What is the difference between Colorimetry, Spectrophotometry and Chromatography?

Question

Could someone please explain, in reasonably simple terms, what is the difference between the methods listed above. Can they all be used for quantitative analysis of foods? I've tried looking them up on the internet but am getting a bit confused. What about Kjeldahl analysis? Can this be used to determine protein in food samples?

Answer 1

Spectrometry looks at how light interacts with matter. This my be in the form of a NMR spectrometer which looks how matter interacts with radio waves, or IR spec etc. Different atoms or groups within compounds will react with light in different ways allowing those atoms/groups to be identified.

Colorimetry, as far as I know, is just a form of spectrometry which looks at the visible colour of a solution and relates this to its concentration.

Chromatography involves passing a mobile phase, i.e the liquid you are looking at or a gas, over a stationary phase,(e.g paper, or a chromatography column filled with silica gel). It will take different molecules within the mobile phase different times to pass through the stationary phase, allowing parts of a solution to be seperated.

Chromatography is generaly used to separate compounds but need to be conected to other equipment, e.g spectrometers, to give quantitative analysis of the separated parts of the solution.
Most spectrometry is just used to identify what compounds/ functional groups are present although some spectrometry , e.g colorimetry can be used to give direct quantitative measurements throught beers law.

Answer 2

spectrophotometry is a method based on light passing through a solution. Colorimetry usually compares the colour of a sample with a standard or reference. Chromatography separates components of a mixture.
They are all routinely used in the food industry for both qualitative and quantitative analysis.
And Kjehldahl is the industry standard for determining protein content. Actually it determines nitrogen content so you need to know WHICH protein is being determined.

Answer 3

i don't know about colorimetry but i know that the spectrophotometry usually uses a device such as a spectrophotometer(ex. spec 20) and works based on beers law.
It passes different wavelengths of light through a substance and gives % transmittance, absorbance etc. Chromatography usually requires a special paper that you would blot with a certain chemical and treat it to other reagents.
how it helped
:-)

Answer 4

Spectrophotmetry is a widespread term applicable to quantitative study of electromagnetic spectra. It applies to Visible,UV and near-IR regions of the electromagnetic spectrum.

Spectrophotometers are generally employed to measure light absorption of a sample (UV/Vis spectrophotometry). Absorbance readings are collected over a range of concentrations to form calibration curves - from which, unknown analyte concentrations may be determined. UV/Visible spectrophotometry was specifically designed to determine the vitamin content of food during the outbreak of World War II, but is far from limited to this area of nutritional science. Molecules without chromophores (unsaturated functional groups) do not absorb in the UV/Visible region and are unsuitable for this method of analysis.

Colorimetry is method of analysis pertaining to analytes requiring ligand complexing in order to obtain accurate absorbance readings. An example of colorimetric determination is the 1,10-phenanthroline method used to determine iron content in water samples. 1,10-phenanthroline complexes to iron to form ferroin - forming an orange/red tris-ligand complex. Without forming the complex, the content of iron cannot be measured by absorbance accurately. The greater the complexing, the stronger the colour. Colorimetric measurements are performed in the spectrophotometer usually in the visble region of the electromagnetic spectrum. Absorbance readings are collected in a similar fashion to UV/Visible spectrophotometry together with subsquent analysis.

Chromatography is the term given to methods of separating mixtures into their individual components. Many forms of chromatography exist (HPLC, GLC, thin layer etc.), and are primarily used as a basis of separation. However, chromatography may also be applied (with other techniques) as a method of both qualitative and quantitative analysis. As example, High Pressure Liquid Chromatography (HPLC) is widely employed by numerous industry sectors (including food science) as both a qualitative and quantitive method of analysis.

Analysis of food therefore is suited to spectrophotometry and calorimetry. Unsaturated compounds are suitable for UV/Vis spectrophotometry, colorimetric methods employed for complexing samples without chromophores, and forms of chromotagraphy for samples unsuitable for the above methods. As example, solids are not used in spectrophotometry, but may be quantitively analysed using Gas liquid chromatography (where solids are ionised and enter the gas mobile phase).