chemistry

Columns in LC/HPLC are considered the “heart of the separation”. Controlling a separation process means understanding and controlling the physics and the chemistry inside the column. To do so, it is necessary to understand how columns are packed and how packings are prepared. Amongst, the most popular columns in liquid chromatography are the so called C18 columns . These are silica bonded phase columns that are used for the separation of nonpolar compounds. How these bonded phase columns are prepared ? The first step called silylation involves the reaction of fully hydroxylated silica with chlorodimethylalkylsilane and heating to drive off  HCl (Fig. 1). Variations in the chain length and functional groups on the alkyl group produce the wide variety of bonded-phase columns . If we would stop at this point we would have a column with 10%  free silanol sites (Si-OH sites) because of steric hindrance. The column would work well for the separation of acidic or neutral com...

Advantages and Disadvantages of Atomic Absorption Spectrometry and Graphite Furnace Home > Analytical Chemistry > Analytical Chemistry - Atomic Absorption > Atomic Absorption Spectrometry (AAS) > Advantages and Disadvantages of Atomic Absorption Spectrometry and Graphite Furnace   Advantages and Disadvantages of Atomic Absorption Spectrometry and Graphite Furnace Atomic Absorption Spectrometry (AAS) is an analytical technique that measures the concentration of an element by measuring the amount of light (intensity of light) that is absorbed - at a characteristic wavelength - when it passes through a cloud of atoms of this element. As the number of atoms in the light path increases, the amount of light absorbed increases in a predictable way. The main advantages of AAS   are given below: High sample throughput Easy to use High precision Inexpensive technique The main disadvantages of  AAS...

  Troubleshooting in liquid chromatography / HPLC can be made easier, if one learns to recognize the symptoms produced by an instrument malfunction, leaks, or column problems. Some of the symptoms are described below:     Symptom: Column pressure erratic in an HPLC system Possible Cause: Leak in high pressure system before column Action: Locate and repair leak Possible Cause: Foreign material in column pump check valves Action: Disconnect liquid inlet and outlet lines. Syringe 20 ml of fresh solvent through liquid end.  Reconnect lines. If the above fails, disassemble liquid end and clean check valves Symptom: No column flow or column pressure Possible Cause: Leak in system before column Action: Locate and repair leak Possible Cause: Air in column pump liquid end Action: Disconnect liquid outlet line and pump at maximum until no bubbles appear Symptom: Poor peak shape (Fig. 1) Fig. 1: Poor peak shape in a liquid chromatogram   Possible Cause: Column overl...