Method in quality control of a spectrophotometer
The present invention relates to a method in quality control of a spectrophotometer, comprising the steps of determining with the spectrophotomer a spectrum A m (λ) of a fluid QC sample containing a dye, and determining a wavelength shift Δλ from C Δλ (λ), A m (λ), in which C Δλ (λ) is a predetermined coefficient vector previously stored in a memory of the spectrophotometer.
1. A quality control method for a spectrophotometer, comprising the steps of:
determining with the spectrophotometer an absorption spectrum A m (λ) of a fluid quality control sample containing a dye selected from such dyes which provide the quality control sample with an absorption spectrum with a significant absorbance peak showing a steep flank,
determining a wavelength shift Δλ between the absorption A m (λ) of the actually measured quality control sample and a reference absorption spectrum A 0 (λ) of a reference quality control sample containing the dye stored in a memory of the spectrophotometer, and
comparing Δλ with Δλ qc , wherein Δλ qc is a wavelength shift assigned to the quality control sample.
2. A method according to claim 1 , wherein the wavelength shift Δλ is determined from A m (λ) and a predetermined mathematical parameter stored in the memory of the spectrophotometer.
3. A method according to claim 2 , wherein the mathematical parameter is a coefficient vector C Δλ (λ) and wherein the wavelength shift Δλ is determined from C Δλ (λ)·A m (λ).
4. A method according to claim 3 , wherein the vector C Δλ (λ) fulfills the equation
Δλ= C Δλ (λ)· A m (λ).
5. A method according to claim 4 , wherein C Δλ (λ) has been determined from a Taylor series of the reference absorption spectrum A 0 (λ).
6. A method according to claim 5 , wherein C Δλ (λ) has been determined from a combination of the reference absorption spectrum A 0 (λ) and a first derivative A 0 ′(λ) of said reference absorption spectrum.
7. A method according to claim 1 , wherein the wavelength shift Δλ is determined after normalisation of the determined spectrum A m (λ) with an estimate of the concentration of the dye.
8. A method according to claim 1 , wherein the quality control sample has a known dye concentration C qc and the dye comprises a first and a second component, the method further comprising the steps of
calculating parameters s 1 and s 2 from
s 1 =C 1 (λ)·A m (λ)
s 2 =C 2 (λ)·A m (λ)
in which C 1 (λ) and C 2 (λ) are predetermined vectors previously stored in the memory of the spectrophotometer, and
calculating an estimated concentration C est of the dye from
C est =a s 1 +b s 2
in which a and b are predetermined constants previously stored in the memory of the spectrophotometer.
9. A method according to claim 8 , further comprising the step of comparing C est and C qc .
10. A method according to claim 8 , further comprising the step of calculating a variable Q est =s 2est /S 1est .
11. A method according to claim 10 , wherein the quality control sample has an assigned value of Q qc =s 2qc /s 1qc , which method further comprises the step of comparing Q est with Q qc .
12. A method according to claim 1 , wherein the spectrophotometer is an oximeter.
13. A method according to claim 12 , wherein spectra are measured in the wavelength range from 400 to 800 nm.
14. A method according to claim 12 , further comprising the step of determining estimated errors in blood parameter values reported by the oximeter caused by the wavelength shift Δλ.
15. A method according to claim 8 , wherein the spectrophotometer is an oximeter, further comprising the step of determining estimated errors in blood parameter values reported by the oximeter caused by a difference between C est and C qc .
16. A method according to claim 11 , wherein the spectrophotometer is an oximeter, further comprising the step of determining estimated errors in blood parameter values reported by the oximeter caused by a difference between Q est and Q qc .
17. A method according to claim 1 further comprising the steps of:
determining a first reference absorption spectrum A 01 (λ) of a reference sample containing a dye in a first concentration with a reference spectrophotometer,
determining a first derivative A 01 ′(λ) of the first reference spectrum, and
determining from at least the first reference spectrum A 01 (λ) and the first derivative A 01 ′(λ) a mathematical parameter from which a wavelength shift Δλ of the spectrophotometer can be determined, and
storing the mathematical parameter in a memory of the spectrophotometer.
18. A method according to claim 17 , wherein the step of determining the mathematical parameter comprises the steps of
calculating a set of calibration vectors B i (λ) according to
B i (λ)=s i A 1 (λ)+s i3 A 01 ′(λ)
in which i=1, 2, . . . , N (N>1) and s i and s i3 are constants of selected values,
determining a coefficient vector C Δλ (λ) constituting the mathematical parameter so that each set of corresponding values s i3 , B i (λ) satisfies:
s i3 =C Δλ (λ)·B i (λ), i=1,2, . . . , N.
19. A method according to claim 17 , wherein the dye comprises a first component and a second component, and further comprising the step of determining a second reference A 02 (λ) of a second reference sample containing the dye in a second concentration with the reference spectrophotometer, and wherein the step of determining a mathematical parameter comprises the steps of
calculating a set of vectors B i (λ) from
B i (λ)=s i1 A 1 (λ)+s i2 A 2 (λ)+S i3 A 0 ′ (λ)
in which A 1 (λ) and A 2 (λ) are derived from the first and second reference spectra A 01 (λ), A 02 (λ) and represent spectral information about the first and second components, respectively, and i=1, 2, . . . , N (N>1), and S i1 , S i2 and S i3 are constants of selected values,
determining a vector C Δλ (λ) constituting the mathematical parameter so that
s i3 C Δλ (λ)·B i (λ).
20. A spectrophotometer comprising a processor that is adapted to determine the wavelength shift Δλ between an absorption spectrum A m (λ) determined with the spectrophotometer on a fluid quality control sample containing a dye selected from such dyes which provide the quality control sample with an absorption spectrum with a significant absorbance peak showing a steep flank and a reference absorption spectrum A 0 (λ) of a reference quality control sample containing the dye, stored in a memory of the spectrophotometer wherein the quality control sample has an assigned wavelength shift Δλ qc , and wherein the processor is adapted to compare Δλ with Δλ qc .
21. A spectrophotometer according to claim 20 , wherein the wavelength shift Δλ is determined from A m (λ) and a predetermined mathematical parameter stored in the memory of the spectrophotometer.
22. A spectrophotometer according to claim 21 , wherein the mathematical parameter is a coefficient vector c Δ2 (λ) and wherein the wavelength shift Δ is determined from C Δλ (λ)·A m (λ).
23. A spectrophotometer according to claim 22 , wherein the vector C Δλ (λ) fulfills the equation
Δλ=C Δλ (λ)·A m (λ).
24. A spectrophotometer according to claim 23 , wherein C Δλ (λ) has been determined from a Taylor series of the reference absorption spectrum A 0 (λ).
25. A spectrophotometer according to claim 24 , wherein C Δλ (λ) has been determined from a combination of the reference absorption spectrum A 0 (λ) and a first derivative A 0 ′(λ) of said reference absorption spectrum.
26. A spectrophotometer according to claim 20 , wherein the wavelength shift Δλ is determined after normalisation of the determined spectrum A m (λ) with an estimate of the concentration of the dye.
27. A spectrophotometer according to claim 20 , wherein the quality control sample has a known dye concentration C qc and the dye comprises a first and a second component, and wherein the processor is adapted to
calculate parameters s 1 and s 2 from
s 1 =C 1 (λ)·A m (λ)
s 2 =C 2 (λ)·A m (λ)
in which C 1 (λ) and C 2 (λ) are predetermined vectors previously stored in the memory of the spectrophotometer, and
calculate an estimated concentration C est of the dye from
C est =a s 1 +b s 2
in which a and b are predetermined constants previously stored in the memory of the spectrophotometer.
28. A spectrophotometer according to claim 27 , wherein the processor is further adapted to compare C est with C qc .
29. A spectrophotometer according to claim 27 , wherein the processor is further adapted to calculate a variable Q est =s 2est /s 1est .
30. A spectrophotometer according to claim 29 , wherein the quality control sample has an assigned value of Q qc =s 2qc /s 1qc and wherein the processor is further adapted to compare Q est and Q qc .
31. A spectrophotometer according to claim 20 which is an oximeter.
32. A spectrophotometer according to claim 31 , wherein spectra are measured in the wavelength range from 400 to 800 nm.
33. A spectrophotometer according to claim 31 , wherein the processor is adapted to determine estimated errors in blood parameter values reported by the spectrophotometer caused by the wavelength shift Δλ.
34. A spectrophotometer according to claim 27 , wherein the spectrophotometer is an oximeter and the processor is further adapted to determine estimated errors in blood parameter values reported by the spectrophotometer caused by a difference between C est and C qc .
35. A spectrophotometer according to claim 30 , wherein the spectrophotometer is an oximeter and the processor is further adapted to determine estimated errors in blood parameter values reported by the spectrophotometer caused by a difference between Q est and Q qc .
36. A spectrophotometer according to claim 20 for the determination of a concentration c y of a component y of a sample and wherein the memory further comprises
at least one vector A int (λ) representing spectral information of an interfering component in the sample at a concentration C ref , and
at least one predetermined vector K int (λ) and wherein
the processor is further adapted to
calculate the concentration C int of the interfering component according to
C int =K int (λ)·A m (λ), and
if C int is greater than a predetermined threshold value, C ref , calculate a modified absorbance spectrum A mod (λ) according to
A
mod
(
λ
)
=
A
m
(
λ
)
-
C
int
C
ref
A
int
(
λ
)
,
and
determine c y from the modified spectrum A mod (λ) according to
C y =K y (λ)·A mod (λ)
where K y (λ) is a predetermined vector and whereby the effect of interfering components on determined concentrations C y is minimised.
37. A spectrophotometer according to claim 36 , wherein the interfering component is fetal hemoglobin.