Dynamic labeling of diagnostically significant microbial cells in cerebrospinal fluid by red chromophoric non-ionogenic surfactant for capillary electrophoresis separations

During bacterial infections of the central nervous system the number of microorganisms in the cerebrospinal fluid is often ranging from few up to hundreds of cells per milliliter. The electrophoretic techniques with the UV-detection reach a detection limit for whole cells of approximately 107 cells per milliliter. The coupling of the filtration cartridge with capillary isoelectric focusing can improve the detection limit by four orders of magnitude. In order to improve the detection limit the red non-ionogenic surfactant 1-[[4-(phenylazo)phenyl]azo]-2-hydroxy-3-naphthoic acid polyethylene glycol ester, PAPAN 1000, has been prepared and used for the dynamic labeling of analytes before filtration of the sample with a concentration modulation in the analysis of proteins or microorganisms. Values of isoelectric points of labeled analytes have been calculated using pI markers detectable at 515 nm and have been found comparable with pI of the native compounds. Minimum detectable amounts of proteins and microorganisms were lower than nanograms and a hundred labeled cells, respectively. The introduced method, coupling of the filtration cerebrospinal fluid spiked with microorganisms and labeled by PAPAN, facilitates their rapid CIEF separation in the pH gradient pH range of 2-5 at their clinically important level 101 to 102 cells per milliliter. .