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mass spectrometry
Journal of Analytical and Applied Pyrolysis 45 (1998) 111 – 119
Quick identification of polymeric dye transfer inhibitors in laundry detergents by pyrolysis-gas chromatography/mass spectrometry Toshihiko Uchiyama, Akihiko Kawauchi *, Dean L. DuVal Procter & Gamble Asia, Research and De6elopment Department, Kobe Technical Center, 17, Koyo-cho, Naka 1 -chome, Higashinada, Kobe 658, Japan Received 18 September 1997; accepted 6 January 1998
Abstract This report summarizes method development for the simultaneous identification of dye transfer inhibitors (DTIs) using pyrolysis-gas chromatography with mass detection (Py-GC/ MS). Ground detergent products are directly pyrolyzed and pyrolysis fragments introduced into a GC column. Key fragments separated via GC are detected by selected ion monitoring (SIM) to achieve the high sensitivity and selectivity necessary to measure markers of DTIs in the presence of high levels of surfactant by products. Trace levels of DTIs, poly-Nvinylpyrrolidone (PVP), copolymer of N-vinylpyrrolidone and N-vinylimidazole (PVPVI), and poly-4-vinylpyridine-N-oxide (PVNO) in laundry detergent products were quickly identified. Detection limits were 0.05% for PVP and 0.1% for PVPVI and PVNO. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Pyrolysis; Mass spectrometry; Polyvinylpyrrolidone; Vinylpyrrolidone-vinylimidazole copolymer; Polyvinylpyridine N-oxide
1. Introduction Dye transfer is the loss of dye from one item in a washload and deposition of that dye onto another item or another part of the same item. Cellulose has a hydrophilic surface and is the most important fiber for dye transfer worldwide [1–5]. It tends to readily release dyes into the washwater and is highly absorptive of fugitive dyes. In general, hydrophilic fibers like cellulose are dyed in aqueous * Corresponding author. Tel.: + 81 78 8456466; fax: + 81 78 8456950; e-mail: [email protected] 0165-2370/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII S0165-2370(98)00061-8
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baths with water soluble dyes that are subsequently responsible for staining of other cellulosic material in a washload. There are several ways to reduce the severity of dye transfer. These include reducing wash temperature, shortening wash time, adding bleach or dye adsorptive polymers in detergents, etc. [1]. However, none of these eliminate the problem of dye transfer. A combination of the approaches is essential for optimal dye transfer inhibition. Several investigations were made on the effect of polymers on dye transfer [1,2]. Polymeric materials were used either to deposit on the surface of fibers and block dye-available sites, or as soluble ‘sponges’ to adsorb and suspend the fugitive dyes in the wash solution. Polyvinylpyrrolidone, a vinylpyrrolidone-vinylimidazole copolymer and polyvinylpyridine N-oxide act as polymer absorbents and decrease apparent transfer of dyes to cotton when blended into detergent products [1,2]. In this paper, a quick method to identify these three polymers was investigated. By using selected ion monitoring, characteristic pyrolysis fragments could be detected without interferences from matrices such as surfactants present in detergent products.
2. Experimental
2.1. Reagents and apparatus 2.1.1. Reagents The following chemicals were purchased from Wako Pure Chemical Industries: polyvinylpyrrolidone K25 (PVP), sodium metasilicate enneahydrate, zeolite (synthetic A-4 powder 200 mesh), sodium tripolyphosphate anhydrous, sodium carbonate anhydrous, sodium sulfate anhydrous, polyethyleneglycol 6000, carboxy methyl cellulose sodium salt. Dodecylbenzene sulfonic acid sodium salt was purchased from Sigma. The following materials were internally synthesized: copolymer of vinylpyrrolidone-vinylimidazole (PVPVI) and polyvinylpyridine N-oxide (PVNO). 2.1.2. Apparatus Identification of the pyrolysis fragments of polymeric dye transfer inhibitors was accomplished by means of a curie-point pyrolyzer (Model JHP-330; Japan Analytical Industry Co.) and a GC system (HP5980 Series II) equipped with a mass selective detector (HP5971A). The system was equipped with a fused silica capillary column (Supelco WAX10, 0.25 mm I.D.×6.5 m, 0.25 mm df, Supelco Japan, Division of Sigma-Aldrich Japan K.K.) connected with deactivated fused silica capillary tubes, as a pre-column (0.25 mm I.D.×2 m) and as a post-column (0.18 mm I.D.× 5 m). 2.2. Preparation 2.2.1. Preparation of detergent mixture A detergent mixture was prepared by mixing 72 g dodecylbenzene sulfonic acid (sodium salt), 25 g sodium metasilicate (enneahydrate), 40 g synthetic A-4 powder
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200 mesh (Zeolite A), 40 g sodium tripolyphosphate (anhydrous), 20 g sodium carbonate (anhydrous), 112 g sodium sulfate (anhydrous), 1 g polyethyleneglycol 6000, and 10 g carboxymethyl cellulose sodium salt. Then, the mixture was divided into four portions using a sample riffler for preparing the following DTI spiked samples (see Sections 2.2.2, 2.2.3 and 2.2.4) and a reference sample (see Section 2.2.5).
2.2.2. Preparation of PVP spiked sample PVP K25 (0.051 g) was mixed with the detergent mixture (50.8 g) then finely ground using a sample mill. This sample contains 0.10% PVP by weight. 2.2.3. Preparation of PVPVI spiked sample PVPVI (0.063 g) was mixed with the detergent mixture (51.3 g) and finely ground using a sample mill. This sample contains 0.11% PVPVI by weight. 2.2.4. Preparation of PVNO spiked sample PVNO (0.054 g) was mixed with the detergent mixture (52.1 g) and finely ground using a sample mill. This sample contains 0.093% PVNO by weight. 2.2.5. Preparation of reference sample (DTIs free sample) A reference sample for investigating specificity, detection limits and GC column deterioration was prepared by finely grinding the detergent mixture (Section 2.2.1) using a sample mill. 2.3. Methods 2.3.1. GC conditions Initial column temperature, 90°C; holding time at initial temperature, 0 min; final column temperature, 250°C; holding time at final temperature, 5 min; ramp rate, 20°C min − 1. GC column used is specified in Section 2.1.2. 2.3.2. Identification of fragments of thermally decomposed DTI materials Fragments of thermally decomposed DTIs were measured by Py-GC/MS. PVP solution (100 mg ml − 1) was prepared by dissolving reagent PVP in deionized water. This solution (5 ml) was placed onto a pyrofoil. In the same manner, PVPVI (100 mg ml − 1) and PVNO (100 mg ml − 1) solutions were prepared. Pyrofoils were subjected to Py-GC/MS. Analytical conditions were as follows: Mass scanning range; m/z 50 – 300 with sampling rate of 1.5 scans s − 1 Pyrolysis at 650°C for 10 s Carrier gas; helium at 20 kPa Temperature of interface; Py-GC (250°C) and GC-MS (280°C)
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2.3.3. In6estigation of specificity Specificity was investigated using the reference sample (Section 2.2.5). Approximately 1 mg of the reference sample was placed onto a pyrofoil. The pyrofoil was subjected to pyrolysis-GC/MS. Analytical conditions were as follows: Monitored ions; m/z 94, 105 and 111 Other conditions used are the same as those specified in Section 2.3.2. 2.3.4. In6estigation of detection limits Reagent PVP was dissolved in deionized water and three concentrations of PVP (0.5, 1.0, and 5.0 mg ml − 1) were prepared. Each PVP solution (1 ml) was placed onto a pyrofoil together with approximately 1 mg of the reference sample (Section 2.2.5). (A total of three pyrofoils were prepared.) The pyrofoils were subjected to pyrolysis-GC/MS. In the same manner, PVPVI and PVNO solutions (1.0, 2.0 and 4.0 mg ml − 1) were prepared. Then pyrofoils prepared were subjected to pyrolysis-GC/MS. 2.3.5. In6estigation of GC column deterioration Approximately 1 mg of the PVPVI and PVNO samples were placed onto a pyrofoil, respectively. They were analyzed to calculate the initial partition ratios of 4-vinyl pyridine, N-vinyl-2-pyrrolidone and N-vinylimidazole. Then approximately 1 mg of the reference sample (Section 2.2.5) was pyrolyzed and injected into a GC column thirty times. After thirty injections of the reference sample, the PVPVI and PVNO samples were analyzed again to calculate the change in partition ratios of 4-vinyl pyridine, N-vinyl-2-pyrrolidone and N-vinylimidazole.
3. Results and discussion
3.1. Pyrolysis fragments Fragments of thermally decomposed polymers reflect the original structure of polymers and thus, they can be used for polymer identification. Fig. 1 shows the molecular structures of PVP, PVNO, and PVPVI. Pyrograms of those materials pyrolyzed at 650°C are shown in Figs. 2–4, m/z 94 (N-vinylimidazole; retention time (RT): 2.4 min.), m/z 105 (4-vinyl pyridine; RT: 1.7 min.) and m/z 111 (N-vinyl-2-pyrrolidone; RT: 2.8 min.). Peak assignment was confirmed by its EI mass fragmentation pattern and the results are summarized in Table 1. No monomer peak was detected for PVNO but 4-vinyl pyridine was the main pyrolysis product. As described later, 4-vinyl pyridine was not produced from the classical detergent mix and was employed as an evidence of PVNO presence in detergent products. Ion chromatograms at m/z 94, 105 and 111 were superimposed on the Figs. 2–4.
T. Uchiyama et al. / J. Anal. Appl. Pyrolysis 45 (1998) 111–119
115
Fig. 1. Structures of PVP, PNPVI and PVNO.
3.2. Monomer production 6ersus pyrolysis temperature The efficiency of monomer production of each polymer was investigated. Ericsson and Ljunggren [6] reported that the monomer production of PVP by pyrolysis reached the maximum at around 700°C. Our data supports this result. The monomer production of PVP reached maximum at 650°C. PVPVI and PVNO also showed the same tendency as PVP. Based on these results, 650°C was employed as the pyrolysis temperature in this investigation.
Fig. 2. A total ion chromatogram and an ion chromatogram (m/z 111) of PVP.
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Fig. 3. A total ion chromatogram and an ion chromatogram (m/z 105) of PVNO.
Fig. 4. A total ion chromatogram and an ion chromatogram (m/z 94 and 111) of PVPVI.
3.3. Specificity DTIs are blended in detergent products at around 0.5% or less [7]. On the other hand, surfactants are present at 100 times the level of DTIs in detergent products. They are potential interferences in the DTI identification by pyrolysis. The selected ion chromatograms of the reference sample (Section 2.2.5) with DTIs are shown in Figs. 5–7, m/z 94 (N-vinylimidazole), m/z 105 (4-vinyl pyridine) and m/z 111 (N-vinyl-2-pyrrolidone). There is a small peak observed at the retention of N-vinylTable 1 List of fragments used for this investigation (production rate was analyzed twice) DTIs
PVP PVPVI PVNO
Fragments used for identification
N-vinyl-2-pyrrolidone N-vinyl-2-pyrrolidone N-vinylimidazole PVNO monomer 4-Vinyl pyridine
Production ratio against all the fragments detected 1st Analysis
2nd Analysis
75.8% 35.2% 34.6% Not detected 31.7%
76.9% 23.2% 23.3% Not detected 31.5%
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Fig. 5. A selected ion chromatogram (m/z 94) of the reference material. (¡) Retention time of N-vinylimidazole (RT: 2.4 min).
2-pyrrolidone on the ion chromatogram at m/z 111. This peak is 100 times smaller in intensity than the N-vinyl-2-pyrrolidone peak (as 0.5 mg PVP) and does not affect the detection limit as shown in the following section. No pyrolysis peaks from the reference sample interfere with the detection of N-vinylimidazole and 4-vinyl pyridine on the pyrograms.
3.4. Detection limit PVP monomer was observed on a pyrogram when 0.25 mg PVP standard was pyrolyzed alone; however, the monomer peak could not be detected when being pyrolyzed together with the reference sample (Section 2.2.5). This observation suggests that the PVP monomer radical produced during pyrolysis reacts with other radicals from surfactants or other ingredients. As a result, the amount of PVP monomer being introduced into the GC column decreases. The monomer peak could be detected on the pyrogram provided spiked PVP was 0.50 mg or more. The same phenomena were observed for PVNO and PVPVI. Key fragments from these materials were detected when spiked PVNO or PVPVI was 1.0 mg or more.
Fig. 6. A selected ion chromatogram (m/z 105) of the reference material. (¡) Retention time of 4-vinyl pyridine (RT: 1.7 min).
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Fig. 7. A selected ion chromatogram (m/z 111) of the reference material. (¡) Retention time of N-vinyl-2-pyrrolidone (RT: 2.8 min).
The 99% confidence interval for each DTI and the reference sample are calculated as shown in Table 2. Because the lower limit of the 95% confidence interval of each material is higher than the upper limit of the 95% confidence interval of the reference sample, it is clear that 0.50 mg PVP, 1.0 mg PVNO, 1.0 mg PVPVI or higher levels of these materials in product can be detected and identified using the procedure described in this paper. These detection levels are equivalent to 0.05% PVP, 0.1% PVNO and 0.1% PVPVI in product.
3.5. GC column deterioration In the procedure described in this investigation, a significant quantity of pyrolysis materials from surfactants and other organics contained in detergents were introduced into the GC column. GC column deterioration resulting from this deposition was investigated. Partition ratios (k%) on the first injection and on the 30th injection were calculated for the three fragments of interest. The drop in k% for 4-vinyl pyridine was 3.2%, 1.1% for N-vinyl-2-pyrrolidone and 2.0% for N-vinylimidazole after 30 injections. No significant changes in peak symmetry were observed. Table 2 95% Confidential interval of DTIs and the reference at the detection limit
PVP PVPVI
PVNO
Fragments used for identification
95% Confidence interval of DTI fragments
95% Confidence interval of reference sample
N-Vinyl-2pyrrolidone N-Vinyl-2pyrrolidone N-Vinylimidazole 4-Vinyl pyridine
19 1719 1521
137 9126
10 6009 1676
137 9126
8572 9 1764 32 8369 1056
268 9137 824 92787
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119
4. Conclusions Polyvinylpyrrolidone, vinylpyrrolidone-vinylimidazole copolymer and polyvinylpyridine N-oxide can be simultaneously identified in detergent products by pyrolysis-GC/MS. The polymers blended in detergent products did not have to be extracted or separated from the surfactants present in the products prior to analysis by Py-GC/MS. A ground sample can be directly analyzed, and characteristic pyrolysis fragments detected by MS (SIM mode) without significant interference from the matrix.
References [1] [2] [3] [4] [5] [6] [7]
R. Panandiker, W. Wertz, L. Hugues, PCT Publication Number WO95/13354, 1995. M. Sugihara, Kagaku-to-kougyou 37 (1963) 204. T. Kariyone, Kaimenkasseizai-no-seishitsu-to-ouyou, Saiwai-shobou, Tokyo, 1988. T. Fujii, Senzai, Saiwai-shobou, Tokyo, 1991. S. Tsuji, Senjou-to-senzai, Chijin-shokan, Tokyo, 1992. I. Ericsson, L. Ljunggren, J. Anal. Appl. Pyrolysis 17 (1990) 251. G.B. Levy, D. Fergus, Anal. Chem. 25 (1953) 1408.
.
Quick identification of polymeric dye transfer inhibitors in laundry detergents by pyrolysis-gas chromatography/mass spectrometry Toshihiko Uchiyama, Akihiko Kawauchi *, Dean L. DuVal Procter & Gamble Asia, Research and De6elopment Department, Kobe Technical Center, 17, Koyo-cho, Naka 1 -chome, Higashinada, Kobe 658, Japan Received 18 September 1997; accepted 6 January 1998
Abstract This report summarizes method development for the simultaneous identification of dye transfer inhibitors (DTIs) using pyrolysis-gas chromatography with mass detection (Py-GC/ MS). Ground detergent products are directly pyrolyzed and pyrolysis fragments introduced into a GC column. Key fragments separated via GC are detected by selected ion monitoring (SIM) to achieve the high sensitivity and selectivity necessary to measure markers of DTIs in the presence of high levels of surfactant by products. Trace levels of DTIs, poly-Nvinylpyrrolidone (PVP), copolymer of N-vinylpyrrolidone and N-vinylimidazole (PVPVI), and poly-4-vinylpyridine-N-oxide (PVNO) in laundry detergent products were quickly identified. Detection limits were 0.05% for PVP and 0.1% for PVPVI and PVNO. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Pyrolysis; Mass spectrometry; Polyvinylpyrrolidone; Vinylpyrrolidone-vinylimidazole copolymer; Polyvinylpyridine N-oxide
1. Introduction Dye transfer is the loss of dye from one item in a washload and deposition of that dye onto another item or another part of the same item. Cellulose has a hydrophilic surface and is the most important fiber for dye transfer worldwide [1–5]. It tends to readily release dyes into the washwater and is highly absorptive of fugitive dyes. In general, hydrophilic fibers like cellulose are dyed in aqueous * Corresponding author. Tel.: + 81 78 8456466; fax: + 81 78 8456950; e-mail: [email protected] 0165-2370/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII S0165-2370(98)00061-8
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baths with water soluble dyes that are subsequently responsible for staining of other cellulosic material in a washload. There are several ways to reduce the severity of dye transfer. These include reducing wash temperature, shortening wash time, adding bleach or dye adsorptive polymers in detergents, etc. [1]. However, none of these eliminate the problem of dye transfer. A combination of the approaches is essential for optimal dye transfer inhibition. Several investigations were made on the effect of polymers on dye transfer [1,2]. Polymeric materials were used either to deposit on the surface of fibers and block dye-available sites, or as soluble ‘sponges’ to adsorb and suspend the fugitive dyes in the wash solution. Polyvinylpyrrolidone, a vinylpyrrolidone-vinylimidazole copolymer and polyvinylpyridine N-oxide act as polymer absorbents and decrease apparent transfer of dyes to cotton when blended into detergent products [1,2]. In this paper, a quick method to identify these three polymers was investigated. By using selected ion monitoring, characteristic pyrolysis fragments could be detected without interferences from matrices such as surfactants present in detergent products.
2. Experimental
2.1. Reagents and apparatus 2.1.1. Reagents The following chemicals were purchased from Wako Pure Chemical Industries: polyvinylpyrrolidone K25 (PVP), sodium metasilicate enneahydrate, zeolite (synthetic A-4 powder 200 mesh), sodium tripolyphosphate anhydrous, sodium carbonate anhydrous, sodium sulfate anhydrous, polyethyleneglycol 6000, carboxy methyl cellulose sodium salt. Dodecylbenzene sulfonic acid sodium salt was purchased from Sigma. The following materials were internally synthesized: copolymer of vinylpyrrolidone-vinylimidazole (PVPVI) and polyvinylpyridine N-oxide (PVNO). 2.1.2. Apparatus Identification of the pyrolysis fragments of polymeric dye transfer inhibitors was accomplished by means of a curie-point pyrolyzer (Model JHP-330; Japan Analytical Industry Co.) and a GC system (HP5980 Series II) equipped with a mass selective detector (HP5971A). The system was equipped with a fused silica capillary column (Supelco WAX10, 0.25 mm I.D.×6.5 m, 0.25 mm df, Supelco Japan, Division of Sigma-Aldrich Japan K.K.) connected with deactivated fused silica capillary tubes, as a pre-column (0.25 mm I.D.×2 m) and as a post-column (0.18 mm I.D.× 5 m). 2.2. Preparation 2.2.1. Preparation of detergent mixture A detergent mixture was prepared by mixing 72 g dodecylbenzene sulfonic acid (sodium salt), 25 g sodium metasilicate (enneahydrate), 40 g synthetic A-4 powder
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200 mesh (Zeolite A), 40 g sodium tripolyphosphate (anhydrous), 20 g sodium carbonate (anhydrous), 112 g sodium sulfate (anhydrous), 1 g polyethyleneglycol 6000, and 10 g carboxymethyl cellulose sodium salt. Then, the mixture was divided into four portions using a sample riffler for preparing the following DTI spiked samples (see Sections 2.2.2, 2.2.3 and 2.2.4) and a reference sample (see Section 2.2.5).
2.2.2. Preparation of PVP spiked sample PVP K25 (0.051 g) was mixed with the detergent mixture (50.8 g) then finely ground using a sample mill. This sample contains 0.10% PVP by weight. 2.2.3. Preparation of PVPVI spiked sample PVPVI (0.063 g) was mixed with the detergent mixture (51.3 g) and finely ground using a sample mill. This sample contains 0.11% PVPVI by weight. 2.2.4. Preparation of PVNO spiked sample PVNO (0.054 g) was mixed with the detergent mixture (52.1 g) and finely ground using a sample mill. This sample contains 0.093% PVNO by weight. 2.2.5. Preparation of reference sample (DTIs free sample) A reference sample for investigating specificity, detection limits and GC column deterioration was prepared by finely grinding the detergent mixture (Section 2.2.1) using a sample mill. 2.3. Methods 2.3.1. GC conditions Initial column temperature, 90°C; holding time at initial temperature, 0 min; final column temperature, 250°C; holding time at final temperature, 5 min; ramp rate, 20°C min − 1. GC column used is specified in Section 2.1.2. 2.3.2. Identification of fragments of thermally decomposed DTI materials Fragments of thermally decomposed DTIs were measured by Py-GC/MS. PVP solution (100 mg ml − 1) was prepared by dissolving reagent PVP in deionized water. This solution (5 ml) was placed onto a pyrofoil. In the same manner, PVPVI (100 mg ml − 1) and PVNO (100 mg ml − 1) solutions were prepared. Pyrofoils were subjected to Py-GC/MS. Analytical conditions were as follows: Mass scanning range; m/z 50 – 300 with sampling rate of 1.5 scans s − 1 Pyrolysis at 650°C for 10 s Carrier gas; helium at 20 kPa Temperature of interface; Py-GC (250°C) and GC-MS (280°C)
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2.3.3. In6estigation of specificity Specificity was investigated using the reference sample (Section 2.2.5). Approximately 1 mg of the reference sample was placed onto a pyrofoil. The pyrofoil was subjected to pyrolysis-GC/MS. Analytical conditions were as follows: Monitored ions; m/z 94, 105 and 111 Other conditions used are the same as those specified in Section 2.3.2. 2.3.4. In6estigation of detection limits Reagent PVP was dissolved in deionized water and three concentrations of PVP (0.5, 1.0, and 5.0 mg ml − 1) were prepared. Each PVP solution (1 ml) was placed onto a pyrofoil together with approximately 1 mg of the reference sample (Section 2.2.5). (A total of three pyrofoils were prepared.) The pyrofoils were subjected to pyrolysis-GC/MS. In the same manner, PVPVI and PVNO solutions (1.0, 2.0 and 4.0 mg ml − 1) were prepared. Then pyrofoils prepared were subjected to pyrolysis-GC/MS. 2.3.5. In6estigation of GC column deterioration Approximately 1 mg of the PVPVI and PVNO samples were placed onto a pyrofoil, respectively. They were analyzed to calculate the initial partition ratios of 4-vinyl pyridine, N-vinyl-2-pyrrolidone and N-vinylimidazole. Then approximately 1 mg of the reference sample (Section 2.2.5) was pyrolyzed and injected into a GC column thirty times. After thirty injections of the reference sample, the PVPVI and PVNO samples were analyzed again to calculate the change in partition ratios of 4-vinyl pyridine, N-vinyl-2-pyrrolidone and N-vinylimidazole.
3. Results and discussion
3.1. Pyrolysis fragments Fragments of thermally decomposed polymers reflect the original structure of polymers and thus, they can be used for polymer identification. Fig. 1 shows the molecular structures of PVP, PVNO, and PVPVI. Pyrograms of those materials pyrolyzed at 650°C are shown in Figs. 2–4, m/z 94 (N-vinylimidazole; retention time (RT): 2.4 min.), m/z 105 (4-vinyl pyridine; RT: 1.7 min.) and m/z 111 (N-vinyl-2-pyrrolidone; RT: 2.8 min.). Peak assignment was confirmed by its EI mass fragmentation pattern and the results are summarized in Table 1. No monomer peak was detected for PVNO but 4-vinyl pyridine was the main pyrolysis product. As described later, 4-vinyl pyridine was not produced from the classical detergent mix and was employed as an evidence of PVNO presence in detergent products. Ion chromatograms at m/z 94, 105 and 111 were superimposed on the Figs. 2–4.
T. Uchiyama et al. / J. Anal. Appl. Pyrolysis 45 (1998) 111–119
115
Fig. 1. Structures of PVP, PNPVI and PVNO.
3.2. Monomer production 6ersus pyrolysis temperature The efficiency of monomer production of each polymer was investigated. Ericsson and Ljunggren [6] reported that the monomer production of PVP by pyrolysis reached the maximum at around 700°C. Our data supports this result. The monomer production of PVP reached maximum at 650°C. PVPVI and PVNO also showed the same tendency as PVP. Based on these results, 650°C was employed as the pyrolysis temperature in this investigation.
Fig. 2. A total ion chromatogram and an ion chromatogram (m/z 111) of PVP.
T. Uchiyama et al. / J. Anal. Appl. Pyrolysis 45 (1998) 111–119
116
Fig. 3. A total ion chromatogram and an ion chromatogram (m/z 105) of PVNO.
Fig. 4. A total ion chromatogram and an ion chromatogram (m/z 94 and 111) of PVPVI.
3.3. Specificity DTIs are blended in detergent products at around 0.5% or less [7]. On the other hand, surfactants are present at 100 times the level of DTIs in detergent products. They are potential interferences in the DTI identification by pyrolysis. The selected ion chromatograms of the reference sample (Section 2.2.5) with DTIs are shown in Figs. 5–7, m/z 94 (N-vinylimidazole), m/z 105 (4-vinyl pyridine) and m/z 111 (N-vinyl-2-pyrrolidone). There is a small peak observed at the retention of N-vinylTable 1 List of fragments used for this investigation (production rate was analyzed twice) DTIs
PVP PVPVI PVNO
Fragments used for identification
N-vinyl-2-pyrrolidone N-vinyl-2-pyrrolidone N-vinylimidazole PVNO monomer 4-Vinyl pyridine
Production ratio against all the fragments detected 1st Analysis
2nd Analysis
75.8% 35.2% 34.6% Not detected 31.7%
76.9% 23.2% 23.3% Not detected 31.5%
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Fig. 5. A selected ion chromatogram (m/z 94) of the reference material. (¡) Retention time of N-vinylimidazole (RT: 2.4 min).
2-pyrrolidone on the ion chromatogram at m/z 111. This peak is 100 times smaller in intensity than the N-vinyl-2-pyrrolidone peak (as 0.5 mg PVP) and does not affect the detection limit as shown in the following section. No pyrolysis peaks from the reference sample interfere with the detection of N-vinylimidazole and 4-vinyl pyridine on the pyrograms.
3.4. Detection limit PVP monomer was observed on a pyrogram when 0.25 mg PVP standard was pyrolyzed alone; however, the monomer peak could not be detected when being pyrolyzed together with the reference sample (Section 2.2.5). This observation suggests that the PVP monomer radical produced during pyrolysis reacts with other radicals from surfactants or other ingredients. As a result, the amount of PVP monomer being introduced into the GC column decreases. The monomer peak could be detected on the pyrogram provided spiked PVP was 0.50 mg or more. The same phenomena were observed for PVNO and PVPVI. Key fragments from these materials were detected when spiked PVNO or PVPVI was 1.0 mg or more.
Fig. 6. A selected ion chromatogram (m/z 105) of the reference material. (¡) Retention time of 4-vinyl pyridine (RT: 1.7 min).
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Fig. 7. A selected ion chromatogram (m/z 111) of the reference material. (¡) Retention time of N-vinyl-2-pyrrolidone (RT: 2.8 min).
The 99% confidence interval for each DTI and the reference sample are calculated as shown in Table 2. Because the lower limit of the 95% confidence interval of each material is higher than the upper limit of the 95% confidence interval of the reference sample, it is clear that 0.50 mg PVP, 1.0 mg PVNO, 1.0 mg PVPVI or higher levels of these materials in product can be detected and identified using the procedure described in this paper. These detection levels are equivalent to 0.05% PVP, 0.1% PVNO and 0.1% PVPVI in product.
3.5. GC column deterioration In the procedure described in this investigation, a significant quantity of pyrolysis materials from surfactants and other organics contained in detergents were introduced into the GC column. GC column deterioration resulting from this deposition was investigated. Partition ratios (k%) on the first injection and on the 30th injection were calculated for the three fragments of interest. The drop in k% for 4-vinyl pyridine was 3.2%, 1.1% for N-vinyl-2-pyrrolidone and 2.0% for N-vinylimidazole after 30 injections. No significant changes in peak symmetry were observed. Table 2 95% Confidential interval of DTIs and the reference at the detection limit
PVP PVPVI
PVNO
Fragments used for identification
95% Confidence interval of DTI fragments
95% Confidence interval of reference sample
N-Vinyl-2pyrrolidone N-Vinyl-2pyrrolidone N-Vinylimidazole 4-Vinyl pyridine
19 1719 1521
137 9126
10 6009 1676
137 9126
8572 9 1764 32 8369 1056
268 9137 824 92787
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119
4. Conclusions Polyvinylpyrrolidone, vinylpyrrolidone-vinylimidazole copolymer and polyvinylpyridine N-oxide can be simultaneously identified in detergent products by pyrolysis-GC/MS. The polymers blended in detergent products did not have to be extracted or separated from the surfactants present in the products prior to analysis by Py-GC/MS. A ground sample can be directly analyzed, and characteristic pyrolysis fragments detected by MS (SIM mode) without significant interference from the matrix.
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