Faraday collector configuration (please share)

03 Oct 2014

Hi guys,

I am curious to know what lab has what configuration when it comes to your collector. This will probably impact the method one would choose to correct for PBL, so it would be nice if could share their configuration. At IC, we have all collectors with a narrow slit (1.5 mm). Our resistors are registered for 3*1083*1010, and 1*1011 ohm for masses 44, 45, 46 (respectively), and 1*1012 ohm for masses 47-49.

Grateful if other labs can share theirs here, and what PBL method(s) you have adopted.

Cedric

hagit
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Joined: Dec 21 2011
I think we have the same,

I think we have the same, with the exception of a wide (3.5) cup for mass 49.

No PBL so far but if the new filament forces us to do it, I will use the baseline after the peak, which is stable/flat (~-20mV) in 47 and more or less stable in 48 and 49. My before the peak baseline is very not flat.

hagit

Kate Huntington's picture
Kate Huntington
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Joined: Sep 21 2011
Cups 1-8 slit widths are as

Cups 1-8 slit widths are as follows: 3.5, 1.5, 1.5, 1.5, 3.5, 1.5, 1.5, 1.5

Resistors are, respectively: 3E+8, 3E+8, 3E+10, 1E+11, 1E+11, 1E+12, 1E+12, 1E+12

We measure PBL as follows:

Our PBL measurement replaces the traditional background measurement through a modification of the ISL script (we do measure traditional background, i.e., with no gas, for a "water background" measurement each acquisition (measure mass 18 on 45 cup, peakcenter, for SA and ST), but the traditional background measurement is not used to correct clumped data).

Our PBL is measured 0.08 kV (525 steps) left of peak center, before each acquisition (i.e., each 10 sample-standard comparisons of 26 sec SA, 15 sec wait, 26 sec ST, 15 sec wait). Within the ISL script, a peak center is first executed (within +/- 100 mV of m/z 47 @ 2550 mV). We then adjust the high voltage 525 steps to the left of that peak center and integrate the signal on each cup for 1 integration cycle (26 seconds). This is done on the reference gas.

FYI, With PBL correction, our reference frame slope of all three temperature equilibrated CO2 (4°C, 60°C, 1000 °C) is 0.002. We use local tap water composition and an evaporatively enriched composition to create a 40 per mil (in d47 space) range. We are about to re-do our reference frame next week, though, because on our prep line this week we replaced as much of the stainless tubing as possible with nickel tubing and removed some superfluous volume of flexible stainless tubing near the common acid bath (90 °C), to eliminate a source of occasional water contamination. The PBL-corrected ref frame had not changed since our last big instrument/prepline reconfiguration 9 months ago. Since we are not modifying the mass spec or PBL procedure, I do not expect the reference frame slope to change.  

- Kate, U of Washington

Kate Huntington, nee Ruhl
Associate Professor, Dept. of Earth and Space Sciences
University of Washington, Seattle, WA
kate1@uw.edu; http://faculty.washington.edu/kate1

Kate Huntington's picture
Kate Huntington
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Joined: Sep 21 2011
Cups 1-8 slit widths are as

Cups 1-8 slit widths are as follows: 3.5, 1.5, 1.5, 1.5, 3.5, 1.5, 1.5, 1.5

Resistors are, respectively: 3E+8, 3E+8, 3E+10, 1E+11, 1E+11, 1E+12, 1E+12, 1E+12

We measure PBL as follows:

Our PBL measurement replaces the traditional background measurement through a modification of the ISL script (we do measure traditional background, i.e., with no gas, for a "water background" measurement each acquisition (measure mass 18 on 45 cup, peakcenter, for SA and ST), but the traditional background measurement is not used to correct clumped data).

Our PBL is measured 0.08 kV (525 steps) left of peak center, before each acquisition (i.e., each 10 sample-standard comparisons of 26 sec SA, 15 sec wait, 26 sec ST, 15 sec wait). Within the ISL script, a peak center is first executed (within +/- 100 mV of m/z 47 @ 2550 mV). We then adjust the high voltage 525 steps to the left of that peak center and integrate the signal on each cup for 1 integration cycle (26 seconds). This is done on the reference gas.

FYI, With PBL correction, our reference frame slope of all three temperature equilibrated CO2 (4°C, 60°C, 1000 °C) is 0.002. We use local tap water composition and an evaporatively enriched composition to create a 40 per mil (in d47 space) range. We are about to re-do our reference frame next week, though, because on our prep line this week we replaced as much of the stainless tubing as possible with nickel tubing and removed some superfluous volume of flexible stainless tubing near the common acid bath (90 °C), to eliminate a source of occasional water contamination. The PBL-corrected ref frame had not changed since our last big instrument/prepline reconfiguration 9 months ago. Since we are not modifying the mass spec or PBL procedure, I do not expect the reference frame slope to change.  

- Kate, U of Washington

Kate Huntington, nee Ruhl
Associate Professor, Dept. of Earth and Space Sciences
University of Washington, Seattle, WA
kate1@uw.edu; http://faculty.washington.edu/kate1

Paul Dennis's picture
Paul Dennis
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Joined: Sep 16 2011
On the UEA MIRA instrument

On the UEA MIRA instrument our collector configuration is 6 faraday cups, all with 2mm slit widths (mass resolution = 250) and amplifier gains as follows:

44 - 1e8; 45 - 1e10; 46 - 1e10; 47 - 1e12; 48 - 1e12; 49 - 1e12.

We see no PBL effect at 47, 48 or 49. As a result MIRA is linear when plotting D47 and D48 versus measured d47, and d48.

Paul

Paul Dennis, Stable Isotope Laboratory, Environmental Sciences, UEA