Instrumental Analysis

Question 1

Analytical chemistry

Answer 1

the study of the separation, identification, and quantification of the chemical components of natural and artificial materials

Question 2

Qualitative vs quantitative analysis

Answer 2

Qualitative = determination of what the unknown substance (analyte) is in sample

Quantitative = determination of amount of concentration of the substance (analyte) in sample

Question 3

Calibration

Answer 3

Process of relating a physical quantity (such as mass, volume, concentration) to the quantity indicated on the scale of an instrument

Determines relationship between measured values and analytical qualities allowing for characterization types of analytes and their amount

Question 4

Standards

Answer 4

Materials containing precisely known amounts of a substance for use in quantitative analysis. A standard provides a reference that can be used to determine unknown concentrations or to calibrate analytical instruments

Question 5

Blank

Answer 5

Specimen that contains none of the analytes of interest which is subjected to the same measurement process to establish a zero baseline or background value

Question 6

Calibration check

Answer 6

Analysis of a solution formulated by the analyst to contain a known concentration of analyte. It is the analyst’s own check that procedures and instruments are functioning correctly.

Question 7

Calibration curve

Answer 7

Graph showing the value of some property (typically a value obtained on the scale of an instrument) versus concentration of analyte. If a linear relationship can be established between the property and analyte concentration then the corresponding property of an unknown can be measured and its concentration can be determined from the graph.

Question 8

Methods employed for calibration

Answer 8

1) External standard calibration
2) Internal standard calibration
3) Standard addition calibration

Question 9

Method limits

Answer 9

All analytical methods have sensitivity limits called limit of detection (LOD) and limit of quantification (LOQ). There are a number of different definitions for LOD and LOQ available in the literature so it is important when providing these values to also provide the definition used.

Question 10

Limit of detection (LOD)

Answer 10

Can refer to (a) the limit of detection of an instrument or (b) the limit of detection of a method. These should not be used interchangeably, so care has to be taken in the description to establish if the value reported is a method LOD or an instrument LOD.

Note: the type of LOD is not typically labelled as method or instrument but inferred through other information provided.

Question 11

Limit of quantification

Answer 11

The lowest concentration or amount of analyte that has been quantified with an acceptable level of accuracy and precision by the identified analytical method and identification criteria. This generally corresponds to the lowest calibration level in a linear calibration curve and is higher than the LOD.

Question 12

Signal to noise ratio

Answer 12

Signal: magnitude of response for the analyte
Noise: Magnitude of response when no analyte is present
Signal to noise ratio: response ratio