Molecular Formula From Exact Mass Calculator

Molecular Formula Determination:

\[ \text{Molecular Formula} = \text{Combinations where Exact Mass matches input mass} \]

Possible Molecular Formulas:

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1. What is Molecular Formula Determination?

Molecular formula determination from exact mass involves calculating all possible combinations of elements that sum to within a specified tolerance of the input mass. This is a fundamental technique in mass spectrometry for identifying unknown compounds.

2. How Does the Calculator Work?

The calculator uses combinatorial algorithms to generate possible molecular formulas:

\[ \text{Molecular Formula} = \text{Combinations where Exact Mass matches input mass} \]

Where:

Exact Mass — The measured mass of the molecule (in Daltons)
Mass Tolerance — Acceptable deviation from input mass
Elements — Set of elements to consider in combinations

Explanation: The algorithm generates all possible combinations of the specified elements that sum to within the tolerance of the input mass.

3. Importance of Exact Mass Analysis

Details: Exact mass measurement is crucial for identifying unknown compounds, determining elemental composition, and distinguishing between isobaric species in mass spectrometry.

4. Using the Calculator

Tips: Enter the exact mass in Daltons, specify mass tolerance (typically 0.001-0.01 Da for high-resolution instruments), and list elements to consider (e.g., C,H,N,O,P,S).

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between exact mass and molecular weight?
A: Exact mass uses the most abundant isotope masses for calculation, while molecular weight uses average atomic masses weighted by natural abundance.

Q2: How many elements should I include?
A: Typically 4-6 common elements (C,H,N,O,S,P). Adding more elements increases computation time exponentially.

Q3: What mass tolerance should I use?
A: For high-resolution instruments (Orbitrap, FT-ICR), 1-5 ppm is typical. For unit mass instruments, use larger tolerances.

Q4: Why do I get multiple possible formulas?
A: Different combinations of elements can sum to similar masses (e.g., C3H4 vs. N2O). Additional data (MS/MS, isotope patterns) helps narrow possibilities.

Q5: How can I improve formula assignment confidence?
A: Combine with isotope pattern matching, heuristic rules (e.g., nitrogen rule), and fragmentation pattern analysis.