LOWER LIMITS FOR MOLECULAR WEIGHTS OF ANY CHEMICAL CLASS

                      SCOTT'S SIMPLE RULE

THIS LOWER LIMIT HAS BEEN TESTED FOR A LARGE NUMBER OF CHEMICAL CLASSES AND COMPOUNDS. IT IS CORRECT EVEN FOR LOW MASS TRUNCATED SPECTRA AND WILL ALSO WORK WITH MIXTURES. THE MOLECULAR WEIGHT DISCUSSED HERE IS THAT OBTAINED FROM ISOTOPICALLY AVERAGED ATOMIC WEIGHTS. FOR DETAILS SEE THE ABSTRACT OF PUBLICATION # 2 GIVEN HERE.

PROCEDURE

1. FIND THE HIGHEST MASS IN THE SPECTRUM WITH AN INTENSITY OF 5% OF THE BASE PEAK.  THIS IS DESIGNATED AS MAXMASS.

2. FIND THE HIGHEST MASS IN THE SPECTRUM WITH AN INTENSITY OF 1% OF THE BASE PEAK.  THIS IS CALLED HIMAX1. HIMAX1 AND MAXMASS MAY BE EQUAL, BUT HIMAX1 MUST BE EQUAL TO OR GREATER THAN MAXMASS!

3. TAKE THE AVERAGE OF THESE TWO MASSES AND SUBTRACT 5 FROM THIS AVERAGE.

4. THE RESULT IS A RIGOROUS LOWER LIMIT TO THE MOLECULAR WEIGHT.

SEE EXAMPLE BELOW

SIMPLE ISN'T IT!!!

EXAMPLE

CAFFEINE                                              MW =  194 DALTONS

MAXMASS = 195 DALTONS

HIMAX1 = 195 DALTONS

AVERAGE - 5 = 195 - 5 = 190

MW LOWER LIMIT = 190 DALTONS VS. 194 ACTUAL MW