The Mass Spectrograph & Average Atomic Mass

1. The Mass Spectrograph & Average Atomic Mass

2. Inventor • Francis William Aston won the 1922 Nobel Prize in Chemistry for his work in mass spectrometry

3. The First Mass Spectrograph

4. How Does it Work? Schematics of a simple mass spectrometer with sector type mass analyzer. This one is for the measurement of Carbon dioxide isotope ratios (IRMS) as in the carbon-13urea breath test

6. The Detector A continuous dynode particle multiplier detector.

7. The Data Mass Spectrograph of a protein

11. The Data as a Bar Graph

12. The Modern Mass Spectrograph

14. Use of Inductively Coupled Plasma-Mass Spectrometry in Boron-lO Stable Isotope Experiments with Plants, Rats, and Humans Richard A. Vanderpool1, Deb Hoff1, and Phyllis E. Johnson2 'United States Department of Agriculture, Agricultural Research Service, Grand Forks, North Dakota; 2United States Department of Agriculture, Agricultural Research Service, Albany, California The commercial availability of inductively coupled plasma-mass spectrometry technology (ICP-MS) has presented the opportunity to measure the boron concentrations and isotope ratios in a large number of samples with minimal sample preparation. A typical analytical sequence for fecal samples consists of 25 acid blanks, 1 digestion blank, 5 calibration solutions, 4 standard reference material solutions, 10 samples, and 4 natural abundance bias standards. Boron detection limits (3 x 1a) for acid blanks are 0.11 ppb for '0B, and 0.40 ppb for " B. Isotope ratios were measured in fecal samples with 20 to 50 ppb boron with <2% relative standard deviation. Rapid washout and minimal memory effects were observed for a 50 ppb beryllium internal standard, but a 200 ppb boron biological sample had a 1.0 ppb boron memory after a 6-min washout. Boron isotope ratios in geological materials are highly variable; apparently this variability is reflected in plants. The lack of a fixed natural abundance value for boron requires that a natural abundance ratio be determined for each sample or related data set. The natural abundance variability also prevents quantitation and calculation of isotope dilution by instrument-supplied software. To measure boron transport in animal systems, 20 pg of '°B were fed to a fasted rat. During the 3 days after a 10B oral dose, 95% of the '0B was recovered from the urine and 4% from the feces Urinary isotope ratios, I B/°0B, changed from a natural abundance of 4.1140 to an enriched value of 0.9507, a 77% change. The '°B label in perfused rat livers peaked within 3 hr (>90% recovery, 56% change in " B/`B) and returned to a natural abundance ratio within 24 hr. In summary, boron concentrations and enriched isotope ratios have

15. Note: • Percent = out of 100 % • Relative abundance = out of one whole • Average Atomic Mass – the average mass of all the naturally occuring isotopes of an element expressed in atomic mass units.

16. The Mass Spectrograph for the common isotopes of Boron The relative sizes of the peaks gives you a direct measure of the relative abundances of the isotopes. The tallest peak is often given an arbitrary height of 100 - but you may find all sorts of other scales used. It doesn't matter in the least. You can find the relative abundances by measuring the lines on the stick diagram. In this case, the two isotopes (with their relative abundances) are: boron-10 18.70%, 10.013 g/mol boron-11 81.30%, 11.009 g/mol

17. Sample Problems • What is average atomic mass of Lithium if 7.42% exists as 6Li (6.015 g/mol) and 92.58% exists as 7Li (7.016 g/mol)? • Two isotopes of silver are found using the mass spectrograph. Silver – 107 has an atomic mass of 106.91 amu and an abundance of 51.86 %. The second isotope has an abundance of 48.14 %, but its atomic mass was unable to be determined. What is the atomic mass and the mass number(identity) of this isotope?