spectrometry. Gas chromatography (GC), high-performance liquid chromatography (HPLC), and capillary electrophoresis (CE) have been extremely successful. HPLC has become the backbone of the pharmaceutical industry, providing essential information on purity (chemical and isomeric) of candidate and manufactured drug agents. GC is routinely the method of choice for gaseous or easily volatilized mixtures, and is commonly used with a mass spectrometer to identify the mixture components as well as to detect and measure their quantities. CE is the most powerful existing separations method (by orders of magnitude), and it is used for very difficult separations. As analytical chemistry has advanced into the world of molecules that biology creates, CE is the method of choice for the hugely complex mixtures of chemicals present in living organisms and their cellular subcomponents. CE has been employed for separation of the contents of individual cells and subcellular compartments (organelles), and it is the enabling analytical method for the Human Genome Project. An important frontier continues to be practical ways to combine the merits of different separation methods, such as HPLC-CE, to create hybrid separation techniques.

Other analytical approaches to complex systems include methods that respond selectively to individual chemicals (or a selected class), the detection of which is of paramount importance. Examples are chemical and biological warfare agents, industrial pollutants and toxins, and carbon monoxide in the air in our homes. Attaining analytical selectivity outside a pristine laboratory setting is one of the most difficult and widely unsolved analytical needs. Ion mobility spectrometry (IMS) and gas chromatography/mass spectrometry (GC/MS) are on trial in airport security checkpoints. While one can point to many successes, including the CO detector in your home, analytical chemistry continues to struggle for sensitivity and selectivity in competition with nose-based odor detection by dogs!

The birth of polymer science provoked numerous new analytical challenges several decades ago; the existing thrust of chemical sciences into molecular biology is now provoking many more challenges at a rapid pace. Polymers, along with pharmaceuticals, are arguably the most important and beneficial substances that synthetic chemistry has brought to the human race. Synthetic polymers generally consist of individual molecules having different chain lengths and molecular weights. This complexity is an important factor in determining properties of the polymer. Understanding of relations between polymer structure and properties has been aided enormously by the development of gel permeation chromatography (which measures the dispersity of polymer chain length), of infrared spectroscopy (which measures functional groups), and of thermal methods like differential scanning calorimetry (which detects polymer crystallinity).

There have likewise been early successes in addressing measurements of biopolymers, particularly their molecular weights, and to a more limited extent