Voltammetry in its modern, software-controlled guise now offers a useful alternative to atomic absorption spectroscopy and inductively coupled plasma (AAS/ICP) techniques
Chemists who remember when voltammetry involved vats of mercury hanging precariously over their heads, and tangles of wire and blocked capillaries may not recognise its modern, self-contained counterpart.
The Metrohm model 797 can be used by operators without specialist knowledge of electrochemistry.
Software control allows this instrument to operate in various modes: it also calculates the baseline and permits the user to zoom in on segments of the curve.
Criteria for automatically identifying samples can be programmed as part of the method sequence, which also allows for sample-dependent selection of methods, electrode types and standard addition solutions.
Memory cards store results.
Although the field of inorganic analysis is dominated by atomic absorption spectroscopy and inductively coupled plasma, voltammetry deserves to be seen as a useful complementary technique.
For example, although a wide range of metals can be determined equally well by each method - analysing for zinc, cadmium, lead and copper in soils and sludges by both methods produces comparable standard deviations - there are analyses for which one method is clearly better than the other.
VA equipment is also a great deal less expensive than AAS, and cheaper to run; and it requires no fume extraction apparatus.
For metals that absorb much below 260nm (such as arsenic and selenium), voltammetry is superior because AAS is difficult at these wavelengths.
Also, for metals that form refracting oxides in a flame, VA methods provide more easily obtainable data, however, for metals that absorb strongly in the central visible region and whose electroactive potential is quite negative (such as sodium, lithium, potassium, calcium and magnesium), flame spectroscopic techniques are usually preferable.
Also, the limits of detection for many metal ions are better than for AAS.
For example, measuring low lead levels by AAS requires the use of flameless attachments, and determining arsenic, mercury and selenium requires hydride generation equipment.
Both of these add-ons are expensive: although limits of detection comparable to voltammetry can be achieved, the cost is often prohibitive.
Voltammetry can also be used to identify species in order to elucidate the form in which each metal is present in solution, while ICP/AAS can only provide a total figure.
Voltammetry offers simultaneous analyses of a variety of metals, and provides both qualitative as well as quantitative information; using AAS multi-element screening requires a lamp for each element.
Finally, while VA and AAS/ICP both suffer from interferences, they are different interferences: if an ion interferes spectroscopically with copper, it is extremely unlikely to also interfere with voltammetric determinations of copper.
This means that laboratories confronted with a wide range of problems are likely to benefit from being able to employ both techniques.
