Peroxides (peracetic acid and hydrogen peroxide)

Transcription

1 1 Peroxides (peracetic acid and hydrogen peroxide) Method number 1 Application Air analysis Analytical principle High performance liquid chromatography (HPLC) Completed in May 2011 Summary The analytical method described here permits determination of the exposure at the workplace to peracetic acid and hydrogen peroxide that are released during activities that involve the use of disinfectants containing peracetic acid. Peracetic acid and hydrogen peroxide can be determined together in concentrations ranging from 0.08 to 1.7 mg/m 3.Based on the maximum workplace concentration (MAK value) for hydrogen peroxide proposed by the Deutsche Forschungsgemeinschaft (DFG), concentrations from aninth to twice the limit value can be determined [1]. For sampling a suitable pump draws ambient air through an impinger filled with water. Immediately after sampling, methyl-p-tolyl sulphide and a buffer solution are added to an aliquot of the absorption solution, and the sample is left to react in the dark for 10 minutes. Then triphenylphosphine is added to the sample as a reagent. The absorbed peracetic acid oxidises the methyl-p-tolyl sulphide to the corresponding sulphoxide and in the following reaction the hydrogen peroxide reacts with triphenylphosphine to form the stable compound triphenylphosphine oxide. The two oxides obtained are separated by means of high performance liquid chromatography (HPLC) and detected by photometry with a diode array detector (DAD). The quantitative determination is based on calibration curves of a reference standard containing defined masses of peracetic acid and hydrogen peroxide. Characteristics of the method Precision: Peracetic acid Repeatability: Standard deviation (rel.): s=1.3% Expanded uncertainty: U =3.5% at aconcentration of 1.27 μg/ml or 0.61 mg/m 3 and for n=6 determinations The MAK-Collection Part III, Air Monitoring Methods 2013 DFG, Deutsche Forschungsgemeinschaft 2013 Wiley-VCH Verlag GmbH & Co. KGaA

2 2 Analytic Methods Reproducibility: Standard deviation (rel.): s =4.5% Expanded uncertainty: U =11% at aconcentration of 2.1 μg/ml or 1.0 mg/m 3 and for n=6 determinations Hydrogen peroxide Repeatability: Standard deviation (rel.): s =0.4% Expanded uncertainty: U =2.7% at aconcentration of 1.18 μg/ml or 0.5 mg/m 3 and for n=6 determinations Reproducibility: Standard deviation (rel.): s =8.3% Expanded uncertainty: U =9% at aconcentration of 2.1 μg/ml or 0.84 mg/m 3 and for n=6 determinations Limit of quantification: Peracetic acid Absolute: 1.5 ng equivalent to 0.07 mg/m 3 at an air sample volume of 83 L Hydrogen peroxide Absolute: 2.0 ng equivalent to 0.08 mg/m 3 at an air sample volume of 83 L Recovery: Peracetic acid η = 0.84 (84%) at asampling duration of 1h η= 1.0 (100%) at asampling duration of 15 min Hydrogen peroxide η =1.0 (100%) Sampling recommendation: Sampling duration: 1h Air sample volume: 83 L For short-term measurements: 15 min, 21 L Description of the substances Peracetic acid [CAS No ] CH 3 CO OOH Synonyms: Peroxyacetic acid Ethaneperoxoic acid 1mL/m 3 (ppm) ¼b 3.16 mg/m 3 Peracetic acid (PAA) is a colourless liquid with a pungent odour (molar mass g/mol, boiling point 105 C (40% solution in glacial acetic acid), melting point 0.1 C, vapour pressure hpa at 20 C). It is astrongly oxidising organic acid with marked bactericidal, fungicidal and virucidal effects. It is completely miscible with water. PAA exists only in an equilibrium between acetic acid and hydro-

3 Peroxides 3 gen peroxide. Whereas concentrated solutions are relatively stable, dilution, temperature increases and impurities cause it to decompose. PAA is used as asterilisation agent and disinfectant, normally in 0.03 to 2% solution. In the List of MAK and BAT Values peracetic acid is classified in Carcinogen Category 3B [1]. Detailed information on the toxicity of peracetic acid is found in the MAK Value Documentations [2]. Hydrogen peroxide [CAS No ] HOOH Synonyms: Perhydrol Hydrogen superoxide Dihydrogen dioxide 1mL/m 3 (ppm) ¼b 1.4 mg/m 3 Hydrogen peroxide (H 2 O 2 )isacolourless liquid with aslightly pungent odour (molar mass g/mol, melting range 0.04 to 43 C, boiling range 150 to 152 C at 1013 hpa, vapour pressure 3hPa at 25 C and 6.6 hpa at 30 C). Hydrogen peroxide is widely used. Highly concentrated solutions can spontaneously decompose causing explosions: for this reason at most 35% solutions in water are commercially available. Concentrations up to 50% of hydrogen peroxide in water are available for industrial use. Hydrogen peroxide mainly serves as a bleaching agent in the textile, paper, and cellulose industries. In addition, it is used as ableaching agent in food and in cosmetics as well as for synthesis and for disinfection [3]. The currently valid MAK value for hydrogen peroxide is 0.7 mg/m 3 (0.5 ml/m 3 ) [1]. The short-term exposure value is assigned to Peak Limit Category I with an excursion factor of 1 in the List of MAK and BAT Values [1]. Detailed information on the toxicity of hydrogen peroxide is found in the MAK Value Documentations [4]. Author: C. Schuh Examiner: R. Hebisch

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5 Peroxides 5 Peroxides (peracetic acid and hydrogen peroxide) Method number 1 Application Air analysis Analytical principle High performance liquid chromatography (HPLC) Completed in May 2011 Contents 1 General principles 2 Equipment, chemicals and solutions 2.1 Equipment 2.2 Chemicals 2.3 Solutions 2.4 Reference standards 2.5 Calibration standards 3 Sampling and sample preparation 3.1 Sampling 3.2 Sample preparation 4 Operating conditions for chromatography 5 Analytical determination 6 Calibration 7 Calculation of the analytical result 8 Reliability of the method 8.1 Precision 8.2 Accuracy 8.3 Expanded uncertainty of the entire procedure 8.4 Limit of quantification 8.5 Storage stability 8.6 Interference 8.7 Blank values 9 Discussion

6 6 Analytic Methods 1 General principles For sampling a suitable pump draws peracetic acid and hydrogen peroxide through an impinger filled with water. Immediately after sampling is complete, methyl-p-tolyl sulphide and a buffer solution are added to an aliquot of the absorption solution,and the sample is left to react in the dark for 10 minutes. Then triphenylphosphine is added to the sample as a reagent.in this reaction the absorbedperaceticacidoxidises the methyl-p-tolylsulphide tothe corresponding sulphoxide, while hydrogenperoxide reacts with triphenylphosphine to form the stable compound triphenylphosphine oxide. The two oxides are then separated by means of liquid chromatography and quantified with a diode array detector [4]. The calibration is carried out by analysing calibration standards in the same manner as the samples to be tested. 2 Equipment, chemicals and solutions 2.1 Equipment Pump for personal sampling, flow rate 83 L/h Gas meter or volumetric flow meter (e.g. DryCal DC-1, DEHA Haan & Wittmer, Heimsheim, Germany) Ultrasonic bath Analytical balance High performance liquid chromatograph with DAD (e.g. Agilent HP1100) Column (e.g. Nucleosil C8, Macherey&Nagel, Düren, Germany) Volumetric flasks 10, 50, 100 and 200 ml Erlenmeyer flasks, 100 ml Burettes, 25 ml Automatic piston pipette (e.g. Multipette pro (from 1 μl to 10 ml) Eppendorf, Hamburg, Germany) Measuring cylinder, 100 ml Spatula, funnel SKC midget impinger with frit insert (25 ml) from Analyt MTC, Müllheim, Germany, Article No Impinger holder Sample vials for autosampler: amber glass and sealable, nominal volume 2mL Climatic chamber Laboratory refrigerator

7 Peroxides 7 Whole-body exposure chamber with metering pump 80 LTedlar gas sack 2.2 Chemicals Acetonitrile, gradient grade (e.g. from Merck, Darmstadt, Germany) Water for chromatography Distilled water Disodium hydrogen phosphate (e.g. from Merck) Sodium dihydrogen phosphate monohydrate (e.g. from Merck) Triphenylphosphine (Sigma-Aldrich, Taufkirchen, Germany) Methyl-p-tolyl sulphide (e.g. from Sigma-Aldrich) Methyl-p-tolyl sulphoxide, 97% (e.g. from Sigma-Aldrich) Triphenylphosphine oxide, 98% (e.g. from Sigma-Aldrich) P3 Oxonia Active 150 (Ecolab, Düsseldorf, Germany) (content approx. 18% of hydrogen peroxide and approx. 18% of peracetic acid) as a reference standard 0.01 Npotassium permanganate solution (Titrosol) (e.g. from Merck) Sulphuric acid, 25% Starch solution, p.a. (e.g. from Merck) 0.01 NSodium thiosulphate solution (Titrosol) (e.g. from Merck) Potassium iodide (e.g. from Merck) 2.3 Solutions Reagent Solution I: MTS solution (4 mm) 270 μl of methyl-p-tolyl sulphide are pipetted into a 100 ml volumetric flask, the flask is then filled to the mark with acetonitrile and shaken. This stock solution is subsequently diluted in the ratio of 1:5 with acetonitrile. For example, 2000 μl of the stock solution are pipetted into a10mlvolumetric flask, the flask is then filled to the mark with acetonitrile and shaken. Reagent Solution II: TPP solution (1 mm) 130 mg of triphenylphosphine are weighed in a 100 ml volumetric flask, the flask is then filled to the mark with acetonitrile and shaken. This stock solution is subse-

8 8 Analytic Methods quently diluted in the ratio of 1:5 with acetonitrile. For example, 2000 μl of the stock solution are pipetted into a 10 ml volumetric flask, the flask is then filled to the mark with acetonitrile and shaken. Buffer solution: 1.42 g of disodium hydrogen phosphate and 21 mg of sodium dihydrogen phosphate monohydrate are dissolved in 100 ml of water for chromatography. 1% Aqueous starch solution: 0.1 g of starch is weighed in a 10 ml volumetric flask and dissolved in several ml of distilled water. The volumetric flask is then filled to the mark with distilled water and shaken. 2.4 Reference standards Reference Stock Solution I: 1 ml of P3 Oxonia Active 150 is pipetted into a 200 ml volumetric flask. The flask is then filled to the mark with distilled water and shaken (concentrations: approx. 900 mg/l each of peracetic acid and hydrogen peroxide). Reference Stock Solution II: 1 ml of Reference Stock Solution I is pipetted into a 50 ml volumetric flask. The flask is then filled to the mark with distilled water and shaken (concentrations: approx. 18 mg/l each of peracetic acid and hydrogen peroxide). Reference Standard I: 250 μl ofdistilled water and 100 μl ofbuffer solution are placed in an amber glass 2 ml autosampler vial, then 50 μl of Reference Stock Solution II are added with a pipette and the vial is shaken. Then 100 μl ofreagent Solution Iare added to the solution. After a reaction time of 10 minutes, 500 μl of Reagent Solution II are added. The target concentrations of the prepared sample solution are approx. 0.9 mg/l of peracetic acid and 0.9 mg/l of hydrogen peroxide. Reference Standard II: 150 μl ofdistilled water and 100 μl ofbuffer solution are placed in an amber glass 2 ml autosampler vial, then 150 μl of Reference Stock Solution II are added with a pipette and the vial is shaken. Then 100 μl of Reagent Solution I are added to the solution. After areaction time of 10 minutes, 500 μl ofreagent Solution II are added.

9 Peroxides 9 The target concentrations of the prepared sample solution are approx. 2.7 mg/l of peracetic acid and 2.7 mg/l of hydrogen peroxide. Two blanks, each containing 300 μl of distilled water and 100 μl of buffer solution, are prepared in the same manner as the reference standards in amber glass 2 ml autosampler vials. The exact content of peroxides in the P3 Oxonia Active 150 solution is determined by titration as follows: The P3 Oxonia Active 150 solution used as areference standard is diluted in the ratio of 1: μl of this solution are pipetted into a 100 ml volumetric flask. The volumetric flask is then filled to the mark with distilled water and shaken. 25 ml of this dilute P3 Oxonia Active 150 solution are transferred to a100 ml Erlenmeyer flask and 20 ml of 25% sulphuric acid are added. Then this solution is titrated with a 0.01 N potassium permanganate solution until the solution turns slightly pink. The sample must be discarded if overtitration has occurred. Then the following steps must be carried out immediately: Apinch of potassium iodide (i.e. enough to fit on the tip of aspatula) and 2mL of the 1% starch solution are added to the slightly pink titrated solution and then immediately titrated with a 0.01 N sodium thiosulphate solution until the blue coloration disappears. In addition, a blank (distilled water) is analysed by titration in the same manner as the sample solution. The contents of hydrogen peroxide and peracetic acid in the P3 Oxonia Active 150 solution are then determined, taking the following relationship into account: 1 ml of 0.01 N potassium permanganate solution is equivalent to 6.8 mg/l of hydrogen peroxide. 1 ml of 0.01 N sodium thiosulphate solution is equivalent to 15.2 mg/l of peracetic acid. The resulting contents of hydrogen peroxide and peracetic acid are multiplied by the dilution factor of 1000 and then the blank values are subtracted. The exact concentrations of peracetic acid and hydrogen peroxide in the original P3 Oxonia Active 150 solution in %by weight are obtained by dividing the concentrations by the factor 10, Calibration standards Stock solution: 2mgofMTSO and 10 mg of TPPO/mL acetonitrile 20 mg of methyl-p-tolyl sulphoxide (MTSO) and 100 mg of triphenylphosphine oxide (TPPO) are weighed into a 10 ml volumetric flask. The flask is then filled to the mark with acetonitrile and shaken. The exact contents are documented. The purity of the calibration standards must be taken into account when the concentrations are calculated.

10 10 Analytic Methods The calibration standards used for calibration are prepared in 50 ml volumetric flasks. For this purpose approx. 30 ml of the solvent (60% acetonitrile and 40% distilled water) are placed in each 50 ml volumetric flask. Then the volumes of the stock solution defined in the pipetting scheme shown in Table 1(5, 25, 45, 65, 85, 105, 125, 145, 165 and 185 μl) are pipetted into the volumetric flasks, which are then filled to the mark with the solvent and shaken. The calibration standards must be kept cool and dark (e.g. in the laboratory refrigerator) until analysis by HPLC. Table 1 Pipetting scheme for the preparation of the calibration standards Calibration standard No. Volume of the stock solution [μl] Final volume of the calibration solution [ml] Concentration of peracetic acid in the solution [mg/l] Concentration of hydrogen peroxide in the solution [mg/l] The contents of peracetic acid (PAA) and hydrogen peroxide (H 2 O 2 )are calculated via the ratios of the molar masses (M) of the peroxides to the oxides that are formed. M MTSO = g/mol M TPPO = g/mol M PAA =76.04 g/mol M H2 O 2 =34.02 g/mol Example: At apurity of 97% and 98% respectively, 20 mg of MTSO and 100 mg of TPPO (dissolved in 10 ml of acetonitrile) are equivalent to a concentration of 1.94 mg/ ml of MTSO and 9.8 mg/ml of TPPO. In Calibration Standard I(5 μl/50 ml) the content of MTSO is μg/ml and the content of TPPO is 0.98 μg/ml. When these concentrations of peracetic acid and hydrogen peroxide are calculated for this standard, the following contents are obtained: μg/ml of peracetic acid and 0.12 μg/ml of hydrogen peroxide.

11 Peroxides 11 3 Sampling and sample preparation 3.1 Sampling 10 ml of distilled water are placed in amidget impinger, whereby only one impinger is required for sampling. Sampling can be carried out as stationary or personal sampling. For sampling a flow-regulated pump draws ambient air at a flow rate of 1.38 L/min through the impinger. The sampling duration can be 15 minutes (to check the short-term values) or 1hour. As the samples are not stable, they must be prepared on the spot within 15 minutes after sampling is complete. 3.2 Samplepreparation Duplicate determinations are always performed. Aliquots of the sample solution are taken from the impinger for sample preparation. For this purpose 300 μl ofthe sample solution are placed in a2ml amber glass autosampler vial, 100 μl of the buffer solution and 100 μl of Reagent Solution I(MTS) are added and then the mixture is allowed to stand for 10 min in the dark. 500 μl of Reagent Solution II (TPP) is subsequently added and the sample is allowed to react while being kept cool in the dark for at least 30 min (e.g. in acool box). If stored in acool dark place (e.g. in the refrigerator), samples are stable for up to 14 days. Each sample series must include a blank sample (field blank), i.e. instead of 300 μl of sample solution, 300 μl of distilled water are subjected to the same sample preparation on the spot. 4 Operating conditions for chromatography The analytical measurements are performed with a combination of instruments comprising an HPLC system with a binary pump, column oven, degasser and autosampler, as well as adiode array detector (DAD). Note: The method can also be carried out with auvdetector at 225 nm.

12 12 Analytic Methods Apparatus: High performance liquid chromatograph with DAD, e.g. Agilent HP1100 Separation Column: Material: Stainless steel Length: 70 mm Inner diameter: 3mm Column packing: Nucleosil C8 Particle size: 5 μm Detector: Diode array detector (DAD) Column temperature: 20 C Mobile phase: Eluent A: Acetonitrile, gradient grade Eluent B: Water for chromatography Gradient: See Table 2 Flow rate: 1mL/min Injection volume: 10 μl Measurement wavelength: 225 nm; Reference wavelength 360 nm Table 2 Time [min] Gradient program of the binary pump Eluent A %byvolume Eluent B %byvolume Figure 1shows achromatogram of asample solution obtained under the conditions stated above. Under these conditions MTSO from peracetic acid elutes after 0.75 minutes and TPPO from hydrogen peroxide after 1.9 minutes. The reagents used, MTS and TPP, elute after 2.5 and 4.6 minutes respectively. 5 Analytical determination In order to analyse the samples prepared as described in Section 3.2, 10 μl ofthe samples are injected into the high performance liquid chromatograph and analysed under the operating conditions stated in Section 4. If the measured concentrations are above the calibration range, then suitable dilutions must be prepared

13 Peroxides 13 Peak number Retention time [min] Substance [CAS Number] Methyl-p-tolyl sulphoxide [ ] Triphenylphosphine oxide (TPPO) [ ] Methyl-p-tolyl sulphide [ ] Triphenylphosphine [ ] Fig. 1 Example of achromatogram for the liquid chromatographic separation ofastandard (cf. Section 4for the chromatographic conditions) and the analysis must be repeated. Furthermore, the prepared blank (field blank) must be analysed in the same manner as the samples. In addition to the samples, two reference standards and their blanks (chemical blanks) (see Section 2.4) are included in each analytical series to check the retention times and the calibration curves. The mean values of the chemical blanks must be taken into account for the reference standards. The peaks in the chromatograms are identified by the retention times of the reference standards. Note: Before each analysis, the exact content of the peroxides PAA and H 2 O 2 in the P3 Oxonia Active 150 solution must be determined by titration (see Section 2.4). 6 Calibration The calibration standards described in Section 2.5 are analysed by means of high performance liquid chromatography and used to obtain the calibration functions. For this purpose 10 μl ofeach calibration standard are injected into the HPLC and analysed in the same manner as the sample solutions. The peak areas obtained are plotted versus the corresponding concentrations, and the calibration functions for hydrogen peroxide and peracetic acid are calculated. The calibration curves are linear in the investigated concentration ranges. The calibration curves for peracetic acid and hydrogen peroxide are shown in Figures 2and 3. At least one control

14 14 Analytic Methods Fig. 2 Graph of the calibration function for quantitative determination of peracetic acid (PAA) in the concentration range from 0.1 to 3.5 μg/ml Fig. 3 Graph of the calibration function for quantitative determination ofhydrogen peroxide in the concentration range from 0.1 to 4.4 μg/ml

15 Peroxides 15 sample with achemical blank must be analysed each working day to check the calibration functions. The calibration must be performed anew if the analytical conditions change or the quality control results indicate that this is necessary. 7 Calculation of the analytical result The concentration of peracetic acid and hydrogen peroxide in the workplace air is calculated by the data analysis system from the concentration of the substances in the measured solution. For this purpose the data analysis system uses the calculated calibration functions obtained from the calibration. The concentrations of peracetic acid and hydrogen peroxide in the workplace air are calculated from the concentrations, taking the dilutions and the air sample volume into account. The concentration by weight () ofthe two peroxides in the air sample in mg/m 3 is calculated using equation (1): ¼ ðm m Blank ÞE MV Air ð1þ where is the concentration by weight of peracetic acid (PAA) or hydrogen peroxide (H 2 O 2 )inthe ambient air in mg/m 3 m is the mean mass of peracetic acid (PAA) or hydrogen peroxide (H 2 O 2 )in the sample solution in μg m Blank is the mean mass of the blank value (field blank) of peracetic acid (PAA) or hydrogen peroxide (H 2 O 2 )inthe sample solution in μg E is the absorption mass in the impinger in ml (target volume 10) M is the sample volume in ml (target volume 0.3) η is the recovery V Air is the air sample volume in L(calculated from the flow rate and the sampling duration; 1.38 L/min 60min =83L) 8 Reliability of the method The characteristics of the method were calculated as stipulated in EN 482 [6] and DIN [7].

16 16 Analytic Methods 8.1 Precision The reproducibilities were determined in awhole-body exposure chamber. For this purpose 35% aqueous peracetic acid, 36% aqueous hydrogen peroxide solution and a disinfectant mixture composed of approx. 16% each of peracetic acid and hydrogen peroxide were continuously evaporated in several tests. Between 2 and 4 ml of peroxide solution per hour were dosed by a metering pump. Then the mixture was evaporated at a temperature of 60 C and passed with a gas flow of 14 m 3 /h into achamber with avolume of 1.4 m 3.The target concentrations in the chamber were between 0.9 and 1.9 mg/m 3 for peracetic acid and in the range of 0.9 to 2.8 mg/m 3 for hydrogen peroxide. 6samples per concentration were taken with asampling duration of one hour, and 6with asampling duration of 15 minutes. In order to check the breakthrough rates, two impingers were connected in series and the solutions were subsequently prepared separately. As the efficiency of the chamber was between 50 and 76% for hydrogen peroxide, hydrogen peroxide was additionally determined by means of photometry [8]. The content of H 2 O 2 obtained in this manner was taken as the reference value. There was 100% recovery of peracetic acid when its aqueous solution was evaporated. In contrast, the efficiency of the chamber was approx. 84% when the aqueous disinfectant mixture was evaporated. The reproducibilities were at most 4.5% and 8.3% respectively for peracetic acid and hydrogen peroxide in all the tests. Hydrogen peroxide was not detected in the second impinger, therefore any breakthrough can be ruled out. The absorption of H 2 O 2 is complete in the first impinger. On average, 16% of the total concentration of peracetic acid was detected in the second impinger at a sampling time of one hour, regardless of its concentration. At a sampling duration of 15 minutes the content in the second impinger was always below the limit of quantification. The results are shown in Tables 3 and 4. Table 3 Standard deviation (rel.) and content in the 2nd impinger for n=6determinations of peracetic acid at asampling duration of one hour or 15 minutes Sampling time of 1h Sampling time of 15 minutes * Target concentration [mg/m 3 ] Actual concentration determined [mg/m 3 ] Standard deviation (rel.) [%] Content in 2nd impinger with respect to the total content [%] Actual concentration determined [mg/m 3 ] Standard deviation (rel.) [%] * The contents in the 2nd impinger were all below the limit ofquantification.

17 Peroxides 17 Table 4 Standard deviation (rel.) for n = 6determinations of hydrogen peroxide at asampling duration of one hour or 15 minutes Sampling duration of 1h Sampling duration of 15 minutes Target concentration [mg/m 3 ] Reference concentration * [mg/m 3 ] Actual concentration determined [mg/m 3 ] Standard deviation (rel.) [%] Reference concentration * [mg/m 3 ] Actual concentration determined [mg/m 3 ] Standard deviation (rel.) [%] * Determined by means of photometry [8] for n =6determinations The repeatability is 0.4% at a concentration of hydrogen peroxide of 1.18 μg/ml of the final solution and 1.3% for peracetic acid at a concentration of 1.27 μg/ml. The repeatability was determined for a prepared standard solution over a period of 6days. 8.2 Accuracy Several recovery experiments were carried out to test the accuracy of the method. Direct spiking The absorption solution of the impinger was directly spiked with disinfectant solution. Then air that did not contain disinfectant was drawn through the impinger. The recovery of the peroxides was 91% and 105% respectively at concentrations of 0.85 mg/m 3 of peracetic acid and 1.48 mg/m 3 of hydrogen peroxide and asampling time of 15 minutes. Spiking in agas sack Recovery experiments were performed in the climatic chamber to determine peracetic acid. For this purpose 6Tedlar gas sacks were each filled with 80 litres of nitrogen and brought to atemperature of 40 C for aperiod of 30 minutes. Acommercially available product containing peracetic acid was injected with a syringe. The concentration in the air was about 0.7 mg/m 3.The spiked gas sacks were stored at atemperature of 40 C in the climatic chamber for 1hour. Then sampling was carried out at 30 C with two impingers connected in series. Absorption solution (10 ml in each case) was directly spiked with the same masses of peroxide for the sake of comparison. The reagents were added to the samples and calibration solutions as described in Sections 3.2 and 5(asample quantity of 400 μlinstead of

18 18 Analytic Methods 300 μl), and they were analysed. The recovery in the 1st impinger was 84% for peracetic acid, whereby the content in the 2nd impinger was approx. 8%. The evaporation of hydrogen peroxide is not complete in the gas sack under these climatic conditions. No breakthrough of hydrogen peroxide occurred. At high concentrations of peracetic acid (5.3 mg/m 3 )11% of the total mass was detected in the second impinger. Exposure measurement At workplaces 11% of peracetic acid was detected in the 2nd impinger when sampling was carried out for one hour. The peracetic acid concentration in workplace air was 0.7 mg/m 3. Furthermore, hydrogen peroxide was measured with both procedures at workplaces. The measured results for asampling duration of one hour were 1.4 mg/m 3 for photometric determination and 1.3 mg/m 3 for determination by HPLC. Arelative recovery of η = 1.0 was obtained from recovery experiments for hydrogen peroxide. For peracetic acid the relative recovery is η = 0.84 when sampling is carried out for one hour and η =1.0 at asampling duration of 15 minutes. 8.3 Expanded uncertainty of the entire procedure All the relevant influencing factors are estimated to determine the uncertainty (bottom-up procedure) [6, 9]. The uncertainty of the entire procedure mainly consists of the following contributions of the analytical method: Uncertainty contribution of the air sample volume, Uncertainty contribution of the volumes of the absorption solution and the sample solution used for oxidation, Uncertainty contribution of the recoveries, as well as the factors influencing the measured values, in particular the scatter of the calibration graphs, uncertainty of the calibration points and the laboratory s own reproducibility (precision). The corresponding expanded uncertainties (U exp )that simultaneously represent the substance-dependent and concentration-dependent uncertainty of the entire procedure are obtained by multiplication with aprobability factor (e.g. k=2for 95% confidence level). All the determined uncertainty contributions are listed in Table 5, whereby depending on the calibration curve adifferentiation is made between high (Calibration Standard 9), medium (Calibration Standard 5) and low concentration (Calibration Standard 2) as well as between a sampling duration of 15 and of 60 minutes. The conversion to the air concentrations is shown in Table 6.

19 Peroxides 19 Table 5 Contributions to uncertainty Uofthe entire procedure in% Component U AV (60 min) U AV (15 min) U E-Abs U S U Rec Peracetic acid Hydrogen peroxide Component U Meas.value h U Meas.value m U Meas.value l U comb. h (60 min) U comb. m (60 min) Peracetic acid Hydrogen peroxide Component U comb. l (60 min) U comb. h (15 min) U comb. m (15 min) U comb. l (15 min) Peracetic acid Hydrogen peroxide Component U expanded m (60 min) U expanded l (60 min) U expanded h (15 min) U expanded m (15 min) Peracetic acid Hydrogen peroxide U expanded h (60 min) U expanded l (15 min) where U AV (60 min) U AV (15 min) U E-Abs U S U Rec U Meas.value h U Meas.value m U Meas.value l U comb. h U comb. m U comb. l U expanded h U expanded m U expanded l is the uncertainty of the air sample volume at asampling duration of 60 minutes is the uncertainty of the air sample volume at asampling duration of 15 minutes is the uncertainty of the volume of the absorption solution is the uncertainty of the sample solution used for oxidation is the uncertainty of the recovery is the uncertainty of the measured value at ahigh concentration (Calibration Standard 9) (includes precision and scatter of the calibration curve) is the uncertainty of the measured value at amedium concentration (Calibration Standard 5) is the uncertainty of the measured value at alow concentration (Calibration Standard 2) is the combined uncertainty at ahigh concentration is the combined uncertainty at amedium concentration is the combined uncertainty at alow concentration is the expanded uncertainty at a high concentration is the expanded uncertainty at a medium concentration is the expanded uncertainty at a low concentration

20 20 Analytic Methods Table 6 Air concentrations to determine the expanded uncertainties Air concentration [mg/m 3 ] Low Medium High PAA sampling duration 1h H 2 O 2 sampling duration 1h PAA sampling duration 15 min H 2 O 2 sampling duration 15 min Limit of quantification The limits of quantification were determined as stipulated in DIN [7] from the measured results of a 10-point calibration. Calibration standards with contents from 0.1 to 4.4 μg/ml of hydrogen peroxide and 0.1 to 3.54 μg/ml of peracetic acid were tested for this purpose. The limit of quantification was 0.20 mg/l for hydrogen peroxide and 0.15 mg/l for peracetic acid. Based on an air sample volume of 83 L, this is equivalent to arelative limit of quantification of 0.08 mg/m 3 for hydrogen peroxide and 0.07 mg/m 3 for peracetic acid. 8.5 Storagestability In order to check the storage stability, both air samples taken from atedlar gas sack (with concentrations of 2.1 or 3.9 μg/ml of peracetic acid and 0.7 or 1.75 μg/ ml of hydrogen peroxide) and also a reference standard of medium concentration (2.4 and 2.3 μg/ml respectively of peracetic acid and hydrogen peroxide; cf. Section 2.4) were tested. The samples were prepared as described in Section 3.2. Blanks were also prepared in the same manner as the samples. The prepared sample solutions, standards and blanks were analysed on the same day as well as after storage in the refrigerator for 15 days. No losses of peracetic acid or hydrogen peroxide could be ascertained. Storage stability over aperiod of 15 days is ensured. 8.6 Interference The analytical procedure by means of HPLC is specific under the conditions stated here. Interference by other components was not observed in the investigated working ranges.

21 Peroxides Blank values Blank values are also taken into account by means of the parallel processing of the prepared field blanks at the same time as the sample preparation. When selecting the reagents methyl-p-tolyl sulphide (MTS) and triphenylphosphine (TPP), it is important to ensure that they are p.a. grade. On principle, they must be checked for blank values before use. 9 Discussion The concentrations of peracetic acid and hydrogen peroxide in the workplace air can be selectively determined with the analytical method presented here. The procedure is suitable for monitoring the maximum workplace concentration for hydrogen peroxide proposed by the DFG (Deutsche Forschungsgemeinschaft). However, several points should be noted before carrying out the analysis. When selecting the reagents methyl-p-tolyl sulphide (MTS) and triphenylphosphine (TPP), it is important to ensure that they are p.a. grade. On principle, they must be checked for blank values before use. It has been shown that the use of TPP of lower quality, despite a purity of 99%, can lead to considerably elevated blank values and to distinctly poorer reproducibility. If hydrogen peroxide occurs alone in the workplace air, it can also be determined with the photometric procedure [8]. References 1 Deutsche Forschungsgemeinschaft (2013) List of MAK and BAT Values Commission for the Investigation of Health Hazards of Chemical Compounds inthe Work Area, Report No. 49, Wiley-VCH,Weinheim. 2 Greim H.(ed.) Peracetic acid. Occupational Toxicants: Critical Data Evaluation for MAK Values and Classification of Carcinogens, Volume 7: Wiley-VCH, Weinheim. 3 EU (European Union) (2003) Risk assessment report, hydrogen peroxide, Vol. 38, EU, Brüssel 4 Hartwig A.(ed.) Hydrogen peroxide. The MAK-Collection for Occupational Health and Safety, Part 1: MAK Value Documentations, Volume 26: Wiley-VCH, Weinheim. 5 Pinkernell U, Effkemann S, Karst U (1997) Simultaneous HPLC Determination of Peroxyacetic Acid and Hydrogen Peroxide. Anal. Chem. 69,

22 22 Analytic Methods 6 EN 482 (2012) Workplace atmospheres General requirements for the performance of procedures for the measurement of chemical agents. Beuth Verlag, Berlin. 7 DIN (2008) Chemical analysis Decision limit, detection limit and determination limit under repeatability conditions Terms, methods, evaluation. Beuth Verlag, Berlin. 8 Breuer D, Adelmann M (2001) Hydrogen Peroxide Method No. 1. In: Deutsche Forschungsgemeinschaft (Kettrup A, Greim H, eds.) Analyses of Hazardous Substances in Air, Volume 8: Wiley-VCH, Weinheim /topics 9 EN 1076 (2010) Workplace exposure Procedures for measuring gases and vapours using pumped samplers Requirements and test methods.beuth Verlag, Berlin Author: C. Schuh Examiner: R. Hebisch