Amperometric detection of carbohydrates with a portable silicone/quartz capillary microchip by designed fracture sampling.

A silicone/quartz capillary microchip (SQCM) coupled with an ultranarrow sampling fracture was for the first time constructed without any micromachining. The SQCM could be used for direct determination of carbohydrates at a detection potential of +0.8 V (vs Ag/AgCl) with a copper microdisk electrode. The ultranarrow sampling fracture could be conveniently formed on a quartz capillary, which was fixed by a frame of poly(dimethylsiloxane) (PDMS). The designed fracture sampling suppressed the leakage of sample, thus simplifying the power supply. Furthermore, it thinned the sample plug for enhancing the resolution. The quartz capillary reduced the adsorption of analytes on the separation channel wall compared with a general PDMS microchip, thus enhanced the separation efficiency up to 239 000 plates/m for carbohydrates. This proposed system could satisfactorily separate eight carbohydrates within 180 s with good reproducibility and sensitively detect them in the linear ranges from 1 microM to 0.5 mM for trehalose and sucrose, 2.5 microM to 0.5 mM for lactose, galactose, glucose, and mannose, and 2.5 microM to 1.5 mM for fructose and xylose with the detection limit down to 90 amol. The designed microchip was successfully applied to detect carbohydrates in a practical acacia honey sample.