ARTICLE pubs.acs.org/ac
High-Sensitivity Analysis of Six Synthetic Musks by Ultra-Performance Liquid ChromatographyAtmospheric Pressure PhotoionizationTandem Mass Spectrometry Shih-Chun Candice Lung*,†,‡ and Chun-Hu Liu† † ‡
Research Center for Environmental Changes, Academia Sinica, Nankang, Taipei, Taiwan 115 Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan ABSTRACT: The occurrence and potential toxicity of synthetic musks in environmental media have aroused concerns for the impacts of these chemicals on ecosystems and human health. Here, we present the first method using ultra-performance liquid chromatographyatmospheric pressure photoionization tandem mass spectrometry (UPLC-APPI-MS/MS) for analysis of the six most important synthetic musks. Analysis was performed on an API 3000 triple quadrupole equipped with a PhotoSpray APPI source. Two pairs of precursor/product ions are presented that are essential for confirmation. Chromatographic separation is completed in 7 min in the positive mode and 5.1 min in the negative mode. Furthermore, three dopant solutions (0.5% anisole in toluene, 0.5% 2,4-difluoroanisole (DFA) in bromobenzene, and 0.5% DFA in chlorobenzene) are compared in terms of sensitivity, linearity, precision, and accuracy. The best sensitivity is associated with 0.5% anisole in toluene as the dopant; all LODs are below 6 pg. The linear range is 5 to 500 ppb with fairly good precision and accuracy. This analytical method has also proven its applicability by analyzing real air samples. In summary, we present a fast, sensitive, and reliable UPLC-APPI-MS/ MS method for six important synthetic musks; it can be readily applied to environmental studies.
T
he occurrence and potential toxicity of ingredients in the pharmaceuticals and personal care products (PPCPs) in environmental media have aroused concerns about the impacts of these chemicals on ecosystems and human health; one of the major classes of PPCPs are synthetic musks.1 Worldwide, more than 5000 tons per year of synthetic musks are produced.2 They have widespread use as a substitute for natural musks and are used as fragrances and as fixatives in a number of consumer products such as laundry detergents, fabric softeners, cleaning agents, and cosmetic and hygiene products (soaps, shampoos, deodorants, body lotions, perfumes, toiletries, etc).3 They were first identified in environmental samples almost 30 years ago.4,5 Nevertheless, scientists did not pay much attention to them until 15 years ago when they realized the important characteristics of synthetic musks such as their persistence in the environment, bioaccumulative tendency, and potential toxicity to aquatic organisms and humans.3 Up to now, synthetic musks have been detected in the air, water (sewage, surface water, and marine environments), biota (fish and mussel), and humans (blood, milk, and adipose samples) in American, Euporean, and Asian countries.615 Atmospheric transport is thought to be the major path for their presence in remote regions.16 Synthetic musks can be classified into two major groups, nitro and polycyclic musks. It was estimated that the contribution of the polycyclic musks to the global production of synthetic musks is about 85% compared to only 12% for nitro musks.2 The major polycyclic r 2011 American Chemical Society
musks are 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta[g]-2-benzopyran (HHCB, trade name Galaxolide) and 7-acetyl1,1,3,4,4,6-hexamethyltetraline (AHTN, trade name Tonalide). These two products represent about 96% of the EU market and 95% of the US market for all polycyclic musks.17 Both of them and another member of this group 4-acetyl-1,1-dimethyl-6-tert-butylindane (ADBI, trade name Celestolide) are the three most frequently found polycyclic musks in environmental samples and human tissues.315 The nitro musks make up less than 7% of the synthetic musks volume in the EU and less than 6% of the US volume. The major nitro musks are musk xylene (1-tert-butyl-3,5-dimethyl-2,4,6trinitrobenzene, MX), musk ketone (1-tert-butyl-3,5-dimethyl-2, 6-dinitro-4-acetylbenzene, MK), and musk moskene (1,1,3,3,5pentamethyl-4,6-dinitroindane, MM).17 The toxicity of nitro musks and their amino transformation products in aquatic organisms and humans has been recognized for some time,18 and the potential toxic effects of polycyclic musks were also demonstrated in several publications.19 It was found that polycyclic musks showed higher potentials to induce cytotoxicity compared to nitro musks in aquatic environment, and the combined toxicity of mixtures was even higher than additive for those mixtures that included one compound from Received: March 18, 2011 Accepted: May 4, 2011 Published: May 04, 2011 4955
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Table 1. Abbreviation, Chemical Formula, and Molecular Weight of Six Selected Musks and Three Deuterated Standards compound
abbreviation
chemical
molecular
formula
weight
benzo[a]anthracene D12
BAA-D12
C18D12
240.3
Celestolide
ADBI
C17H24O
244.4
Galaxolide
HHCB
C18H26O
258.4
Tonalide Tonalide D3
AHTN AHTN-D3
C18H26O C18H23D3O
258.4 261.4
musk moskene
MM
C14H18N2O4
278.3
musk ketone
MK
C14H18N2O5
294.3
musk xylene
MX
C12H15N3O6
297.3
musk xylene D15
MX-D15
C12D15N3O6
312.4
each class.19 In addition, it was found that musk compounds can act as long-term inhibitors of cellular xenobiotic defense systems, which has significant implication on human health because of possible prolonged exposure to all toxicants as a result of inhibited defense systems.20 The current analysis methods for synthetic musks in the environmental media use gas chromatography-related instrumentation such as gas chromatography/mass spectrometry (GC/MS).21,22 GC/MS with electron impact ionization (GC/ MS-EI) is sensitive to both nitro musks and polycyclic musks, while GC/MS with negative chemical ionization (GC/MS-NCI) is more sensitive to nitro musks. However, because these musk compounds have molecular weights greater than 240 amu, using GC/ MS to analyze these low volatility analytes may not be the best choice. Liquid chromatography/mass spectrometry (LC/MS) can overcome such limitations. This work presents a method for the simultaneous analysis of six important synthetic musks with ultra-performance liquid chromatographyatmospheric pressure photoionization tandem mass spectrometry (UPLC-APPI-MS/MS). Three popular ionization sources used on LC/MS are electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photoionization (APPI). The former two fail to effectively ionize nonpolar compounds while APPI has been developed to analyze a broad spectrum of polar, medium polar, and nonpolar compounds.23,24 To date, there is no literature presenting LC-APPI-MS methods for synthetic musk analysis; this work was conducted with the state-of-theart APPI-tandem mass spectrometry (APPI-MS/MS). The great advantage of using tandem MS is that it can provide two pairs of precursor and product ions, which is important for confirmation because there may be other inferences in analysis. Moreover, dopant is required in APPI; this work evaluated three different choice of dopants in terms of limits of detection (LOD), linear range, precision, and accuracy. In addition, ultra-performance liquid chromatography (UPLC) is a new instrumentation available only in the past 6 years. The benefit of using UPLC compared to traditional highperformance liquid chromatography (HPLC) is shorter analytical time with superior resolution and sensitivity.25 This work presents a method with UPLC and a UPLC column for chromatographic separation of six important synthetic musks. In short, this is the first manuscript presenting an analytical method with UPLC coupled with APPI-MS/MS for the analysis of synthetic musks.
Figure 1. The molecular structures of six musks: (a) ADBI, (b) HHCB, (c) AHTN, (d) MM, (e) MK, and (f) MX.
’ EXPERIMENTAL SECTION Choices of Musks. Six musks were selected, namely, ADBI, HHCB, AHTN, MM, MK, and MX, in the order of increasing molecular weights (Table 1). They are the top three most important polycyclic musks and nitro musks, respectively, in terms of their production and environmental occurrence. Their structures are shown in Figure 1. Chemicals and Reagents. Individual standards for ADBI and AHTN were purchased from LGC Standards (Wesel, Germany) with concentrations of 100 ng/μL in cyclohexane. Standards for MM, MK, and MX were obtained from Sigma-Aldrich (St. Louis, MO) with concentrations of 100 ng/μL in acetonitrile. HHCB (10 ng/μL in cyclohexane), MX-D15 (100 ng/μL in acetone), AHTN-D3 (100 ng/μL in iso-octane), and benzo[a]anthraceneD12 (BAA-D12, 10 ng/μL in acetonitrile) were purchased from Dr. Ehrenstorfer GmbH (Augsburg, Germany). Acetonitrile (LC/MS grade, 0.2 μm prefiltered), methylene chloride (Ultra resi-analyzed), and chlorobenzene (99.5%, analytical grade) were purchased from J. T. Baker (Phillipsburg, NJ). Bromobenzene (99.5%), anisole (99%), and 2,4-difluoroanisole (98%) were obtained from Merck (Hohenbrunn, Germany), Alfa Aesar (Lancashire, UK), and Sigma-Aldrich, respectively. Milli-Q water (Millipore, Tokyo, Japan) was used for UPLC analysis. Instruments. The mass spectrometer was an API 3000 triple quadrupole from Applied Biosystems/MDS SCIEX, equipped with a PhotoSpray APPI source (Toronto, Canada). This APPI source was purchased in 2006; thus, it is a modified PhotoSpray APPI source.23 The APPI source’s transfer voltage was 1500 V, its 4956
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Table 2. Two Pairs of Precursor/Product Ions and the Associated MS/MS Parameters for Six Musks and Three Deuterated Standardsa MRM1 compound
DP, V
MRM2
polarity
Q1
Q3
FP, V
EP, V
BAA-D12
þ
240.3
236.2
39.9
5.2
56.4
ADBI
þ
243.4
187.1
14.1
93.3
10.3
18.6
9.3
HHCB AHTNb
þ þ
258.3 259.4
188.1 175.1
20.3 29.7
107.9 128.4
6.9 10.8
22.0 26
15.0 14.2
189
CE, V
CXP, V
2ndQ3
CE, V
CXP, V
14
238.2
47.2
14
145.1
21.4
11.6
243.1
17.1
19.0
second MRM
þ
243.4
187.1
25.2
127.2
5.0
17.6
14.0
AHTN-D3b
þ
262.4
178.1
29.2
165.0
5.1
27.1
12.0
second MRM
þ
246.4
190.1
129.7
154.5
4.9
18.8
15.2
MM
248.3
203.1
20.0
117.9
10.3
35.8
17.3
218.0
24.3
12.3
MK
264.3
206.0
28.1
130.1
8.2
26
12.0
234.0
21.9
13.6
MX
267.3
175.0
33.0
161.5
10.3
37.1
9.1
192.0
31.9
10.0
MX-D15
282.4
186.1
12.3
70.3
8.0
35.1
10.4
234.2
30.1
12.6
Note: þ: positive mode, : negative mode, MRM: multiple reaction monitoring, Q1: precursor ion, Q3: product ion, DP: declustering potential, FP: focusing potential, EP: entrance potential, CE: collision energy, and CXP: collision cell exit potential. b The second precursor ions and associated product ions are presented. a
probe temperature was 400 °C, and the flow rate of the lamp gas was 1.5 L/min. Nitrogen was used as nebulizer, drying, curtain, and collision gases. The settings for the nebulizer, curtain, and collision gases were 6, 8, and 7 (instrument units). A Waters UPLC system (Acquity UPLC column manager, sample manager, binary solvent manager, Waters, Milford, MA) was used for LC analysis. Control of the instruments, data acquisition, and analysis were performed with Analyst software version 1.4.2. Preparation of Standards. Working standard solutions were prepared from the above individual component stock solutions by series dilution method in acetonitrile. BAA-D12 and MX-D15, prepared in acetonitrile with 1 ng/μL, were used as internal standards in positive and negative modes, respectively. AHTN-D3 (1 ng/μL in acetonitrile) was used as a surrogate standard which is spiked into samples in the beginning of the sample preparation process to assess the recovery. The optimized MS/MS parameters of these standards were also assessed along with the selected musk target analytes. Optimization of Tune Page Parameters. The optimization of MS/MS parameters was obtained by manual tuning to obtain the best response signals via ramping various electric potentials. Standard solutions with 0.5 μg/mL concentrations in acetonitrile were injected to MS/MS in 20 μL/min. A mixed standard was injected with infusion and m/z ratio of 200350 with full scan was used to search for the overall best response to set nebulizer gas and curtain gas parameters. Then, the optimized parameters of declustering potential (DP), focusing potential (FP), and entrance potential (EP) were determined by continuous infusion with individual standards to search for precursor ions with (3 m/z range. Afterward, product ions were scanned and collision energy (CE) and collision cell exit potential (CXP) were optimized accordingly. Choice of Dopant. Initially, toluene and anisole were selected as the dopant. Additionally, recent publications have identified chlorobenzene and bromobenzene as potentially effective dopants for analysis of nonpolar compounds under reversed-phase LC conditions.26,27 2,4-Difluoroanisole (DFA) introduced as a diluted solution was shown to provide high sensitivity for LCAPPI-MS.26 Thus, these compounds were tested as dopants for musk analysis. Here we present test results of three different dopant solutions, namely, 0.5% anisole in toluene (dopant A),
0.5% DFA in bromobenzene (dopant B), and 0.5% DFA in chlorobenzene (dopant C). LODs of analytes with these dopants are presented and compared. Optimization of Multireaction Monitoring Data Acquisition Parameters. The scan type was “Multiple Reaction Monitoring” (MRM), the polarity was positive for three polycyclic musks and negative for three nitro musks, and the Q1 and Q3 resolutions were “unit” (0.7 ( 0.1 amu). The masses scanned are listed in Table 1. The dwell times were 50 and 200 ms for positive and negative modes, respectively. For the infusion experiments, where analytes were introduced individually, all scan parameters were the same, except that the dwell time was 200 ms. Column Separations and Analysis. To achieve the highest selectivity and sensitivity, both UPLC and MS/MS conditions must be optimized. Different analytical columns and separation conditions were investigated with the aim of achieving a short separation time. Sufficient separation of the target analytes was finally achieved with the conditions presented below. Chromatographic separation was performed using a Pinnacle DB PAH 100 mm 2.1 mm 1.9 μm UPLC column, from Restek (Bellefonte, PA), connected to a Acquity UPLC BEH C18 VanGuard Precolumn (2.1 mm 1.7 μm, Waters, Milford, MA). The column was at 30 °C. Column separation was achieved using water/acetonitrile as a binary mobile phase system. The mobile phase solvents were 100% water (A) and 100% acetonitrile (B). The mobile phase flow rate was 300 μL/min. The elution gradient was 50%(A)/50%(B) initially, 100%(B) at 810 min, and 50%(A)/50%(B) at 10.1 min. Sample injection volume was 5 μL. An amount of 5 μL of standard solutions was injected on column using a 10 μL loop with “partial loop with needle overfill” method. For the infusion experiments, 20 μL/min analyte solution and 2 μL/min dopant were delivered via syringe pumps from KD Scientific (KDS-100, Holliston, MA). For all the experiments except infusion, dopant was delivered at 30 μL/min. Field Sampling and Extraction. To assess the applicability of this analytical method, two days of field sampling were conducted at the campus of National Taiwan University (NTU) located in the center of Taipei city on June 78, 2010. Mean temperature of these two days was 19.5 and 20.2 °C, with relative humidity 82% and 80%, respectively. PM2.5 (particulate matter 4957
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Figure 2. MRM ion chromatograms of six musks and three deuterated standards with on-column injection amounts of 25 pg in (a) the positive mode: for RT 5.46, ADBI; 5.86, AHTN-D3; 5.89, AHTN; 6.04, HHCB; and 6.91, BAA-D12; and in (b) the negative mode: 3.93, MK; 4.56, MX-D15; 4.63, MX; and 5.08, MM; the dopant was 0.5% anisole in toluene.
with aerodynamic diameter equal to or less than 0.25 μm) samples were collected for daytime (8 am to 8 pm) and nighttime (8 pm to 8am) with a high-volume sampler (Tisch, Cleves, OH). One-eighth of the filters was spiked with ANTH-D3 and extracted three times with hexane:methylene chloride (1:4). The extracts were concentrated down to 0.5 mL with nitrogen, cleaned-up with HLB cartridges (WAT106202, Waters), and filtered with a 0.22 μm PTFE filters (GET00048, Great Engineering Technology Corp., Taipei, Taiwan). The elutants were solvent-exchanged with 0.2 mL of acetonitrile, spiked with internal standards, and analyzed with the presented UPLCAPPI/MS/MS method.
’ RESULTS AND DISCUSSION Two pairs of precursor/product ions of these synthetic musks and the corresponding optimized MS/MS parameters are
summarized in Table 2. Six of them are presented with the second product ions with the same precursor ions, and two of them (AHTN and AHTN-D3) are with the second precursor ions and associated product ions. For these synthetic musks, these two pairs of precursor/product ions, essential for confirmation, in LC/MS/MS are reported for the first time. Figure 2 shows MRM ion chromatograms of six selected musks and three deuterated standards with on-column injection amounts of 25 pg using the parameters and conditions described earlier. They are well separated and quantified in 7 min in the positive mode and 5.1 min in the negative mode. Compared to 1020 min required for separating these musks in GC/MS analysis,28,29 this UPLC-APPI-MS/MS method has shorter analysis time. Limits of Detection with Different Dopants. Table 3 shows the LODs of six selected synthetic musks and two musk standards using UPLC-APPI-MS/MS with three different 4958
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Table 3. LODs of Six Musks and Two Deuterated Musk Standards Using UPLC-APPI-MS/MS with Three Different Dopant Solutions (0.5% anisole in toluene (dopant A), 0.5% DFA in bromobenzene (dopant B), and 0.5% DFA in chlorobenzene (dopant C))a APPI dopant compound
a
0.5% anisole in toluene
polarity
injection amount (pg)
0.5% DFA in bromobenzene S/N
injection amount (pg)
S/N
0.5% DFA in chlorobenzene injection amount (pg)
S/N
ADBI
þ
5
3.6
4
3.1
3
3.7
HHCB
þ
2
3
2
3.3
2
3.5
AHTN
þ
4
3.2
AHTN-D3
þ
2
MM MK
MX MX-D15
15
3
25
3
3
8
3
7
3
4 5
5 6
150 150
3
5
90
6
5
135
3 3.5
3 11
3 6.2
4
6
3.5
3
4
3
S/N: signal to noise ratio.
Table 4. The Linear Range, R2, Precision, and Accuracy of Six Musks Using UPLC-APPI-MS/MS with (a) 0.5% Anisole in Toluene (dopant A) and (b) 0.5% DFA in Chlorobenzene (dopant C) as the Dopant (n = 3) (a) precision (%) compound
linear range
2
R
low (10 ppb)
accuracy (%)
high (500 ppb)
low (10 ppb)
high (500 ppb)
ADBI
5500
0.9988
5.9
3.3
99.9 ( 5.9
99.1 ( 3.2
HHCB AHTN
5500 5500
0.9982 0.9986
5.7 1.4
3.1 1.0
99.2 ( 5.7 99.3 ( 1.4
96.5 ( 3.0 94.7 ( 0.9
MM
5500
0.9986
6.3
3.9
104.9 ( 6.6
95.9 ( 3.7
MK
5500
0.9994
1.2
2.3
105.5 ( 1.6
98.0 ( 2.3
MX
5500
0.9996
3.4
6
101.4 ( 3.4
96.4 ( 5.8
(b) precision (%) compound
linear range
R2
low (10 ppb)
accuracy (%)
high (500 ppb)
low (10 ppb)
high (500 ppb)
ADBI
5500
0.9984
4.9
2.0
93.2 ( 4.5
98.5 ( 2.0
HHCB
5500
0.9988
7.7
2.9
99.6 ( 7.7
97.5 ( 2.9
AHTN
5500
0.9994
5.4
1.6
94.3 ( 5.1
98.1 ( 1.5
MM
5500
0.9980
7.1
1.2
96.0 ( 6.9
97.4 ( 1.1
MK
5500
0.9982
5.7
1.8
100.1 ( 5.7
97.8 ( 1.8
MX
5500
0.9988
9.7
1.6
98.3 ( 9.6
96.8 ( 1.6
dopant solutions. In general, the best sensitivity of these musks is associated with dopant A (0.5% anisole in toluene); all the LODs are below 6 pg. Most of the LODs with dopant C (0.5% DFA in chlorobenzene) are comparable to those with dopant A except for AHTN which is 1 order of magnitude higher. In addition, the LODs of nitro musks associated with dopant B (0.5% DFA in bromobenzene) are 2 to 3 orders of magnitude higher than those with dopants A and C. In the next section, further evaluation of linearity, precision, and accuracy were conducted with dopants A and C only. Previous work has presented that bromobenzene showed signals in APPI-MS/MS slightly stronger than that of chlorobenzene as dopants,26 in contrast to our results. Especially in the negative mode, the signals of analytes associated with dopant B in our work are much weaker compared to dopant C, resulting in 3 orders of magnitude higher LODs. Furthermore, the weaker
responses in both the positive and the negative modes of APPI with bromobenzene compared to chlorobenzene are consistent with another work performed in our laboratory using these two dopants for nitro-PAH analysis.30 The current results confirm our previous findings. In addition, it was mentioned that bromobenzene and chlorobenzene with relatively higher ionization energy (IE) of 9.00 and 9.07 eV, respectively, are more effective dopants in LC-APPIMS/MS, compared to toluene (IE = 8.83) and anisole (IE = 8.20),26 especially for those high-IE compounds poorly ionized by anisole/toluene. In a follow-up study, toluene and anisole showed signals weaker than those of bromobenzene and chlorobenzene in LC-APPI-MS/MS for analysis of 16 priority PAHs.23 However, our works showed that LODs of musks with 0.5% anisole in toluene are the lowest among the three dopants. In fact, previous works performed in our laboratory using these 4959
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Figure 3. MRM ion chromatograms of four musks detected in the real air samples in (a) the positive mode and (b) the negative mode.
Table 5. Concentrations (pg/m3) of Six Musks in Taipei Air Obtained by the Presented Analytical Methoda ADBI
a
HHCB
AHTN
MM
MK
MX
20100607D
b
447.47
253.90
26.21
20100607N
293.17
320.12
41.89
14.61
20100608D
344.48
216.32
32.57
23.61
20100608N
323.36
322.05
15.80
D: day time; N: night time. b Nondetectable.
dopants for PAH and nitro-PAH analysis showed consistent results, i.e., LODs associated with 0.5% anisole in toluene as a dopant are at least comparable to those with 0.5% DFA in chlorobenzene and bromobenzene. One possible explanation for such a discrepancy is that our modified PhotoSpray APPI source offers better ionization; thus, minor differences in ionization energy of dopants might not be so critical. This requires further evaluation. Our LODs, in the range of 26 pg, are compared with those in the literature. Xie et al.22 summarized method detection limits (MDLs) of musks in air samples. The MDLs are around 510 pg/m3 for polycyclic musks (HHCB and AHTN) with GC/MSEI and 0.20.5pg/m3 for nitro musks (MX and MK) with GC/ MS-NCI, respectively.31 With typical sampling rates of 1400 m3 in 24 h and the final volume of 200 μL with 5 μL injection, the estimated MDLs of our method are in the range of 0.09 0.17 pg/m3 for both polycyclic musks and nitro musks. In addition,
Comez et al.29 and L. I. Osemwengie32 used GC/MS to analyze water and sewage samples, respectively; according to their MDLs, the estimated injection amounts were 12.587.5 pg and 1125 pg, respectively, much higher than our injection amounts. These results suggest that our method is more sensitive than previous ones for both groups of musk compounds. Linearity, Precision, and Accuracy. The linear ranges of musk responses were assessed in order to establish applicable ranges for calibration curves in environmental studies. It shows that R2 values are all higher than 0.998 at 5500 ppb with both dopants A and C (Table 4a,b). Moreover, the precision and accuracy with dopant A are all within 6.6% for both low (10 ppb) and high (500 ppb) concentrations. With dopant C, the precision and accuracy are all within 10% and 3% for low and high concentrations, respectively. The precision and accuracy with dopant C are slightly better in high concentrations and worse in low levels compared to those associated with dopant A. In summary, the results show that the signals of six synthetic musks in our method are linear over 5500 ppb with fairly good precision and accuracy with both dopants. Field Sample Evaluation. Based on the above assessment, the analytical method with dopant A has the best sensitivity and linear range of 5500 ppb with good precision and accuracy. Thus, real air samples collected at NTU campus were analyzed with this method; the MRM ion chromatograms of four synthetic musks detected are presented in Figure 3a,b. The concentrations are presented in Table 5. The field blank values were below the LODs except for AHTN (9.2 pg/μL); the reported 4960
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Analytical Chemistry concentrations of AHTN were corrected by blanks. The recovery rates of the spiked surrogates were 7389%; the presented results were corrected by recovery rates. The matrix spikes of these target compounds had recovery rates of 7097%. The results show that the levels of HHCB and AHTN were in the range of 200450 pg/m3, while those of MK and MX were in the range of 1442 pg/m3. No trace amounts of ADBI and MM were found in the air of Taipei. To date, the concentrations of these synthetic musks in the aerosol phase in the air have been scarcely studied and reported. Peck and Hornbuckle (2006)33 studied the gas-phase levels of musks in the air and found that HHCB and AHTN were detected most frequently and at the highest concentrations and MX was detected more frequent than MK, consistent with our results in the aerosol phase. In summary, the above results indicate that our analytical method is well applicable in environmental studies.
’ CONCLUSION This work presents the first UPLC-APPI-MS/MS method for high-sensitivity analysis of six important synthetic musks; it can be readily applied in environmental studies. With a Pinnacle DB PAH 100 mm 2.1 mm 1.9 μm UPLC column and a water/ acetonitrile binary mobile phase, musk compounds are well separated and quantified in 7 min in the positive mode and 5.1 min in the negative mode, shorter than the GC/MS analysis time. In addition, two pairs of precursor/product ions of these musks in LC/MS/MS are reported for the first time, which are essential for confirmation. Furthermore, three dopant solutions are compared in terms of sensitivity, linearity, precision, and accuracy. The best sensitivity is associated with 0.5% anisole in toluene; all LODs are below 6 pg, and the responses are linear at 5500 ppb with fairly good precision and accuracy. This analytical method has also proven its applicability for the analysis of real air samples. In summary, we present a fast, sensitive, and reliable UPLC-APPI-MS/MS method for six important synthetic musks; this method can be applied to a wide range of environmental studies to facilitate the understanding of fate and transport of synthetic musks. ’ AUTHOR INFORMATION Corresponding Author
*Tel: 886-2-26539885 ext. 277. Fax: 886-2-27833584. E-mail:
[email protected].
’ ACKNOWLEDGMENT This study was funded by grant number 93-2111-M-001-005, 94-2111-M-001-005, and 95-2111-M-001-002 from National Science Council (NSC), Executive Yuan, Republic of China. Its contents are solely the responsibility of the authors and do not necessarily represent the official view of the NSC.
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dx.doi.org/10.1021/ac2006872 |Anal. Chem. 2011, 83, 4955–4961
