Three new simple and selective assays were developed for the analysis of binary mixture
containing timolol maleate (TM) and brimonidine tartarate (BT) in the presence of benzalkonium chloride
(BZ) as a preservative in eye drops. The first derivative ultraviolet spectrophotometry was used with zerocrossing
measurements at 313 nm for TM and 386 nm for BT, respectively. The second method depends on the
first derivative of the ratio spectra with zero-crossing measurements at 313 nm and 391 nm for TM and BT,
respectively using 0.25 μg/mL BZ as a divisor. The assays were linear over the concentration ranges 5-85 μg/
mL and 2-35 μg/mL for TM and BT, respectively. The third method was based on isocratic and mobile phase
saving micellar liquid chromatographic method with a Biobasic phenyl column (150 x 1.0 mm, 5 μm particle
size) and micellar mobile phase composed of 0.1M SDS, 10 % of 1-propanol and 0.1 % of TEA in 0.035M
ortho phosphoric acid. UV detection was adjusted at 298 nm and 250 nm for TM and BT, respectively performed
at room temperature. The linearity range for TM and BT was 2-100 μg/mL and 1-50 μg/mL, respectively. The
proposed methods showed high percentage recovery, good accuracy and precision.

In a continuation of our earlier work, a multiresidual analytical method using 48 frequently used neutral pesticides in a water matrix was developed and validated in this study. The samples were extracted with dichloromethane and the pesticides were analyzed via GC-NPD followed by confirmation with GC-MS. Good linearity was detected over a concentration range of 0.01-1.0 microg/mL with correlation coefficients (r(2) ) in excess of 0.982. The recoveries were measured between 70.7 and 111.4% for the majority of the targeted pesticides with relative standard deviations (RSDs) of less than 20%. The LODs and LOQs were in ranges of 0.1-2 and 0.33-6.6 microg/L, respectively. A total of 66 water samples were collected from different locations in Yeongsan and the Sumjin River, Republic of Korea, and were analyzed in accordance with the developed method. None of the water samples were determined to contain any of the targeted pesticides. The method has been shown to be simpler, faster, and more cost-effective than the method established by the Environmental Protection Agency (EPA).