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Evaluation of GC-ICP-MS/MS as a New Strategy for Specific Hetero-Atom Detection of Phosphorus, Sulfur, and Chlorine Determination in Foods Jenny Nelson, Helene Hopfer, Fabio Silva, Steve Wilbur, Jian-min Chen, Kumi Shiota Ozawa, and Philip Wylie J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/jf506372e • Publication Date (Web): 23 Mar 2015 Downloaded from http://pubs.acs.org on March 26, 2015

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Journal of Agricultural and Food Chemistry

Evaluation of GC-ICP-MS/MS as a New Strategy for Specific Hetero-Atom Detection of Phosphorus, Sulfur, and Chlorine Determination in Foods

Jenny Nelson1-3*, Helene Hopfer1-2,4, Fabio Silva3, Steve Wilbur3, Jianmin Chen3, Kumi Shiota Ozawa3, and Philip L. Wylie5 1

Department of Viticulture and Enology, University of California-Davis, One Shields

Avenue, Davis CA 95616, USA 2

Food Safety and Measurement Facility, University of California-Davis, One Shields

Avenue, Davis CA 95616, USA 3

Agilent Technologies, Inc., 5301 Stevens Creek Blvd, Santa Clara CA 95051, USA

4

HM Clause, 9241 Mace Boulevard, Davis CA 95618, USA

5

Agilent Technologies, Inc., 2850 Centerville Rd., Wilmington DE 19808, USA

Email: [email protected]; Telephone: +1 517 510 6475 Fax: 302-636-1584

ACS Paragon Plus Environment

1

1

Abstract


Page 2 of 20

2 3

For the first time in the literature, application of a GC-ICP-MS/MS method for the selective,

4

sensitive detection of specific hetero-atoms of phosphorus, sulfur, and chlorine has been

5

accomplished. As a proof of concept, organophosphorus, organosulfur, and organochlorine

6

pesticides in various food matrices have been studied. For the detection of organophosphorus and

7

organosulfur pesticides, oxygen was used in the collision reaction cell (CRC) to convert P (m/z

8

31) to PO+ (m/z 47) and S (m/z 32) to SO+ (m/z 48). Similarly, ClH2+ (m/z 37) was monitored

9

after reacting Cl (m/z 35) with hydrogen in the CRC for the determination of organochlorine

10

pesticides. Real food samples (baby food purees, fresh vegetables, loose tea) were screened for

11

their pesticide content, following preparation of triplicate extracts using QuEChERS (Quick,

12

Easy, Cheap, Effective, Rugged and Safe). Excellent linearity with correlation coefficients R>

13

0.997 was achieved, and the lowest detection limits obtained for the organophosphorus,

14

organosulfur, and organochlorine pesticides were 0.0005, 0.675, and 0.144 µg/Kg respectively.

15

Keywords. GC-ICP-MS/MS, organophosphorus, organosulfur, organochlorine, pesticide


2

Page 3 16 of 20

17

INTRODUCTION


Accurate and reliable determination of pesticide residues in food products is of great interest

18

to the general public because of the implications for human health, over the short- and long-term.

19

Vulnerable populations, i.e., infants and children, are of particular concern because of their high

20

intake of food per kilogram of body weight, and the potential for more severe impact from

21

pesticide exposure as their bodies develop1. Many pesticides are known or suspected endocrine

22

disrupting chemicals (EDCs), and there is increasing evidence of carcinogenicity and

23

genotoxicity of this class of compounds2. The effects from pesticide exposure can occur at

24

concentrations much lower than are needed to trigger acute effects. Therefore, many researchers

25

are concerned about the long-term implications of low-dose exposure through food consumption

26

and the persistence of pesticides in the environment3,4.

27

To address these concerns, highly sensitive analytical methods have been developed, combining

28

rapid sample preparation techniques with hyphenated separation and detection. The nature of the

29

analytes of interest dictates the analytical method of choice, and pesticide residues used in foods

30

span a broad spectrum of physical and chemical properties. Depending on the analytes, gas

31

chromatography (GC), liquid chromatography (LC) and capillary electrophoresis (CE) have been

32

coupled to various detectors, including specific and general detectors (mass spectrometry (MS),

33

nitrogen/phosphorus detector (NPD), flame photometric detector (FPD), electron capture

34

detector (ECD), UV, fluorescence detectors, etc). Today, most pesticide residue laboratories

35

employ some variation of the QuEChERS extraction method5,6,7. The QuEChERS extract is then

36

analyzed with gas chromatography-tandem mass spectrometry (GC-MS/MS) for the thermally

37

stable, less polar pesticides and liquid chromatography-tandem mass spectrometry (LC-MS/MS)

38

analysis for the less volatile and/or more polar ones8,9.

39

Most pesticides contain heteroatoms, with O, P, S, F, Cl, and Br being the most commonly

40

found elements. For this reason, element selective detectors such as the ECD, NPD, FPD and

41

atomic emission detector (AED) have been coupled to GC for the selective detection of


3

42

heteroatom-containing pesticides. the use ofFood element-selective JournalHowever, of Agricultural and Chemistry detectors has been

43

largely supplanted by MS detection, especially tandem MS (MS/MS), because of its greater

44

selectivity. Frenich et al. and Words compared the ECD and NPD to MS/MS for the analysis of

45

organophosphorus (NPD) and organochlorine (ECD) pesticides. These two studies reported

46

similar detection limits, but also found that in real samples, interferences and co-elution reduced

47

the obtainable sensitivities of the NPD and ECD compared to MS/MS10,11.

48

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However, if these elemental interferences could be overcome, element-specific detection has

49

the potential to further improve the pesticide detection limits by lowering the background

50

chemical noise. The recent combination of tandem MS detection with inductively-coupled

51

plasma (ICP-MS/MS or ICP-QQQ) is a way to address this challenge. Similar to GC or LC-

52

MS/MS, in ICP-MS/MS the first quadrupole (Q1) acts as a mass filter. In the collision reaction

53

cell (CRC) that follows, analytes or interferences react with various gases in a very selective way

54

to produce a product ion which is then accepted (analyte) or rejected (interference) by the second

55

quadrupole (Q2) prior to detection (Figure 1). Using this approach, background levels are

56

dramatically reduced, thus increasing the sensitivity of the detection.

57

Presented here is the first application of a GC-ICP-MS/MS method for selective and sensitive

58

detection of hetero-atom containing pesticides in various food matrices. For the detection of

59

organophosphorus pesticides, oxygen was used in the reaction cell to convert P (m/z 31) to PO+

60

(m/z 47). Similarly, SO+ (m/z 48) was monitored after reacting S (m/z 32) with oxygen for the

61

detection of organosulfur pesticides. For detecting chlorine pesticides Cl (m/z 35) was reacted in

62

the CRC with H2 to form ClH2 (m/z 37).

63

The developed method is an attractive alternative to existing highly sensitive and selective

64

organophosphorus detection methods, with comparable, or even slightly lower, detection limits

65

to GC-MS/MS. The GC-ICP-MS/MS method is easy to set up and does not require retention

66

time based acquisition conditions such as selected ion monitoring windows or the development


4

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of multiple reaction monitoring (MRM) settings. Due the Chemistry detection of hetero-atoms instead of Journal of Agricultural and to Food

68

compounds, GC-ICP-MS/MS allows the quantification of unknown peaks by Compound

69

Independent Calibration (CIC). The use of the MS/MS mode dramatically reduces background

70

levels for interference-prone elements such as P, S, and Cl, thereby increasing the sensitivity of

71

the method significantly compared to single quadrupole ICP-MS detection.

72

Although this paper focuses on the analysis of pesticides by GC-ICP-MS/MS, it is understood

73

that this system is unlikely to replace conventional GC-MS/MS approaches for the analysis of

74

pesticide residues. Most pesticide residue laboratories have already invested in GC-MS/MS and

75

LC-MS/MS equipment and, in most cases, these instruments provide more than adequate

76

sensitivity. Furthermore, such methods have already been validated by the laboratory, a process

77

that can be time-consuming. However, pesticides are a good model for other organophosphorus

78

compounds (e.g., fire retardants and polymer additives) and sulfur compounds that can have a

79

significant influence on flavor and aromas at trace levels. This GC-ICP-MS/MS approach may

80

be useful where extremely low detection limits are desirable, such as for the analysis of

81

pesticides in drinking water or baby food.

82 83

MATERIALS AND METHODS

84

Materials

85

A variety of food matrices were tested for their pesticide content including baby food fruit

86

purees, green onions, tea (3 types), green peppers and yellow onion. The baby food purees were

87

purchased in San Paulo, Brazil, the fresh vegetables were purchased at various produce markets

88

in San Francisco, CA, USA, and the loose tea was purchased in various locations in China. All

89

food matrices were extracted in triplicate using the AOAC 2007.1QuEChERS method before

90

analysis by GC-ICP-MS/MS. HPLC grade acetonitrile was purchased from JT Baker (Center

91

Valley, PA, USA). Calibration was performed using three standard pesticide mixes obtained

92

from Ultra Scientific (Kingstown, RI, USA) and Agilent Technologies (Santa Clara, CA, USA).


5

93

The three mixed standard solutions were diluted with to form intermediate solutions, Page 6 of 20 Journal of Agricultural andacetonitrile Food Chemistry

94

which were then used to prepare calibration standard solutions following serial dilutions in

95

acetonitrile. QuEChERS kits were obtained from Agilent.

96

Samples Preparation

97

Apart from the pre-homogenized baby food purees, all samples were ground in a food

98

processor to obtain a homogenous sample (NutriBullet, LLC, Porcomia, CA, USA).

99

Approximately 15 ± 0.1 g of sample (5 ± 0.1 g in case of the tea due to their low density) were

100

weighed into 50 mL centrifuge tubes, then 15 mL of acetonitrile and 2 ceramic bars were added.

101

This mixture was homogenized for 1 min on a vortex mixer. Then, pre-packaged amounts of

102

MgSO4 and NaCl were added, and the system was agitated for 1 min again. The mixture was

103

centrifuged at 2600 x g for 5 min. An 8-mL aliquot of the upper acetonitrile layer was transferred

104

to 15 mL centrifuge tubes containing the dispersive and clean up agents (PSA, MgSO4). The tube

105

was homogenized for 1 min and centrifuged at 2600 x g for 5 min. The resultant upper layer was

106

transferred to an amber glass vial (Agilent Technologies) for analysis.

107

Instrument Set-up

108

All measurements were carried out using an Agilent 7890 GC (Agilent Technologies, USA)

109

coupled via an Agilent GC-ICP-MS transfer line (Agilent Technologies, Japan) to an Agilent

110

8800 ICP-QQQ instrument (Agilent Technologies, Japan). The chromatographic separation

111

parameters were used as previously published12. The GC system was equipped with fast oven

112

heating (240 V), a split/splitless inlet, a 7693A autosampler, auxiliary electronic pressure control

113

(aux EPC) and a column backflushing system based on a purged union. Two columns were

114

configured in an arrangement that allowed the first column to be backflushed shortly before the

115

run had ended or during a post-run period13. The first column was a 5 m × 0.25 mm i.d. × 0.25

116

µm film thickness DB-5MS UI capillary column (cut from a 30-m DB-5MS UI column obtained

117

from Agilent), which was installed between the inlet and one end of the purged union. Column

118

two was a 15 m × 0.25 mm i.d. × 0.25 µm film thickness DB-5MS UI capillary column (Agilent


6

Page 7119 of 20

Technologies) installed between theofother end of the union and the transfer line Journal Agricultural andpurged Food Chemistry

120

connection inside the GC oven. Injections (1 µL) were made under splitless conditions with the

121

inlet held at 280°C. The GC oven temperature program started at 60°C (held for 1.5 min),

122

followed by a 50°C/min ramp to 150°C, then 8°C/min to 240°C, then 50°C/min to 280°C (2.5

123

min), and finally 100°C/min to 290°C (held for 2.05 min). The helium carrier gas was controlled

124

in constant flow mode. The flow rate settings for analysis and back-flushing mode were used as

125

described previously 12. Helium make-up gas (0.7 mL/min, controlled by an aux EPC module on

126

the ICP-MS/MS) was passed through a metal tube placed in the GC oven and connected to the

127

transfer line interface. The pre-heated make-up gas was used to sweep the GC column effluent

128

efficiently into the plasma.

129

During ICP-MS/MS tuning, the helium carrier gas supplying the GC inlet and aux EPC module

130

was replaced by argon containing H2S at 100 ppm. The oxygen flow rates in the reaction cell and

131

the quadrupole energy settings of the ICP-MS/MS were optimized by manually following the

132

32 +

133

background for several days after switching back to pure helium, so an alternative position to

134

feed the tuning gas into the ICP-MS/MS is recommended. The optimal operating conditions for

135

the ICP-MS/MS are shown in Table 1.

136

The ICP-MS/MS includes an Octopole Reaction System (ORS3) that is positioned between two

137

quadrupole analyzers, as shown in figure 1. The width of the bandpass of the first quadrupole

138

analyzer can be varied from ‘fully open’ down to a unit mass filter, restricting the ions entering

139

the CRC to a single mass to charge ratio (m/z) at any given time. For this study, two separate

140

time resolved analysis (TRA) methods were run simultaneously. P and S were analyzed using the

141

same method as they both react spontaneously (∆Hreaction < 0) with oxygen:

142

31 +

∆Hreaction = -3.17 eV

143

32 +


S signal from the H2S-spiked Ar gas. As discussed below, this resulted in a high sulfur

P + 16O2 →31P16O+ + 16O S + 16O2 →32S16O+ + 16O


7

144

For the determination of P and S, Q1 set to transmit m/zChemistry 31 (for 31P) and m/z 32 (for 32S). O2 Page 8 of 20 Journal of was Agricultural and Food

145

was used as a reaction gas in the CRC. Q2 was set to monitor m/z 47 and m/z 48 so that the

146

product ions 31P16O+ and 32S16O+ could be detected free of any interferences. Besides the single

147

oxides, the PO2+ and SO2+ masses at m/z 63 and 64 were monitored. Both P and S show high

148

isotope purity (P: 31 (100%), S: 32 (94.99%), 33 (0.75%), 34 (4.25%), 36 (0.01%)14), thus only

149

the major isotope of each element was monitored.

150

An illustration of the theory of the mass-shift method using oxygen reaction gas is shown in

151

Figure 1.

152

Even though the reaction between Cl+ and O2 is exothermic (∆Hreaction = -0.91 eV), the dominant

153

process in the CRC under the conditions used is charge transfer (Cl+ + O2 → Cl + O2+).

154

Consequently H2 was used as the cell gas for the analysis of the Cl based pesticides based on the

155

following theoretical reactions:

156

35

157

35

158

Q1 was set to m/z 35, where 35Cl reacts with H2 in the CRC to form 35Cl1H1H+.15 The Q2 was set

159

to m/z 37, allowing the product ion ClH2+ to pass to the detector. Chlorine shows high isotopic

160

purity (Cl: 35 (75.78%), 37 (24.22%)14), thus, only the major isotope was monitored.

Cl+ + 1H2 → 35Cl1H+ + 1H


Cl1H+ + 1H2 → 35Cl1H1H+ + 1H


161 162

Results and Discussion

163

It has been shown previously that GC is an excellent sample introduction system for ICP-MS

164

detection of organophosphorus compounds10,16,17,18,19,20,21. Compared to liquid sample

165

introduction into the ICP-MS, the GC delivers dry helium carrier gas containing relatively little

166

matrix. However, GC-ICP-MS is limited to the determination of heteroatom containing

167

compounds which are volatile and thermally stable, or can be converted to a volatile form by

168

derivatizaton before injection into the GC-ICP-MS. Tuning of the GC-ICP-MS/MS was done by

169

substituting the helium carrier gas with 100 ppm H2S spiked in Ar. As has already been


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Page 9170 of 20

discussed in the literature22,Journal the optimal instrumental for GC-ICP-MS are different of Agricultural andparameters Food Chemistry

171

than those required under wet plasma conditions. Thus, tuning for optimal parameter settings is

172

required. For this study, optimization of the GC-ICP-MS/MS instrumental settings was carried

173

out manually following the 32S+ signal from the Ar gas spiked with 100 ppm H2S. The optimized

174

plasma parameters are shown in Table 1.

175

In retrospect, introducing the Ar/H2S tuning mixture through the EPC modules and carrier gas

176

lines of the GC was problematic. H2S contaminated the flow system and continued to bleed out

177

for the duration of these experiments. A better choice would be to introduce the H2S/argon

178

mixture as close to the ICP torch as possible, thereby minimizing the contact area for H2S

179

adsorption. This approach will be tested in future studies.

180

Once the GC-ICP-MS/MS was optimized for S sensitivity, the same instrument conditions were

181

used for both S and P. The limits of detection were calculated based on the standard deviations (3

182

x σ, where σ is the standard deviation) from 7 replicate blank samples, as shown in Table 2.

183

Compound LODs and element specific LODs results are summarized in Table 2.

184

Careful optimization of the GC-ICP-MS/MS instrumental setup provides improved elemental

185

detection limits compared to previously published GC-ICP-MS methods shown in Table 3.

186

Currently, one of the best ways to analyze GC-amenable pesticides is by GC-MS/MS with

187

electron impact ionization.30 This approach has largely replaced the use of traditional element-

188

selective detectors such as the NPD, ECD and FPD. GC-MS/MS offers high selectivity based

189

upon molecular fragmentation and the ability to detect any pesticide using a single detector.

190

Detection limits for pesticides using current GC-MS/MS instrumentation typically vary from

191

about 0.1 to 10 µg/Kg depending on the pesticide and instrument used.23,24 The data in Table 2

192

would suggest that the GC-ICP-MS/MS is about an order of magnitude more sensitive than GC-

193

MS/MS for organophosphorus pesticides. Using S or Cl, detection limits are similar to those

194

achieved by GC-MS/MS. It is likely that detection limits using S will improve if the instrument

195

can be tuned without contaminating the GC with H2S. With one exception (dioxathion using S),


9

196

all of the pesticides in TableJournal 2 couldofbe detected well 10 µgL-1 which is the LOQ required Page 10 of 20 Agricultural andbelow Food Chemistry

197

by most food safety laboratories.

198

After instrumental conditions were optimized, mixtures of the three Ultra Scientific standard

199

solutions were diluted with acetonitrile. Figure 1 shows chromatograms showing the hetero-atom

200

traces for P, S, and Cl of the calibration standard with identified pesticide compounds. The

201

chromatogram for P and S was run in the same TRA run, and the Cl chromatogram trace was run

202

in a separate TRA run and overlaid.

203

For a real world application, real food samples (baby food purees, fresh vegetables, loose tea)

204

were screened for their pesticide content. Every real world food sample that was tested showed

205

positive traces of pesticides in the chromatograms. Figure 3 shows an example of the P

206

chromatogram of some of the analyzed food samples, together with a 200ppb calibration

207

standard.

208

This work clearly shows the potential of GC-ICP-MS/MS to be used for the ultra-trace analysis

209

of P, S, and Cl-containing compounds such as the pesticides in our test samples. GC-ICP-

210

MS/MS optimization is essential to achieve the ultra trace LODs achieved in this study. There is

211

also the possibility of using a CIC hetero-atom method for quantification without the need for

212

individual pesticide standards as shown by Bouyssiere et al.25 and González-Gago et al.26

213

Calibrating with pesticide mixes containing all analytes in the method is both time-consuming

214

and expensive, especially as analyte lists grow. In theory, one could calibrate for a long list of

215

pesticides using a single compound containing the heteroatoms common to the target pesticides.

216

However, this approach does not account for the behavior of individual pesticides (adsorption,

217

degradation, etc.) during the chromatographic analysis. Future investigations will also target the

218

application of GC-ICP-MS/MS for other matrices that would benefit from ultra trace detection

219

limits, and will look at ways of tuning the GC-ICP-MS/MS instrument that do not result in sulfur

220

contamination.

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222of 20ACKNOWLEDGMENTSJournal of Agricultural and Food Chemistry Page 11 223

The authors would like to thank Harry Prest and Dan Manuto, Charles Thomson for the use of

224

the GC and assistance in setting up the GC. Harry Prest also donated standards for the method

225

development. The authors would also like to thanks Craig Jones and Emmett Soffey for the use

226

of the 8800 ICP-MS/MS and their advice with setting up the ICP-MS/MS.

227 228

REFERENCES

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Tables


Page 12 of 20

12

279

Page 13 of 20

Table 1: ICP-MS/MS settings for the two different detection modes (Oxygen for P and S, Hydrogen for Cl detection).


Cell Mode

O2

H2

Scan mode

MS/MS

MS/MS

RF Power

1600

900

Sampling Depth (mm)

3

3

Dilution Gas (L/min)

0.6

0.5

Octopole bias (V)

-0.5

-0.5

Octopole RF (V)

150

150

KED (V)

-13

-13

Cell gas

O2

H2

Cell gas flow rate (%)

20

7

Cell entrance (V)

-50

-30

Cell exit (V)

-70

-70

Deflect (V)

10

10

Plate bias (V)

-60

-60

Q1 » Q2 Q1 » Q2 Monitored Masses

31 » 47 35 » 37 32 » 48

280 281


13

282

Table 2: Retention time (RT), detection limits for compound and for element and background-equivalent concentration

283

(BEC).


P Compound

RT ± 0.3 (min)

Compound LOD

S

Element LOD BEC

Compound LOD

Page 14 of 20

Cl

Element LOD BEC

Compound LOD

Element LOD BEC

(µg L-1)

Trichlorfon Thionazin Dicrotophos

4.103 5.926

0.028

0.004

0.013 0.009

1.236

0.159

4.038

Terbufos

7.071

0.019

0.002

0.005

1.298

0.432

Fonofos

7.185

0.047

0.006

0.045

0.649

0.169

Phosphamidon

7.299

0.015

0.002

Dichlofenthion

7.858

0.010

0.001

0.005

0.666

0.068

0.741 0.382 0.282

0.191

Chloropyrifosmethyl Fenitrothion Aspon

7.973

0.015

0.001

0.019

1.710

0.170

8.440 8.705

0.005 0.009

0.001 0.002

0.011 0.007

3.032 0.885

0.350 0.150

Chlorfenvinphos

9.486

0.033

0.003

0.005

Crotoxyphos Carbophenothion Ethion Famphur Phosmet Leptophos Azinphos-ethyl Dioxathion

9.541 11.158 11.527 12.547 12.851 13.263 13.827 14.587

0.033 0.004 0.024 0.036 0.258 0.032 0.103 0.265

0.003 0.000 0.004 0.003 0.025 0.002 0.009 0.036

0.037 0.008 0.054 0.083 0.111 0.019 0.004 0.027

0.336 0.287 0.282 0.366

0.980 2.830 2.162

0.274 0.942 0.425

0.649

6.077 2.802 34.000

0.472 0.519 9.533

0.377 2.056

0.671

0.149

0.166

1.478

0.481

4.103

1.746

0.510

4.415

1.868

0.191

2.678

1.327

0.225

2.592

1.965

284


14

285

Page 15 of 20

Table 3: Elemental detection limits comparison among some GC-ICP-MS methods


Analysis

LOD for P (µg L-1)

Volatile S compounds in human breath Total homocysteine in human serum Petroleum products

Organopesticides in food

LOD for Cl (µg L1 )

22 0.2 - 0.3

Petroleum products Organophosphorus fire retardants and plasticizers in wastewater Trihalomethanes in drinking water Organophosphorus nerve agent degradation products in pesticide Mixtures Thiophene derivates in Petroleum products

LOD for S (µg L1 ) 8.0 33.0

3.0 11

1.0 3.0

0.6

GC-ICP-HRMS (resolution 3000) GC-ICP-HRMS (resolution 3000) GC-ICP-MS collision cell with He GC-ICP-MS modified interface and Ar purification to reduce the O2 interference GC-ICP-MS collision cell with He

3.2 - 4.2

0.35 5000 (working range)

GC-ICP-MS GC-ICP-MS no gas cell, monitoring 31P+ and 31P16O+

7 0.00040.0359

Instrumental Details

0.079.5

0.150.51

GC-ICP-MS no cell Isotopic Dilution GC-ICP-MS/MS with mass shift for P (31P+→31P16O+), S (32S+→32S16O+) and Cl (35Cl+→35Cl1H1H+)

Reference 27

28

25

29

19

30

31

32

This Work

286 287


15


Page 16 of 20

288

Figures Captions

289

Figure 2: MS/MS mass-shift mode using oxygen cell gas for the measurement of P and S. Q1 is

290

set to m/z 31 and m/z 32, allowing 31P+ and 32S+ and any other ions at m/z 31 and m/z 32 to enter

291

the CRC. All other ions are rejected. In the cell, P and S react with oxygen to form PO+ at m/z 47

292

and SO+ at m/z 48. Q2 is set to m/z 47 and m/z 48, allowing PO+ and SO+ to pass to the detector.

293

Since no NO+ ions react with oxygen, they are rejected by Q2.

294

Figure 3: Chromatograms showing the hetero-atom traces for P, S, and Cl of the calibration

295

standard with identified pesticide compounds.

296

Figure 3: Example chromatogram showing the P trace of the analyzed food samples, together

297

with a 200ppb calibration standard. Baby food purple line or Baby food 1: Papaya + Orange

298

Purée, Baby food yellow line or Baby food 3: Grape Purée.


16

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1


Figure 1

2



1

Figure 2

2


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1


Figure 3

2



254x190mm (96 x 96 DPI)


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MS as a New Strategy for Specific

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