I'M USING HPLC TO MEASURE XYLOSE AND GLUCOSE.  WHY TRY THE YSI?

In applications where near real time measurements are important to your study the YSI may be a very useful tool that complements HPLC results.  After simple filtration, and sometimes dilution, results are available in one minute.  performance specifications are comparable to HPLC; however HPLC is more costly to operate and slower to give results than the YSI method.

HOW DOES THE YSI METHOD WORK? 

The YSI method uses immobilised enzyme electrodes to measure the glucose and xylose present.  Just 13 µL of sample are automatically aspirated and delivered to the elctrode chamber.  Two electrodes develop signals proportional to the glucose and xylose present.  Results are printed, displayed and stored after about 30 seconds.  The system automatically clears the sample from the elctrode chamber and the next sample is ready to run.  Turn around time is typically under two minutes.

HOW LONG DO THE YSI ELECTRODES LAST?

The electrodes last for years if properly maintained.  There are enzyme-specific membranes that fit onto the face of each electrode.  These must be replaced periodically.  Glucose oxidase membranes last about 21 days and pyranose oxidase membranes last about 10 days.  Replacement of membranes takes only a few minutes and the instrument automatically recalibrates after a short acclimation time.

HOW MANY SAMPLES CAN BE MEASURED WITH A NEW ENZYME MEMBRANE?

Membrane sensor life is time-dependent, not sample-dependent.  The enzyme is immobolised so that it gets used over and over.  That is one reason the YSI method is ideal for monitoring.  When the speed of measurement and the cost of membranes are figured, glucose and xylose results may be just pennies per test.

DOES ANYTHING INTERFERE WITH THE YSI ELECTRODE MEASUREMENTS? 

Interferences are relatively rare.  Visible particles should be filtered.  Electrodes are not affected by colour, turbidity, viscosity or pH.  The sample is delivered to an electrode chamber that contains buffer so only extreme pH (as in concentrated acids/bases) is a problem.  Some chemicals may interfere.  Electrochemical interferences are rare.  The 'xylose electrode' uses immobilised pyranose oxidase in the sensor.  Although glucose is a good substrate for pyranose oxidase and xylose a weak substrate for glucose oxidase, the YSI method 'subtracts' interference signals, thus solving problems in mixed samples of glucose and xylose.  Cellobiose, arabinose and mannose are very weak substrates to pyranose oxidase, but rarely are found in concentrations that affect the measurement.  Galactose in concentrations higher than xylose is a potential interferent.  Since the YSI 2700 can measure galactose, there may be ways to correct for this interference with a YSI 7100 or with a second YSI 2700 system. 

WHAT RANGE OF CONCENTRATIONS CAN THE YSI METHOD HANDLE?

Glucose concentrations from 0.05 to 9 g/L and xylose concentrations from 0.5 to 30 g/L may be run without dilution.  In mixed samples of glucose and xylose dilution may be required for accuracy; as will dilutions be necessary for concentrations higher than the limits reported above.  YSI provides a 'dilution estimator' program to maximize accuracy if the user can roughly estimate the xylose and glucose concentrations for the sample.

 WHAT ARE THE PRECISION AND ACCURACY PERFORMANCE SPECIFICATIONS?

Xylose precision of <2% or 0.5 g/L (the greater) and glucose precision of <2% or 0.1 g/L (the greater) have been determined in aqueous-based mixed samples.  Accuracy in spiked samples varies depending on dilution optimisation and the specific combinations of xylose and glucose.  Xylose at 30 g/L is specified at +/-15% and Glucose at 9 g/L is +/- 5%, while optimally diluted samples near calibration values may be better than +/-5% for both analytes.

I HAVE THE YSI 2700; DO I NEED TO UPGRADE TO MEASURE XYLOSE?

There are no major upgrades necessary if you own a two-electrode version of the YSI 2700 (2700D).  If you have the one-electrode version (YSI 2700S) you will need to upgrade.

There are two options to simultaneously measure xylose and glucose; one involves manual entry of results from the YSI printed report and the second involves a PC-based user interface by using the seial port of the YSI 2700.  In the manual option, purchase the xylose sensor membranes and reasgents and then download the free Microsoft Excel™ spreadsheet file from YSI to run samples.  In the PC-based user interface, purchase the serial interface cable and Lab View™ software customised for this application.  With this option the sampling configurations are entered at the PC.  The YSI 2700 switches to remote mode and the PC sends commands to and collects data from the 2700 'slave' unit.

I HAVE THE YSI 7100; DO I NEED TO UPGRADE TO MEASURE XYLOSE?

Yes you will need to update the on-board software.  This can be via a download from the YSI Life Sciences website.  If your 7100 has more than one enzyme electrode module, you may measure other analytes like glucose, ethanol and/or lactate on the same 7100 platform.

WHAT OTHER ANALYTES CAN I MEASURE WITH THE YSI 2700?

Keep in mind that only two analytes may be measured in a configured system; and it is not practical to change enzyme membranes and configurations back and forth within a one week period.  However, applications measuring residual ethanol in corn stillage (beers), glucose and/or ethanol during fermentation, and glucose and/or lactate during fermentation are the most commonly used measurements in the biofuels market.

CAN I MEASURE ACETATE (ACETIC ACID) WITH THE YSI 2700?

No not at this time.  YSI enzyme electrodes require an oxidase enzyme that produces H2O2.  There is no enzyme or combination of enzymes that currently work with the YSI 2700 or YSI 7100.