Anal. Chem. 1998, 70, 3857-3862
Liquid Chromatographic Simultaneous Determination of Peroxycarboxylic Acids Using Postcolumn Derivatization S. Effkemann,† U. Pinkernell,† R. Neumu 1 ller,‡ F. Schwan,‡ H. Engelhardt,‡ and U. Karst*,†
Abteilung Analytische Chemie, Anorganisch-Chemisches Institut, Westfa¨ lische Wilhelms-Universita¨ t, Wilhelm-Klemm-Strasse 8, D-48149 Mu¨ nster, Germany, and Instrumentelle Analytik/Umweltanalytik, Universita¨ t des Saarlandes, Postfach 151 150, D-66041 Saarbru¨ cken, Germany
The first liquid chromatographic method with postcolumn derivatization for the simultaneous determination of peroxycarboxylic acids is described. Aliphatic peracids with chain lengths from C2 to C12 are separated by HPLC on a reversed-phase C18 column with acetonitrile/water gradient elution. For improved peak shape, tetrahydrofuran and acetic acid are added to the aqueous eluent. After chromatographic separation, the peroxycarboxylic acids react with 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonate, a popular substrate for the enzyme peroxidase. Iodide traces are added as catalyst. The oxidation product, a green radical cation, is determined using a UV/ visible detector in four characteristic regions of the visible and near-infrared spectrum in the range 405-815 nm. The advantages of the new method are detection limits in the low micromolar range, negligible matrix interferences, high reproducibility, and the possibility for simultaneous determination of several peroxycarboxylic acids. Peroxycarboxylic acids are important reagents in industrial and household bleaching, in disinfection in the food and beverages industries, and as oxidants in organic synthesis.1 The peroxycarboxylic acids are synthesized technically in aqueous solution by the reaction of carboxylic acids with hydrogen peroxide in the presence of sulfuric acid:2
Sulfuric acid serves as a catalyst to accelerate the formation of the peroxycarboxylic acids in aqueous solutions. Problems may arise in case of carboxylic acids with chain lengths of more than five C atoms. The very low solubility of these peroxycarboxylic acids in aqueous media decreases the reaction rate considerably. In ref 3, concentrated sulfuric acid is suggested as a suitable †
Westfa¨lische Wilhelms-Universita¨t. Universita¨t des Saarlandes. (1) Swern, D. Organic Peroxides; Wiley-Interscience: New York, 1970; p 360. (2) Boullion, G.; Lick, C.; Schank, K. In The Chemistry of Functional Groups, Peroxides; Patai, S., Ed.; John Wiley & Sons: London, 1983; pp 287-298. (3) Parker, W. E.; Ricciuti, C.; Ogg, C. L.; Swern, D. J. Am. Chem. Soc. 1955, 77, 4037-4042. ‡
S0003-2700(98)00256-X CCC: $15.00 Published on Web 08/14/1998
© 1998 American Chemical Society
solvent for carboxylic acids with chain lengths between C6 and C18. On one hand, concentrated sulfuric acid serves as a solvent for the carboxylic acids; on the other hand, it removes water from the right side of eq 1 to shift the equilibrium to the side of the peroxycarboxylic acid. A method for the in situ preparation of peroxycarboxylic acids in laundry detergents is the reaction of hydrogen peroxide with a bleach activator. In most cases, carboxylic acid esters or amides are used for this purpose.4 Significant differences concerning the nature of the formed peroxycarboxylic acids are observed between North American and European laundry detergents.5 In most European laundry detergents, peroxyacetic acid is formed as an active species. In contrast, long-chain peroxycarboxylic acids in the range between C7 and C12 are generated in many North American laundry detergents. Most analytical methods for the determination of peroxycarboxylic acids are based on the redox properties of these peroxides. An early approach to peroxyacetic acid (PAA) determination involves a two-step titration.6,7 D’Ans and Frey6 oxidized hydrogen peroxide with potassium permanganate in the first step. After addition of an excess of iodide and the oxidative formation of iodine by PAA, a thiosulfate titration provides indirect information on the PAA content in solution. This method is a convenient way to determine the concentration of both analytes quasi-simultaneously with no need of external calibration. However, its application is limited by high limits of detection and reproducibility problems.7 In the literature, several methods for the photometric determination of peroxycarboxylic acids have been described.8-15 (4) Hauthal, H. G.; Schmidt, H.; Scholz, H. J.; Hofmann, J.; Pritzkow, W. Tenside, Surfactants, Detergents 1990, 27, 187-193. (5) Kirk, O.; Damhus, T.; Christensen, M. W. J. Chromatogr. 1992, 606, 4953. (6) D’Ans, J.; Frey, W. Chem. Ber. 1912, 45, 1845. (7) Greenspan, F. P.; McKellar, D. G. Anal. Chem. 1948, 20, 1061-1063. (8) Frew, J. E.; Jones, P.; Scholes, G. Anal. Chim. Acta 1983, 155, 139-150. (9) Davies, D. M.; Deary, M. E. Analyst 1988, 113, 1477-1479. (10) Christner, J. E.; Lucchese, L. J. (Serim Research Corp.). WO 92/22806, 1992. (11) Kru ¨ ssmann, H.; Bohnen, J. Tenside, Surfactants, Detergents 1994, 31 (4), 229-232. (12) Mallard de la Varende, J.; Crisinel P. (L’Air Liquide S.A.). US 5 438 002, 1995. (13) Williams J. (Interox Chemicals Ltd.). EP 0 150 123, 1985. (14) Fischer, W.; Arlt, E.; Braba¨nder, B. (Merck Patent GmbH). DE 37 43 224, 1987; EP 322 631, 1988; US 4 900 682, 1988.
Analytical Chemistry, Vol. 70, No. 18, September 15, 1998 3857
Table 1. Preparation of the Peroxycarboxylic Acids in the Range C3-C12
n(carboxylic acid) (mmol) m(carboxylic acid) (mg) V(sulfuric acid) (µL) n(hydrogen peroxide) (mmol) V(hydrogen peroxide) (µL)
C3
C4
C5
C6
C7
C8
C9
C10
C12
1 74 125 1.5 146
1 88 125 1.5 146
1 102 125 1.5 146
2 232 464 3 291
2 260 464 3 291
1.5 216 324 2.25 219
1.5 237 300 2.25 219
1 172 430 1.5 146
1 200 600 1.5 146
Direct photometric determination of the peracids is not possible due to their UV absorption maxima at low wavelengths and small extinction coefficients. The photometric method described in ref 15 is based on the iodide-catalyzed selective oxidation of 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonate diammonium salt (ABTS) to a green radical cation by PAA or m-chloroperoxybenzoic acid (mCPBA).
The detection of the product can be performed at 405, 415, 649, 732, and 815 nm.15 Further methods for the determination of PAA include the use of electrochemical sensors16-19 and chromatographic methods.5,20-27 Recently, we have developed a method for the simultaneous determination of peroxyacetic acid and hydrogen peroxide.26 This method is based on the selective oxidation of methyl p-tolylsulfide (MTS) to the corresponding sulfoxide (MTSO) by PAA. In a second step, triphenylphosphine is oxidized to the corresponding phosphine oxide by hydrogen peroxide. All four compounds can be separated easily using HPLC with UV detection. MTSO and triphenylphosphine oxide are commercially available and can be used for external calibration. Unfortunately, the HPLC and photometric methods described above do not allow a specification of the peroxycarboxylic acids in the range from C2 to C12. If several peroxycarboxylic acids occur in combination, only a sum parameter for these substances is obtained. (15) Pinkernell, U.; Lu ¨ ke, H.-J.; Karst, U. Analyst 1997, 122, 567-571. (16) Birch, B. J.; Marshman C. E. (Unilever NV). EP 0 333 246, 1989. (17) Pinkowski, A. (ProMinent Dosiertechnik GmbH). US 5 395 493, 1995. (18) Teske, G. (Dr. Thiedig & Co.). US 5 503 720, 1996. (19) Kaden, H.; Herrmann S. (Forschungsinstitut “Kurt Schwabe” Meinsberg). DE 43 19 002, 1995. (20) Cairns, G. T.; Ruiz Diaz, R.; Selby, K.; Waddington, D. J. J. Chromatogr. 1975, 103, 381-384. (21) Di Furia, F.; Prato, M.; Scorrano, G.; Stivanello, M. Analyst 1988, 113, 793795. (22) Di Furia, F.; Prato, M.; Quintly, U.; Salvagno, S.; Scorrano G. Analyst 1984, 109, 985-987. (23) Baj, S. Fresenius J. Anal. Chem. 1994, 350, 159-161. (24) Pinkernell, U.; Karst, U.; Cammann, K. Anal. Chem. 1994, 66, 2599-2602. (25) Pinkernell, U.; Effkemann, S.; Nitzsche, F.; Karst, U. J. Chromatogr. A 1996, 730, 203-208. (26) Pinkernell, U.; Effkemann, S.; Karst, U. Anal. Chem. 1997, 69, 3623-3627. (27) Effkemann, S.; Pinkernell, U.; Karst, U. Anal. Chim. Acta 1998, 363, 97103.
3858 Analytical Chemistry, Vol. 70, No. 18, September 15, 1998
The first application for the simultaneous determination of several peroxycarboxylic acids in laundry detergents using amperometric detection was published by Kirk et al.5 In this work, no gradient elution was used due to the amperometric detection system. It was not possible to separate the peroxycarboxylic acids in the range between C2 and C12 within one chromatogram because different mobile phases had to be used for the separation and detection of different peroxycarboxylic acids. Here, 100 mM phosphate buffer (adjusted to pH 6) for the detection of peroxyacetic acid and 15 mM phosphate buffer (adjusted to pH 6)/ methanol (30:70 v/v) for the separation and detection of peroxycarboxylic acids in the range between C8 and C12 were used. Therefore, the simultaneous determination of the complete series of peroxycarboxylic acids in the range between C2 and C12 with gradient elution was the major objective of the present work. As stated above, the analytical chemistry of the peroxycarboxylic acids is based on their oxidation properties. This leads to the formation of the same oxidation product in the case of all peracids. Therefore, postcolumn derivatization is best suited to determine several peroxycarboxylic acids in one sample. EXPERIMENTAL SECTION Safety Note: Peroxycarboxylic acids are strong oxidizers and may react with organic substances. Pure peroxycarboxylic acids or their concentrated solutions may cause severe explosions. They should never be mixed with organic substances. The procedures mentioned within this publication have been investigated for peroxycarboxylic acid concentrations up to 100 mM. Chemicals. Hydrogen peroxide, PAA, mCPBA, all carboxylic acids, MTS, MTSO, and ABTS were purchased from Aldrich Chemie (Steinheim, Germany) in the highest quality available. Potassium iodide was obtained from Merck (Darmstadt, Germany). Solvents for HPLC were Merck (Darmstadt, Germany) LiChroSolv gradient grade. Ultra Biz is a laundry detergent which is distributed in the United States by Procter & Gamble (Cincinnati, OH). Persil Megaperls is a laundry detergent which is distributed in Germany by Henkel (Du¨sseldorf, Germany). Preparation of the Peroxycarboxylic Acids. All peroxycarboxylic acids with the exception of PAA and mCPBA were prepared according to ref 3. PAA and mCPBA were purchased from Aldrich Chemie. In ref 3, only the preparation of the peroxycarboxylic acids in the range from C6 to C18 is described. The method has been adapted for the preparation of the peracids C3-C5. Some modifications have been made: the carboxylic acid was dissolved in concentrated sulfuric acid, the solution was cooled to -5 to -10 °C, and hydrogen peroxide (35%) was added dropwise and very slowly to the stirred solution. In Table 1, the composition of the reaction mixtures for the preparation of all used peroxycarboxylic acids is illustrated.
Figure 1. Schematic assembly of the HPLC system with postcolumn derivatization.
The reaction mixtures were stirred for an additional 3 h at room temperature. The pure peracids were not isolated from their solutions to avoid an explosion hazard.28 The reaction mixture was diluted with 25 mL of acetonitrile/water mixture (80:20 v/v) to a concentration range between 10 and 100 mM. These solutions were stored at -20 °C. No significant decomposition of the peroxide solutions was observed under these storage conditions. Postcolumn Derivatization. The separations were performed with a modular HPLC system consisting of a MerckHitachi (Darmstadt, Germany) gradient pump L6200 as eluent pump, a Knauer (Berlin, Germany) HPLC pump 64 as reagent pump, a Waters 484 tunable absorbance detector, and a Rheodyne injection valve with a 5-µL sample loop. The reversed-phase column was Merck LiChroSorb RP18 (125 × 4 mm), 5 µM particle size. Gradient elution was carried out using binary mixtures of acetonitrile (eluent A) and water plus additives (eluent B) as the mobile phase at a flow rate of 1.4 mL/min. To optimize the peak shape, water with 2% acetic acid and 1% tetrahydrofuran (THF) (v/v) as additives was used as eluent B. The linear gradient used was from 25% eluent A up to 100% A within 4 min, 2.5 min isocratic at 100% eluent A, and from 100% eluent A down to 25% A within 0.5 min. Six milliliters of acetic acid, 2 mg of potassium iodide, and 50 mg of ABTS15 were dissolved in water and diluted to 300 mL. This reagent solution was stored under protection from light at 4 °C in a refrigerator. The reagent solution with 0.3 mL/min was mixed with the HPLC effluent using a 1 µL turbo mixing chamber.29,30 A 10-m knitted Teflon capillary30,31 with 0.3-mm diameter and an internal volume of approximately 0.7 mL was integrated in an oven and was used as a manifold for the postcolumn derivatization. Under these conditions, 24 s is available for the reaction in the oven. An oven temperature of 110 °C was selected unless stated otherwise. An additional 1-m (28) Swern, D. Organic Peroxides; Wiley-Interscience: New York, 1970; pp 476498. (29) Engelhardt, H.; Lillig, B. Chromatographia 1986, 21, 136-142. (30) Engelhardt, H.; Neue, U. D. Chromatographia 1982, 15, 403-408. (31) Krull, I. S. Reaction Detection in Liquid Chromatography; Chromatography Science Series 34; M. Dekker: New York, 1986; pp 1-61.
knitted capillary was used as a heat-exchanger before entering the UV/visible detector. Detection was performed at the UV/ visible maximum of the ABTS radical cation at 415 nm. In Figure 1, the schematic assembly of the HPLC instrumentation is shown. Gradient profiles displayed in the chromatograms recorded without a column are the effective profiles determined by using methanol with 200 ppm toluene instead of eluent A and methanol instead of eluent B and the reagent solution. The increasing toluene concentration was used to monitor the gradient profile (λ ) 254 nm). It should be noted that these gradient profiles report the composition of the mobile phase at the head of the column. The resulting time delay between the chromatogram and the gradient profile is due to the void volume of the respective column. Chromatographic MTS Method.24-26 One hundred microliters of the peracid in the concentration range from 1 to 100 mM was added to 1000 µL of 20 mM MTS solution in acetonitrile/ water (50:50 v/v). After a reaction time of 15 min, 10 mL of acetonitrile/water (50:50 v/v) was added to obtain a suitable concentration range for HPLC analysis. The HPLC configuration described above without the reagent pump and the postcolumn detection system was used. Isocratic elution was carried out with acetonitrile/water (75:25 v/v) as the mobile phase at a flow rate of 1.5 mL/min. Detection was performed by UV spectroscopy at 230 nm. Commercially available MTSO was used for external calibration. Photometric ABTS Method.15 Prior to derivatization, the prepared peracid solutions were diluted by a factor of 1000 using acetonitrile/water (50:50 v/v). Photometric measurements were carried out with an SQ 118 filter photometer (Merck, Darmstadt, Germany) using quartz cuvettes with an optical pathway of 1 cm and a volume of 3 mL. A filter with a wavelength of 405 nm is used. The molar absortivity at this wavelength is ) (3.16 ( 0.02) × 104 L mol-1 cm-1 and was used for the quantitative determination according to Pinkernell et al.15 RESULTS AND DISCUSSION First, the suitability of ABTS as a reagent for the photometric determination of peroxycarboxylic acids with chain lengths between C2 and C12 was subject to investigations. The content of Analytical Chemistry, Vol. 70, No. 18, September 15, 1998
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Table 2. Comparative Measurements of Different Peroxycarboxylic Acids MTS
ABTS
peracid
c (mM)
RSD (%) (n ) 3)
c (mM)
RSD (%) (n ) 3)
mCPBA C2 C3 C4 C5 C6 C7 C8 C9 C10 C12
17.6 15.4 33.2 39.3 36.0 68.5 42.0 41.9 37.5 30.0 47.6
3.3 3.2 4.2 4.6 3.0 0.4 1.9 1.4 1.9 1.7 2.5
18.2 16.0 33.0 37.9 33.3 63.4 41.5 43.0 40.8 33.6 47.2
4.9 3.1 2.1 1.1 2.1 1.3 1.9 3.0 3.0 1.2 0.6
peroxycarboxylic acids of several solutions which were prepared according to the method stated above was determined using the photometric ABTS and the liquid chromatographic MTS method. These two methods have been especially adapted to the analyte concentration range of the prepared solutions. In the case of lower peracid contents, the RSD increases are caused by significant blanks of the MTS and ABTS reagents, respectively. The results of both methods are presented in Table 2. In a quantitative reaction, a green radical ion is formed by the iodide-catalyzed reaction between ABTS and the peroxycarboxylic acids. Selectivity of ABTS toward all of these peracids in the presence of hydrogen peroxide is observed. Both methods lead to comparable results with excellent reproducibility. Using the concentration data determined above, several mixtures containing 1, 2.5, 5, 10, 25, 50, 100, 250, 500, and 1000 µM of each of the aliphatic peracids were prepared (dilution matrix: acetonitrile/water (50:50 v/v)). Five microliters of the respective solution was injected in the HPLC system using the HPLC conditions stated above without additives in the mobile phase. In the UV/visible spectrum, a maximum at 206 nm is observed for organic peracids.5 This wavelength was chosen as the detection wavelength for the direct determination of these peroxides. The limits of detection using direct UV/visible detection without postcolumn derivatization are in the range of only 250 µM for all aliphatic peracids. Therefore, the use of ABTS as a reagent for postcolumn derivatization of several peroxycarboxylic acids was investigated in the following. Using the HPLC and derivatization conditions with acetonitrile/ water elution (without additives) as described above, 5 µL of a solution containing 100 µM of the aliphatic peracids (dilution matrix: acetonitrile/water (50:50 v/v)) was injected. Here, 415 nm was chosen as the wavelength for the detection of the ABTS radical cation. In Figure 2, the resulting chromatogram and the effective gradient are presented. All peroxycarboxylic acids can be detected but with bad peak shape and high limits of detection. The obvious reason for the peak shape is the equilibrium between the peracids and their corresponding anions.
Addition of acetic acid to the aqueous eluent should shift the 3860 Analytical Chemistry, Vol. 70, No. 18, September 15, 1998
Figure 2. Chromatogram of the separation of several peroxycarboxylic acids using acetonitrile and water without any additives as eluents (s, chromatogram; ‚‚‚, effective gradient).
Figure 3. Chromatogram of the separation of several peroxycarboxylic acids using acetonitrile and water with addition of 2% acetic acid and 1% THF as eluents (s, chromatogram; ‚‚‚, effective gradient).
equilibrium to the left in eq 3. Some 2% acetic acid was added to the aqueous eluent to optimize the peak shape. Further addition of 1% tetrahydrofuran inhibits secondary interactions between the analytes and the free silanol groups of the stationary phase. Using both additives, the same peroxycarboxylic acid solution was injected again. In Figure 3, the resulting chromatogram is presented. The chromatogram shows a strong improvement compared to Figure 2. The peak shapes are significantly better. Hydrogen peroxide passes the column unretained, and the peroxycarboxylic acids elute as expected in the order of increasing chain lengths. Peak identification was performed by injection of each peroxycarboxylic acid. The time discrepancy between the programmed gradient and the real gradient is caused by the void volume of the HPLC system. To maximize the peak height and peak area, the temperature of the postcolumn oven with the integrated reaction capillary is another important parameter. Increasing the temperature should accelerate the derivatization reaction during the flow of the reaction partners through the capillary. Five microliters of a solution containing 100 µM of each aliphatic peracid (dilution matrix: acetonitrile/water (50:50 v/v)) was injected using different oven temperatures between 20 and 120 °C. The peak area of each
Table 3. Calibration Data of Several Peroxycarboxylic Acids RSD (%) peracid
tR (min)
mCPBA C2 C3 C4 C5 C6 C7 C8 C9 C10 C12
4.85 1.36 1.64 2.35 3.93 4.87 5.49 5.97 6.40 6.79 7.55
r
slope (µM-1)
>0.998 >0.999 >0.998 >0.998 >0.997 >0.998 >0.999 >0.999 >0.999 >0.999 >0.999
363 309 264 276 237 224 218 221 174 170 183
LOD (µM)
linear range (µM)
c ) 25 µM, n ) 5
c ) 100 µM, n ) 5
c ) 250 µM, n ) 5
2.5 5 5 5 5 5 5 5 5 5 5
5-250 10-250 10-500 10-500 10-500 10-500 10-500 10-500 10-500 10-500 10-500
7.4 8.2 8.4 8.8 9.0 10.0 7.1 8.8 8.2 7.1 9.8
5.6 4.0 4.0 2.9 6.7 5.8 5.1 5.3 5.8 5.8 6.9
3.2 1.8 2.2 4.9 4.7 3.1 4.1 6.7 4.2 4.6 3.0
Figure 4. Dependence of the peak area from the postcolumn oven temperature (9, C2; b, C3; 2, C4; 1, C5; [, C6; +, C7; ×, C8; *, C9; -, C10; |, C12.
peracid was plotted versus the respective temperature. The results are presented in Figure 4. A sigmoid course of the plot is observed in the case of all investigated peroxycarboxylic acids. Up to 70 °C, a strong increase of the peak area of all peracids can be observed. Temperatures higher than 70 °C lead to a further increase of the peak area only in the case of the long-chain peracids. It is noteworthy that the peak area decreases with increasing numbers of C atoms of the respective peroxycarboxylic acids at each temperature. This indicates that the reaction is obviously not quantitative in the case of the long-chain peracids under the reaction conditions used. A temperature of 110 °C was selected for the postcolumn derivatization reaction. On one hand, a suitable reaction rate is guaranteed at this temperature, and on the other hand, the Teflon capillary will not yet be affected by destruction. The conditions stated above were used to record calibration curves of the investigated aliphatic peroxycarboxylic acids and mCPBA. Therefore, the peracid content of each prepared peracid was determined by using the MTS method24-26 as stated above. Each of these solutions was diluted with acetonitrile/water (50: 50 v/v) to the following concentrations: 1, 2.5, 5, 10, 25, 50, 100, 250, 500, and 1000 µM. The obtained calibration data are presented in Table 3. Each solution was injected five times. Additionally, the RSD (n ) 5) given in Table 3 was determined for the peracid concentrations 25, 100, and 250 µM.
Figure 5. Chromatogram of the American laundry detergent Ultra Biz (s, Ultra Biz sample; ‚‚‚, C8, C9, C10 peracid standards).
As shown in Table 3, the calibration curves of the highly reactive peracids as PAA and mCPBA are linear only up to 250 µM. A further increase of the PAA or mCPBA concentration exceeds the linear range of the method. In the case of the less reactive peracids, linearity is observed up to a concentration of 500 µM. This is an additional indication of a lower reaction rate in the case of the less reactive long-chain peroxycarboxylic acids. mCPBA, the most reactive peracid of all the investigated compounds, can be detected down to a concentration of 2.5 µM. This new method has been used to study the formation of different peracids from commercially available laundry detergents. One gram of Ultra Biz, a laundry detergent available in the United States, was dissolved in 100 mL of water at a temperature of 20 °C using a magnetic stirrer. After 5 min, a sample of 100 µL was diluted with 1000 µL of 0.1 M acetic acid. The diluted solution was centrifuged for 5 min at 10 000 rpm to remove the turbidity. Five microliters of this solution and a standard containing 100 µM of each peracid between C8 and C10 were injected into the HPLC system using the standard parameters described above. The resulting chromatogram is presented in Figure 5. It is obvious that peroxynonanoic acid is formed in the aqueous solution of the American detergent. To investigate the formation of a peracid in a typical European laundry detergent, 1 g of Persil Megaperls was dissolved in 100 mL of water at a temperature of 20 °C using a magnetic stirrer. After 15 min, a sample of 50 µL was diluted with 1000 µL of 0.1 M acetic acid. The diluted solution was centrifuged for 5 min at 10 000 rpm to remove the turbidity. Analytical Chemistry, Vol. 70, No. 18, September 15, 1998
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In contrast to the American laundry detergents, peroxyacetic acid is formed from most of the commercially available European laundry detergents, as is the case in the investigated Persil Megaperls sample. The developed method is, therefore, valuable for investigations on American as well as European laundry detergents. CONCLUSIONS ABTS is a well-suited reagent for postcolumn derivatization of several peroxycarboxylic acids. The first method for the identification and the simultaneous quantitative determination of peroxycarboxylic acids in the range from C2 to C12 was developed. All peroxycarboxylic acids can easily be separated within 8 min. Addition of small amounts of acetic acid and tetrahydrofuran to the aqueous eluent are required to obtain good peak shapes. Figure 6. Chromatogram of the European laundry detergent Persil Megaperls (s, Persil Megaperls sample; ‚‚‚, C2, C3, C4, C5 peracid standards).
Five microliters of this solution and a standard containing 100 µM of each peracid between C2 and C5 were injected in the HPLC system using the parameters described above. The resulting chromatogram is presented in Figure 6.
3862 Analytical Chemistry, Vol. 70, No. 18, September 15, 1998
ACKNOWLEDGMENT S.E. thanks the Hala´sz Foundation (Saarbru¨cken, Germany) for the Applied Physical Chemistry Award 1997 and the FAZITStiftung (Frankfurt, Germany) for a scholarship. Received for review March 6, 1998. Accepted June 30, 1998. AC980256B
