Determination of Chlorine in Milk via Molecular Absorption of SrCl

Subscriber access provided by - Access paid by the | UCSB Libraries

Article

Determination of Chlorine in Milk via Molecular Absorption of SrCl using HR-CS GFAAS Nil Ozbek, and Suleyman Akman J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b02024 • Publication Date (Web): 27 Jun 2016 Downloaded from http://pubs.acs.org on June 27, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Journal of Agricultural and Food Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 26

Journal of Agricultural and Food Chemistry

1 2

Determination of Chlorine in Milk via Molecular Absorption of SrCl using HR-CS GFAAS

3

Nil Ozbek, Suleyman Akman*

4

Istanbul Technical University, Faculty of Arts and Sciences, Department of Chemistry, 34469

5

Maslak, Istanbul, Turkey

6

Abstract

7

Total chlorine in milk was determined via the molecular absorption of diatomic strontium

8

monochloride at 635.862 nm using high-resolution continuum source graphite furnace atomic

9

absorption spectrometry (HR-CS GFAAS). The effects of coating the graphite furnace, using

10

different modifiers, amount of molecule forming element and different calibrants were

11

investigated and optimized. Chlorine concentrations in milk samples were determined in a Zr

12

coated graphite furnace using 25 µg of Sr as the molecule forming reagent, applying a

13

pyrolysis temperature of 600 oC and a molecule forming temperature of 2300 oC. l-Linearity

14

was maintained up to 500 µg mL-1 of Cl. The method was tested by analyzing a certified

15

reference waste water. The results were in the uncertainty limits of the certified value. The

16

limit of detection of the method was 1.76 µg mL-1. The chlorine concentrations in various

17

cow milk samples taken from the market were found in the range of 588-1472 mg L-1.

18

Keywords: High-resolution continuum source graphite furnace atomic absorption

19

spectrometry (HR-CS GFAAS); molecular absorption spectrometry (MAS); chlorine

20

determination; strontium monochloride (SrCl); milk

21

*Corresponding author: Tel: +902122853160; Fax. +902122856386

22

E-mail address: [email protected] (S.Akman)

1 ACS Paragon Plus Environment


Page 2 of 26

23

1. Introduction

24

Chloride is a highly important vital element required for both human and animal life. Without

25

chloride, the human body would be unable to maintain fluids in blood vessels, conduct nerve

26

transmissions, move muscles, or maintain proper kidney function. It helps keep the amount of

27

fluid inside and outside of cells in balance in the body. It also helps to maintain proper blood

28

volume, blood pressure, and pH of body fluids 1. Chloride is important for maintaining water

29

balance, and is an essential component of gastric juice. On average, an adult human body

30

contains approximately 115 grams of chloride, making up about 0.15% of total body weight..

31

The suggested amount of chloride intake ranges from 750 to 900 milligrams per day, based on

32

the fact that total obligatory loss of chloride in the average person is close to 530 milligrams

33

per day 2.

34

The mineral fraction of milk is about 8–9 g L–1 and mainly contains calcium, magnesium,

35

sodium, potassium, inorganic phosphate, citrate and chloride. Potassium, sodium and chloride

36

are essentially present as free ions although calcium, inorganic phosphate and magnesium are

37

partly bound to the casein micelles and play an important role in their structure and stability 3-

38

5

39

chlorides are useful in the construction of organs as well as in the preparation of digestive

40

secretions in cows 6. The average Cl content of cow milk is around 1000 mg L-1 7.

41

Chloride in milk samples were previously determined by Volhard titration 8, mono-segmented

42

flow potentiometric titration 9, sequential injection titration potentiometric titration

43

selective electrodes (ISE) 11, ion chromatography (IC) 12, 13. All of them respond to free ions,

44

require a sample pretreatment step that leads to waste of time, effort, analyte loss,

45

contamination and none of them is free from interferences. For example, in volumetric

46

techniques, silver ions react more favorably with bromide and iodide. ISE is simple, practical

. Milk contains a large amount of chlorine which may be explained by the fact that the


10

, ion

Page 3 of 26


47

and fast but respond to only free chloride (covalently bonded chlorine cannot be determined)

48

in aqueous phase. Ionic strength should be strictly controlled. Chloride selective electrode

49

may respond to S2-, OH-, I- Br- etc as well depending on the interferent to analyte ratio. In

50

addition, IC requires specific columns and ultrapure reagents. In all those methods, sample

51

should be decomposed to obtain free ions. Inductively coupled plasma optical emission

52

spectrometry (ICP-OES) is suitable for chlorine determination via atomic emission of Cl

53

atoms. Nevertheless, the method suffers from spectral interferences of matrix components.

54

Therefore, a careful separation may be needed. For example, in the paper by Naozuka et al.,

55

for the determination of Cl, Br and I in milk, samples were mineralized and anions were

56

precipitated as their low solubility products (AgCl, AgBr and AgI). The precipitates were then

57

dissolved with ammonia and introduced to the ICP-OES

58

ICP-MS; however, when conventional sample introduction with a nebulizer/spray chamber is

59

used, matrix interferences and memory effects may be observed.

60

Other chromatographic techniques such as high performance liquid chromatography (HPLC),

61

liquid chromatography-mass spectrometry (LC-MS), gas chromatography (GC) and gas

62

chromatography-mass spectrometry (GC-MS) can be used only to determine chlorine-

63

containing molecules rather than Cl itself. However, all those methods require appropriate

64

standards, recorded information in the library of the instrument, specific columns. The

65

physical properties of the sample should be suitable to the column and detector15. The

66

properties of HR-CS AAS and other techniques commonly used for chloride/chlorine

67

determination are concisely compared in Table 1.Atomic absorption spectrometry is an

68

analytical method for the determination of trace metals and metalloids. Since resonance

69

absorption lines of nonmetals are in vacuum ultraviolet region, it can not be used for

70

determination of F, Br, I, S and Cl. However after the development of high resolution

71

continuum source atomic absorption spectrometers (HR-CS AAS), determination of non-

14

. Chlorine can be determined by



72

metals becomes possible via molecular absorption of their diatomic molecules with a metal.

73

Till now, various molecule forming agents have been used for the determination of fluorine 16-

74

20

75

Welz et al. 29, Butcher 30 and Resano et al. 31.

76

Previously, chloride was determined in food samples and in a rye flour CRM via AlCl by HR-

77

CS AAS using a graphite furnace

78

atomizer 23 and in biological CRMs 24 and coal 32 via SrCl using a graphite furnace with solid

79

sampling and in crude oil via AlCl, InCl and SrCl in graphite furnace 33. The most remarkable

80

advantages of the methods are minimum or almost no sample preparation and determination

81

of total (covalently bound and free) chlorine.

82

In this study, strontium was used for the determination of total chlorine in milk samples via

83

formation of SrCl using high-resolution continuum source graphite furnace atomic absorption

84

spectrometry (HR-CS GFAAS). The effects of permanenet zirconium modifier, amount of

85

molecule forming element and different calibrants were investigated and experimental

86

conditions were optimized.

87

2. Experimental

88

2.1 Instrumentation

89

All experiments were carried out using an Analytik Jena ContrAA 700 high-resolution

90

continuumsource atomic absorption spectrometer equipped with a transversely heated

91

graphite furnace, MPE 60 autosampler (Analytik Jena, Jena, Germany) and a 300W xenon

92

short-arc lamp (XBO 301, GLE, Berlin, Germany) operating in hot-spot mode as a continuum

93

radiation source. The equipment includes a compact high-resolution double Echelle

94

monochromator and a CCD array detector with a resolution of approximately 1 to 5 pm per

95

pixel between 200 and 800 nm. The molecular absorption for SrCl was measured at 635.862

, chlorine 21-24, bromine 25-27 and iodine 28. All of these works were reviewed extensively by

21, 22

, in some reference materials via InCl using flame


Page 4 of 26

Page 5 of 26


96

nm. Three pixels of the array detector (central pixel±1) was used for evaluation of SrCl line.

97

All measurements were performed using pyrolytically coated graphite tubes with an

98

integrated PIN platform (Analytik Jena Part No. 407-A81.025). All solutions were pipetted as

99

10 µL.

100

2.2. Reagents and solutions

101

All glassware and polyethylene flasks used for the preparation of solutions were previously

102

immersed in a 10% (v/v) HNO3 bath overnight and then rinsed with ultra pure water to avoid

103

contamination. High-purity water with 18.2 MΏ.cm resistivity was obtained from a TKA

104

reverse osmosis connected with a deionizer (TKA Wasseraufbereitungsysteme GmbH,

105

Niederelbert Germany). All chemicals were of analytical reagent grade (Merck, Darmstad,

106

Germany). The stock solutions of 1000 mg L-1 of chlorine prepared from hydrochloric acid

107

(HCl), sodium chloride (NaCl), potassium chloride (KCl), ammonium chloride (NH4Cl) and

108

10000 mg L-1 of strontium solution prepared from strontium nitrate (Sr(NO3)2 were further

109

diluted daily. For interference studies, potassium nitrate (KNO3), sodium nitrate (NaNO3),

110

calcium nitrate (Ca(NO3)2.4H2O) and magnesium nitrate (Mg(NO3)2.6H2O) (Merck,

111

Darmstad, Germany) were used. In order to coat the graphite tube and platform, 1000 mg L-1

112

Ir (Sigma-Aldrich), 1000 mg L-1 Ru (Merck, Germany) and 1000 mg L-1 Zr were prepared

113

from their nitrates. For modifier purposes, mixture of Pd and Mg nitrate ( Merck, Germany)

114

was used. The waste water standard reference material SPS-NUTR-WW2, which includes

115

10.0±0.1 mg L-1 of F-, 50.0±0.5 mg L-1 of Cl-, 7.5±0.08 mg L-1 of PO43-, 5.0±0.05 mg L-1 of

116

NO3-and 100±1 mg L-1 of SO42- , was provided from LGC Standards (Middlesex, England).

117

Milk samples were purchased from market in Istanbul, Turkey.

118

2.3 Procedure



Page 6 of 26

119

Matrix-free calibration solutions of chlorine, certified waste water reference solution, milk

120

samples and blanks were co-injected to graphite furnace together with 2500 mg L

121

strontium (molecule forming element) prepared from strontium nitrate. The optimized

122

graphite furnace program is given in Table 2. To cover the graphite tube and platform with

123

zirconium, 20 µL of 1 mg mL-1 Zr as the nitrate was pipetted, dried and then thermally treated

124

at 1100 °C for 10 s 16. The procedure was repeated 10 times. For Ir or Ru, the same procedure

125

was applied

126

were diluted 20-fold prior to analysis. Therefore, no deposition and clogging in the capillar

127

tube of the autosampler occured during pipetting. The results were given as the mean of 3

128

repetitive injections.

129

3. Results and Discussion

130

3.1. Selection of molecule forming element and wavelength

131

To decide fort he selection of molecule forming element, various elements were overwieved.

132

The thermal stability of the diatomic molecule is a very important criteria in order to avoid its

133

dissociation readily in the flame or furnace and to obtain sufficient sensitivity. The

134

dissociation energy around 500 kJ mol-1 is usually considered ideal

135

energy of SrCl is 409 kJ mol-1 and also sufficient to obtain stable diatomic molecules in the

136

gas phase. The molecular absorption band head chosen for SrCl is 635.862 nm which is in

137

visible range where the risk of an overlap with atomic lines and molecular bands is less likely.

138

The wavelength-resolved absorption spectra obtained in the vicinity of 635.862 nm for a

139

chlorine standard (HCl) and a milk sample are depicted in Fig.1. The two spectra are exactly

140

the same, There is no additional atomic or molecular absorption line originated from sample

141

to overlap with working wavelength which means Cl could be determined with good

142

specificity with no spectral interference. On the other hand the band heads used for AlCl and

-1

of

34

. Since chlorine concentrations in milk were out of the linear range, samples


15, 29

. The dissociation

Page 7 of 26


143

InCl 21-23 which were used for Cl determination as well are relatively broader and in UV range

144

where the risk of overlapping with atomic and molecular lines of matrix species is more

145

likely. Since the chlorine concentrations in the samples are high and the samples need to be

146

diluted, there was no problem with respect to sensitivity of the working line. As a result, Sr

147

was used as a molecule forming element for the formation of Cl due to the adequeate

148

sensitivity and free of spectral interferences of SrCl line at 635.862 nm. Figure 1

149

150

3.2. Optimization of graphite furnace program and the use of modifier

151

The effects of Zr, Ir and Ru permanent modifiers with and without a Pd+Mg modifier on the

152

signal shape and sensitivity were investigated. The permanent Zr without a Pd+Mg modifier

153

was selected as the most appropriate permanent modifier which is also used by Pereira et al in

154

solid sampling analysis of Cl

155

investigated and found no significant improvement. For optimum pyrolysis and volatilization

156

temperatures, 600°C and 2300°C were selected which are also the same as those applied by

157

Pereira et al

158

generally quite similar to those of aqueous standards. This means that the same furnace

159

program for aqueous standards and the milk could be used. The optimized graphite furnace

160

program used for Cl determination in milk is given in Table 2.

161

24

. Also effect of using a Pd+Mg mixture as modifier was

24

. The behaviors of pyrolysis and volatilization curves for diluted milk were

--Table 2

162

3.2. Optimization of the strontium mass and linearity

163

The effects of different masses of Sr on the sensitivities of SrCl using both a 500 ng (10 µL of

164

50 mg L-1) of aqueous Cl solution and a diluted milk solution were investigated. In matrix-

165

free aqueous standards, maximum sensitivity for SrCl was obtained above 20 µg of Sr. 7 ACS Paragon Plus Environment


166

The linearity and the sensitivities of chloride salts were also studied. As depicted in Fig.2,

167

using HCl, NaCl and NH4Cl, good linearities (R :0.9998) were obtained up to 500 µg mL-1 of

168

Cl. On the other hand, the sensitivities evaluated with potassium salts were lower than others,

169

which could not be reasonably explained. The calibration was made using HCl,throughout

170

this study.

171

- Figure 2

172

Since the concentration of Cl in milk samples were out of linear range, the samples were

173

diluted. When all the milk samples were diluted 20-fold, the absorbances for SrCl fell in the

174

linear range, with smooth Gaussian time-resolved absorbance signals. It should be stated that

175

in a milk sample chlorine does not react with only Sr. It may competitively react with other

176

elements in the milk such as Ca, Mg, Na, K etc as well. Since Cl would be distributed

177

amongst many metals of the milk matrix upon condensed phase and/or gas phase reactions,

178

the sensitivity may be different compared to matrix free standards. Moreover, strontium may

179

also react with some other species in the milk, too. Therefore, the 20 µg of Sr, which is

180

suitable for matrix free standards, may not be sufficient for the Cl in milk. In this case, the

181

results found using aqueous standards would inavoidably be wrong. The overall situation is

182

complicated and it is hardly possible to calculate the overall partition of species. Therefore,

183

the amount of strontium was optimized for milk as well. Similar with aqueous standards, in

184

the presence of around 20 µg of Sr, the absorbances for SrCl in the 20-fold diluted milk

185

samples reached to plateau and remained stable as well. This means that the amount of Sr,

186

even if it reacts with other species, is enough to convert all the Cl in the diluted milk together

187

with other components. Otherwise, constant absorbances could have not been obtained above

188

20 µg of Sr. Obviously, upon dilution of milk samples 20-fold, the concentrations of matrix

189

components were reduced significantly so that the amount of Sr was much higher than the

190

elements to be interacted with Cl. Therefore, chlorine in diluted milk reacts mostly with the 8 ACS Paragon Plus Environment

Page 8 of 26

Page 9 of 26


191

excessive amount of Sr rather than other metals as well as the amount of Sr is more than

192

enough to react with some species, too. Almost all the chlorine reacted with Sr and the

193

competitive reactions of matrix components with Cl and Sr were at negligible level.

194

Nevertheless, in order to tolerate further minimized effects of non-spectral interferences due

195

to competitive reactions of matrix constituents with Sr or Cl and to be on the safe side, in all

196

quantifications, 25 µg of Sr was used excessively.

197

The effects of Na, K, Ca and Mg on SrCl signal in the presence of 25 µg of Sr were also

198

investigated. As seen from Figure 3, matrix effects and repeatability of results caused by these

199

cations changes variably. However, when the milk samples were diluted excessively (20-fold)

200

the sensitivities i.e. slopes of the linear calibration (0.0017 L mg-1) and the standard addition

201

graphs (0.00175 L mg-1) were not significantly different which means that interferences

202

became negligible and calibration against aqueous standards can be applied for

203

quantifications.

204

-Figure 3

205

Moreover, in order to check the effect of competitive reactions of Cl with matrix elements, the

206

Cl in milk was determined by standard addition technique and the results were compared with

207

those found using aqueous standards. In standard addition technique, the calibration standard

208

is present together with matrix components and influenced from competitive reactions equally

209

with the analyte in the sample. The results found using aqueous standards and standard

210

addition technique were not significantly different and almost in the range of standard

211

deviations of each other. This showed that the competitive reactions of Cl with sample

212

components (non-spectral interferences) did not influence the sensitivity and aqueous

213

standards could be used for calibration.



214

Finally, irrespective of a sample was diluted 20-fold and 25-fold, almost the same results were

215

obtained which means there is no effect of matrix on the analyte sensitivity,it should be

216

emphasized one more time that the appropriate results with aqueous standards were obtained

217

upon dilution of samples excessively due to reduction of interfering matrix concentrations

218

compared to molecule forming element.

219

Since samples were diluted 25-fold the ratios of Sr to Cl as well as Sr to interferents became

220

larger so that the amount of Sr was more than enough to obtain stable and maximum

221

absorbances for SrCl in the matrix of milk and the effect of competitive reactions of matrix

222

components were reduced.

223

3.4. Figures of merit and analysis in milk

224

The limit of detection (LOD) was calculated as 3 times the standard deviation (σ) for 10

225

repetitive introduction of a blank. For this purpose, a diluted milk and 10 µL of 2500 µg mL-1

226

of Sr, which gave an absorbance for SrCl almost at baseline level, were introduced 10 times

227

as a blank and LOD was calculated from 3σ /slope of calibration graph. The limit of

228

quantification (LOQ) was calculated similar to LOD with only difference that 10 times of the

229

standard deviation was taken. The LOD, and LOQ of the method together and other chlorine

230

studies were given in Table 3. The values in this study were higher than those reported in the

231

literature

232

which the blanks were empty furnace and only Sr whereas in this study diluted milk+Sr+Zr

233

mixture was used as a blank. The experiments for LOD were repeated on different days at

234

optimized conditions and the same values were found insistently. Though, since the

235

concentrations of chlorine in all milk samples were much above the LOD (in fact samples

236

were had to be diluted), the analysis was performed without problem. The method was tested

24, 32

. However, some studies in the literature were performed by solid sampling in


Page 10 of 26

Page 11 of 26


237

by with a waste water certified reference material (SPS-NUTR WW2). The Cl concentration

238

found (53±3 mg L-1) was in good agreement with the certified value (50 ±3 mg L-1).

239

Table 3

240

Finally, Cl concentrations in several milk samples were determined applying the optimized

241

experimental/instrumental conditions and the results were given in Table 4. All

242

determinations were performed using aqueous standards for calibration. As mentioned

243

previously, to check the effect of matrix, the same samples were analyzed by standard

244

addition techniques as well. There were no significant differences between the results found

245

by the two techniques which clearly proved that the effects of non-spectral interferences were

246

negligible.

247

Owing to the high Cl concentrations, milk samples could be diluted 20-fold without falling

248

below LOD. This is a great advantage because the concentration of matrix components were

249

reduced so much that non-spectral interferences were almost negligible. Therefore aqueous

250

standard could be used for calibration without problem. However, if concentrations of matrix

251

concomitants were high and/or Cl concentration were too low to be diluted excessively due to

252

the LOD limitation, then non-spectral interferences due to competitive reaction between Cl

253

and matrix components might not be tolerated even in the presence of excessive molecule

254

forming element. In this case, aqueous standards could not be used for calibration. Since milk

255

could be excessively diluted (20-fold) due to its high enough Cl concentration, direct

256

calibration with aqueous standards could be applied without any problem. Calibration curve

257

for SrCl was linear up to 500 mg L-1. However, since samples were diluted and the Cl

258

concentrations in the samples introduced to the graphite furnace were reduced considerably,

259

the calibration curves used for Cl determination in milk was established in a narrower range

260

up to 100 mg L-1. 11 ACS Paragon Plus Environment


261

This study describes a dilute-and-assay method for the determination of Cl in milk via SrCl

262

using high-resolution continuum source graphite furnace molecular absorption spectrometry.

263

Owing to the relatively high Cl concentrations in milk, samples could be diluted so that the

264

non-spectral interferences due to competitive reactions of Cl and Sr with matrix constituents

265

became negligible. By taking this advantage, aqueous standards were successfully used for

266

calibration. Nevertheless, especially in the analysis of samples with low Cl and high

267

interferent concentrations, the effects of competitive reactions should be carefully controlled.

268

One more time, Sr was proved to be a useful molecule forming element to determine Cl in

269

milk. The figures of merit are sufficient to determine total Cl in milk easily and rapidly with

270

minimum effort.

271

Acknowledgements

272

We are grateful to Đlknur Yavas for her helps in this study.


Page 12 of 26

Page 13 of 26


273

REFERENCES

274

1.

275

http://www.traceminerals.com/research/chloride

276

2.

277

111, 525-525.

278

3.

Gaucheron, F., The minerals of milk. Reprod. Nutr. Dev. 2005, 45, 473-483.

279

4.

Holt, C., The Milk Salts and Their Interaction with Casein. In Advanced Dairy

280

Chemistry Volume 3, Fox, P. F., Ed. Springer US: 1997; pp 233-256.

281

5.

Walstra, P.; Jenness, R.; Badings, H. T., Dairy chemistry and physics. Wiley: 1984.

282

6.

Carque, O., Rational Diet: An Advanced Treatise on the Food Question. Health

283

Research: 1996.

284

7.

Kinsella, J. E., Advances in Food and Nutrition Research. Elsevier Science: 1993.

285

8.

Sanders, G. P., The Determination of Chloride in Milk. J. Dairy Sci. 1939, 22, 841-

286

852.

287

9.

288

N., Monosegemented flow potentiometric titration for the determination of chloride in milk

289

and wine. Journal of the Brazilian Chemical Society 2003, 14, 259-264.

290

10.

291

titration of chloride in milk with potentiometric detection. Food Control 2004, 15, 609-613.

292

11.

293

327-335.

294

12.

295

determination of some trace elements in milk. Microchem. J. 2002, 72, 277-284.

296

13.

297

ion chromatography. Lait 1996, 76, 433-443.

298

14.

299

Determination of chlorine, bromine and iodine in milk samples by ICP-OES. J. Anal. At.

300

Spectrom. 2003, 18, 917-921.

301

15.

302

Function and Effects. In Food and Nutritional Components in Focus, Preedy, V., Ed. RSC

303

Publishing: 2015.

304

16.

305

molecular absorption of gallium mono-fluoride in a graphite furnace using a high-resolution

Meletis,

C.

Chloride:

The

Forgotten

Essential

Mineral.

Hopper, J., PHYSIOLOGY OF THE HUMAN KIDNEY. California Medicine 1969,

Vieira, J. A.; Raimundo Jr., I. M.; Reis, B. F.; Montenegro, M. C. B. S. M.; Araújo, A.

Reis Lima, M. J.; Fernandes, S. l. M. V.; Rangel, A. O. S. S., Sequential injection

Davies, W. L., 199. The chloride content of milk. Journal of Dairy Research 1938, 9,

Buldini, P. L.; Cavalli, S.; Sharma, J. L., Matrix removal for the ion chromatographic

Gaucheron, F.; LeGraet, Y.; Piot, M.; Boyaval, E., Determination of anions of milk by

Naozuka, J.; Mesquita Silva da Veiga, M. A.; Vitoriano Oliveira, P.; de Oliveira, E.,

Akman, S.; Welz, B.; Ozbek, N.; Pereira, E. R., Fluorine Chemistry, Analysis,

Gleisner, H.; Welz, B.; Einax, J. W., Optimization of fluorine determination via the



306

continuum source spectrometer. Spectrochimica Acta Part B: Atomic Spectroscopy 2010, 65,

307

864-869.

308

17.

309

toothpaste via molecular absorption of aluminum mono fluoride using a high-resolution

310

continuum source nitrous oxide/acetylene flame atomic absorption spectrophotometer.

311

Talanta 2012, 94, 246-250.

312

18.

313

samples via the molecular absorption of strontium monofluoride formed in an electrothermal

314

atomizer. Spectrochim Acta B 2012, 69, 32-37.

315

19.

316

absorption of barium monofluoride by high-resolution continuum source atomic absorption

317

spectrometer. Microchem. J. 2014, 117, 111-115.

318

20.

319

absorbance of CaF using a high resolution continuum source atomic absorption spectrometer.

320

LWT - Food Science and Technology 2015, 61, 112-116.

321

21.

322

samples via the AlCl molecule using high-resolution continuum source molecular absorption

323

spectrometry in a graphite furnace. Spectrochimica Acta Part B: Atomic Spectroscopy 2012,

324

71–72, 98-101.

325

22.

326

of non-metals via molecular absorption using high-resolution continuum source absorption

327

spectrometry and graphite furnace atomization. J. Anal. At. Spectrom. 2006, 21, 1314-1320.

328

23.

329

of halogens via molecules in the air–acetylene flame using high-resolution continuum source

330

absorption spectrometry, Part II: Chlorine. Spectrochimica Acta Part B: Atomic Spectroscopy

331

2006, 61, 959-964.

332

24.

333

L. G.; Carasek, E.; de Andrade, J. B., Strontium mono-chloride — A new molecule for the

334

determination of chlorine using high-resolution graphite furnace molecular absorption

335

spectrometry and direct solid sample analysis. Spectrochimica Acta Part B: Atomic

336

Spectroscopy 2014, 102, 1-6.

337

25.

338

absorption of strontium mono bromide generated in a graphite furnace. Microchem. J. 2014,

339

116, 1-6.

Ozbek, N.; Akman, S., Method development for the determination of fluorine in

Ozbek, N.; Akman, S., Method development for the determination of fluorine in water

Ozbek, N.; Akman, S., Determination of fluorine in milk and water via molecular

Ozbek, N.; Akman, S., Determination of fluorine in Turkish wines by molecular

Fechetia, M.; Tognon, A. L.; da Veiga, M. A. M. S., Determination of chlorine in food

Heitmann, U.; Becker-Ross, H.; Florek, S.; Huang, M. D.; Okruss, M., Determination

Huang, M. D.; Becker-Ross, H.; Florek, S.; Heitmann, U.; Okruss, M., Determination

Pereira, É. R.; Welz, B.; Lopez, A. H. D.; de Gois, J. S.; Caramori, G. F.; Borges, D.

Gunduz, S.; Akman, S., Determination of bromine by high resolution molecular


Page 14 of 26

Page 15 of 26


340

26.

Limburg, T.; Einax, J. W., Determination of bromine using high-resolution continuum

341

source molecular absorption spectrometry in a graphite furnace. Microchem. J. 2013, 107, 31-

342

36.

343

27.

344

de Andrade, J. B., Method development for the determination of bromine in coal using high-

345

resolution continuum source graphite furnace molecular absorption spectrometry and direct

346

solid sample analysis. Spectrochimica Acta Part B: Atomic Spectroscopy 2014, 96, 33-39.

347

28.

348

Determination of iodine via the spectrum of barium mono-iodide using high-resolution

349

continuum source molecular absorption spectrometry in a graphite furnace. Spectrochimica

350

Acta Part B: Atomic Spectroscopy 2009, 64, 697-701.

351

29.

352

Becker-Ross, H., Determination of phosphorus, sulfur and the halogens using high-

353

temperature molecular absorption spectrometry in flames and furnaces—A review. Anal.

354

Chim. Acta 2009, 647, 137-148.

355

30.

356

Anal. Chim. Acta 2013, 804, 1-15.

357

31.

358

metalloids and non-metals by means of high-resolution continuum source atomic or molecular

359

absorption spectrometry. A critical review. Analytical and Bioanalytical Chemistry 2013, 406,

360

2239-2259.

361

32.

362

Andrade, J. B., Determination of chlorine in coal via the SrCl molecule using high-resolution

363

graphite furnace molecular absorption spectrometry and direct solid sample analysis.

364

Spectrochimica Acta Part B: Atomic Spectroscopy 2015, 114, 46-50.

365

33.

366

Flores, E. M. M.; Müller, E. I., Determination of Chlorine in Crude Oil by High-Resolution

367

Continuum Source Graphite Furnace Molecular Absorption Spectrometry Using AlCl, InCl,

368

and SrCl Molecules. Energy & Fuels 2015.

369

34.

370

Sampling High-Resolution Continuum Source Graphite Furnace Molecular Absorption

371

Spectrometry. J. Agric. Food. Chem. 2013, 61, 4816-4821.

Pereira, É. R.; Castilho, I. N. B.; Welz, B.; Gois, J. S.; Borges, D. L. G.; Carasek, E.;

Huang, M. D.; Becker-Ross, H.; Florek, S.; Okruss, M.; Welz, B.; Morés, S.,

Welz, B.; Lepri, F. G.; Araujo, R. G. O.; Ferreira, S. L. C.; Huang, M.-D.; Okruss, M.;

Butcher, D. J., Molecular absorption spectrometry in flames and furnaces: A review.

Resano, M.; Flórez, M. R.; García-Ruiz, E., Progress in the determination of

Pereira, É. R.; Rocha, L. M.; Cadorim, H. R.; Silva, V. D.; Welz, B.; Carasek, E.; de

Enders, M. S. P.; Gomes, A. O.; Oliveira, R. F.; Guimarães, R. C. L.; Mesko, M. F.;

Ozbek, N.; Akman, S., Determination of Total Sulfur in Food Samples by Solid

372



373

List of Tables

374

Table 1: Comparison of HR-CS MASa with most commonly techniques for chloride/chlorine

375

determination.

376

Table 2: Optimized graphite furnace program for Cl determination via SrCl.

377

Table 3: Chlorine concentrations in various cow milk samples produced by different

378

companies (N:3).

379

Table 4: Comparison of figures of merit for the determination of Cl by HR-CS-AAS using

380

different molecule forming elements.

381


Page 16 of 26

Page 17 of 26

382


Table 1: Comparison of HR-CS MASa with most commonly techniques for chloride/chlorine determination. LOD

Volumetric Methods

Cost to

Analysis

Sample

Interferences

Remarks

Operate

Time

Pretreatment

High

Low

Medium

Yes

Yes

Br- and I- interfere

Low

Low

Fast

Yes

Yes

Respond to S-2, OH- etc.,

(Argentometric Methods) ISE

sensitive to only free ionic ClIC

Low

High

Long

Yes

Yes

sensitive to ions

ICP-OES

Low

Medium-

Fast

Yes

Yes

Spectral and non-spectral

High

(for heavy matrices) (spectral and non-

interferences

spectral) ICP-MS

Low

High

Fast

-

No

Memory effects

HR-CS-MAS

Low-

Medium-

Fast

No

Yes (non-spectral)

Total chlorine

(this study)

Medium

High

a

383

a

This study, high resolution-continuum source molecular absorption spectrometry.

17

ACS Paragon Plus Environment


384

Page 18 of 26

Table 2: Optimized graphite furnace program for Cl determination via SrCl Temperature, °C

Ramp, °C s-1

Hold, sG Gas Flow, mL min-1

1

Drying-1

80

6

20

2.0

2

Drying-2

110

5

5

2.0

3

Pyrolysis

600

200

10

2.0

4

Gas Adaption

600

0

5

-

5

Vaporized

2300

1200

5

-

6

Cleaning

2500

500

4

2.0

385

386

387

388

389


Page 19 of 26


390

Table 3: Chlorine concentrations in various cow milk samples produced by different

391

companies (N:3) by linear calibration results and standard addition results.

Cl Concentration (mg L-1)

Milk Sample 1

Linear Calibration 764±30

Standard Addition 774±26

Milk Sample 2

831±33

852±41

Milk Sample 3

1098±55

1075±65

Milk Sample 4

973±43

983±53

Milk Sample 5

773±33

786±43

Milk Sample 6

685±12

670±34

Milk Sample 7

970±55

984±65

Milk Sample 8

714±64

734±43

Milk Sample 9

676±14

687±65

Milk Sample 10

588±15

590±46

Milk Sample 11

534±23

645±65

Milk Sample 12

1472±58

1564±78

Milk Sample 13

855±41

795±56

Milk Sample 14

922±45

877±53

Milk Sample 15

1148±52

1198±65

Milk Sample 16

820±23

860±43

Milk Sample 17

812±13

832±43

Milk Sample 18

567±9

512±21

692±36

687±45

Milk Sample 19 (Claimed Value on the milk box: 650 mg L-1)a,b



Page 20 of 26

Milk Sample 20 (Claimed Value on the milk box: 960 mg L-1)a, c

1010±47

970±53

392

a

Claimed values are not certified.

393

b

Claimed value on the box for Ca: 700 mg L-1, Mg: 60 mg L-1, Zn: 8.9 mg L-1 and K: 900 mg

394

L-1.

395

c

396

L-1.

Claimed value on the box for Ca: 940 mg L-1, Mg: 94 mg L-1, Zn: 9 mg L-1 and K: 1050 mg


Page 21 of 26

397


Table 4: Comparison of figures of merit for the determination of Cl by HR-CS-AAS using different molecule forming elements. SrCl (This study)

InCl 33

InCl 23

AlCl 33

AlCl 21

SrCl 33

SrCl 24

SrCl 32

Graphite Furnace

Graphite Furnacesolid sampling

Flame

Graphite Furnace

2300

2000

-

Graphite Furnacesolid sampling 2300

2200




Pyrolysis Temperature, ºC

600

700

-

600

500

600

600

700

Modifier

Zr

Sr

-

Sr

Al–Ag–Sr

Zr

Zr

Zr

635.862

267.218

267.24

261.418

261.418

635.862

635.862

635.862

25 µg

2 µg

10000 g L-1

2 µg

10 µg

100 µg

100 µg

100 µg

0-500 mg L-1

0-50 ng

nd-1800 mg L-1

0-50 ng

300-1800 µg L-1

0-50 ng

2-100 ng

2-80 ng

3.5 ng

3 mg L-1

2.1 ng

2.4 ng

0.7 ng

1 ng

0.85 ng

nd

nd

nd

0.9974

nd

0.997

nd

Atomizer

Molecule Forming Temperature, ºC

Absorption Wavelength Concentration of molecule forming agent Linear range

(or 0-5000 ng) Limit of detection

1.76 mg L-1 (or 17.6 ng)

Coefficient of determination, R

0.9998

21

ACS Paragon Plus Environment


List of Figures Figure 1: Spectral window between 623.443-636.276 nm for (a) 100 µg mL-1 of aqueous Cl prepared from HCl and (b) a milk sample diluted 20-fold, co-injected with 25 µg Sr wavelength Figure 2: Linear calibration graphs prepared from various standards using 25 µg of Sr: HCl (□), NaCl (+) and NH4Cl (○) Figure 3: Effect of Na, K, Ca and Mg on SrCl signal Cl: 50 mg L-1 Sr: 25 µg (N:3)


Page 22 of 26

Page 23 of 26


Figure 1: Spectral window between 623.443-636.276 nm for (a) 100 mg L-1 of aqueous Cl prepared from HCl and (b) a milk sample diluted 20-fold, co-injected with 25 µg of Sr wavelength



Page 24 of 26

0.9 Integrated Absorbance

0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0

100

200

300

400

500

Concentration of Cl (mg L-1)

Figure 2: Linear calibration graphs prepared from various standards using 25 µg of Sr: HCl (□), NaCl (+) and NH4Cl (○)


Page 25 of 26


0.16

Integrated Absorbance

0.14 0.12 0.1 Na

0.08

K

0.06

Ca

0.04

Mg

0.02 0 0

50 100 500 Concentration of Interferent (mg L-1)

1000

Figure 3: Effect of Na, K, Ca and Mg on SrCl signal Cl: 50 mg L-1 Sr: 25 µg (N:3)



Graphic for Table of Contents


Page 26 of 26

Determination of Chlorine in Milk via Molecular Absorption of SrCl

Recommend Documents