What reagents are you using?
There are many reagents not presently marketed. However, most of these either do not react with a large range of drugs, are extremtly toxic, have poor shelf life or contain very expensive chemicals. So in many ways the best are already available.
It's important to remember that kits are only intended as presumptive tests, used to
indicate the possible presence of a specific drug or drug type.
Thin Layer Chromatography (TLC) is a somewhat more fiddly technique which also often employs spot test reagents such as Marquis. Ideally, a mixture of compounds is separated using TLC and the reagent is sprayed on the TLC plate. The reagent then produces the familiar colours with different compounds. The distance a spot travels along the plate is determined and shown as a ratio to the distance of the solvent face (known as the Rf value). By comparing the Rf value of a known sample of the drug in question, it's usually relatively easy to identify whether or not the drug is present. If a mixture of drugs is evident, ideally they will separate into distinct spots (also depends somewhat on the solvents used) but the target drug - if present -
should be the only one that travels the same distance as the pure sample. By repeating using a different solvent mixture (or changing the ratios) a positive can be further confirmed as the Rf values will change from solvent to solvent.
Aside from being a bit more time consuming than the average Testing Kit, the major disadvantages with TLC involve costs and the range of solvents sometimes required. A UV (extended bamdwidth) light source is often also required for viewing the spots. TLC plates are quite expensive, but large plates can be purchased and cut down to size, thereby saving money. Many of the usual solvents are inflamable and some are toxic.
Basic TLC tutorial
