Determination Of Copper In Blood
To give an overview of the copper blood test, all of the direct measurements of blood copper concentration rely on atomic spectroscopy. Traditionally, copper concentrations were measured from serum after extraction into methyl isobuyl ketone on a flame atomic absorption spectrometer (AAS). This device measures the reduction in a specific wavelength of light due to absorption by ground-state copper atoms as they pass through the flame. This measurement is directly proportional to the concentration of copper in the sample.
AAS can only determine a single element at a time and its use is being gradually reduced in clinical laboratories around the world as more and more labs turn to inductively coupled plasma optical emission spectroscopy (ICP-OES). In this technique, the sample (requiring a different preparation) is presented to an argon gas plasma which ionises virtually all elements reaching it. The light emitted by these ions is collected at specific wavelengths and quantified to provide a direct determination of the copper concentration in the sample presented to the ICP-OES. By the nature of the technique, information can be gathered simultaneously on a number of different elements which are present in the sample, depending upon the specifics of the ICP-OES device used.
As the cost of inductively coupled plasma mass spectrometers devices has fallen, more ICP-MS are being bought by routine clinical laboratories. In these instruments, the ions formed within the plasma are sampled by a mass spectrometer which produces a signal at the mass to charge ratio of the ion. ICP-MS is capable of providing coverage of almost the entire periodic table and is the most sensitive technique available for trace metal analysis. By virtue of the fact that ions are measured at their characteristic charge to mass ratio, the instrument can also be used to determine isotopic ratios in the sample which offers a range of possibilities for metabolic and multi-factorial studies.
On a personal note, my scientific career started in a clinical biochemistry laboratory performing trace metal analysis by atomic spectroscopy, notably with ICP-MS.