# How do you analyze GC-MS results?

The Y-Axis: Concentration or Intensity Counts Typically, the y-axis, or the area of the peak, is a reflection of the amount of a specific analyte that’s present. When looking at a GC/MS chromatogram, the area will be based on the number of counts taken by the mass spectrometer detector at the point of retention.

## How do you measure uncertainty in chemistry?

The uncertainty of a measuring instrument is estimated as plus or minus (±) half the smallest scale division. For a thermometer with a mark at every 1.0°C, the uncertainty is ± 0.5°C. This means that if a student reads a value from this thermometer as 24.0°C, they could give the result as 24.0°C ± 0.5°C.

## How do you find the uncertainty of concentration?

Finally, the expanded uncertainty (U) of the concentration of your standard solution is U = k * u_combined = 1,2% (in general, k=2 is used). The molality is the amount of substance (in moles) of solute (the standard compound), divided by the mass (in kg) of the solvent.

## What is the formula for calculating uncertainty?

The relative uncertainty or relative error formula is used to calculate the uncertainty of a measurement compared to the size of the measurement. It is calculated as: relative uncertainty = absolute error / measured value.

## What does GC-MS measure?

GC/MS is a commonly used platform for measuring oxidized amino acids. As separation in GC occurs in an oven at high temperatures, analytes need to be volatile and thermally stable and it is therefore necessary to derivatize samples prior to analysis.

## What are the limitations of using GC-MS to measure purity?

However, GC–MS suffers from two major limitations: First, only a relatively small range of volatile, thermally stable compounds are amenable for analysis, and second, EI mass spectra suffer from a frequent absence or weakness of the molecular ions.

## How do I report GC-MS data?

1. Retention Time. Retention time refers to the time a compound is retained in the gas chromatography column.
2. Size of the peaks of the spectra. Peak size is another parameter that is used to present the results of gas chromatography.
3. Mass-to-charge Ratio (m/z)

## What is the uncertainty of molecular mass?

The uncertainty of the mass m and the molar mass M are given as u(m)=0.0004 g and u(M)=0.001 g mol−1, respectively. The uncertainty of the volume V is not given; however, when a number is given without any further information, it is generally interpreted so that the last digit is rounded.

## How do you analyze uncertainty?

1. Identify the measurement function,
2. Identify the measurement range,
3. Identify the test points,
4. Identify the method,
5. Identify the equipment,
6. Record your results.

## Is uncertainty a measure of accuracy or precision?

Uncertainty is a quantitative measure of how much your measured values deviate from a standard or expected value. If your measurements are not very accurate or precise, then the uncertainty of your values will be very high. In more general terms, uncertainty can be thought of as a disclaimer for your measured values.

## Is uncertainty the same as accuracy?

While accuracy indicates how close a measurement is to its true value, uncertainty takes into account any statistical outliers that don’t conform. These may exist due to anomalies, adjustments or other outside factors. To factor these anomalies directly into an instrument’s accuracy would be misleading.

## What is a good uncertainty percentage?

Converting from an absolute uncertainty to a percentage uncertainty give us a much better idea of whether our results are reliable or not. In general, any result with a percentage uncertainty of 10% or less can be considered reliable.

## How is GC-MS used for quantification?

Analyzing small and volatile molecules When combined with the detection power of mass spectrometry (MS), GC-MS can be used to separate complex mixtures, quantify analytes, identify unknown peaks and determine trace levels of contamination.

## What is difference between GC and GC-MS?

GC is used for analyzing volatile organics, and generally separating by boiling points. GCMS indicates that a mass spectrometer is used as the detector for the GC.

## What is the difference between GC-MS and GC-MS MS?

Low resolution GC/MS provides the ability for fast screening of samples, while GC/MS/MS gives fast and specific confirmation of samples found to contain TCDD in the presence of interferences.

## What is M Z ratio in GC-MS?

m/z represents mass divided by charge number and the horizontal axis in a mass spectrum is expressed in units of m/z. Since z is almost always 1 with GCMS, the m/z value is often considered to be the mass.

## What is a disadvantage of using gas chromatography?

The disadvantages of gas chromatography are due to the reliance on volatile compounds. It is not a reliable method for non-volatile substances. The reliance on volatility also means it must be performed at high temperatures. This means compounds that degrade with heat can’t be analysed through gas chromatography.

## What are the limitations of paper chromatography?

• Large quantity of sample cannot be applied on paper chromatography.
• In quantitative analysis paper chromatography is not effective.
• Complex mixture cannot be separated by paper chromatography.
• Less Accurate compared to HPLC or HPTLC.

## How do you identify peaks in GC-MS?

you can identify the GC-MS peaks by searching in the NIST Library and also confirmed with known standards. There are a lot of good comments listed, such as using the manufacturer software. Also, as mentioned above by using the NIST Library search is probably the easiest way to narrow your identification.

## How do you reduce uncertainty in chemistry?

Reducing uncertainties in a titration To reduce the uncertainty in a burette reading it is necessary to make the titre a larger volume. This could be done by: increasing the volume and concentration of the substance in the conical flask or by decreasing the concentration of the substance in the burette.

## Why do we do uncertainty analysis?

Uncertainty analysis is a key component of model-based risk analysis and decision-making because it provides risk assessors and decision-makers with information about the accuracy of model outputs.

## Can uncertainty be measured?

To calculate the uncertainty of a measurement, firstly you must identify the sources of uncertainty in the measurement. Then you must estimate the size of the uncertainty from each source. Finally the individual uncertainties are combined to give an overall figure.

## Is error and uncertainty the same?

‘Error’ is the difference between a measurement result and the value of the measurand while ‘uncertainty’ describes the reliability of the assertion that the stated measurement result represents the value of the measurand.

## What is measurement uncertainty in laboratory?

Measurement Uncertainty (MU) relates to the margin of doubt that exists for the result of any measurement, as well as how significant the doubt is. For example, a piece of string may measure 20 cm plus or minus 1 cm, at the 95% confidence level. As a result, this could be written: 20 cm ±1 cm, with a confidence of 95%.