Automated clinical chemistry analyzer
An automated photometer: it pipettes samples and reagents into cuvettes, incubates them at a controlled temperature, and measures colour change or ion potentials to calculate analyte concentrations.
Principle
Most routine chemistry tests are photometric: a sample is mixed with reagents that produce a coloured product or change in absorbance in proportion to the analyte (end-point methods) or to the rate of an enzymatic reaction (kinetic methods). The analyser automates this: a sample probe and reagent probes aspirate and dispense microlitre volumes into cuvettes on a reaction disk held at a stable temperature (commonly 37 °C), mixers stir the reaction, and a photometer measures absorbance at chosen wavelengths through each cuvette over time. Turbidimetric methods measure light lost to scattering (immunoassays for specific proteins). Electrolytes such as sodium, potassium and chloride are usually measured by ion-selective electrodes (ISE), which develop a potential related to ion activity. Results are calculated against calibrators and checked with quality-control samples. Analytical quality depends as much on water, temperature, pipetting precision and clean cuvettes as on the optics, so most service work is fluidics and cleanliness.
The chain, block by block
| Block | What it does | How it fails |
|---|---|---|
| Sample handling: racks, tubes, barcode reader | Loads and identifies samples, positions tubes for aspiration, often with a STAT position. | Barcode read errors from poor labels or dirty readers, rack transport jams, sample position errors. |
| Sample and reagent probes with level and clot detection | Probes on moving arms aspirate and dispense; capacitive or pressure-based detection senses liquid level, clots and short samples; probes are washed between uses. | Imprecision from bent or coated probes, crashed probes, false level detection, clot detection errors, carryover from poor washing. |
| Syringes, valves and fluidics | Precision syringe pumps and valves drive pipetting and washing. | Leaking syringe seals or valves give imprecision and air bubbles; tubing wear; slow drift in results. |
| Reagent storage | Refrigerated reagent carousel keeps reagents stable onboard. | Cooling failure shortens reagent stability and causes calibration drift; condensation and ice; barcode issues on reagent bottles. |
| Reaction disk, cuvettes and incubation | Cuvettes on a disk in a temperature-controlled bath (water, oil or air/dry), with mixers. | Temperature drift affects kinetic methods; dirty, scratched or contaminated cuvettes cause high blanks and random errors; bath contamination or bubbles. |
| Photometer: lamp, optics, detector | Light source (often halogen) and filter or grating optics with photodiode detection at several wavelengths. | Lamp aging reduces light energy and raises noise; dirty optics; detector drift. Checked through photometer and cuvette blank checks. |
| Cuvette wash station | Aspirates reaction mixtures, washes cuvettes with detergent and water, dries them. | Blocked nozzles, poor drying, detergent supply issues lead to carryover and high cuvette blanks. |
| ISE module | Ion-selective electrodes with a reference electrode measure Na, K, Cl. | Electrode aging (slope out of range), protein coating, reference electrode problems, air bubbles; electrodes are consumables. |
| Water supply, waste and LIS connection | Purified water feeds the analyser; liquid waste drains or is collected; results are sent to the laboratory information system. | Poor water quality (conductivity, bacteria) causes calibration and QC failures; blocked waste; LIS communication errors. |
Symptom → where to look first
| Symptom | Suspect first |
|---|---|
| QC out of range on many tests at once | Common factors first: water quality, incubation temperature, photometer lamp energy, cuvette cleanliness. |
| QC out on a single test | Reagent (lot, onboard stability, storage) and calibration for that test, before hardware. |
| Poor precision / random outliers | Sample probe and syringe: bent or dirty probe, leaking seal, air bubbles, clot detection. |
| High cuvette blank or photometer error | Cuvettes and wash station, then lamp and optics. |
| Kinetic (enzyme) tests drifting | Incubation temperature and reaction bath. |
| ISE slope or calibration failure | Electrodes aging or coated, reference electrode, ISE fluidics bubbles. |
| Sample short or clot errors without cause | Level/clot detection setup, probe condition, earthing of the probe system. |
| Results not reaching LIS | LIS interface configuration and network, test code mapping. |
Safety
Site and infrastructure
- Purified water system meeting the manufacturer's water quality specification (resistivity/conductivity, microbiological limits) and supply flow; water quality monitored.
- Drain for liquid waste or approved waste containers, compliant with local biohazard and chemical waste rules.
- Stable mains supply with UPS of adequate capacity; protective earth.
- Room temperature and humidity within manufacturer limits and stable; no direct sunlight or air conditioning blowing on the analyser.
- Level, vibration-free bench or floor with service clearance around the analyser.
- Network connection to the LIS.
Preventive maintenance basics
- Inspect and clean sample and reagent probes; check alignment and level detection; replace worn probes.
- Replace syringe seals, valve parts and tubing per schedule; check for leaks and bubbles.
- Clean and check cuvettes, run cuvette blank and photometer checks; replace lamp per hours or energy check.
- Verify incubation temperature with a calibrated thermometer.
- Clean wash station nozzles and check detergent and water supply.
- Maintain ISE: replace electrodes and reference as needed, check slopes.
- Verify water quality and clean water tank, filters and lines; check waste lines.
- After maintenance run calibration and QC to confirm performance; document.
Safety
- Treat all samples and the analyser's wetted parts and waste as potentially infectious; wear gloves, gown and eye protection and decontaminate before service.
- Reagents and detergents can be corrosive or toxic; follow safety data sheets.
- Moving arms and probes can cause puncture injuries; stop the analyser or enter maintenance mode before reaching into the work area.
- Lamps run hot; allow to cool before replacement and do not touch the glass.
- Dispose of waste and replaced parts as biohazardous according to local regulations.
Manufacturers
Roche Diagnostics · Abbott · Siemens Healthineers · Beckman Coulter · Ortho Clinical Diagnostics (QuidelOrtho) · Mindray · Sysmex · Randox · Snibe · Dirui · Erba Mannheim · Hitachi High-Tech