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Cost Effective Measurements of Elements in Food

Samples

Arun Kumar Raju

Application Chemist – ICPMS

Agilent Technologies India

How Are Elements Typically Measured in Food?

In order to cover all of the elements that should be analysed at the appropriate ranges, several traditional techniques are used

• As/Se/Sn – hydride generation AAS or AFS

• Hg – cold vapour AFS

• All other elements at sub ppb level GFAAS or FAAS

• All other elements at ppb – ppm - % level ICP-OES

In many large laboratories, all of the above techniques have been replaced with a single ICP-MS

Typical Workflow in an Older Food Laboratory

Sample Prep 1 (Hg analysis)

Sample Prep 2 (As analysis)

Sample Prep 3 (Cd, Pb)

Cold Vapour AFS

Hydride Generation

AAS

GFAAS or ICP-OES

Dat

a C

olla

tion

Final Report

Bottlenecks – Productivity reduced here

So, What is ICP-MS?

ICP - Inductively Coupled Plasma

• high temperature ion source

• decomposes, atomizes and ionizes the sample

MS - Mass Spectrometer

• featuring quadrupole mass analyzer

• mass range - 5 to 260 amu (Li to U...)

– separates all elements in rapid sequential scan

• ions measured using dual mode detector

– ppt to ppm levels

– isotopic information available

An inorganic (elemental) analysis technique

ICP-MS has the detection limits of GFAA and the sample throughput of ICP-OES

Low flow sample introduction system

27MHz solid state RF plasma generator

Multi-element interference removal by on-axis octopole reaction cell

High frequency hyperbolic quadrupole

Fast simultaneous dual mode detector (9 orders dynamic range)

Agilent 7500cx ICP-MS System withOctopole Reaction System (ORS)

Off-axis Lens

Helium Inlet

OctopolePlasma

The Octopole Reaction System (ORS)

Molecular InterferencesContribute to Noise

51V35Cl16O, 37Cl14N

52Cr36Ar16O, 40Ar12C, 35Cl16OH, 37Cl14NH

53Cr 36Ar16OH, 40Ar13C, 37Cl16O, 35Cl18O, 40Ar12CH54Fe 40Ar14N, 40Ca14N55Mn 37Cl18O, 23Na32S,56Fe 40Ar16O, 40Ca16O57Fe 40Ar16OH, 40Ca16OH58Ni 40Ar18O, 40Ca18O, 23Na35Cl59Co 40Ar18OH, 41K18O, 43Ca16O60Ni 44Ca16O, 23Na37Cl61Ni 44Ca16OH, 38Ar23Na, 23Na37ClH63Cu 40Ar23Na, 12C16O35Cl, 12C14N37Cl64Zn 32S16O2,

32S2, 36Ar12C16O,

38Ar12C14N, 48Ca16O65Cu 32S16O2H, 32S2H, 14N16O35Cl, 40Ar25Mg, 48Ca16OH66Zn 34S16O2,

32S34S, 33S2, 48Ca18O

67Zn 32S34SH, 33S2H, 48Ca18OH, 14N16O37Cl, 16O235Cl

68Zn 32S18O2, 34S2

69Ga 32S18O2H, 34S2H, 16O237Cl

70Zn 34S18O2, 35Cl2

71Ga 34S18O2H72Ge 40Ar32S, 35Cl37Cl, 40Ar16O2

73Ge 40Ar33S, 35Cl37ClH, 40Ar16O2H74Ge 40Ar34S, 37Cl275As

40Ar34SH, 40Ar 35Cl, 40Ca 35Cl

77Se40Ar 37Cl, 40Ca 37Cl

78Se40Ar 38Ar

80Se40Ar2,

40Ca2, 40Ar40Ca, 40Ar 39KH, 79BrH

Main Polyatomic Ion interferences arising from a

matrix containing:Plasma Components

(Ar, O, N, H)

Plus

Matrix Components(Cl, S, C, Ca, Mg, Na, K etc)

Commonly observed matrix components in environmental, food, agricultural, clinical and many other sample matrices

Mass Spectrum He Mode – Espresso Coffee

Only isotopesNO interferences

Wide Analytical Range- these 4 calibration plots were generated simultane ously in a single run

1180 ppm Sodium

As

Se

Hg

Na

Calibration rangesHg (0.01 – 2ppb) – Std ModeAs (0.1 – 200 ppb) – He ModeSe (0.1 – 200 ppb) – H2 ModeNa (0.05 – 1180 ppm) – He Mode

Overall calibration range 10ppt (Hg) to 1180 ppm (Na) in a single method- without attenuating ion transmission to increase working range

NaTypically, ICP-MS cannot measure above 200ppm Na without changing quad resolution or ion lens settings

HgHg detection limit by 7500ce is about 3ppt – 7500ce can QUANTIFY at 10ppt!

7500cx can measure both Na and Hg in the same run!

Advantages of ICP-MS

Excellent detection limits

• ppt to low ppb for all elements

Wide elemental coverage - from Li - U

• Over 70 elements measurable in a single acquisition

Simple to use He only collision/reaction cell (Agilent ORS)

• Improve accuracy through removal of interferences

High throughput

• All elements determined simultaneously• 20 element run/3 replicates/washout in

4 minutes

Wide dynamic range

• linear over 9 orders

Powerful semiquantitative analysis

• no standards needed

Isotopic analysis

• isotope ratios

• isotope dilution

Routine technique

• many users run systems overnight

Small size

• saves lab space

• mobile installations

=PRODUCTIVITY

Analysing Food samples by ICP-MS

More difficult than most environmental samples because of the huge range of matrices

Regulated elements tend to be the “toxic heavies”

• As, (Se), Cd, Hg, Pb

• But other elements may also be measured

Very dependant on sample preparation

Sample PreparationSample preparation for ICP-MS is relatively simple

• Consists of converting solid samples into solutions (digestion)• Usually involves a oxidizing environment

– Nitric acid/hydrogen peroxide– Nitric acid/perchloric acid– Nitric acid/sulfuric acid– Sometimes (usually in high cellulose plants/seeds), a small amount of HF is

requiredThe high carbon content of most food matrices make sample preparation relatively straightforward

• High fat content can cause problemsTypically samples are digested using one of the following

• Acid digestion in an open vessel• Pressurized digestion

– Simple uncontrolled– Automated

• Microwave aided digestionGood sample preparation is the key to success

Typical Digestion Mixtures for Food Sample Prep

Cellulose and starches

• HNO3 (sometimes HOCl4)

Leaves and grains

• HNO3 / HF

Meat and other high protein samples

• HNO3 (plus H2O2 )

Foods containing high amounts of fats and oils

• HNO3 and H2O2

• Sometimes HNO3 and H2SO4

Simple Acid Digestion

Typically samples are typically heated with a mixture of concentrated nitric acid plus hydrogen peroxide in an open vessel

• Boiling point of the acid mixture controls the maximum temperature • Special care must be taken if hydrofluoric or perchloric acids are used

– For hydrofluoric acid, PTFE or other plastic materials must be used– Because of the risk of explosion, perchloric acid concentration must never

exceed 72%Advantages

• Inexpensive/simple• Okay for some (but not all) matricesDisadvantages

• Slow• Risk of contamination• Poor/no control• Volatile metals such as As, Sn, Hg will be lost

Simple Pressurised PTFE “Bomb”Digestion performed in a pressurized container (often called a “bomb”)

• Closed system avoids contamination and loss of volatile elements

Most commonly used design was introduced by Tölg in 1972

• Tölg’s “bomb” consists of– Pressure valve, screw-cap, pressure spring, metal lid, PTFE lid, PTFE insert and

a pressure vessel (lined with stainless steel and thermal insulation)

An aluminum heating block with a thermal probe is used to heat the device

Kotz, L.; Kaiser, G.; Tschöpel, P.; Tölg, G.;Fresenius Z. Anal. Chem. 1972, 260, 207.

Advantages

• Low cost

• Contamination free

• Closed system so no loss of volatile elements

Disadvantages

• Potential for explosions so care must be exercised

• Use of PTFE limits the temperature to approx 170oC

• Limited control

Typical Digestion Mixtures and Preparation Times

Matrix Typical Sample weight

Digestion Matrix

Temperature Time

Cellulose/starches 1000 mg HNO3 140-160°C 1-2 hr.

Leaves / grain 1000 mg HNO3 / HF 150-180°C 2-3 hr.

Meat/ High Protein 1000 mg HNO3 170-190°C 2-4 hr.

Fats / oils 500 mg HNO3 (H2O2) 180-200°C 3-4 hr.

High Pressure Digestion

Source: http://www.berghof-instruments.de

Automated High Pressure DigestionCommercial systems are available that automate high pressure digestion

• Use the same wet chemical pressure digestion• Better controlledMost products avoid PTFE

• High purity quartz glass or glassy carbon– Compatible with most digesting acid mixtures

• Temperatures up to 320°C• Pressures up to 130 bar • Produces complete mineralization of even the most difficult samplesAdvantages

• Relatively fast• Complete decomposition • Contamination free• Closed system so no loss of volatile elements• Some level of control over digestion temperatures and pressuresDisadvantages

• Relatively high cost

Microwave DigestionMany laboratories have turned to microwave digestion to improve productivity

• Samples and digestion mixture in sealed container within a microwave oven– Sample tubes are made of glass, quartz or PTFE

• “Transparent” to microwave radiation

• Very high pressures generated within sample containers• Typical digestion time is 15 min to 1 hour

Advantages

• Relatively fast• Complete decomposition • Contamination free• Closed system so no loss of volatile elements• Digestion temperatures and pressures can be controlled• USEPA methods

Disadvantages

• Relatively high cost

Typical Digestion Mixtures and Preparation Times

Matrix Typical Sample weight

Digestion Matrix

Temperature Time

Cellulose/starches 500 mg HNO3 160°C 25 min.

Leaves / grain 500 mg HNO3 / HF 190°C 30 min.

Meat/ High Protein 50-250 mg HNO3 170-190°C 25 min.

Fats / oils 700 mg HNO3 (H2O2) 180-210°C 30-40 min.

Microwave Digestion

Source: http://www.berghof-instruments.de

Analysis of Tea CRM using Standard ICP-MS

Element Found standard deviation

Certified concentration

+/-error

% recovery

Mg 2827 57 ppm 2760 240 ppm 102%

Al 5875 78 ppm

P 1545 35 ppm 1480 80 ppm 104%

K 8581 183 ppm 8630 620 ppm 99%

Ca 7610 129 ppm 8000 660 ppm 95%

Cr 2007 21 ppb (2000) ppb 100%

Mn 2062 31 ppm 2170 120 ppm 95%

Fe 362.5 1 ppm 347 12 ppm 104%

Co 184.1 1 ppb (180) ppb 102%

Ni 5064 20 ppb 5090 760 ppb 99%

Cu 8092 67 ppb 8960 580 ppb 90%

Zn 21923 2 ppb 22600 1500 ppb 97%

As 190.3 6 ppb 180 48 ppb 106%

Se 85.22 14 ppb 40 6 ppb 213%

Cd 25.86 2 ppb 23 4 ppb 112%

Ba 107328 75 ppb 120000 10000 ppb 89%

Hg 23.26 1 ppb (17) ppb 137%

Pb 872.2 1 ppb 1000 40 ppb 87%

Th 84.07 0.1 ppb 104 14 ppb 81%

U 34.49 1 ppb

• Samples were digested in a heated PTFE pressure vessel with conc nitric acid

• Note the wide range of concentrations measured (10’s ppb to 1000’s ppm)

• All elements were measured in the same analytical cycle

• Acquisition (3 replicates) was 6 min

GBW 08501 Peach Leaf CRM analysis ICP-ORS-MS

Element unit Reference value

Determined value

Cr (ng/g) 940±140 949

Co (ng/g) (250) 229

Cu (ug/g) 10.4±1.6 9.1

Zn (ug/g) 22.8±2.5 20.7

As (ng/g) 340±60 350

Se (ng/g) (40) 44

Cd (ng/g) 18±8 14.7

Ba (ug/g) 18.4±1.8 17.7

Hg (ng/g) 46±12 58

Pb (ng/g) 990±80 922

Wet Digested with Nitric and Perchloric AcidIn a Pressurised Tolg Bomb

BCR 191 (Brown bread) analysis ICP-ORS-MS

Found Certified

mg/kg

Chromium 0.258 +/- 0.063

Cobalt 0.039 +/- 0.003

Nickel 0.381 +/- 0.051

Copper 2.254 +/- 0.130 2.6±0.1

Zinc 17.38 +/- 1.386 19.5±0.5

Arsenic 0.027 +/- 0.004

Selenium 0.034 +/- 0.017

Molybdenum 0.214 +/- 0.015

Cadmium 0.024 +/- 0.003 0.028±0.002

Barium 1.533 +/- 0.105

Lead 0.198 +/- 0.076 0.187±0.014

Microwave digestion nitric/sulfuricData courtesy of B Zarchinas, CSIRO, S Australia

NIST SRM 8436 Durum Wheat Flour by ICP-ORS-MS

%RSD Reference values(mg/kg)+/-mass fraction

Sodium 14.64 +/- 0.37 2.53% 16.0 +/- 6.1Magnesium 1133 +/- 17 1.50% 1070 +/- 80Aluminium 10.17 +/- 0.16 1.57% 11.7 +/- 4.7Phosphorus 2857 +/- 33 1.16% 2900 +/- 220Potassium 3190 +/- 42 1.32% 3180 +/- 140Calcium 243.8 +/- 6.9 2.83% 278 +/- 26Vanadium 0.027 +/- 0.002 7.41% 0.021 +/- 0.006Chromium 0.018 +/- 0.001 5.56% 0.023+/- 0.009Manganese 16.09 +/- 0.58 3.60% 16.0 +/- 1.0Iron 44.42 +/- 1.2 2.70% 41.5 +/- 4.0Cobalt 0.0069 +/- 0.0004 5.80% 0.008 +/- 0.004Nickel 0.19 +/- 0.01 5.26% 0.17 +/- 0.08Copper 4.483 +/- 0.15 3.35% 4.3 +/- 0.69Zinc 23.68 +/- 0.87 3.67% 22.2 +/- 1.7Arsenic 0.0178 +/- 0.0015 8.43% 0.03Selenium 1.319 +/- 0.036 2.73% 1.23 +/- 0.09Molybdenum 0.6308 +/- 0.021 3.33% 0.7 +/- 0.12Cadmium 0.1155 +/- 0.0048 4.16% 0.11 +/- 0.05Silver 0.0009 +/- 0.0001 11.11% --Tin 0.0092 +/- 0.0005 5.43% --Antimony 0.0021 +/- 0.0001 4.76% --Mercury 0.0006 +/- 0.0001 16.67% 0.0004 +/- 0.0002Lead 0.0218 +/- 0.0009 4.13% 0.023 +/- 0.006

Found +/- SDmg/kg

Wet Digested with Nitric and Perchloric AcidsIn a Pressurised Tolg Bomb

NIST 8435 Whole Milk ICP-ORS-MS

Found Certifiedmg/kg mg/kg

23Na 3677 3560 ± 40024Mg 845 814 ± 7627Al 0.32 0.931P 7965 7800 ± 49034S 2607 2650 ± 35039K 13552 13630 ± 47043Ca 9525 9220 ± 49055Mn 0.18 0.17 ± 0.0556Fe 1.98 1.8 ± 1.160Ni 0.03 0.04 ± 0.0163Cu 0.47 0.46 ± 0.0866Zn 25.8 28 ± 3.175As 0.01 0.00182Se 0.15 0.131 ± 0.01495Mo 0.26 0.29 ± 0.13137Ba 0.59 0.58 ± 0.23208Pb 0.1 0.11 ± 0.05

Wet Digested with Nitric Acid and Hydrogen PeroxideIn a Microwave System

NIST 2387 Peanut Butter analysis ICP-ORS-MS

Element Reference value

mg/kg

Determined value

mg/kg

Value (error) 1 2 3 4 5 Mean % RSDMg 1680 (70) 1,660 1,750 1,690 1,680 1,670 1689.3 2.09P 3378 (92) 3,250 3,420 3,320 3,300 3,410 3341 2.22Ca 411 (18) 396 400 396 384 392 394 1.56Cr n/a 0.0257 0.023 0.021 0.025 0.020 0.023 10.3Mn 16 (0.6) 15.5 16.6 16.2 16.0 15.9 16.0 2.55Fe 16.4 (0.8) 15.7 16.4 15.9 15.7 15.6 15.9 2.07Ni n/a 0.821 0.852 0.834 0.824 0.819 0.8 1.66Cu 4.93 (0.2) 4.78 5.04 4.88 4.94 4.91 4.9 1.88Zn 26.3 (1.1) 26.6 27.9 26.8 26.8 27.0 27.0 1.81As n/a 0.0170 0.0178 0.0178 0.0172 0.0161 0.017 4.13Cd n/a 0.0522 0.0537 0.0523 0.0512 0.0519 0.1 1.74Pb n/a 0.00651 0.0057 0.0059 0.0056 0.0058 0.0059 5.87

Wet Digested with Nitric Acid, Sulfuric Acid and Hydrogen PeroxideIn an open system

Normalised Stability Plot Spiked Rapeseed Oil

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

00:0

0:00

00:2

0:00

00:4

1:00

01:0

2:00

01:2

3:00

01:4

4:00

02:0

4:00

02:2

5:00

02:4

6:00

03:0

7:00

03:2

8:00

03:4

8:00

04:0

9:00

04:3

0:00

04:5

1:00

05:1

1:00

05:3

2:00

05:5

3:00

06:1

4:00

06:3

5:00

06:5

5:00

07:1

6:00

07:3

7:00

07:5

8:00

08:1

9:00

08:4

0:00

09:0

1:00

09:2

1:00

09:4

2:00

10:0

3:00

10:2

4:00

10:4

5:00

11:0

6:00

11:2

7:00

Time

Nor

mal

ised

Con

cent

ratio

n

Be 9 NoGas

P 31 He

S 32 Xe

Ti 47 He

V 51 He

Cr 52 H2

Cr 53 H2

Mn 55 He

Fe 56 He

Co 59 He

Ni 60 He

Cu 63 He

Cu 65 He

Zn 66 He

As 75 He

Sr 88 NoGas

Mo 95 NoGas

Ag 107 NoGas

Cd 111 NoGas

Sn 118 NoGas

Sb 121 NoGas

Ba 137 NoGas

W 182 NoGas

Pb 208 NoGas

Normalized 11.5 hour stability plot for a spiked Rapeseed oil.

Each element measured in the appropriate cell mode (automatically switched during each sample analysis)

Simple Preparation:•Samples and standards

•Prepared in kerosene (Purum, Fluka) •1:3 by weight/weight dilution.

•Standards and internal standard•Prepared from ~1000mgkg-1 metallo-organic oils (Spex Certiprep & Conostan)

•Internal standards were added to all samples and standards prior to analysis.

Calibration plotsGas mode shown (no gas mode inset)

Analysing Soils Featuring the High Matrix Introduction (HMI) System

HMI Schematic

Sample Preparation

Sample preparation was undertaken in accordance with the partner lab’s Standard Operating Procedure

• 1 gram of soil to 8 ml of aqua regia prior to microwave extraction

• Extracted samples were further diluted to 50 ml final volume

– Ultra pure (18.2MΩ) water

• The final acid concentration is 4% HNO3 and 12% HCl.

By permissionWim ProperEurofins AnalyticoBarneveldNetherlands

Calculated Method Detection Limits (Dutch regulation AS3000)

Analyte -isotope

ORS mode MDLintDutch Required

MDLBe 9 He 0.042 0.1V 51 He 0.255 1Cr 52 He 2.300 15Co 59 He 0.147 1Ni 60 He 0.770 3Cu 63 He 0.502 5Zn 66 He 1.704 17As 75 He 0.549 4Se 78 H2 0.832 10Se 78 He 1.064 10Mo 95 He 0.195 1.5Ag 107 He 0.278 1Cd 114 He 0.058 0.17Sn 118 He 0.589 6Sb 121 He 0.333 1Te 125 He 1.217 10Ba 135 He 3.041 15Hg 201 He 0.014 0.05Tl 203 He 0.285 3Pb 208 He 1.197 13


Certified Reference Material Analysis FeNeLab FeNeLab River Clay (mg kg -1)

AnalyteORS Mode

Measured (ave, n=10)

Certified Rec. %(ave)

Be 9 He 1.6V 51 He 59.6Cr 52 He 191.9 187 103Co 59 He 19.8 18.7 106Ni 60 He 55.7 52.9 105Cu 63 He 153.9 156 99Zn 66 He 1031.6 970 106As 75 He 44. 7 44 102Se 78 H2 2.0Se 78 He 2.4Mo 95 He 1.3Ag 107 He 2.9Cd 114 He 8.5 8.07 105Sn 118 He 0.02Sb 121 He 1.6Te 125 He 0.3Ba 135 He 828.3 817 101Hg 201 He 4.1 3.83 107Tl 203 He 1.1Pb 208 He 297.0 274 108

Replicate (n=10) analyses (mg kg-1) of FeNeLab Reference Clay

Superb recoveries

Regulatory requirement 80 - 110%.


Certified Reference Material Analysis BCR144RBCR144R Sewage Sludge

AnalyteORS Mode

Measured (ave, n=10)

Certified Rec. %(ave)

Be 9 He 0.2V 51 He 13.9Cr 52 He 88.8 90 99Co 59 He 13.6 13.3 102Ni 60 He 40.7 44.9 91Cu 63 He 270.0 300 90Zn 66 He 825.1 919 90As 75 He 3.2Se 78 H2 1.7Se 78 He 1.5Mo 95 He 6.9Ag 107 He 8.2Cd 114 He 1.7 1.84 90Sn 118 He 36.0 40.8 88Sb 121 He 2.8 3.05 92Te 125 He 0.1Ba 135 He 319.2 367 87Hg 201 He 3.2 3.11 102Tl 203 He 0.1 0.14Pb 208 He 94.9 96 99

Replicate (n=10) analyses (mg kg-1) of BCR144R Reference Sewage Sludge

Superb recoveries

Regulatory requirement 80 - 110%.


CCV Stability – 235 Soil Samples

1.6

1.7

1.8

1.9

2

2.1

2.2

2.3

2.4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

QC solution #

conc

entr

atio

n [p

pm]

Be / 9 [#3] Ti / 47 [#3]Ti / 48 [#3] V / 51 [#3]Cr / 52 [#3] Cr / 53 [#3]Mn / 55 [#2] Mn / 55 [#3]Ni / 58 [#3] Co / 59 [#3]Ni / 60 [#3] Ni / 61 [#3]Cu / 63 [#3] Zn / 64 [#3]Cu / 65 [#3] Zn / 66 [#3]Zn / 68 [#3] Se / 77 [#3]Se / 78 [#2] Se / 78 [#3]Se / 82 [#3] Mo / 95 [#3]Mo / 98 [#3] Cd / 111 [#3]Cd / 114 [#3] Sn / 118 [#3]Sn / 120 [#3] Sb / 121 [#3]Sb / 123 [#3] Ba / 135 [#3]Ba / 137 [#3] Pb / 208 [#3] #2: H2 mode, #3: He mode

Control limits +/- 10%

All Elements 2 mg kg-1


Continuing Calibration Check (CCV) Recoveries (n-21) = As

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

CCV # (QC solution #)

conc

entr

atio

n [p

pm]

1 mg kg-1 As

Control limits +/- 10%By permissionWim ProperEurofins AnalyticoBarneveldNetherlands

Continuing Calibration Check (CCV) Recoveries (n-21) Hg

40

42

44

46

48

50

52

54

56

58

60

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

CCV # (QC solution #)

conc

entr

atio

n [p

pb]

50 µg kg-1 Hg

Control limits +/- 10%


Agilent’s HMI Advantages

Speed

• HMI does not require liquid dilution of sample and stabilization of diluted sample. • It also permits the use of Agilent’s pre-emptive rinse function

– which allows rinsing of the sample tubing to begin before acquisition has finished.Low maintenance

• No tubing to replace, no moving parts to maintainSimple

• No critical timing issues or plumbing common to continuous flow autodilutorsFlexibility

• Since hardware changes or reconfigurations are not required after installation of HMI,

• The system can be switched between conventional mode and HMI mode on the fly.7500cx ICP-MS fitted with HMI to replace several instruments

• Including conventional ICP-MS, ICP-OES and a dedicated mercury analyzer.

However ICP-MS is MORE than a simple replacement for GFAAS or ICP-OES

Isotope ratio measurements

1. Isotope dilution

2. Stable (non-radioactive) isotope tracer studies

Speciation

2. LC-ICP-MS

3. GC-ICP-MS

ICP-MS offers: Isotope Ratio Measurements

Quadrupole based systems offer a simple means of measuring isotope ratios

• Not as precise as Thermal Ionisation Mass Spectrometry

• But faster and cheaper

ICP-MS opens the door to

• Stable isotope tracer (e.g element uptake in plants)

– Non-radioactive

– Relatively inexpensive

• Isotope dilution calibration

– Extremely accurate

The ORS improves precision

• As well as removing potential isobaric overlaps

Isotope Ratio Measurements (NIST 982)

Day Two

Uncorrected data Corrected for mass bias

run 1 - am run 2 - pm run 1 - am run 2 - pm

208/206 208/206 208/206 208/206

1 1.02124 1.02218 0.99954 1.00046

2 1.02145 1.02155 0.99974 0.99984

3 1.02218 1.02187 1.00046 1.00015

4 1.02124 1.02124 0.99954 0.99954

5 1.02218 1.02155 1.00046 0.99984

6 1.02197 1.02270 1.00025 1.00097

7 1.02323 1.02197 1.00148 1.00025

8 1.02135 1.02155 0.99964 0.99984

9 1.02166 1.02260 0.99995 1.00087

Mean 1.00012 1.00020

Measured bias factor Std dev 0.00063 0.00049

1.021877 %RSD 0.06% 0.05%

Day One

Uncorrected data Corrected for mass bias

run 1 – am run 2 - pm run 1 - am run 2 - pm

208/206 208/206 208/206 208/206

1 1.02438 1.02312 1.00080 0.99957

2 1.02427 1.02364 1.00069 1.00008

3 1.02354 1.02448 0.99998 1.00090

4 1.02385 1.02427 1.00029 1.00069

5 1.02406 1.02417 1.00049 1.00059

6 1.02406 1.02291 1.00049 0.99936

7 1.02385 1.02291 1.00029 0.99936

8 1.02312 1.02406 0.99957 1.00049

9 1.02249 1.02385 0.99896 1.00029

Mean 1.00017 1.00015

Measured bias factor Std dev 0.00059 0.00059

1.023728 %RSD 0.06% 0.06%

NIST 982 certificate value 208/206 1.00016+/- 0.000 36

ICP-MS As A Detector – Interfacing Options

OptionalConventionalDetector(s)

GC

LC/IC

CE

ICP-MS

Laser Ablation

LC-ICP-MS Instrumentation and Applications

Determination of just about any elemental species

Cr, As, Se, Sn, P, Br, Fe, Hg, Pb etc. etc. etc…..

Based upon their oxidation state and/or organic complex

LC-ICP-MS – As Speciation

Phenylarsonic acids used for the control of parasites and as growth promoters in poultry – concerns are raised as to the safety in excretions


Intensity

Retention time [min]

0 5 10 15 20 25

0

5000

10000

15000

20000

250004-APA

4-HPA

2-NPA

PA

3-NHPA

4-NPA

0.10 ng As0.25 ng As0.50 ng As1.00 ng As2.50 ng As5.00 ng As

Phenylarsonic acids determined in one run using Agilent LC-ICP-MS

Data kindly provided by Walter Goessler et. al. (U. Graz)


Data kindly provided by Walter Goessler et. al. (U. Graz)

During storage of chicken litter, the phenylarsonic compounds are converted to arsenate, arsenite, methylarsonic- and dimethylarsinic acid, probably by bacteria, significantly increasing the toxicity.

Retention time [min]

0 5 10 15 20 25

Intensity

0

10000

20000

30000

Uncomposted Chicken Litter

3-NHPA

4-HPA

PA

4-APA +As(V)

Composted Chicken Litter– expanded scale

As(V)

As(III)

DMA

MA

Methyl Mercury

Methyl mercury is highly toxic and is readily absorbed by the body

• USEPA's current reference dose for methylmercury is 0.1 micrograms per kilogram of body weight per day

The species is formed by biotic and abiotic methylation of the inorganic metal ion

• It has been used as a fungicide, disinfectant, and in industrial processes

Some fish appear to accumulate methyl mercury and this is how the majority of the material enters the human food chain

GC with MIP or ECD is the normal means of analysis

• New lower levels of detection are required to meet reduction in international standards

Mercury Species by LC-ICP-MS

0.501.001.502.002.503.003.504.004.505.005.506.006.507.007.508.000

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

24000

26000

28000

30000

32000

34000

Time-->

Abundance

TIC: HG-JLU.D (+,-) 2.48

3.21

6.54

MeHg

Hg2+EtHg

Agilent GC-ICP-MS Interface

GC-ICP-MS System used:

ICP-MS: Agilent 7500

GC: Agilent 6890

Interface: Agilent G3158A

Fully heated and insulated GC transfer lineModified torch with heated injector replaces standard demountable torch. “Silicosteel” transfer line and injector liner for inertnessGC capillary can be inserted to tip of injector or terminated in GC ovenGC effluent injected directly into base of plasma –essential for high boiling point compoundsSpecies decomposed to atoms - atoms then ionized and passed into MS

Initial investigations into the coupling of GC to ICP-MS, for the analysis of organotin compounds

GC-ICP-MS used to separate and quantify organotin compounds in marine environmental samples of oyster tissue and sediment

– monobutyltin (MBT)– dibutyltin (DBT)– tributyltin (TBT)– monophenyltin (MPhT)– diphenyltin (DPhT)– triphenyltin (TPhT)

GC-ICP-MS – Organotin (OT) Speciation

Determination of Organotin Species in Sediment

200 250 300 350 400 450 500 550 600 650

2.5E5

5.0E5

[2] TIC:4-std3.d [Count]

sec->

TPhT590 sec

DPhT425 secTBT

328 sec

MPhT315 sec

DBT287 sec

TPrT264 sec

MBT243 sec

Retention time (sec)

Concentration PACS -2 CRM (pg l -1 Sn)

Values MBT DBT TBT MPhT DPhT TPhT

Certified (300) 1090±150 980±130 250±20*

250±20* 250±20*

Found 947±27 914±74 947±28 230±17 219±17 228±30

(xxx) = non-certified* = spiked species

Data Courtesy of Dr Olivier Donard,

U. Pau, France

GC-ICP-MS for OT Speciation

Ion 12.00 (11.70 to 12.70): CICCAL3.D

Ion 31.00 (30.70 to 31.70): CICCAL3.D

Ion 34.00 (33.70 to 34.70): CICCAL3.D

Carbon

Phosphorus

Sulphur

Ion 35.00 (34.70 to 35.70): CICCAL3.D

Ion 79.00 (78.70 to 79.70): CICCAL3.D

3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.00

Ion 127.00 (126.70 to 127.70): CICCAL3.D

Chlorine

Bromine

Iodine

Pesticide Calibration Standard - Extracted Element Chromatograms

Sulfur ResponseR2 = 0.9996

0

100000

200000

300000

400000

500000

600000

700000

800000

900000

0 500 1000 1500 2000 2500

Concentration

Are

a

Phosphorous Response

R2 = 0.9935

0

1000000

2000000

3000000

4000000

5000000

6000000

7000000

8000000

9000000

0 200 400 600 800 1000 1200Concentration

Are

a

Malathion

Phorate

Dursban

Terbufos

Diazinon

Compound Independent Calibration

compound

Compound Concentration

pg/uL RT (min)P conc (ppb)

P response

Phorate 2102 7.01 250.14 1813218Terbufos 7454 7.87 735.71 5470509Diazinon 9755 8.1 955.01 7644808Malathion 1072 9.75 100.45 728914Dursban 5690 9.94 501.86 4205767

EthopropMalathion

Dursban Phorate

Diazinon

Terbufos

Compound

Compound Concentration

pg/uL RT (min)S conc (ppb)

S response

Ethoprop 385 6.4 101.64 23544Phorate 2102 7.01 775.64 261462Terbufos 7454 7.87 2280.92 785089Diazinon 9755 8.1 1024.28 360585

Malathion 1072 9.75 207.97 62313Dursban 5690 9.94 597.45 197738

GC-ICP-MS for Headspace Sampling

Supplementation of food and beverage products –Coffee contains low natural levels of volatile Se species (measured in headspace of brewed coffee). After supplementation by soaking beans in SeMet solution (2ppm), several Se species can be determined in the headspace of the brewed coffee

Service and Applications Support

Agilent is World #1 in ICP-MS units supplied since 1994. Largest user base community gives unprecedented expertise and support for new users.

Agilent on-line community is available to share ideas

Agilent ICP-MS Journal - the only regular ICP-MS users newsletter - produced 4 times/year featuring applications techniques, user stories, news, features and product information

Extensive Worldwide teams of Hardware and Applications Support staff, covering all time zones and with extensive industry expertise

Agilent ICP-MS training - extensive schedule of training classes and customized on-site training available

Committed to ongoing communications via online user forum, newsletters and a very popular an successful annual ICP-MS user meeting

Agilent ICP-MS Webpage

Bottlenecks in the laboratory workflow affect PRODUCTIVITY

• Limit the turnaround time of the lab

Agilent ICP-MS can unleash the potential of a food lab and maximise productivity

• Measure all elements on a single instrument

– Low detection limits replaces GFAAS, CVAFS, Hydride generator AAS and ICP-OES

• Wide dynamic range means fewer reruns

• Unique He collision/reaction cell (Agilent ORS) provides freedom from interferences and true accuracy

ICP-MS delivers FLEXIBILITY

• HMI to handle samples with high dissolved solids

• Use it as a detector for chromatography

• Isotope ratio capability for isotope dilution or stable tracer experiments

Summary

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