Electrophoretic mobility and zeta potential of lysozyme crystals.

Using free-solution capillary electrophoresis, the electrophoretic mobility of micro m-sized lysozyme crystals in their growth solution at 283 K, 1.5%(w/v) NaC1, and over a range of pH values between 3.59 and 5.70 has been measured. Under these conditions, the mobility is independent of crystal size, while the calculated zeta potential increases from +8 to +24 mV as the pH decreases. Since the pH dependence of the zeta potential mirrors the pH dependence of charge on the free molecule, as determined by acid titration, it is concluded that the charge on the crystal is a result of H(+) adsorption from solution.

Urine monitoring of textile workers exposed to dichlorobenzidine-derived pigments.

Urine samples from 36 workers exposed to dichlorobenzidine (DCB)-derived pigments and 12 controls were screened for aromatic amines by a nonspecific colorimetric method and then further analyzed by GC/MS specifically for DCB and monoacetyldichlorobenzidine. Of the samples screened for aromatic amines, six (17%) of the exposed population and one (7%) of the control population registered positive (1.0 part per billion [ppb] or greater). One of the positive samples (5.6 ppb) reflected medication, and the remainder (1.1 to 1.8 ppb) were due to high urinary background. The specific analyses were negative (less than 0.2 ppb) for DCB or monoacetyldichlorobenzidine in all samples.