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

Code Display Definition
qs QS As much as is sufficient.
trace Trace Very 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>