This code system http://hl7.org/fhir/CodeSystem/medication-ingredientstrength defines the following codes:

CodeDisplayDefinition
qs QSAs much as is sufficient.
trace TraceVery small amount.
<status value="active"/><experimental value="false"/><publisher value="HL7 International"/><description value="Medication Ingredient Strength Codes"/><jurisdiction><coding><system value="http://unstats.un.org/unsd/methods/m49/m49.htm"/><code value="001"/><display value="World"/></coding></jurisdiction><caseSensitive value="true"/><valueSet value="http://hl7.org/fhir/ValueSet/medication-ingredientstrength"/><content value="complete"/><concept><code value="qs"/><display value="QS"/><definition value="As much as is sufficient."/></concept><concept><code value="trace"/><display value="Trace"/><definition value="Very small amount."/></concept></CodeSystem>