Hi Mohanad,

In every case, e.g. organisms, extracts, type of compounds etc., heavily impact your choice for analytical instrumentation regarding their physico-chemical structure and properties. And there is, indeed, a plethora of analytical techniques. But most of analytical researcher, like me, do not have every instrumentation for every case.

You have to consider two major things, how do you want/can separate your compounds, and how can you "visualize" them, e.g. what information do you want.

- Separation:

The usual instrumentation needed for an analytical laboratory would be High Pressure/Performance Liquid Chromatography HPLC and/or Ultra HPLC (UHPLC) and/or GC these are for soluble and volatile compounds. Then you have to choose between reverse and normal phase in HPLC/UHPLC regarding the polarity of your compounds. Another thing to consider, is the ratio costs/efficiency-quality. You may want to know that side costs of these techniques are solvents (for HPLC/UHPLC) and gas (for GC). A lower cost technique is the well-known Thin Layer Chromatography (TLC) and HPTLC (useful for quantification). You also have the CounterCurrrent Chromatography (CCC) or even easier vacuum Liquid Chromatography (VLC). And others like Supercritical Fluid Chromatography (SFC) useful for high polar compounds.

- Detection:

I will limit my example for HPLC/UHPLC and GC. the most common detector to "vizualise" your compounds is a Diode Array Detector (DAD) for HPLC/UHPLC where you can observe the UV/Vis absorbance, but you need to looking for U.V. active compounds. Another common detector is Evaporative Light Scattering Detector (ELSD), able to detect any compound which can be separated during the chromatography process.These two type of detection are the base of liquid chromatographic analysis. Depending on which information you want to know for your project, you may need to use a mass spectrometer (MS) and/or High Resolution Mass spectrometer (HRMS) hyphenated with HPLC/UHPLC techniques. For GC the most common detector is the Flame Ionization Detector (FID) and/or MS. This is only for volatile or volatilized compounds. In every case, at last but certainly not least, you can use Nuclear Mgnetic Resonance (NMR) for better characterization of your compound. Finally you Infrared spectroscopy (IR), Optical Rotation (OR), Circular Dichroism (CD) and many others...

I will end my long answer by invite you to read one of my paper for example, http://www.bio-protocol.org/e1625 where I provide a detail protocol for a chemical characterization of some alkaloids compounds. On the basis of my answer you can also find many publications and articles showing how to choose an adapted analytical instrumentation, based on the chemical properties of the compounds you are looking for.

Cheers,

Nicolas.

Hi Mohanad,

In every case, e.g. organisms, extracts, type of compounds etc., heavily impact your choice for analytical instrumentation regarding their physico-chemical structure and properties. And there is, indeed, a plethora of analytical techniques. But most of analytical researcher, like me, do not have every instrumentation for every case.

You have to consider two major things, how do you want/can separate your compounds, and how can you "visualize" them, e.g. what information do you want.

- Separation:

The usual instrumentation needed for an analytical laboratory would be High Pressure/Performance Liquid Chromatography HPLC and/or Ultra HPLC (UHPLC) and/or GC these are for soluble and volatile compounds. Then you have to choose between reverse and normal phase in HPLC/UHPLC regarding the polarity of your compounds. Another thing to consider, is the ratio costs/efficiency-quality. You may want to know that side costs of these techniques are solvents (for HPLC/UHPLC) and gas (for GC). A lower cost technique is the well-known Thin Layer Chromatography (TLC) and HPTLC (useful for quantification). You also have the CounterCurrrent Chromatography (CCC) or even easier vacuum Liquid Chromatography (VLC). And others like Supercritical Fluid Chromatography (SFC) useful for high polar compounds.

- Detection:

I will limit my example for HPLC/UHPLC and GC. the most common detector to "vizualise" your compounds is a Diode Array Detector (DAD) for HPLC/UHPLC where you can observe the UV/Vis absorbance, but you need to looking for U.V. active compounds. Another common detector is Evaporative Light Scattering Detector (ELSD), able to detect any compound which can be separated during the chromatography process.These two type of detection are the base of liquid chromatographic analysis. Depending on which information you want to know for your project, you may need to use a mass spectrometer (MS) and/or High Resolution Mass spectrometer (HRMS) hyphenated with HPLC/UHPLC techniques. For GC the most common detector is the Flame Ionization Detector (FID) and/or MS. This is only for volatile or volatilized compounds. In every case, at last but certainly not least, you can use Nuclear Mgnetic Resonance (NMR) for better characterization of your compound. Finally you Infrared spectroscopy (IR), Optical Rotation (OR), Circular Dichroism (CD) and many others...

I will end my long answer by invite you to read one of my paper for example, http://www.bio-protocol.org/e1625 where I provide a detail protocol for a chemical characterization of some alkaloids compounds. On the basis of my answer you can also find many publications and articles showing how to choose an adapted analytical instrumentation, based on the chemical properties of the compounds you are looking for.

Cheers,

Nicolas.

You make your choice of technique based on the stability of the compound, its known chemical and physical properties and most importantly, what you wish to know (e.g. MW, Viscosity, Decomposition, "purity", structure, absorption, solubility...).

Some of my thoughts on method selection:

1) Sensitivity

2) Selectivity

3) Accuracy

4) Precision

5) Cost/time

There are many analytical techniques.  The selection of method depends on many factors like what exactly you want to do, type of samples, sample characteristics,  detection level required, sensitivity of the technique etc.

Depends on the analyte in question , should be exploited their physicochemical characteristics and the matrix in which it is included. also it depends on whether the determination will be quantitative or qualitative , and of course the availability of equipment and reagents in the laboratory there .

I agree with all the posters...but you must answer some critical questions before you proceed with choosing a suitable analytical technique viz:

1. What is the matrix of the sample?

2. What sample prep options are available  any possible interferences?

3. What analytical technique(s) can be used to analyse the sample?

4. Is it easily acessable? Depending on the frequency of the analysis

5. What is the cost?

These are some basic questions that aid in your selection or choice.

In addition to all the previous and very useful answers, I would say that every analytical technique is designed or best suited to answer a kind of question. So, the choice of the technique depends on the question(s) we want to answer about our sample. A few examples:

- What is it? identification techniques such as GC-MS, HPLC-MS, IR...

- What is the amount/content/concentration? Quantification techniques such as GC-FID, GC-ECD, HPLC-UV/Vis...

- How old is it? Datation wit 14C...

- Who is it? DNA techniques...

- Where does it come from? IRMS...

I would like to give a specific example to answer this question.

Let us consider pectic raw materials. The standard method of analysis to find out uronic acid content is traditionally based on the carbazole colorimetric assay which gives blue coloration in presence of strong H2SO4 and the intensity of blue color is measured in the range so that it follows Beer's and Lambert's law giving a straight line relationship between the absorbance and the analyte concentration. However if you go for ion exchange chromatography you will be in a position to differentiate between glucuronic acid and galacturonic acid. Obviously when you are interested to find out say % pectin in the raw material, you need to know what is the precise concentration of galacturonic acid in the raw material rather than a combined concentration of galacturonic and glucuronic acid. (Pectin is poly galacturonic acid which is esterified with methanol and depending on the degree of esterification one gets HMP or LMP as two distinct products with quite different physicochemical properties of the resultant hydrocolloide as a gelling agent.) Pectic raw materials are invariably associated with hemicelluloses and glucuronic acid is an important component of hemicelluloses from various  pectic raw materials in addition to other sugars and uronic acids etc.

In short as the specific knowledge about the advancement on a particular subject matter is available ( Padhye, A. D., Studies on Pectin, Ph. D. (Tech) thesis, 1989, University of Bombay.)  such changes are required to be made.

In general, ion-exchange chromatography is also more sensitive method than colorimetric assay.

Thus selectivity becomes most important aspect along with sensitivity, accuracy, precision apart from other aspects such as cost/ time and convenience associated with a particular analytical method chosen.