taken as the basis of OSHA policy.)
“Inhalation of high concentrations of the vapor or the mist of hydrogen peroxide has caused extreme irritation and inflammation of the nose and throat. Severe systemic poisoning has also caused headache, dizziness, vomiting, diarrhea, tremors, numbness, convulsions, pulmonary edema, unconsciousness and shock.”^5
1.1.3 Workplace exposure
Hydrogen peroxide is used in “the bleaching or deodorizing of textiles, wood pulp, hair, fur, and foods; in the treatment of water and sewage; as a disinfectant; as a component of rocket fuels; and in the manufacture of many chemicals and chemical products.” 6 In 2000 the estimated U.S. production of hydrogen peroxide was 7 × 10^5 tons.^7
(^1) Hydrogen Peroxide (OSHA Method VI-6), 1977. United States Department of Labor, Occupational Safety and Health Administration Web site. http://www.osha.gov/dts/sltc/methods/inorganic/id006/hydrogen_peroxide.html (accessed May
2 2015). Hydrogen Peroxide (OSHA Method ID-126-SG). United States Department of Labor, Occupational Safety and Health Administration Web site. http://www.osha.gov/dts/sltc/methods/partial/t-id126sg-pv-01-0201-m/t-id126sg-pv-01-0201-m.html
3 (accessed May 2015). Christensen, C. S.; Brødsgaard, S.; Mortensen, P.; Egmose, K.; Linde, S. A. Determination of hydrogen peroxide in workplace air: interferences and method validation. J. Environ. Monit., 2000 , 2 , pp 339-343. (^4) Hecht, G.; Héry, M.; Hubert, G.; Subra, I. Simultaneous Sampling of Peroxyacetic Acid and Hydrogen Peroxide in Workplace
5 Atmospheres.^ Ann. occup Hyg.,^^2004 ,^^8 , pp 715-721. American Conference of Governmental Industrial Hygienists, Inc. Documentation of the Threshold Limit Values and Biological Exposure Indices , 7th ed.; Cincinnati, OH, 2001; Vol. 2, pp. Hydrogen Peroxide – 1 through Hydrogen Peroxide – 2. (^6) American Conference of Governmental Industrial Hygienists, Inc. Documentation of the Threshold Limit Values and Biological
7 Exposure Indices ,^ 7th ed.; Cincinnati, OH, 2001; Vol. 2, pp. Hydrogen Peroxide^ –^ 1 through Hydrogen Peroxide^ –^ 2. Kirk-Othmer Encyclopedia of Chemical Technology , 4th^ ed.; Kroschwitz, J. I., Ex. Ed.; John Wiley & Sons, Inc.: New York, 1993; Vol. 13, pp 981.
Sample for up to 240 min at 1 L/min (240 L) to collect TWA (long term) samples.
Sample for up to 120 min at 2 L/min (240 L) to collect TWA vapor and mist (long term) samples.
Sample for 15 min at 2 L/min (30 L) to collect short term samples.
After sampling for the appropriate time, remove the sample and seal the cassette with plastic end plugs. Wrap each sample with aluminum foil and seal end-to-end with a Form OSHA-21 as soon as possible.
Submit at least one blank sample with each set of samples. Handle the blank sample in the same manner as the other samples except draw no air through it.
Record sample air volume (liters), sampling time (min), and sampling rate (L/min) for each sample, along with any potential interference on the Form OSHA-91A.
Submit the samples to the laboratory for analysis as soon as possible after sampling. If a delay is unavoidable, store the samples in a refrigerator as a precaution.
- Analytical Procedure
3.1 Apparatus
Spectrophotometer. A PerkinElmer Lamda EZ210 UV/Vis Spectrophotometer was used in this validation.
Disposable cuvettes. BRAND GMBH + CO KG UV-Cuvette semi-micro cuvettes were used in this validation (catalog no. 7591 50).
Cuvette caps. Globe Scientific Inc. square plug caps were used in this validation (catalog no. 111167).
Water purifier. A Barnstead NANOpure Diamond system was used to produce 18.0 MΩ-cm DI water in this validation.
Filters and syringes for the filtration of sample solutions prior to analysis. Pall Corporation IC Acrodisc® 25 mm Syringe Filters with 0.45 μm Supor® (PES) Membranes were used in this validation (catalog no. AP-4585).
A means to dispense and dilute solutions. A Hamilton Microlab 600 Series dual syringe diluter/dispenser was used in this validation.
A mechanical shaker. An Eberbach mechanical shaker was used in this evaluation.
Class A 10-mL, 50-mL, and 500-mL volumetric flasks.
Watch glass and 100-mL glass beaker.
Hot plate. A Corning PC-351 hot plate was used in this evaluation.
Sample preparation vials. Kimble 20-mL glass screw-thread scintillation vials were used in this validation (catalog no. 74505-20).
Scintillation vial racks. Polypropylene Scienceware scintillation racks were used in this evaluation.
Analytical balance capable of weighing at least 0.01 mg. A Mettler Toledo XP205 DeltaRange analytical balance was used in this evaluation.
3.2 Reagents
Hydrogen peroxide (H 2 O 2 ), [CAS no. 7722-84-1], for ultratrace analysis. The hydrogen peroxide solution used in this evaluation was ≥30% T race SELECT Ultra, for ultratrace analysis, purchased from Sigma Aldrich (product no. 16911, lot no. 05735JH). See Section 4.11 for more information.
Titanium(IV) oxysulfate (TiOSO 4 ), [CAS no. 13825-74-6]. The titanium(IV) oxysulfate used in this evaluation was ≥29% Ti (as TiO 2 ) purchased from Sigma Aldrich (product no. 14023, lot no. SZBB2340).
Sulfuric acid (H 2 SO 4 ), [CAS no. 7664-93-9]. The sulfuric acid used in this evaluation was Baker Instra-Analyzed Reagent for trace metal analysis (95.0 – 98.0%) purchased from J.T. Baker.
DI water, 18.0 MΩ-cm.
TiOSO 4 /H 2 SO 4 solution. Prepare by adding 3.5 g TiOSO 4 , 2.5 mL H 2 SO 4 , and 40 mL DI water to a 100 mL beaker. Cover beaker with watch glass, place on a hot plate and heat at about 90 °C, swirling occasionally, until solution becomes clear. Remove from hot plate and allow solution to cool to room temperature. Transfer to a 50-mL volumetric flask, rinsing beaker with several milliliters of DI water, and dilute to mark. Solution can be stored in an air-tight container for 6 months.
Two molar H 2 SO 4 solution. Prepare by adding 55 mL of H 2 SO 4 to a 500-mL volumetric flask containing approximately 400 mL of DI water. Allow solution to cool to room temperature and dilute to mark.
3.3 Standard preparation
Immediately before preparing working standards prepare a stock standard by injecting 50 μL of an approximately 30% H 2 O 2 solution into a 10-mL volumetric flask and diluting to mark with DI water. Use the density and concentration of the 30% H 2 O 2 solution provided by the manufacturer. For example:
(50 μL × 1.11 mg/μL x 0.308) / 10.0 mL = 1.709 mg/mL of H 2 O 2
[Density (1.11 mg/μL) and concentration (30.8%) as reported by the manufacturer of the solution used in validation of method.]
Prepare working standards by injecting microliter amounts of the stock standard into a 10-mL volumetric containing 400 μL TiOSO 4 /H 2 SO 4 solution and 5 mL of 2 M H 2 SO 4. Dilute to the mark with water. For example, to prepare a target level standard of 333.3 μg/sample H 2 O 2 , inject 195 μL of the stock standard into a 10-mL volumetric flask containing 400 μL TiOSO 4 /H 2 SO 4 solution and 5 mL of 2 M H 2 SO 4 then dilute to the mark with water. Prepare new working standards weekly and store in air-tight containers when not in use.
Transfer working standards to plastic disposable cuvettes and cap. Inspect the solution in each cuvette for air bubbles and gently tap cuvette if necessary to remove air bubbles.
Bracket sample concentrations with standard concentrations. If sample concentration falls outside the range of prepared working standards dilute with 50:50 2 M H 2 SO 4 :DI water and reanalyze.
E
M
VE
M
C
3.7 Calculations
The amount of H 2 O 2 per sample is obtained from the appropriate calibration curve in terms of micrograms per sample, uncorrected for extraction efficiency. This amount is then corrected by subtracting the total amount (if any) found on the blank. The air concentration is calculated using the following formulas.
- Method Validation
Where applicable, this method follows validation protocols drawing from the OSHA SLTC “Validation Guidelines for Air Sampling Methods Utilizing Chromatographic Analysis”^10. These Guidelines detail required validation tests, show examples of statistical calculations, list validation acceptance criteria, and define analytical parameters. Air concentrations listed in ppm are referenced to 25 °C and 760 mmHg (101.3 kPa).
4.1 Detection limit of the analytical procedure (DLAP)
The DLAP is measured as concentration of the analyte detected by the spectrophotometer. Ten analytical standards were prepared with approximately equal descending increments of analyte with the highest standard containing 1.98 μg/mL. This is the concentration that would produce a response approximately 10 times the reagent blank. These standards and the reagent blank were analyzed with the recommended analytical parameters. The data obtained were used to determine the required parameters (standard error of estimate and slope) for the calculation of the DLAP. Values of 0.0196 and 0.0016 were obtained for the slope and standard error of estimate respectively. The DLAP was calculated to be 0.24 μg/mL.
(^10) Eide, M.; Simmons, M.; Hendricks, W. Validation Guidelines for Air Sampling Methods Utilizing Chromatographic Analysis, 2010. United States Department of Labor, Occupational Safety & Health Administration Web site. http://www.osha.gov/dts/sltc/methods/chromguide/chromguide.pdf (accessed December 2013).
r
M M V
M
V C
C
where CV is concentration by volume (ppm) VM is 24.46 (molar volume at NTP) CM is concentration by weight (mg/m^3 ) M r is molecular weight of H 2 O 2 (34.01 g/mol)
where CM is concentration by weight (mg/m^3 ) M is micrograms per sample V is liters of air sampled EE is extraction efficiency in decimal form
Table 4. Detection Limit of the Analytical Procedure concentration (μg/mL)
absorbance
0
030
Figure 4.1. Plot of data to determine the DLAP (y = 0.0196x + 0.0031).
4.2 Detection limit of the overall procedure (DLOP) and reliable quantitation limit (RQL)
The DLOP is measured as mass per sample and expressed as equivalent air concentrations based on the recommended sampling parameters. Ten samplers were spiked with approximately equal descending increments of analyte, such that the highest sampler loading was 19.8 μg/sample. This is the amount spiked on a sampler that would produce a response approximately 10 times the response of a sample blank. These spiked samplers and the sample blank were analyzed with the recommended analytical parameters, and the data obtained used to calculate the required parameters (standard error of estimate and the slope) for the calculation of the DLOP. Values of 0.0020 and 0.0024 were obtained for the slope and standard error of estimate respectively. The DLOP was calculated to be 3.6 μg/sample (10. ppb or 15.0 μg/m^3 at 240 L).
Table 4. Detection Limit of the Overall Procedure mass per sample (μg)
absorbance
0
0.046 Figure 4.2. Plot of data to determine the DLOP/RQL (y = 0.0020x + 0.0075).
The RQL is considered the lower limit for precise quantitative measurements. It is determined from the regression line parameters that were obtained for the calculation of DLOP providing 75% to 125% of the analyte is recovered. The RQL is 12.2 μg/sample (36.6 ppb or 50. μg/m^3 ). Recovery at this concentration is 97.0%.
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
DLOP RQL
Mass (g) per Sample
Absorbance at 410.0 nm
0
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.
DLAP
Concentration (g/mL)
Absorbance at 410.0 nm
A low humidity storage test for H 2 O 2 was performed by sampling a dynamically generated controlled test atmosphere using the recommended sampling parameters. The concentration of H 2 O 2 in the test atmosphere was the target concentration (1.06 ppm or 1.48 mg/m^3 ), and the relative humidity was 8.3% at 21 C. Nine storage samples were prepared. Three samples were analyzed on the day of generation. Six samples were protected from light exposure and stored at ambient temperature (about 21 C). At 7 day intervals three samples were selected and analyzed. Sample results are not corrected for extraction efficiency.
A low humidity test, with samplers exposed to light during storage, was performed by sampling a dynamically generated controlled test atmosphere using the recommended sampling parameters. The concentration of H 2 O 2 in the test atmosphere was the target concentration (1.07 ppm or 1.49 mg/m^3 ), and the relative humidity was 9.0% at 21 C. Nine storage samples were prepared. Three samples were analyzed on the day of generation. Six samples were stored on a lab bench at ambient temperature (about 21 C) with no protection from light exposure. At 7 day intervals three samples were selected and analyzed. Sample results are not corrected for extraction efficiency.
A low humidity test, with samplers exposed to light during storage, was performed by sampling a dynamically generated controlled test atmosphere using the recommended sampling parameters. The concentration of H 2 O 2 in the test atmosphere was the target concentration (1.05 ppm or 1.46 mg/m^3 ), and the relative humidity was 9.6% at 21 C. Nine storage samples were prepared. Three samples were analyzed on the day of generation. Six samples were stored in a drawer at ambient temperature (about 21 C) but were not covered. At 7 day intervals three samples were selected and analyzed. Sample results are not corrected for extraction efficiency.
As shown above there is a reduction in recoveries when samples are exposed to light during storage, but when carefully protected the samples are stable. Based on these results it is recommended that samples be wrapped in aluminum foil after sampling. Sampling at low humidity did not affect storage stability.
4.5 Precision (overall procedure)
The precision of the overall procedure at the 95% confidence level is obtained by multiplying the overall standard error of estimate by 1.96 (the z-statistic from the standard normal distribution at the 95% confidence level). Ninety-five percent confidence intervals are drawn about the regression lines in the storage stability figure shown in Section 4.4.
The precision of the overall procedure at the 95% confidence level for the 18-day storage test (at the target concentration) is 11.4%. It was obtained from the overall standard error of estimate (5.84%) of the data shown in Figure 4.4.1. It contains an additional 5% for sampling pump error.
Table 4.4. Low Humidity Ambient Storage Test for H 2 O 2 with Samples Protected from Light time (days)
storage recovery (%) 0 7 14
Table 4.4. 3 Low Humidity Ambient Storage Test for H 2 O 2 with Samples Exposed to Light (Bench Top Storage) time (days)
storage recovery (%) 0 7 14
Table 4.4. Low Humidity Ambient Storage Test for H 2 O 2 with Samples Exposed to Light (Drawer Storage) time (days)
storage recovery (%) 0 7 14
The recovery of H 2 O 2 from samples used in an 18-day storage test remained above 99.2% when stored at 21 C and protected from light exposure.
4.6 Reproducibility
Six samples were prepared by sampling a dynamically generated controlled test atmosphere similar to that used in the collection of the storage samples. The concentration of H 2 O 2 in the test atmosphere was the target concentration (0.996 ppm or 1.38 mg/m^3 ), and the relative humidity was 79% at 22 °C. The samples were submitted to the OSHA Salt Lake Technical Center for analysis. The samples were analyzed after being stored for 30 days at 21 °C. No sample result for H 2 O 2 had a deviation greater than the precision of the overall procedure determined in Section 4.5.
4.7 Sampler capacity
Sampler capacity was tested by sampling a dynamically generated controlled test atmosphere containing H 2 O 2 at two times the target concentration (2.03 ppm or 2.83 mg/m^3 ) and 80% relative humidity at 22 °C. The samples were collected at 1 L/min. A second sampler was placed in a sampling train behind the first sampler. The percentage of the amount found on the second sampler in relation to the concentration of the test atmosphere was defined as breakthrough. There was no significant (˂5%) breakthrough observed after 538 min of testing. This is equivalent to an air volume of 538 L. The recommended air volume for sampling at 1 L/min is 240 L.
Sampler capacity was also tested by sampling a dynamically generated controlled test atmosphere containing H 2 O 2 at two times the target concentration (2.11 ppm or 2.94 mg/m^3 ) and 81% relative humidity at 21 °C. The samples were collected at 2 L/min. A second sampler was placed in a sampling train behind the first sampler. There was no significant (˂5%) breakthrough observed after 330 min of testing. This is equivalent to an air volume of 660 L. The recommended air volume for sampling at 2 L/min is 240 L.
4.8 Extraction efficiency and stability of extracted samples
The extraction efficiency is affected by the extraction solution, the sampling medium, and the technique used to extract the samples. Other reagents and techniques than described in this method can be used provided they are tested as specified in the validation guidelines.^12
Extraction efficiency
The extraction efficiency was determined by liquid-spiking four samplers at each concentration level with H 2 O 2. These samples were stored overnight at ambient temperature and then analyzed. The overall mean extraction efficiency, over the working range of 0.1 to 2 times the target concentration, was 99.3%. The extraction efficiency at the RQL was 99.8%. The presence of water had no significant effect on extraction efficiency. The extraction efficiencies
(^12) Eide, M.; Simmons, M.; Hendricks, W. Validation Guidelines for Air Sampling Methods Utilizing Chromatographic Analysis, 2010. United States Department of Labor, Occupational Safety & Health Administration Web site. http://www.osha.gov/dts/sltc/methods/chromguide/chromguide.pdf (accessed December 2013).
Table 4. Reproducibility Data for H 2 O 2 theoretical (μg/sample)
recovered (μg/sample)
recovery (%)
deviation (%) 339 325 322 326 335 326
311 302 296 304 316 307
Low humidity
The effect of low humidity was tested by sampling a dynamically generated controlled test atmosphere containing two times the target concentration (2.10 ppm or 2.92 mg/m^3 ) of H 2 O 2 at 18% relative humidity and 22 C. The test atmosphere was sampled with three samplers at 1 L/min for 240 min. All of the samples were immediately analyzed. Sample results were 99.0%, 99.2%, and 100.1% of theoretical.
Low concentration
The effect of low concentration was tested by sampling a dynamically generated controlled test atmosphere containing 0.1 times the target concentration (0.0993 ppm or 0.138 mg/m^3 ) of H 2 O 2 at 79% relative humidity and 22 C. The test atmosphere was sampled with three samplers at 1 L/min for 240 min. All of the samples were immediately analyzed. Sample results were 99.3%, 101.0%, and 102.7% of theoretical.
Chemical interference
The effect of a potential chemical sampling interference was tested by sampling dynamically generated controlled test atmospheres containing H 2 O 2 and peracetic acid (PAA). The PAA solution used to generate the test atmospheres was a 39.2% PAA solution (with 4.9% H 2 O 2 , 42.3% acetic acid, and water) purchased from Sigma Aldrich (product no. 77240). The H 2 O 2 of this solution was titrated and the concentration verified. The PAA solution was injected directly into the test atmosphere without dilution to avoid changing the equilibrium concentration of the solution. Three test atmospheres were generated, each with a temperature of 21 C at 9% relative humidity, and sampled with three samples at 1 L/min for 240 min. All samples were immediately analyzed and the data obtained are shown in Table 4.9.2. Results show that above an air concentration of 2 ppm PAA the interference becomes significant. At levels less than 1 ppm PAA, and at the ACGIH TLV-STEL of 0.4 ppm^13 , the interference is not significant.
Potassium permanganate and potassium iodide can interfere with the analysis of H 2 O 2.^14 See Christensen et al. for other potential interferences tested when sampling H 2 O 2 with glass filters impregnated with titanium tetrachloride / sulfuric acid. 15
4.10 Short-term sampling
Short-term sampling was tested by sampling a dynamically generated controlled test atmosphere containing H 2 O 2 at the target concentration (1.00 ppm or 1.40 mg/m^3 ) and 80% relative humidity at 21 °C. The test atmosphere was sampled with three samplers at 2 L/min for 15 min. All of the samples were immediately analyzed. Sample results were 104%, 103%, and 108% of theoretical.
(^13) American Conference of Governmental Industrial Hygienists, Inc. Documentation of the Threshold Limit Values and Biological
14 Exposure Indices ; Cincinnati, OH, 2015; pp. Peracetic Acid^ –^ 1 through Peracetic Acid^ –^ 5. Hydrogen Peroxide (OSHA Method ID-126-SG). United States Department of Labor, Occupational Safety and Health Administration Web site. http://www.osha.gov/dts/sltc/methods/partial/t-id126sg-pv-01-0201-m/t-id126sg-pv-01-0201-m.html
15 (accessed May 2015). Christensen, C. S.; Brødsgaard, S.; Mortensen, P.; Egmose, K.; Linde, S. A. Determination of hydrogen peroxide in workplace air: interferences and method validation. J. Environ. Monit., 2000 , 2 , pp 339-343.
Table 4.9. Interference of PAA on H 2 O 2 recovery of H 2 O 2 (%) PAA / H 2 O 2 test atmosphere concn 1 2 3 mean 1.03 ppm PAA, 0.29 ppm H 2 O 2 105.0 10 1.9 10 1.7 10 2. 1.95 ppm PAA, 0.54 ppm H 2 O 2 1 10.7 110.6 109.7 1 10. 3.93 ppm PAA, 1.10 ppm H 2 O 2 128.9 127.7 125.7 127.
4.11 Hydrogen peroxide standard
The H 2 O 2 solution used in this evaluation was:
≥30% T race SELECT Ultra, for ultratrace analysis, purchased from Sigma Aldrich (product no. 16911, lot no. 05735JH).
The solution was received at SLTC on 4/4/2014. The manufacturer certificate of analysis reported a quality release data of 8/12/2013, a recommended retest date of 1/2017, and a certified concentration of 30.8%. The manufacturer recommended storage of the solution at 2- 8 °C in the dark. During use of this solution it was periodically titrated using a standardized potassium permanganate solution (1 N) and the results are shown in Table 4.11.
Table 4. Titration Results of H 2 O 2 solution Used in this Evaluation test data titration result (%)
vs manufacturer (%) 4/23/2014 31.5 102. 5/1/2014 31.2 101. 9/3/2014 31.5 102. 11/19/ 2014 31 .3 101. 3/11/2015 31.6 102.
Based on these results the concentration listed on the certificate of analysis can be used, and periodic standardization of the solution is not necessary if stored as specified by the manufacturer.
4.12 Cassette wall test
To test the need for an interior wall wipe six cassettes were spiked with 333.3 μg H 2 O 2 ( μL of a 13.33 mg/mL H 2 O 2 solution). For three samples the spike was deposited directly on the titanium oxysulfate coated quartz filter and for the other three the spike was placed on the top (inlet side) of the interior wall. The cassettes were reassembled and stored inlet side down overnight. All six samples were analyzed, without wiping the cassette wall, and the data obtained are shown in Table 4.12. Results demonstrate that the H 2 O 2 had evaporated off the cassette wall and reacted with the titanium oxysulfate coated quartz filter. Wiping of the interior walls is not necessary.
Table 4. Recovery of H 2 O 2 from Spiked Cassette Walls recovery (%) set 1 2 3 mean wall spike 94.8 94.2 94.7 94. filter spike 96.9 96.7 97.0 96.
wall/filter 97.
