Question

YOU MUST SEPARATE AND QUANTIFY GLUCOSE, FRUCTOSE, SUCROSE, LACTOSE, MALTOSE, AND TREHALOSE IN SAMPLES OF INFANT FORMULA. YOU DECIDE TO USE CHROMATOGRAPHY. YOUR METHOD MUST BE ABLE TO QUANTIFY THE ANALYTES AT OR ABOVE 100 ng ON COLUMN. YOU HAVE DEVELOPED A METHOD FOR EXTRACTINGFROM THE MATRIX A RELATIVELY CLEAN FRACTION CONTAINING MONO AND DISSACHARIDES. YOU HAVE A WELL EQUIPPED LABORATORY AND MANY ANALYTICAL INSTRUMENTS MENTIONED DOWN BELOW THAT COULD BE USED TO ACCOMPLISH YOUR GOAL. THOSE INSTRUMENTS ARE:

1.A GAS CHROMATOGRAPHY/MASS SPECTROMETRY

2.A LIQUID CHROMATOGRAPH WITH SEVERAL POSSIBLE DETECTOR OPTIONS:

      a) UV-VIS DIODE ARRAY DETECTOR

      b) REFRACTIVE INDEX DETECTOR

      c) ELECTROCHEMICAL DETECTOR

      d) EVAPORATIVE LIGHT SCATTERING DETECTOR

YOU WANT TO ACCOMPLISH THE TASK WITH THE REQUIRED ACCURACY IN THE SHORTEST POSSIBLE TIME.

SELECT EITHER GAS CHROMATOGRAPHY OR LIQUID CHROMATOGRAPHY FOR YOUR METHOD, THEN DECIDE WHAT TYPE OF STATIONARY PHASE, POLAR OR NON-POLAR YOU WOULD USE. NEXT, SELECT AN APPROPRIATE MOBILE PHASE. LAST BUT NOT LEAST, SELECT THE TYPE OF DETECTOR YOU WOULD USE AND  EXPLAIN THE RATIONALE FOR YOUR CHOICES.

Answer 1

GAS CHROMATOGRAPHY - eg GLUCOSE

Gas chromatography (GC) is widely used for sugar identification.

STATIONARY PHASE

The stationary phase is a microscopic layer of liquid or polymer on an inert solid support, inside a piece of glass or metal tubing called a column.

In normal-phase chromatography, the stationary phase - polar: the mobile phase- nonpolar.

In reversed phase chromatography, the stationary phase - nonpolar : the mobile phase - polar.

Polydimethyl si\oxane (NON-POLAR)

THE RATIONALE FOR CHOICE : Polydimethyl si\oxane are stable, versatile and possess the greatest variety. Besides that, they can resist oxidation and offer high solute diffusivitites into the polymer coupled with excellent chemical and thermal stability.

MOBILE PHASE

The mobile phase is a carrier gas, usually an inert gas such as helium or an unreactive gas such as nitrogen. Helium remains the most commonly used carrier gas in about 90% of instruments although hydrogen is preferred for improved separations.

Acetonitrile/water mobile phase

THE RATIONALE FOR CHOICE : Acetonitrile results in less ghost peaking for gradient baselines and lower the noise in UV detection. Eluotropic strength of water can be increased but elevating temperature.

THE TYPE OF DETECTOR

Evaporative light scattering detection

THE RATIONALE FOR CHOICE: Evaporative Light Scattering Detector (ELSD) is a universal detection system offer benefits in terms of uniformity of response for non-volatile solutes since the response does not vary as a function of extinction coefficient.