Magnesium-selective test strip.

A selective test strip based on an ion-exchange mechanism to determine magnesium is described. This optical and reversible test strip, made on a transparent polyester sheet, has a circular polymeric film of plasticised PVC that contains all of the reagents necessary to produce a response to magnesium, namely, a cation-selective neutral ionophore, 2-amino-N,N'-diheptyl-N,N'-dimethyl-butanediamide, a chromoionophore, N,N-diethyl-5-(octadecanoylimino)-5H-benzo[a]phenoxazine-9-amine, and potassium tetrakis (4-chlorophenyl)borate (TCPB) as a lipophilic salt, which is evaluated by absorbance measurement at 655nm in a standard photometer. The experimental variables that influence test strip response, especially in terms of selectivity and response time, have been studied. The test strip responded linearly to magnesium between 0.009 and 160mM in activities. The reproducibility intermembrane at a medium level of the range was 8.0%, as R.S.D., of [Formula: see text] , and 5.9% as R.S.D. intramembrane. The procedure was applied to the determination of magnesium in different types of waters (tap, well and mineral) validating the results against a reference procedure. This proposed method is quick, inexpensive, selective and sensitive and uses only conventional instrumentation.