An Ion Chromatographic Method for the Quantitative ... · Introduction • Hydrogen Cyanide has long been considered an important smoke compound due to its toxicity • It is considered

An Ion Chromatographic Method for the Quantitative Determination of

Hydrogen Cyanide in Cigarette Smoke using Pulsed Amperometric

Detection Dr W Guthery and Dr M J Taylor

Filtrona Technology Centre

CORESTA Joint Study Group Meeting, Graz 9–13 October 2011

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Introduction

• Hydrogen Cyanide has long been considered an important smoke compound due to its toxicity

• It is considered to be extremely toxic and short-term exposure can lead to headaches, dizziness, nausea

and vomiting. Hydrogen Cyanide is thought to be a respiratory irritant and a contributor to smoking related

chronic obstructive lung disease and cardiovascular disease

• The levels of hydrogen cyanide in smoke have been studied for many years and it has been on the list of

compounds measured and reported in Canada and Brazil for over ten years

•More recently it has been included on the emissions list in Taiwan and Thailand and is also on the FDA draft

list of toxicants and the second WHO list of nine compounds

•Hydrogen cyanide is one of seven compounds on the STMA harm reduction index used in China

• Typical yields of Hydrogen Cyanide in smoke can be up to 500 ppm but the short term WEL in the UK for

continuous exposure is 10 ppm

• The accurate measurement of Hydrogen Cyanide levels in smoke are essential to monitor any reduction in

Hydrogen Cyanide levels

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Background

• Hydrogen Cyanide in whole smoke has in the past been measured by a range of techniques including, ion

selective electrodes, potentiometric titrations, colourmetric titrations, gas chromatography and automated

colourmetric systems using continuous flow analysers

•More recently continuous flow analysers seem to be the method of choice

•Whole smoke Hydrogen cyanide is trapped in impingers containing sodium hydroxide solution

•Cyanides are converted to cyanogen chloride by reaction with chloramine-T and then react with a

pyridine/pyrazolone solution to form a coloured compound measured at 540 nm

• The continuous flow analysers can measure 50 samples per hour and has a reasonable linear range 0.08 to

4 µg /ml

• However, the method has some disadvantages mainly the use of toxic and very odourous pyridine as one

of the required reagents and the lower limit of detection can cause problems for cigarettes with yields below

5 µg/cig

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Continuous Flow Analyser AA3

Waste

2.0 ml/min Wash Solution

5 x Turn Coil

0.32 ml/min Air

0.8 ml/min NaOH Solution

0.80 ml/min Sample

10 x

Turn

Coil

Colourimeter

540 nmComputer

Waste

20 x Turn Coil

Waste

5 x Turn Coil

0.32 ml/min Air

0.23 ml/min Air

0.80 ml/min Phosphate buffer

0.10 ml/min Resample

0.23 ml/min Chloramine - T

0.80 ml/min Pyridine/Pyrazolone Solution

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Ion Chromatography Method - Summary

• Ten cigarettes smoked on rotary smoking machine

•Whole smoke trapped in two impingers

• Aliquot of trap solution syringe filtered

• Analysed using IC with electrochemical detection

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Dionex Ion Chromatograph

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Electrochemical Cell

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Principle of Operation

• The ED40 amperometry cell is a miniature flow-through cell with a titanium cell body (counter electrode) and a Ag/AgCl reference electrode.

• Installed directly after the ion chromatography column (suppressor not required)

• Mobile phase flows in a thin channel (0.2 ml) parallel to the surface of a flat disc electrode.

• A potentiostat diverts the cell current through the counter electrode

• Two modes of operation

- DC Amperometry, a constant voltage is applied to the working electrode and the resulting current is the detector output

- Integrated or Pulsed Amperometry, a repetitive series of potentials is applied to the cell. The integrated current (charge) from the oxidation is measured during a portion of a repeating potential vs. time waveform

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Silver Working Electrodes

• Two types of working electrode solid and disposable

• Disposable electrodes have been reported to have shown comparable or better reproducibility and

linearity compared with solid electrodes1.

• Advantage of ease of use compared with solid electrodes which require regular cleaning.

• Disadvantage is the cost

1 Liang, L et al., J.Chromatogr. A, 2005, 1085, 37-41

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Analytical Conditions

Instrument: Dionex ion chromatography system with gradient pump and ED40 electrochemical

cell

Columns: IonPac® AS7 (4 x 250mm) anion-exchange column with AG7 (4 x 50mm) guard

column and Metal-Free Trap column (MFC-1)

Injection: 25 ml full loop

Column Temp: 30°C

Eluent: 0.1M NaOH/ 0.2M NaOAc

Flow rate: 1 ml/min

Pressure: ~1800 psi

Detection: Pulsed Amperometric Detection (PAD)

Working electrode: Disposable Ag with Ag/AgCl reference electrode

Collection rate: 1.00 Hz

Run time: 20 mins

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The Cyanide Optimised Waveform

• Silver is oxidised in the presence of the cyanide ions and its electrons are released

• A series of potentials is defined as a waveform

• A three-potential PAD waveform using E1, E2 and E3 is applied over 1-sec.

• E1 is the detection potential. The remaining potentials clean and restore the electrode for subsequent

detection

Cyanide Waveform

Time (sec) Potential vs

Ag/AgCl (V)

Gain region Integration Ramp

0.00 -0.10 Off Off On

0.20 -0.10 On On (Start) On

0.90 -0.10 On Off (End) On

0.91 -1.00 On Off On

0.93 -0.30 Off Off On

1.00 -0.30 Off Off On

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Whole Smoke Trapping – Method Summary

• 10 cigs smoked on a Rotary smoking machine

• 8 mm Teflon insert positioned at the MS head

• All of the smoke phases trapped into two impingers containing 100 and 20 ml 0.1M NaOH/0.2M NaOAc

• 55 mm CF pad placed at the syringe head

• Extracts combined then shaken and filtered through 0.45 mm nylon filter

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Example Chromatogram

• Silver electrodes are selective to other ions including sulphides, bromides, and thiosulphates.

• AS7 column demonstrated clear separation from matrix interferences

• AS7 contains a strong anion exchange (SAX) stationary phase (alkyl quaternary ammonium). It was necessary to use a high ionic strength mobile phase to enable elution with a reasonable turnaround time

0.0 1.3 2.5 3.8 5.0 6.3 7.5 8.8 10.0 11.3 12.5 13.8 15.0 16.3 17.5 18.8 20.0

-20

0

20

40

60

80

100

120

14018 MAY 2011_ #17 MS 1R5F 1 ED_1nC

min

1

2:

cyanid

e

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Calibration Data

• Quantitative analysis was performed using standards made up from certified reference material, CN-

standard (1000ppm in OH-), supplied by SPEX CertiPrep.

• Seven calibration standards (0.1 – 10 mg/ml) prepared in 0.1M NaOH

• Linear response; Corr. Coeff. (%) 99.9903

0

100

160

0.0 2.0 4.0 6.0 8.0 10.0 12.0

cyanide External ED_1Area [nC*min]

Concentration mg/ml

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Sample Stability

Storage Time (at 22C)

K3R4F Mean µg/cig

SD

< 12 hours 107.1 1.1

> 24 hours 66.0 2.4

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Reference Cigarette Values

Mean Yield µg/cig Sample

AA 3 IC

K3R4F 120.6 107.1

K1R5F 22.3 17.2

CM6 128.3 117.6

SATF 2006 Collaborative Study Mean Yield for all Laboratories for K1R5F = 20.2 µg/cig

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Comparison of Trapping Techniques K3R4F Cigarettes

Mean Yield µg/cig Sample

AA 3 IC

Impingers 120.6 107.1

Granular Traps 128.5 99.4

Granular Trap

Extended 44 mm CF Holder

Silica Gel Beads 0.5 to 1.5 mm Diameter

Approximately 8 g of beads per trap

3 Cigarettes per trap smoked using linear

smoking machine

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Comparison of Methods

Parameter AA 3 IC

Range mg/ml 0.08 to 4.0 0.025 to 10.0

Samples/Hour 50 3

Reagents Pyridine Aqueous

Overnight Operation No Yes

Coefficient of Linearity 0.995 0.9999

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Conclusions

• A method for the determination of Hydrogen cyanide in whole smoke using IC/PAD is under development

• Yield values are comparable with current methods

• The IC method has lower limits of detection and does not use any organic reagents but is slower

•More work will be carried out on the long term stability of the method and its applicability to sidestream

smoke

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