Shelf life extension of microemulsions containing active aza biocide

A stable o/w microemulsion comprising

• (i) between about 0.01 and about 10 wt. % of a concentrate formulation containing:
• (a) between about 0.05 and about 25% of at least one active aza compound selected from the group consisting of Amitraz and an aza compound having the formula:
• R1—(X)—R2
• wherein one of R1 and R2 is alkenylphenyl, aminophenyl or a sulfur- and/or nitrogen-containing heterocyclic radical containing 3 to 5 carbon atoms in a 4 to 6 membered ring and the other of R1 and R2 is the same or is selected from the group consisting of amidosulfuron, phenyl, sulfonylphenyl, phenyloxy and phenyloxysulfonyl where said phenyl radicals and said heterocyclic radicals of R1 and R2 are optionally substituted with lower alkyl, halo, haloalkyl, cyano, C1 to C4 alkyl ether, C1 to C4 ester, carboxyl, ketone amido and amino and X is:
• 7
• where R3, R4, R5 and R6 are each individually selected from the group consisting of hydrogen, lower alkyl, cyano, and amino,
• (b) between about 2 and about 40% of a lipophilic lactam selected from the group consisting of C8 to C18 N-alkyl pyrrolidone, C8 to C18 alkyl caprolactam and a mixture thereof,
• (c) between about 2 and about 20% of a moisture scavenging agent selected from the group consisting of a hindered carbopolyimide, a molecular sieve and a mixture thereof,
• (d) between about 10 and about 80% of a lipophilic/hydrophilic mixture of having an overall HLB of 7 to 20, comprising at least two emulsifiers wherein at least one of said emulsifiers in the mixture are non-ionic and
• (e) between 0 and about 15% of an aromatic oil;
• (ii) between about 90 and about 99.99 wt. % water and
• (iii) between about 0.01 and about 5 wt. % of a buffering agent selected from the group consisting of a Na, K and/or ammonium salt of a weak acid, a polyalkanol amino C1 to C4 alkane, a polyamine salt of a weak acid, a Na, K and/or ammonium salt of a phenol or polyphenol, an amine salt of a weak acid and a mixture of the foregoing buffering agents.