Wet and Dry Chemistry Techniques (DXC and Vitros)

What is the damper?

alkaline buffer reagent for CO2 measurement that prevents bubbles from entering the flow cell

What tests are run on the Modular Chemistry side of the analyzer?

Urea, creatinine, phosphorus, glucose, total protein, an albumin

Ion-selective electrode

the difference in potential between the reference and measuring electrode can be used to calculate the concentration of the ion in solution

What analytes are measured with an ISE?

Na, K, CL, CO2, and CaWh

What coats sodiums electrode?

Aluminum silicate glass

What coats potassiums electrode?

Valinomycin

What coats chlorides electrode?

Ag/AgCl

What coats Calciums electrode?

ionophore membrane

What coats CO2s electrode?

pH rate change

What is a flow cell?

an acrylic block that holds electrodes for ISE measurements

ISE reference

reference reading is taken after each sample and is subtracted from the buffer/sample dilution reading

ISE buffer

• used to dilute patient sample

  • prevents large pH fluctuations due to acidity/alkalinity of sample

  • suffer contains known concentrations of analytes

What are the advantages of indirect measurement?

• uses less sample

• analysis is quicker

• more consistent measuring environment

• reduces interference

• less protein-coating

Urea MC principles

• urease reagent

• gold conductivity electrode - measures rate of increase in conductivity

Creatinine MC principles

Colorimetric: based on jaffe reaction with alkaline picrate

Glucose MC principles

• polarographic electrode

• measures rate of oxygen consumption in a glucose oxidase reaction

Phosphorus MC principles

Colormetric: ammonium molybdate reagent

Total Protein MC principles

Colormetric: Biuret reaction

Albumin MC principles

Colorimetric: dye binding with BCP

Creatinine MC reagent

combine picric acid with buffer, mix → allow to de-gas overnight

How often do you calibrate electrolytes?

every day

How often do you calibrate Glucose, Urea, Creatinine, and phosphate?

every 48hrs

How often do you calibrate TPm and ALBm?

monthly

Range checks for what?

Accuracy

Back to back checks for what?

Precision (reproducibility)

Span checks for what?

Sensitivity (spread between calibrator levels)

What does failing calibration due to range likely mean?

• switched calibrator cups

• insufficient, expired, or incorrectly prepared reagents

What does failing calibration due to Back to back likely mean?

bubbles in reagent lines or sample

What does failing calibration due to Span likely mean?

• Calibrators: incorrect, reverse positions, contaminated

• Reagents: expired, precipitated, temperature

• Electrode connections or worn membrane

Reflectance photometry

light reflected form a surface is used to measure the amount of product from a colorimetric reaction → amount of light reflected decreased in proportion to the intensity of colour produced

You need one reflectometer for each test zone plus 2 more, what are their roles?

• one to correct for interference due to the colour of the urine

• one that monitors and check that the strip is aligned with the instrument correctly

Reflection Density (RD or Dr)

need to determine ratio of light reflected by the surface containing the chromogenic reaction to the intensity of light reflected from a reference surface

Calibrating reflectance tests

• white reference standard test used

  • white surface gives minimum absorbance

  • all light is reflected or set to 1 = 0abs

• Black standard gives maximum absorbance or ) reflectance = 2.0 OD

Reflectometer test reactions

• colormetric/enzymatic

  • endpoint

• immunoassay

Potentiometric test reactions

an electrochemical technique used to measure the potential (voltage) between two electrodes in a solution to determine the concentration of an ion or the activity of a species.