RADIOMETER FLEX ABL90, Reference Manual

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Appendix – Traceability to the primary standards at Radiometer ABL90 FLEX reference manual
II-4
The primary standards used are the so-called Ca
2+
transfer standards, produced
from CaCO
3
Urtitersubstanz
®
, produced by Merck. The transfer standards are
pH-stabilized to pH = 7.4, with 1 mmol/L HEPES and an ionic strength of 160.0
mmol per kg. Validation of the Ca
2+
transfer standards is done using similar
standards produced from NIST SRM 915.
The transfer standards are used to determine the calcium concentrations of
secondary standards. These measurements take place using ion-selective Ca
electrodes on the ABL735 analyzer.
The primary working standards are gravimetric standards, prepared from KCl
Suprapur, produced by Merck. The primary working standards are validated by
making comparative titrations using similar standards prepared from NIST SRM
999 (KCl). The titrations are done using an AgNO
3
solution as the titrant, and
potentiometric titration equipment.
The standardized AgNO
3
solution is used as the titrant for the determination of
the chloride concentration of the secondary standards, using the potentiometric
titrator (TitraLab 900 from Radiometer Analytical, France).
The primary working standards are prepared from NIST SRM 917a (D-glucose).
These primary standards are used to determine the glucose concentration of
secondary standards. The measurements take place using the glucose reference
method, which is the hexokinase/glucose-6-phosphate dehydrogenase method
recommended by CLSI. This method is described in Ref. 3.
No certified standard reference material for lactate is available at present. The
primary working standards are therefore prepared from a pure commercially
available material, namely the Lithium salt of L (
+
) Lactic Acid (Cat. No, L-2250)
supplied by the Sigma Chemical Company.
These primary standards are used to determine the lactate concentration of
secondary standards.
The measurements take place using a spectrophotometric method. The method
is based on a reaction of lactate, catalyzed by L-Lactate Dehydrogenase (LDH).
The reaction produces dihydronicotinamide (NADH), which is measured at 339
nm. The method is described in Ref. 4.
The primary standard used is an oxygenated whole-blood sample. The
c
tHb
value of this sample is determined by the use of the HiCN reference method.
This method is described in Ref. 5. The HiCN reference method is a
spectrophotometric method. The spectrophotometer used is calibrated using a
NIST SRM 930D filter. This method is further validated using the certified
reference material Hemoglobin-cyanide standard (product no. 3061) produced
by J.T Baker, Holland.
The primary standard is used to calibrate the ABL735 reference instruments.
cCa
2+
cCl
–
cGlu
cLac
ctHb