When using immunoassay test strips for drug checking (as opposed to urine testing), sample preparation is important. Any drug can produce a false positive if over-concentrated, and if you don’t concentrate enough (over-diluting by adding too much water) you run a greater risk of false negatives.
The proper dilution for any drug checking strip is initially determined by laboratory analyses as well as relevant facts about the current status of the illicit drug supply, such as the average concentrations of various adulterants in specific drugs. Over time, field testing supplemented by confirmatory lab analysis (like GC-MS) may change our understanding of the optimum dilution.
As of right now, we have determined that the optimum dilution for using WHPM’s xylazine test strips to test powdered illicit opioids is two milligrams per milliliter (2 mg/mL). This is the equivalent of 10 mg of powder into one teaspoon (5 mL) of water, or one level micro scoop into a normal plastic bottle cap.
