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Concentrations, Stability and Isolation of the Furan Fatty Acid 9-(3-Methyl-5Pentylfuran-2-yl)-Nonanoic Acid (9M5) from Disposable Latex Gloves Marco Müller, Melanie Hogg, Kerstin Ulms, and Walter Vetter J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b02444 • Publication Date (Web): 18 Aug 2017 Downloaded from http://pubs.acs.org on September 1, 2017
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Journal of Agricultural and Food Chemistry
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Concentrations, Stability and Isolation of the Furan Fatty Acid 9-(3-Methyl-5-
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Pentylfuran-2-yl)-Nonanoic Acid (9M5) from Disposable Latex Gloves
3 4
Marco Müller, Melanie Hogg, Kerstin Ulms and Walter Vetter*
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University of Hohenheim, Institute of Food Chemistry, Department of Food Chemistry
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(170b), D-70593 Stuttgart, Germany
9 10 11 12
* Corresponding author
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Phone: +49 711 459 24016
14
Fax: +49 711 459 24377
15
Email:
[email protected]
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ABSTRACT
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Because of their antioxidant properties, furan fatty acids (furan-FA) are valuable
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minor compounds with a widespread occurrence in all living matter. Unfortunately, pure
19
standards are not readily available, as they usually contribute only 1% to the lipid fraction. A
20
known exception of this is the milky fluid of Hevea brasiliensis, commonly known as latex,
21
in which the furan-FA 9-(3-methyl-5-pentylfuran-2-yl)-nonanoic acid (9M5) contributes with
22
about 90% to the triacylglycerides. In this study, we investigated the content of 9M5 in 30
23
different disposable latex gloves, which ranged from 0.7 to 8.2 mg/g glove. The light
24
degradability of 9M5 in latex gloves was investigated and different amounts of 9M5 in
25
disposable latex gloves were attributed to varying exposure time to light. Additionally, over
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100 mg of the methyl or ethyl ester of 9M5 (purity >98%) could be extracted from disposable
27
latex gloves, employing cold extraction and silver ion chromatography. With this method,
28
standards for the quantitation of furan-FA are obtained easily and rapidly in all laboratories.
29 30
KEYWORDS
31
Furan fatty acids, disposable latex gloves, 9M5, Hevea brasiliensis, GC/MS
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Journal of Agricultural and Food Chemistry
INTRODUCTION
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Furan fatty acids (furan-FA) are a group of naturally occurring fatty acids which are
34
characterized by a furan ring in the center of the molecule. The furan moiety is substituted
35
with a straight-chain (usually 9, 11 or 13 carbons) saturated acid in α-position and a short
36
alkyl chain (usually 3 or 5 carbons) in α'-position (Figure 1).1 A typical example for furan-FA
37
is 9-(3-methyl-5-pentylfuran-2-yl)-nonanoic acid (9M5), 1, which is substituted with one
38
methyl group at the β-position (M). Other naturally occurring furan-FA possess two methyl
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groups at the β- and β'-positions (D), while furan-FA without methyl groups (F) are rarely
40
found in nature.2
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Furan-FA are de novo synthesized by various plants and bacteria and can be
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incorporated into the lipids of animals.1,3 Hence, they are found widespread in all living
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matter, albeit at low concentrations.1,3–6 Because of their high radical scavenging activity,
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they are potent antioxidants.7,8 Due to this property they are thought to protect
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polyunsaturated fatty acids (PUFA) from oxidative stress and support them in their beneficial
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effects on the prevention of cardiovascular diseases.1
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Furan-FA are easily transformed into volatile compounds by exposure to light which
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were found to cause off-flavor in spinach,9 soybean oil10 as well as dried herbs and
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vegetables.11 In addition, the potential furan-FA metabolite 3-carboxy-4-methyl-5-propyl-2-
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furanpropionic acid, 2, was found to be significantly high in blood plasma of patients with
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type 2 diabetes.12,13 2 was also found to enhance type 2 diabetes by hampering the insulin
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biosynthesis in β-cells.14 However, high amounts of fish in the diet only moderately increased
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the plasma concentration of 2 and it could not be linked to harmful glucose metabolism.13
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To gain further knowledge of the biological function of furan-FA, pure standards are
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needed to perform tests concerning their biological activity. Unfortunately, isolation of furan-
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FA from natural sources is non-economic because they usually contribute less than 1% to the 3 ACS Paragon Plus Environment
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total fatty acids of plant and animal lipids.1,2,15 Hitherto, the only relevant exception is the
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milky fluid of Hevea brasiliensis, commonly known as latex. About 90% of the fatty acid
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pattern of latex originated from the furan-FA 9M5, 1.16,17 Recently, isolation of pure 9M5, 1,
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from liquid centrifuged latex was achieved by countercurrent chromatography (CCC).17 This
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isolate is suited for the use as an analytical standard in furan-FA analysis15,18,19 and may also
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serve as substrate for in vitro investigations of the relevance of furan-FA. However, the
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isolation procedure is not only time consuming,17 but also CCC instruments and the milky
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latex fluid are not readily available to all researchers interested in such studies.17
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The goal of this study was to select a more convenient source and isolation procedure
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for 9M5, 1, For this purpose, we studied its occurrence in disposable latex gloves, i.e. one
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readily available industrial product made from latex. Disposable latex gloves are widely
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distributed in medical and chemical laboratories, and samples from different producers were
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screened for the presence of 9M5, 1, and possibly other furan-FA. We also studied the
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stability of 9M5, 1, when disposable latex gloves were removed from the (light-protecting)
71
packaging and exposed to daylight. Finally, we present an easy and fast method for the
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isolation of methyl and ethyl esters of 9M5, 1, from disposable latex gloves.
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MATERIALS AND METHODS
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Organic solvents and chemicals. Methanol (>99.8%) and n-hexane (>95%) were
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from VWR Chemicals (Darmstadt, Germany), while ethanol, diethyl ether (both distilled
77
before use) and sulfuric acid were from Carl Roth (Karlsruhe, Germany). Silica gel 60 and
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silver nitrate were from Sigma Aldrich (Taufkirchen, Germany). Sodium chloride and the
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fatty acids palmitic acid (16:0; >98.5%), stearic acid (18:0; >98.5%), oleic acid (18:1∆9;
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>99%), linoleic acid (18:2∆9,12; 99%) and nonadecanoic acid (19:0; >99%) were from Fluka
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Chemicals (Taufkirchen, Germany). Myristic acid (14:0; >99%) was from Merck Chemicals
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(Darmstadt, Germany). A standard of 9M5, 1, was previously isolated from centrifuged latex
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with CCC in our laboratory.17
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Samples and standards. At least one disposable latex glove from 30 different
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products was obtained from 14 producers (Table 1). The quantitation standard 19:0 (ISTD-1)
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was prepared at a concentration of 10.1 mg/mL in n-hexane/diethyl ether (1:1, v/v). For the
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second internal standard (14:0-EE, ISTD-2), 10 mg 14:0 were transesterified as described by
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Wendlinger et al.15 with 2 mL ethanol containing sulfuric acid (1 vol%) instead of methanol.
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The resulting ISTD-2 (14:0-EE, c = 5.61 mg/mL) was transferred into an amber 1.5 mL screw
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cap vial and stored at -20 °C.
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Gas chromatography with flame ionization detector (GC/FID) or mass
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spectrometry (GC/MS). Samples were measured on an Autosystem XL GC/FID instrument
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(Perkin Elmer, Rodgau, Germany) which was equipped with a 25 m x 0.53 mm i.d., 0.5 µm
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DB 23-Megabore (50% cyanopropyl, 50% dimethyl polysiloxane) column (Agilent,
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Waldbronn, Germany). Measurements were carried out with N2 (5.0) as carrier gas (constant
96
pressure, 15 kPa). Injections (1 µL) in split mode (split ratio 1:4.7, flow rate: 20 mL/min)
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were performed at 205 °C. The GC oven program started for 1 min at 60 °C. Then the
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temperature was first raised to 190 °C with a ramp of 20 °C/min and then to 220 °C with 4
99
°C/min. The final temperature of 230 °C was reached with another ramp of 20 °C/min and
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held for 10 min.
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GC/MS measurements were performed on a 6890/5973N GC/MS system (Agilent
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Technologies, Santa Clara, CA), equipped with a 30 m x 0.25 mm i.d., 0.25 µm HP-5MS
103
(95% methyl, 5% phenyl polysiloxane) column (Agilent, Waldbronn, Germany) as recently
104
described (system 1).20 All measurements in full scan mode (m/z 60 - 600) were done with the
105
following oven program: The initial temperature of 60 °C was held for 1 min and was then
106
raised to 180 °C with a ramp of 13 °C/min and further increased to 250 °C with 3 °C/min. The
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final temperature of 300 °C was reached with a ramp of 20 °C/min and held for 5 min, 5 ACS Paragon Plus Environment
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resulting in a total run time of 41.06 min. For measurements in selected ion monitoring (SIM)
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mode characteristic ions were divided into time windows according to Wendlinger et al.15
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Response factors of fatty acid methyl esters (FAME) were also measured on another
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6890/5973 GC/MS system equipped with a cool on-column inlet (Hewlett-Packard/Agilent,
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Waldbronn, Germany) and a 15 m x 0.25 mm i.d., 0.1 µm Rtx-1 (100% dimethyl
113
polysiloxane) column (Restek, Bellefonte, PA) as recently described (system 2).20 All
114
measurements were performed in full scan mode (m/z 30 – 600). Additionally, response
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factors were measured on a 5890 Series II GC/FID instrument (Hewlett Packard) equipped
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with a 60 m Rtx 2330 column (biscyanopropyl cyanopropylphenyl polysiloxane, 0.25 mm
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internal diameter, 0.1 µm film thickness) (Restek, Bellefonte, PA). Injections of 1 µL in split
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mode (1:10) were done with a Hewlett-Packard 7673 autosampler.
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Liquid extraction and determination of the fat content. Initial tests confirmed that
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the extraction efficiency of 9M5, 1, with 25 mL n-hexane was >90%, which was considered
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appropriate. Hence, disposable latex gloves were cut into pieces of ~1 cm2 and 1.5 g of these
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pieces (~30% of one glove) were supplemented with 25 mL n-hexane and extracted by
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ultrasonication for 5 min. The hexane extract was filtered and the residue on the filter was
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washed twice with 5 mL n-hexane. The combined hexane phases were condensed to ~2 mL
125
with a rotary evaporator and transferred into a 10 mL volumetric flask. The volume was
126
adjusted to 10 mL with n-hexane. A 1 mL aliquot of this extract was used for gravimetric
127
determination of the (lipid) extract content, performed in a pre-weighed 1.5 mL screw cap vial
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once the solvent was removed by a gentle stream of air at 40 °C. Due to logistic reasons, air
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had to be used in this experiment instead of nitrogen. Because 9M5, 1, is sensitive to
130
oxidation, the variation of the sample weight under the chosen experimental conditions was
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investigated in additional tests (Figure S1, Supporting Information).
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Formation of methyl esters. Between 3 and 8 mL latex extract (corresponding with
133
~10 mg extract content) were placed in a 10 mL vial and 50 µL ISTD-1 (19:0) was added. 6 ACS Paragon Plus Environment
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The solvent was removed by a gentle stream of nitrogen at 40 °C and the sample was
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transesterified as previously described.15 In short, 2 mL methanol containing 1 vol% sulfuric
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acid was added, heated to 80 °C and extracted with 2 mL n-hexane. About 1 mL of the
137
resulting FAME solution was transferred into an amber 1.5 mL screw cap vial and stored at -
138
20 °C until analysis by GC/FID or GC/MS.
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Determination of the GC/FID response factor of 9M5-ME. The GC/FID response
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of FAMEs in the transesterified sample was found to be nearly the same for all conventional
141
fatty acids.21 The response factor of 9M5-ME was determined with a solution containing
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methyl esters of palmitic acid (16:0), stearic acid (18:0), oleic acid (18:1∆9), linoleic acid
143
(18:2∆9,12) and 9M5, 1, all at the same concentration of 2 mg/mL. This solution was
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measured three times on two different GC/FID systems each and on GC/MS system 2
145
operated in full scan mode.
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Quantitation and quality control. Before GC/FID measurements all FAME solutions
147
of purified samples were spiked with 25 µL of ISTD-2 (14:0-EE) which was used to level out
148
differences in the injection volume. The peak area of 9M5-ME was additionally corrected by
149
its GC/FID response factor. A blank sample containing both internal standards ISTD-1 and
150
ISTD-2 was measured every day and the recovery of ISTD-1 (19:0) was generally >95%.
151
Therefore, the content of 9M5, 1, in the sample was quantified by means of ISTD-1. All peaks
152
in GC/FID chromatograms were verified by means of authentic standards. In addition, the
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lipid extracts of eight samples #9, #10, #12, #13, #20, #22, #28 and #29 (Table 1) were
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measured on GC/MS system 1.
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Exposure of 1 (9M5, 1) to sunlight behind a window (inside). Five gloves from two
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different producers each #13 and #30 (Table 1) were selected and one glove of each producer
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was extracted as shown above and measured by GC/FID. The remaining four gloves from
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each producer (eight total) were exposed to light by placing them on a windowsill inside the
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laboratory, facing north (August 2016). Over the course of four days (including night- and
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daytime), every 24 h one glove from each producer was removed and analyzed.
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Silver ion mini-column chromatography. FAMEs obtained from the latex extracts
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were subjected to silver ion mini-column chromatography according to Wendlinger et al.15 In
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short, ~450 mg silica gel containing 20% silver nitrate deactivated with 1% water was placed
164
into a Pasteur pipette whose conical exit was packed with glass wool. The column was
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conditioned with ~5 mL n-hexane. Then the lipid extract (obtained from 2.5 g disposable
166
latex glove sample) was placed on the column and fractionated with three solvents. Fraction
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(i) was collected with 15 mL n-hexane/diethyl ether (99.5:0.5, v/v), fraction (ii) was eluted
168
with 15 mL n-hexane/diethyl ether (97:3, v/v) and fraction (iii) with 15 mL n-hexane/diethyl
169
ether (80:20, v/v). The solvents of all fractions were then removed by a gentle stream of
170
nitrogen and adjusted to exactly 1 mL with n-hexane. All fractions were measured on GC/MS
171
system 1.
172
Isolation of 9M5, 1, from latex gloves. About 50 g disposable latex gloves (sample
173
#30) (Table 1) were cut into pieces of ~1 cm² and placed in an amber 1 L-glass bottle. After
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the addition of 800 mL n-hexane, extraction was performed by ultrasonication (5 min). The
175
extract was filtered and the residue was washed twice with 50 mL n-hexane. The solvent was
176
removed and the residue was taken up in 50 mL methanol containing 1 vol% sulfuric acid (or
177
ethanol for the extraction of 9M5-EE). The solution was refluxed for 2 h at 80 °C. Then 30
178
mL water and 30 mL saturated NaCl solution were added and fatty acid methyl (ethyl) esters
179
were extracted 3x with 50 mL n-hexane. The solvent was removed by a rotary evaporator at
180
40 °C and 230 mbar and the residue taken up in 1 mL n-hexane. Column chromatography as
181
described before was performed on a large scale. About 5 g silica gel containing 20% silver
182
nitrate deactivated with 1% water was placed in a glass column (inner diameter ~1 cm) and
183
fractionation was done by eluting the sample with 70 mL n-hexane/diethyl ether (99.5:0.5,
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v/v) (fraction 1), 50 mL n-hexane/diethyl ether (97:3, v/v) (fraction 2) and 50 mL n-
185
hexane/diethyl ether (80:20, v/v) (fraction 3).
186
Statistical analysis. After verifying normal distribution with the Anderson-Darling-
187
test (p > 0.05), all results were analyzed using univariate ANOVA tests (α = 0.05) as
188
integrated in Excel and statistical significance was assumed for p > 0.05. Statistical outliers
189
were detected with the David-Hartley-Pearson-test (α = 0.05) and not considered for ANOVA
190
tests. Correlation of the lipid extract and the amount of 9M5, 1, in disposable latex gloves was
191
calculated with the Pearson correlation coefficient (PCC) in Excel.
192 193
RESULTS AND DISCUSSION
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Peak identification in latex gloves. The hexane extracts of disposable latex gloves
195
consisted of 0.6-1.6% of the initial sample weight (mean value: 1.1%) (Table 1). In either
196
case, 9M5, 1, was detected as prominent peak in all samples. In addition to 9M5, 1, the fatty
197
acid pattern of the samples was characterized by 18:2∆9,12; 18:0; 18:1∆9; 16:0; 18:3∆9,12,15
198
and 20:0 as their methyl esters (Figure 2A), which was verified by GC/MS analysis (Figure
199
2B) of eight arbitrarily selected samples #9, #10, #12, #13, #20, #22, #28 and #29 (Table 1).
200
FAMEs were identified by means of the correct retention time and the molecular ions relative
201
to authentic external reference standards. Specifically, m/z 270 (16:0-ME), m/z 292 (18:3n-3-
202
ME), m/z 294 (18:2n-6-ME), m/z 296 (18:1n-9-ME), m/z 298 (18:0-ME) and m/z 326 (20:0-
203
ME). Likewise, 9M5-ME was identified by GC/MS data including the characteristic
204
molecular ion at m/z 322, the McLafferty ion at m/z 109, and the base peak at m/z 165).2
205
Additional GC/MS measurements in SIM mode (Figure 3A) allowed to identify traces of the
206
furan-FA 9M3, 3, 9D5, 4, and 11M5, 5, in two samples #9 and #22 (Table 1) by means of
207
their characteristic MS molecular ion, McLafferty ion, and base peak (Figures 3B-D).2
208
Unfortunately, the producer country of the disposable latex gloves was only listed on four
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samples, but the two samples which featured the minor furan-FA were both produced in
210
Malaysia.
211
Amount of 9M5, 1, in disposable latex gloves. Surprisingly, the GC/FID response of
212
9M5-ME (injected in the same concentration of 2 mg/mL) was considerably lower than those
213
of conventional FAMEs (Figure 4). GC/FID measurements on two instruments showed that
214
the response factor of 9M5-ME was only 40% of the response of conventional FAMEs (16:0-
215
ME, 18:0-ME, 18:1∆9-ME, 18:2∆9,12-ME), which had very similar GC/FID response factors
216
(all >85% compared to 16:0). Standard deviations for the calculated response factor for 9M5-
217
ME were 0.05,
243
ANOVA) was observed for the ratio of 18:2∆9,12 to 18:0 within samples of producers A (p =
244
0.068), B (p = 0.12), C (p = 0.33) and D/E (p = 0.08), for the ratio of 18:2∆9,12 to 18:1∆9 in
245
samples of producer C (p = 0.16) and for gloves of single producers (p = 0.17) as well as for
246
the ratio of 18:2∆9,12 to 16:0 for producer B (p = 0.69) and for gloves of single producers (p
247
= 0.06). Although no general statistical significance was found, the data strongly indicated
248
that the content of 9M5, 1, in the disposable latex gloves was lower and more variable than in
249
fresh liquid latex.16,17,22
250
Processing of crude latex and/or storage could reduce the content of 9M5, 1, but not
251
the content of the more stable conventional fatty acids. For instance, Englert et al.17 noted that
252
9M5, 1, was instable at pH 12 (~30% transformed in 12 h). Thus, partial post-harvest
253
transformation of 9M5, 1, at pH 10 in technical (stabilized) liquid latex could not be excluded.
254
Liengprayoon et al.23 noted that some lipids (saturated and unsaturated fatty acids) are
255
retained in the dry rubber and varied shares of them may have an effect on the plasticizing
256
properties of the product. Hence, 9M5, 1, could have an effect on the product quality of latex.
257
Next to the pH value, the crucial processes could be varying exposure of 9M5, 1, to light.
258
Further investigations were therefore carried out to study the stability of 9M5, 1, in disposable
259
latex gloves when exposed to natural sunlight. 11 ACS Paragon Plus Environment
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Exposure of disposable latex gloves to light. The stability of 9M5, 1, in disposable latex
261
gloves when exposed to daylight inside a room behind a window for 1-4 days (24-96 h) was
262
studied with two types of samples in which 9M5, 1, initially contributed with 68% (sample
263
#30) (Table 1) and 53% to the total fatty acids (sample #13) (Table 1). The contribution of
264
9M5, 1, to the total fatty acids decreased every 24 h (Figure 6). Due to the changing
265
meteorological conditions during the exposure time (Table S1, Supporting Information) a
266
kinetic evaluation was not possible. For instance, higher decomposition rates in the first 24
267
hours (28% and 23%, respectively) (Figures 6A and 6B) were likely due to the higher light
268
intensity on day 1. Nevertheless, our data verifies the sensitivity of 9M5, 1, when exposed to
269
light. Varied exposure to light during production and storage of the disposable latex gloves
270
could also partly explain the varying contribution of 9M5, 1, to the fatty acids in individual
271
samples, which was lower than in the raw material (~90%).16,17,22
272
Additional peaks were not detected in the GC/FID chromatograms of the extracts after
273
exposure to sunlight. Thus, degradation products of 9M5, 1, may either be volatile as
274
suggested previously9,10 for other furan-FA and/or polar compounds that were not extracted or
275
accessible to GC analysis.
276
Isolation of 9M5-ME by silver ion chromatography. Separation of other FAMEs
277
from 9M5-ME in the extract of 2.5 g disposable latex gloves from sample #30 (Table 1) was
278
achieved with silver ion chromatography. Fraction 1 contained the methyl esters of saturated
279
fatty acids (16:0-ME, 18:0-ME and 20:0-ME) (Figure 7A), whereas the methyl esters of
280
unsaturated fatty acids (18:1∆9-ME and 18:2∆9,12-ME, 18:3∆9,12,15-ME) eluted into
281
fraction 3 (Figure 7C). Hence, 9M5-ME in fraction 2 could be obtained with a purity of ~98%
282
(Figure 7B). The yield was ~5 mg (~97% from the calculated content of 9M5, 1, of 5.1 mg in
283
2.5 g disposable latex gloves, Table 1).
284
Functionality of the method was confirmed by the extraction of 50 g disposable latex
285
gloves from sample #30 (Table 1) (corresponding with ~12 gloves) which provided 101 mg 12 ACS Paragon Plus Environment
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9M5-ME after column chromatography. The yield was still very high (99% of the calculated
287
content of 9M5, 1, vs. 97% in the analytical batch) and the purity was ~99%.
288
Furan-FA analysis is currently hampered by the lack of authentic reference standards
289
for quantitation and method verification.24 Recently, we suggested the use of the ethyl ester of
290
9M5 (9M5-EE) as internal standard for the quantitative analysis of furan-FA in fish and butter
291
samples.2,15,18 This standard can easily be prepared when transesterification is performed with
292
ethanol instead of methanol. In this way, 82.1 mg 9M5-EE (purity ~99%) were obtained from
293
50 g latex from sample #30 (Table 1).
294
The presented data shows that disposable latex gloves contain high amounts of 9M5,
295
1, which can easily be extracted with n-hexane. For quality assurance reasons, disposable
296
latex gloves should not be used during analyses on furan-FA. Yet, the simple extraction and
297
isolation protocol described in this study allows access to sufficient amounts of 9M5-ME and
298
9M5-EE in high purity which can be used as internal standard for furan-FA quantitation. Only
299
5 mg 9M5-EE extracted and isolated from 2.5 g disposable latex gloves will be enough for the
300
use as internal standard in ~5,000 quantitative analyses on fatty acids.
301 302
AUTHOR INFORMATION
303
Corresponding Author
304
* (W.V.) E-mail:
[email protected] Phone: +49 711 459 24016. Fax +49 711
305
459 309 24377.
306
Funding
307
No funding was obtained for performing this study.
308
Notes
309
The authors declare no competing interests.
310
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ABBREVIATIONS USED. 9M5, 9-(3-methyl-5-pentylfuran-2-yl)-nonanoic acid; 16:0,
312
palmitic acid; 18:0, stearic acid; 18:1∆9, oleic acid; 18:2∆9,12, linoleic acid; 18:3∆9,12,15, α-
313
linoleic acid; 20:0, arachidic acid; furan-FA, furan fatty acid; FAME, fatty acid methyl ester;
314
ISTD, internal standard; SIM, selected ion monitoring;
315
316
SUPPORTING INFORMATION. Response factors of stearic acid (18:0), oleic acid
317
(18:1∆9), linoleic acid (18:2∆9,12) and the furan fatty acid 9-(3-methyl-5-pentylfuran-2-yl)-
318
nonanoic acid (9M5), 1, compared to palmitic acid (16:0) measured on two different GC/FID
319
systems and weight reduction of the lipid extract of disposable latex gloves when evaporated
320
with air over the period of 10 minutes in two samples. This material is available free of charge
321
via the Internet at http://pubs.acs.org.
322 323
REFERENCES
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Shirasaka, N.; Nishi, K.; Shimizu, S. Biosynthesis of furan fatty acids (F-acids) by a
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occuring furan fatty acids. Biol. Pharm. Bull., 1996, 19, 1607–1610
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aqueous dispersion. J. Am. Oil Chem. Soc., 1990, 67, 858–862
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Technol. 2013, 25, 7–10
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381
CAPTIONS TO FIGURES
382
Figure 1. Chemical structures of (9-(3-methyl-5-pentylfuran-2-yl)-nonanoic acid (9M5)), 1,
383
(3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid), 2, (9-(3-methyl-5-propylfuran-2-yl)-
384
nonanoic (9M3)), 3, (9-(3,4-dimethyl-5-pentylfuran-2-yl)-nonanoic acid (9D5)), 4, and (11-
385
(3-methyl-5-pentylfuran-2-yl)-undecanoic acid (11M5)), 5.
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386 387
Figure 2. Extract of (A) the GC/FID chromatogram and (B) the GC/MS chromatogram
388
(system 1) of the lipid extract from disposable latex gloves, #28 (Table 1). All fatty acids
389
were measured as methyl esters.
390 391
Figure 3. Extract of (A) GC/MS-SIM chromatogram (system 1) and (B-D) mass spectra of
392
the furan fatty acids (9-(3-methyl-5-propylfuran-2-yl)-nonanoic (9M3)), 3, (9-(3,4-dimethyl-
393
5-pentylfuran-2-yl)-nonanoic acid (9D5)), 4, and (11-(3-methyl-5-pentylfuran-2-yl)-
394
undecanoic acid (11M5), 5, detected in disposable latex gloves from Malaysia, #9 and #22
395
(Table 1).
396 397
Figure 4. GC/FID chromatogram of a standard mix containing methyl esters of palmitic acid
398
(16:0), stearic acid (18:0), oleic acid (18:1∆9), linoleic acid (18:2∆9,12) and 9-(3-methyl-5-
399
pentylfuran-2-yl)-nonanoic acid (9M5), 1, in the same concentration (c = 2 mg/mL).
400 401
Figure 5. Share of fatty acids stearic acid (18:0), oleic acid (18:1∆9) and palmitic acid (16:0)
402
compared to linoleic acid (18:2∆9,12) in disposable latex gloves from different producers.
403
Producers D and E and those with only one sample (single gloves) were summed up in one
404
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405 406
Figure 6. Percentage contribution of 9-(3-methyl-5-pentylfuran-2-yl)-nonanoic acid (9M5), 1,
407
to the total fatty acids in disposable latex gloves exposed to daylight from (A) samples #30
408
and (B) #13 (Table 1) at different time points.
409 410
Figure 7. GC/MS chromatograms (system 1) in full scan mode after silver ion mini
411
chromatography of (A) fraction 1, (B) fraction 2 and (C) fraction 3 of the lipid extract of
412
disposable latex gloves, #30 (Table 1).
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Table 1: Share of Lipid Extract per Glove, Contribution of (9-(3-methyl-5-pentylfuran-2-yl)nonanoic acid (9M5)), 1, of the Total Fatty Acids, and Amount of 9M5 in 30 Different Disposable Latex Gloves from 14 Different Producers.
Number
Product
1 A1 2 A2 3 A3 4 A4 5 A5 6 A6 7 A7 8 A8 9 B1 10 B2 11 B3 12 B4 13 B5 14 C1 15 C2 16 C3 17 C4 18 D1 19 D2 20 E1 21 E2 22 F1 23 G1 24 H1 25 I1 26 J1 27 K1 28 L1 29 M1 30 N1 Mean/Median:
Share of lipid extract per glove [%]
Contribution of 9M5 to the total fatty acids [%]
Amount of 9M5 [mg/g glove]
1.4 1.3 1.2 1.2 0.8 0.6 1.6 1.2 1.6 1.2 1.0 1.0 0.9 1.5 1.4 1.1 0.9 0.9 0.9 1.1 0.9 1.6 1.5 1.2 1.2 1.0 1.0 0.9 0.8 0.8 1.1/1.1
67.2 67.2 65.4 58.1 52.3 57.4 51.9 37.9 57.6 74.7 39.4 70.3 52.8 54.9 87.0 47.3 54.7 85.1 66.9 68.2 68.4 59.2 68.7 76.0 60.5 58.3 57.3 56.1 53.0 67.9 61.4/58.8
2.6 2.5 1.9 1.6 0.8 1.1 2.0 0.7 2.9 3.2 0.6 2.9 0.8 2.0 8.2 1.0 1.5 4.4 1.8 2.0 1.7 3.8 2.8 3.8 1.6 2.0 1.7 2.2 1.1 2.1 2.2/2.0
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Figure 1
′ ′
9
1
M
5
2
3
4
5
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Figure 2
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Figure 3 Irel
9M5 (1)
A
9M3 (3) 9D5 (4) 18.0
Irel
19.0
20.0
21.0
22.0
23.0
11M5 (5) 24.0
25.0
137
9M3 (3)
[min]
B
294 109
100
Irel
180
140
260
220
300
9D5 (4)
m/z
C 179
123
100
Irel
336
140
11M5 (5)
180
220
260
165
m/z
D
109
100
300
350
140
180
220
260
300
340
380
m/z
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Figure 4
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share of fatty acid compared to 18:2 9,12 [%]
Figure 5 100 120
18:0 18:1∆9 18:1 16:0
80
60
40
20
0 A
B
C
D/E
single gloves
different producers
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Figure 6
Contribution of 9M5 to total fatty acids [%]
80
60
A 68
49
40
40 34 20
22
0 0
24
48 hours in daylight [h]
72
96
Contribution of 9M5 to total fatty acids [%]
80
B
60 53 40 41 36 31
28
72
96
20
0 0
24
48 hours in daylight [h]
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Figure 7 Irel
Fraction 1
A
18:0
16:0
20:0 14.0 Irel
18.0
20.0
Fraction 2
14.0 Irel
16.0
22.0
24.0
B
9M5
16.0
Fraction 3
18.0
20.0
22.0
[min]
24.0
[min]
C
18:2∆9,12
18:1∆9
18:3∆9,12,15 14.0
16.0
18.0
20.0
22.0
24.0
[min]
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TABLE OF CONTENTS GRAPHIC
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