existing standardization techniques · short-lived halocarbon calibration workshop london, 2008...

Short-lived Halocarbon Calibration WorkshopLondon, 2008

Existing Standardization Techniques

• Compressed Gas Standards• Permeation Tubes• Liquid Standards• Reagent Purity

Brad Hall, Lucy Carpenter, Manuela Martino, Ben Miller, Paul Krummel


Compressed Gas Standards

Basic Idea: Static dilution of a pure compound (or a known mixture) to working concentration levels

Pros: portability, longevity, multiple species, traceableCons: stability, transport issues, multiple steps

NOAA: Gravimetric method, pure starting material(all components added gravimetrically)

SIO: Gravimetric/Bootstrapping, pure starting material

NIES: Gravimetric dilution of commercial mixtures


NOAA method

Pure gas (g)

Pure liquid (mg)

Ultra-pure air (kg)

Primary standard (level 1)

Ultra-pure air (kg)

Primary standard (level 2)(~ ambient concentrations)

(level 1) aliquot


Scale: Dry air mole fraction (not pptv)


SIO method

Pure liquid (mg)

N2O (gravimetric)

“Mixture”

Ultra-pure air

Primary standard(~ ambient concentrations)

GSV

Measure N2O to determine dilution factor.

“Bootstrap to N2O”

N2O bootstrapped to CO2 (Keeling)

“Mixture”


reagent

ppb ppb ppb

ppt

ppt

ppt

ppt

ppt

ppt

NOAA


reagent

mixture

ppt

mixture

ppt

mixture

ppt

mixture

ppt

mixture

ppt

mixture

ppt

SIO


CH3Br: 2008 analysis by ECD

0.5

0.7

0.9

1.1

1.3

1.5

1.7

1.9

2.1

2.3

2.5

5 10 15 20 25

Prepared Value (ppt)

AluminumStainless Steel (Essex)drifting ?Poly. (Stainless Steel (Essex))

Uncertainties (NOAA): ~5% for VSL halocarbons


Limitations: Stability

0.1

2

3

456

1

CH

3I (p

pt)

1/1/96 1/1/00 1/1/042

3

4

5

6

7

8910

(right axis)

filled circles: stainless steel (Essex Cryogenics) open squares,: other stainless steel open triangles: other stainless steel open circles: Aculife-treated Aluminum


Permeation Systems

Basic Idea: Dynamic dilution of a pure compound (or a known mixture) to working concentration levels

Pros: multiple species, simple linearity checkCons: ?


10

100 mL min-1

70oC

40oC

CH3I, C2H5I, CH2ICl, CHCl3, CH2Br2, CHBr2Cl

1-and 2- C3H7I, CH2IBr, CHBr3, CH2I2

Commercial (Ecoscientific) permeation tubes filled in-house

Loop system introduces ppt levelhalocarbons into gas stream

Permeation system used at University of York

See Wevill and Carpenter, 2004


~ 3%

Inject 0- 3 loops into gas stream, determine moles/PA

Assuming normal dist., standard deviation of the slope, sm:

sm =SSresid/(N-2)

(xi – x)2

CH2I2

y = 1.36E-18xR2 = 9.99E-01

0.0E+00

2.0E-14

4.0E-14

6.0E-14

8.0E-14

1.0E-13

1.2E-13

0 20000 40000 60000 80000 100000

Peak area

No.

mol

es

Calculate no. of moles in 1 loop:

= permeation rate (g/min-1) x loop vol (mL)

RMM (g mol-1) x flow rate (mL/min-1)

10

100 mL min-1


Uncertainty in permeation weighings

Data points are average of 6 weighings and include error bars

This can be major uncertainty unless several months of weighings are made.

Standard deviation of slope, sm, for 9 month period of weighings ~ + 5 %

y = -0.0003x + 27.788R2 = 0.9948

15.70

15.72

15.74

15.76

15.78

15.80

15.82

09/03/07 28/04/07 17/06/07 06/08/07 25/09/07 14/11/07 03/01/08 22/02/08

Date

Wei

ght/

g

Hotel room

CH2ICl


Total uncertainty sy/y for y = a x b/c can be estimated as:

sy/y = (sa/a)2 + (sb/b)2 + (sc/c)2Uncertainty associated with gas-phase sampling %RSDa) bias sample line loss 0b) bias sample flow rate 2c) bias atmospheric artefacts 0d) noise reproducibility of repeat air standards (which takes into 4.4

account noise on integration of chromatograms)

Uncertainty associated with water samplinge) bias losses in water sample 0f) bias sample flow rate (manufacturers uncertainty) 2g) noise reproducibility of purge efficiency (which takes into account 10.3

human error on purge volumes + noise on integration of chromatograms)

Uncertainty associated with calibration and detectionh) noise perm tube weighings 5i) bias stated mass balance uncertainty 1j) noise calibration linear regression 3k) bias flow rate through permeation tube + dilution flow 2l) bias loop volume 10

total uncertainty air,% 12.7total uncertainty water,% 15.8

+

+

+

+

+

+

+

+

+


Comparison with AGAGE CHCl3 measurements at Mace Head:

y = 0.8687xR2 = 0.8547

0

10

20

3040

50

60

70

80

0 10 20 30 40 50 60 70

CHCl3 York (pptv)

CH

Cl 3

AG

AG

E (p

ptv)

2002


Liquid Standards

Basic Idea: Static dilution of a pure compound in a solvent using volumetric or gravimetric techniques

Pros: simplicity, direct calibration of sea waterCons: ?


CH3OH

Preparation of liquid halocarbon standards -UEA

1. Preparation of primary standard:• A 50 ml volumetric flask containing methanol near to level is weighed (4 decimals)• The flask is weighed again after addition of 0.5-2 grams of commercial neat halocarbon and then

taken to volume2. Primary standards are shipped into the field on dry ice and are kept in a freezer until use.3. Secondary and tertiary (working) standards are prepared by successive dilution before calibrating.4. For calibrations, variable amounts (µL) of working standard are injected into syringes containing 40 ml of

halocarbon-free seawater. 5. The seawater is injected in the purge vessel and treated in the same manner as the samples.

CH3OH CH3OH

Tertiary (working) standard

By weight

When using class-A glassware and calibrated scales and pipettes, the relative error in the standard concentration is ~ 2%.


Reagent Purity

CHBr3 (Sigma-Aldrich)98%1% CH2Br21% CHBrCBr2

CHCl3 (Sigma-Aldrich)99+ %

Halon-1211 (Scott Specialty Gases)99%1% CHBrF2

CH3Br (Matheson)99%1% CH3Cl


Reagent Purity

CHBr3 (Sigma-Aldrich)98%1% CH2Br21% CHBrCBr2

CHCl3 (Sigma-Aldrich)99+ %

Halon-1211 (Scott Specialty Gases)99%1% CHBrF2

CH3Br (Matheson)99%1% CH3Cl

CHBr3 (Spectrum)94%1% CH2Br22% dichloropropanol3% unknown

CH2BrCl (Sigma-Aldrich)96%3% CH2Cl21% CH2Br2

CH2Br2 (Sigma-Aldrich))90%9% CH2BrCl1% CH2Cl2


END

existing standardization techniques · short-lived halocarbon calibration workshop london, 2008...

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