Having decided which instrumental technique(s) to use, there is still plenty for the test specifier to consider. Exactly what methodology is used? Is it a standard, published method or developed in-house?
Some published methods are more prescriptive than others resulting in differences in price for analysis for the same determinand, even using the same instrumentation. Whatever method is used, it is prudent to ask a number of questions, such as:
Has the method been adequately validated?
Is the laboratory externally accredited for the technique (eg to UKAS)?
Does the laboratory have proficiency testing scheme data to support the analysis (in the UK, such schemes include Aquacheck for waters and CONTEST for soils analysis)?
Does the price quoted include provision of quality assurance data if needed?
Does it meet Limit of Detection requirements?
Will it give all the speciation information required?
Although only a selection of the more common techniques have been discussed here, it is clear that approaching laboratories with a 'shopping list' of determinands with little or no qualification of methodologies (which is still very common, particularly with bills of quantities) may attract the lowest rates but also the lowest common denominator, will trap the unwary and ultimately give rise to data that is next to useless.
Users of analytical data must see their laboratories as more than 'samples in, numbers out' factories and draw on the skills and knowledge of the analytical chemists employed to tailor the analytical options available to the job in hand. Only that way can we avoid the slippery slope to caveat emptor.