Abstract

Accurate concentration measurements of glucose, lactic acid, and creatinine in saline solution have been achieved with near-IR Raman spectroscopy and a partial least-squares analysis. The Raman spectra were acquired remotely through optical fibers. A root-mean-squared prediction error of 1.2 mM for glucose concentration was achieved in 100 s. Concentrations of other analytes were predicted with similar accuracy.

© 1996 Optical Society of America

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  1. M. S. Thorniley, Y. A. P. D. Wickramasinghe, P. Rolfe, “Near infra-red spectroscopy: a new technique for the noninvasive monitoring of tissue and blood oxygenation in vivo,” Biochem. Soc. Trans. 16, 62–63 (1988).
  2. A. Seiyama, O. Hazeki, M. Tamura, “Noninvasive quantitative analysis of blood oxygenation in rat skeletal muscle,” J. Biochem. 103, 419–424 (1988).
    [PubMed]
  3. F. F. Jobsis, “Noninvasive, infrared monitoring of cerebral and myocardial oxygen sufficiency and circulatory parameters,” Science 198, 1264–1266 (1977).
    [CrossRef] [PubMed]
  4. H. Onoe, Y. Watanabe, M. Tamura, O. Hayaishi, “RPM sleep-associated hemoglobin oxygenation in the monkey forebrain studied using near-infrared spectrophotometry,” Neurosci. Lett. 129, 209–213 (1991).
    [CrossRef] [PubMed]
  5. M. R. Robinson, R. P. Eaton, D. M. Haaland, G. W. Koepp, E. V. Thomas, B. R. Stallard, P. L. Robinson, “Noninvasive glucose monitoring in diabetic patients: a preliminary evaluation,” Clin. Chem. 38, 1618–1622 (1992).
    [PubMed]
  6. R. Marbach, T. Koschinsky, F. A. Gries, H. M. Heise, “Noninvasive blood glucose assay by near-infrared diffuse reflectance spectroscopy of the human inner lip,” Appl. Spectrosc. 47, 875–881 (1993).
    [CrossRef]
  7. J. F. Brennan, “Near-infrared Raman spectroscopy for human artery histochemistry and histopathy,” Ph. D. dissertation (Electrical Engineering Department, MIT, Cambridge, Mass., 1995).
  8. S. Y. Wang, C. E. Hasty, P. A. Watson, J. P. Wicksted, R. D. Stith, W. F. March, “Analysis of metabolites in aqueous solutions by using laser Raman spectroscopy,” Appl. Opt. 32, 925–929 (1993).
    [CrossRef] [PubMed]
  9. M. J. Goetz, G. L. Coté, R. Erckens, W. March, M. Motamedi, “Application of a multivariate technique to Raman spectra for quantification of body chemicals,” IEEE. Trans. Biomed. Eng. 42, 728–731 (1995).
    [CrossRef] [PubMed]
  10. R. J. Erckens, J. P. Wicksted, M. Motamedi, W. F. March, “Monitoring of glucose, urea, and lactate through the animal cornea using laser Raman spectroscopy,” Inv. Opthalmol. Visual Sci. 35, 2054 (1994).
  11. J. P. Wicksted, R. J. Erckens, M. Motamedi, W. F. March, “Raman spectroscopy studies of metabolic concentrations in aqueous solutions and aqueous humor specimens,” Appl. Spectrosc. 49, 987–993 (1995).
    [CrossRef]
  12. A. J. Berger, Y. Wang, D. M. Sammeth, I. Itzkan, K. Kneipp, M. S. Feld, “Aqueous dissolved gas measurements using near-infrared Raman spectroscopy,” Appl. Spectrosc. 49, 1164– 1169 (1995).
    [CrossRef]
  13. S. T. Wollman, P. W. Bohn, “Evaluation of polynomial fitting functions for use with CCD arrays in Raman spectroscopy,” Appl. Spectrosc. 47, 125–126 (1993).
    [CrossRef]
  14. D. M. Haaland, E. V. Thomas, “Partial least-squares methods for spectral analyses. 1. Relation to other quantitative calibration methods and the extraction of qualitative information,” Anal. Chem. 60, 1193–1202 (1988).
    [CrossRef]
  15. M. Kohl, M. Cope, M. Essenpreis, D. Bocker, Opt. Lett. 19, 2170–2172 (1994).
    [CrossRef] [PubMed]
  16. A. Lorber, B. R. Kowalski, “Estimation of prediction error for multivariate calibration,” J. Chemometrics 2, 93–109 (1988).
    [CrossRef]
  17. N. W. Tietz, ed., Fundamentals of Clinical Chemistry (Saunders, Philadelphia, 1970), p. 667.
  18. C. C. Chernecky, R. L. Krech, E. J. Berger, Laboratory Tests and Diagnostic Procedures (Saunders, Philadelphia, 1993), p. 401.
  19. K. Tanaka, M. T. T. Pacheco, J. F. Brennan, I. Itzkan, A. J. Berger, R. R. Dasari, M. S. Feld, “Compound parabolic concentrator probe for efficient light collection in spectroscopy of biological tissue,” to be published in Appl. Opt. (1996).
    [CrossRef] [PubMed]

1995

1994

M. Kohl, M. Cope, M. Essenpreis, D. Bocker, Opt. Lett. 19, 2170–2172 (1994).
[CrossRef] [PubMed]

R. J. Erckens, J. P. Wicksted, M. Motamedi, W. F. March, “Monitoring of glucose, urea, and lactate through the animal cornea using laser Raman spectroscopy,” Inv. Opthalmol. Visual Sci. 35, 2054 (1994).

1993

1992

M. R. Robinson, R. P. Eaton, D. M. Haaland, G. W. Koepp, E. V. Thomas, B. R. Stallard, P. L. Robinson, “Noninvasive glucose monitoring in diabetic patients: a preliminary evaluation,” Clin. Chem. 38, 1618–1622 (1992).
[PubMed]

1991

H. Onoe, Y. Watanabe, M. Tamura, O. Hayaishi, “RPM sleep-associated hemoglobin oxygenation in the monkey forebrain studied using near-infrared spectrophotometry,” Neurosci. Lett. 129, 209–213 (1991).
[CrossRef] [PubMed]

1988

M. S. Thorniley, Y. A. P. D. Wickramasinghe, P. Rolfe, “Near infra-red spectroscopy: a new technique for the noninvasive monitoring of tissue and blood oxygenation in vivo,” Biochem. Soc. Trans. 16, 62–63 (1988).

A. Seiyama, O. Hazeki, M. Tamura, “Noninvasive quantitative analysis of blood oxygenation in rat skeletal muscle,” J. Biochem. 103, 419–424 (1988).
[PubMed]

D. M. Haaland, E. V. Thomas, “Partial least-squares methods for spectral analyses. 1. Relation to other quantitative calibration methods and the extraction of qualitative information,” Anal. Chem. 60, 1193–1202 (1988).
[CrossRef]

A. Lorber, B. R. Kowalski, “Estimation of prediction error for multivariate calibration,” J. Chemometrics 2, 93–109 (1988).
[CrossRef]

1977

F. F. Jobsis, “Noninvasive, infrared monitoring of cerebral and myocardial oxygen sufficiency and circulatory parameters,” Science 198, 1264–1266 (1977).
[CrossRef] [PubMed]

Berger, A. J.

A. J. Berger, Y. Wang, D. M. Sammeth, I. Itzkan, K. Kneipp, M. S. Feld, “Aqueous dissolved gas measurements using near-infrared Raman spectroscopy,” Appl. Spectrosc. 49, 1164– 1169 (1995).
[CrossRef]

K. Tanaka, M. T. T. Pacheco, J. F. Brennan, I. Itzkan, A. J. Berger, R. R. Dasari, M. S. Feld, “Compound parabolic concentrator probe for efficient light collection in spectroscopy of biological tissue,” to be published in Appl. Opt. (1996).
[CrossRef] [PubMed]

Berger, E. J.

C. C. Chernecky, R. L. Krech, E. J. Berger, Laboratory Tests and Diagnostic Procedures (Saunders, Philadelphia, 1993), p. 401.

Bocker, D.

Bohn, P. W.

Brennan, J. F.

K. Tanaka, M. T. T. Pacheco, J. F. Brennan, I. Itzkan, A. J. Berger, R. R. Dasari, M. S. Feld, “Compound parabolic concentrator probe for efficient light collection in spectroscopy of biological tissue,” to be published in Appl. Opt. (1996).
[CrossRef] [PubMed]

J. F. Brennan, “Near-infrared Raman spectroscopy for human artery histochemistry and histopathy,” Ph. D. dissertation (Electrical Engineering Department, MIT, Cambridge, Mass., 1995).

Chernecky, C. C.

C. C. Chernecky, R. L. Krech, E. J. Berger, Laboratory Tests and Diagnostic Procedures (Saunders, Philadelphia, 1993), p. 401.

Cope, M.

Coté, G. L.

M. J. Goetz, G. L. Coté, R. Erckens, W. March, M. Motamedi, “Application of a multivariate technique to Raman spectra for quantification of body chemicals,” IEEE. Trans. Biomed. Eng. 42, 728–731 (1995).
[CrossRef] [PubMed]

Dasari, R. R.

K. Tanaka, M. T. T. Pacheco, J. F. Brennan, I. Itzkan, A. J. Berger, R. R. Dasari, M. S. Feld, “Compound parabolic concentrator probe for efficient light collection in spectroscopy of biological tissue,” to be published in Appl. Opt. (1996).
[CrossRef] [PubMed]

Eaton, R. P.

M. R. Robinson, R. P. Eaton, D. M. Haaland, G. W. Koepp, E. V. Thomas, B. R. Stallard, P. L. Robinson, “Noninvasive glucose monitoring in diabetic patients: a preliminary evaluation,” Clin. Chem. 38, 1618–1622 (1992).
[PubMed]

Erckens, R.

M. J. Goetz, G. L. Coté, R. Erckens, W. March, M. Motamedi, “Application of a multivariate technique to Raman spectra for quantification of body chemicals,” IEEE. Trans. Biomed. Eng. 42, 728–731 (1995).
[CrossRef] [PubMed]

Erckens, R. J.

J. P. Wicksted, R. J. Erckens, M. Motamedi, W. F. March, “Raman spectroscopy studies of metabolic concentrations in aqueous solutions and aqueous humor specimens,” Appl. Spectrosc. 49, 987–993 (1995).
[CrossRef]

R. J. Erckens, J. P. Wicksted, M. Motamedi, W. F. March, “Monitoring of glucose, urea, and lactate through the animal cornea using laser Raman spectroscopy,” Inv. Opthalmol. Visual Sci. 35, 2054 (1994).

Essenpreis, M.

Feld, M. S.

A. J. Berger, Y. Wang, D. M. Sammeth, I. Itzkan, K. Kneipp, M. S. Feld, “Aqueous dissolved gas measurements using near-infrared Raman spectroscopy,” Appl. Spectrosc. 49, 1164– 1169 (1995).
[CrossRef]

K. Tanaka, M. T. T. Pacheco, J. F. Brennan, I. Itzkan, A. J. Berger, R. R. Dasari, M. S. Feld, “Compound parabolic concentrator probe for efficient light collection in spectroscopy of biological tissue,” to be published in Appl. Opt. (1996).
[CrossRef] [PubMed]

Goetz, M. J.

M. J. Goetz, G. L. Coté, R. Erckens, W. March, M. Motamedi, “Application of a multivariate technique to Raman spectra for quantification of body chemicals,” IEEE. Trans. Biomed. Eng. 42, 728–731 (1995).
[CrossRef] [PubMed]

Gries, F. A.

Haaland, D. M.

M. R. Robinson, R. P. Eaton, D. M. Haaland, G. W. Koepp, E. V. Thomas, B. R. Stallard, P. L. Robinson, “Noninvasive glucose monitoring in diabetic patients: a preliminary evaluation,” Clin. Chem. 38, 1618–1622 (1992).
[PubMed]

D. M. Haaland, E. V. Thomas, “Partial least-squares methods for spectral analyses. 1. Relation to other quantitative calibration methods and the extraction of qualitative information,” Anal. Chem. 60, 1193–1202 (1988).
[CrossRef]

Hasty, C. E.

Hayaishi, O.

H. Onoe, Y. Watanabe, M. Tamura, O. Hayaishi, “RPM sleep-associated hemoglobin oxygenation in the monkey forebrain studied using near-infrared spectrophotometry,” Neurosci. Lett. 129, 209–213 (1991).
[CrossRef] [PubMed]

Hazeki, O.

A. Seiyama, O. Hazeki, M. Tamura, “Noninvasive quantitative analysis of blood oxygenation in rat skeletal muscle,” J. Biochem. 103, 419–424 (1988).
[PubMed]

Heise, H. M.

Itzkan, I.

A. J. Berger, Y. Wang, D. M. Sammeth, I. Itzkan, K. Kneipp, M. S. Feld, “Aqueous dissolved gas measurements using near-infrared Raman spectroscopy,” Appl. Spectrosc. 49, 1164– 1169 (1995).
[CrossRef]

K. Tanaka, M. T. T. Pacheco, J. F. Brennan, I. Itzkan, A. J. Berger, R. R. Dasari, M. S. Feld, “Compound parabolic concentrator probe for efficient light collection in spectroscopy of biological tissue,” to be published in Appl. Opt. (1996).
[CrossRef] [PubMed]

Jobsis, F. F.

F. F. Jobsis, “Noninvasive, infrared monitoring of cerebral and myocardial oxygen sufficiency and circulatory parameters,” Science 198, 1264–1266 (1977).
[CrossRef] [PubMed]

Kneipp, K.

Koepp, G. W.

M. R. Robinson, R. P. Eaton, D. M. Haaland, G. W. Koepp, E. V. Thomas, B. R. Stallard, P. L. Robinson, “Noninvasive glucose monitoring in diabetic patients: a preliminary evaluation,” Clin. Chem. 38, 1618–1622 (1992).
[PubMed]

Kohl, M.

Koschinsky, T.

Kowalski, B. R.

A. Lorber, B. R. Kowalski, “Estimation of prediction error for multivariate calibration,” J. Chemometrics 2, 93–109 (1988).
[CrossRef]

Krech, R. L.

C. C. Chernecky, R. L. Krech, E. J. Berger, Laboratory Tests and Diagnostic Procedures (Saunders, Philadelphia, 1993), p. 401.

Lorber, A.

A. Lorber, B. R. Kowalski, “Estimation of prediction error for multivariate calibration,” J. Chemometrics 2, 93–109 (1988).
[CrossRef]

Marbach, R.

March, W.

M. J. Goetz, G. L. Coté, R. Erckens, W. March, M. Motamedi, “Application of a multivariate technique to Raman spectra for quantification of body chemicals,” IEEE. Trans. Biomed. Eng. 42, 728–731 (1995).
[CrossRef] [PubMed]

March, W. F.

Motamedi, M.

J. P. Wicksted, R. J. Erckens, M. Motamedi, W. F. March, “Raman spectroscopy studies of metabolic concentrations in aqueous solutions and aqueous humor specimens,” Appl. Spectrosc. 49, 987–993 (1995).
[CrossRef]

M. J. Goetz, G. L. Coté, R. Erckens, W. March, M. Motamedi, “Application of a multivariate technique to Raman spectra for quantification of body chemicals,” IEEE. Trans. Biomed. Eng. 42, 728–731 (1995).
[CrossRef] [PubMed]

R. J. Erckens, J. P. Wicksted, M. Motamedi, W. F. March, “Monitoring of glucose, urea, and lactate through the animal cornea using laser Raman spectroscopy,” Inv. Opthalmol. Visual Sci. 35, 2054 (1994).

Onoe, H.

H. Onoe, Y. Watanabe, M. Tamura, O. Hayaishi, “RPM sleep-associated hemoglobin oxygenation in the monkey forebrain studied using near-infrared spectrophotometry,” Neurosci. Lett. 129, 209–213 (1991).
[CrossRef] [PubMed]

Pacheco, M. T. T.

K. Tanaka, M. T. T. Pacheco, J. F. Brennan, I. Itzkan, A. J. Berger, R. R. Dasari, M. S. Feld, “Compound parabolic concentrator probe for efficient light collection in spectroscopy of biological tissue,” to be published in Appl. Opt. (1996).
[CrossRef] [PubMed]

Robinson, M. R.

M. R. Robinson, R. P. Eaton, D. M. Haaland, G. W. Koepp, E. V. Thomas, B. R. Stallard, P. L. Robinson, “Noninvasive glucose monitoring in diabetic patients: a preliminary evaluation,” Clin. Chem. 38, 1618–1622 (1992).
[PubMed]

Robinson, P. L.

M. R. Robinson, R. P. Eaton, D. M. Haaland, G. W. Koepp, E. V. Thomas, B. R. Stallard, P. L. Robinson, “Noninvasive glucose monitoring in diabetic patients: a preliminary evaluation,” Clin. Chem. 38, 1618–1622 (1992).
[PubMed]

Rolfe, P.

M. S. Thorniley, Y. A. P. D. Wickramasinghe, P. Rolfe, “Near infra-red spectroscopy: a new technique for the noninvasive monitoring of tissue and blood oxygenation in vivo,” Biochem. Soc. Trans. 16, 62–63 (1988).

Sammeth, D. M.

Seiyama, A.

A. Seiyama, O. Hazeki, M. Tamura, “Noninvasive quantitative analysis of blood oxygenation in rat skeletal muscle,” J. Biochem. 103, 419–424 (1988).
[PubMed]

Stallard, B. R.

M. R. Robinson, R. P. Eaton, D. M. Haaland, G. W. Koepp, E. V. Thomas, B. R. Stallard, P. L. Robinson, “Noninvasive glucose monitoring in diabetic patients: a preliminary evaluation,” Clin. Chem. 38, 1618–1622 (1992).
[PubMed]

Stith, R. D.

Tamura, M.

H. Onoe, Y. Watanabe, M. Tamura, O. Hayaishi, “RPM sleep-associated hemoglobin oxygenation in the monkey forebrain studied using near-infrared spectrophotometry,” Neurosci. Lett. 129, 209–213 (1991).
[CrossRef] [PubMed]

A. Seiyama, O. Hazeki, M. Tamura, “Noninvasive quantitative analysis of blood oxygenation in rat skeletal muscle,” J. Biochem. 103, 419–424 (1988).
[PubMed]

Tanaka, K.

K. Tanaka, M. T. T. Pacheco, J. F. Brennan, I. Itzkan, A. J. Berger, R. R. Dasari, M. S. Feld, “Compound parabolic concentrator probe for efficient light collection in spectroscopy of biological tissue,” to be published in Appl. Opt. (1996).
[CrossRef] [PubMed]

Thomas, E. V.

M. R. Robinson, R. P. Eaton, D. M. Haaland, G. W. Koepp, E. V. Thomas, B. R. Stallard, P. L. Robinson, “Noninvasive glucose monitoring in diabetic patients: a preliminary evaluation,” Clin. Chem. 38, 1618–1622 (1992).
[PubMed]

D. M. Haaland, E. V. Thomas, “Partial least-squares methods for spectral analyses. 1. Relation to other quantitative calibration methods and the extraction of qualitative information,” Anal. Chem. 60, 1193–1202 (1988).
[CrossRef]

Thorniley, M. S.

M. S. Thorniley, Y. A. P. D. Wickramasinghe, P. Rolfe, “Near infra-red spectroscopy: a new technique for the noninvasive monitoring of tissue and blood oxygenation in vivo,” Biochem. Soc. Trans. 16, 62–63 (1988).

Wang, S. Y.

Wang, Y.

Watanabe, Y.

H. Onoe, Y. Watanabe, M. Tamura, O. Hayaishi, “RPM sleep-associated hemoglobin oxygenation in the monkey forebrain studied using near-infrared spectrophotometry,” Neurosci. Lett. 129, 209–213 (1991).
[CrossRef] [PubMed]

Watson, P. A.

Wickramasinghe, Y. A. P. D.

M. S. Thorniley, Y. A. P. D. Wickramasinghe, P. Rolfe, “Near infra-red spectroscopy: a new technique for the noninvasive monitoring of tissue and blood oxygenation in vivo,” Biochem. Soc. Trans. 16, 62–63 (1988).

Wicksted, J. P.

Wollman, S. T.

Anal. Chem.

D. M. Haaland, E. V. Thomas, “Partial least-squares methods for spectral analyses. 1. Relation to other quantitative calibration methods and the extraction of qualitative information,” Anal. Chem. 60, 1193–1202 (1988).
[CrossRef]

Appl. Opt.

Appl. Spectrosc.

Biochem. Soc. Trans.

M. S. Thorniley, Y. A. P. D. Wickramasinghe, P. Rolfe, “Near infra-red spectroscopy: a new technique for the noninvasive monitoring of tissue and blood oxygenation in vivo,” Biochem. Soc. Trans. 16, 62–63 (1988).

Clin. Chem.

M. R. Robinson, R. P. Eaton, D. M. Haaland, G. W. Koepp, E. V. Thomas, B. R. Stallard, P. L. Robinson, “Noninvasive glucose monitoring in diabetic patients: a preliminary evaluation,” Clin. Chem. 38, 1618–1622 (1992).
[PubMed]

IEEE. Trans. Biomed. Eng.

M. J. Goetz, G. L. Coté, R. Erckens, W. March, M. Motamedi, “Application of a multivariate technique to Raman spectra for quantification of body chemicals,” IEEE. Trans. Biomed. Eng. 42, 728–731 (1995).
[CrossRef] [PubMed]

Inv. Opthalmol. Visual Sci.

R. J. Erckens, J. P. Wicksted, M. Motamedi, W. F. March, “Monitoring of glucose, urea, and lactate through the animal cornea using laser Raman spectroscopy,” Inv. Opthalmol. Visual Sci. 35, 2054 (1994).

J. Biochem.

A. Seiyama, O. Hazeki, M. Tamura, “Noninvasive quantitative analysis of blood oxygenation in rat skeletal muscle,” J. Biochem. 103, 419–424 (1988).
[PubMed]

J. Chemometrics

A. Lorber, B. R. Kowalski, “Estimation of prediction error for multivariate calibration,” J. Chemometrics 2, 93–109 (1988).
[CrossRef]

Neurosci. Lett.

H. Onoe, Y. Watanabe, M. Tamura, O. Hayaishi, “RPM sleep-associated hemoglobin oxygenation in the monkey forebrain studied using near-infrared spectrophotometry,” Neurosci. Lett. 129, 209–213 (1991).
[CrossRef] [PubMed]

Opt. Lett.

Science

F. F. Jobsis, “Noninvasive, infrared monitoring of cerebral and myocardial oxygen sufficiency and circulatory parameters,” Science 198, 1264–1266 (1977).
[CrossRef] [PubMed]

Other

J. F. Brennan, “Near-infrared Raman spectroscopy for human artery histochemistry and histopathy,” Ph. D. dissertation (Electrical Engineering Department, MIT, Cambridge, Mass., 1995).

N. W. Tietz, ed., Fundamentals of Clinical Chemistry (Saunders, Philadelphia, 1970), p. 667.

C. C. Chernecky, R. L. Krech, E. J. Berger, Laboratory Tests and Diagnostic Procedures (Saunders, Philadelphia, 1993), p. 401.

K. Tanaka, M. T. T. Pacheco, J. F. Brennan, I. Itzkan, A. J. Berger, R. R. Dasari, M. S. Feld, “Compound parabolic concentrator probe for efficient light collection in spectroscopy of biological tissue,” to be published in Appl. Opt. (1996).
[CrossRef] [PubMed]

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Figures (5)

Fig. 1
Fig. 1

Block diagram of the NIR Raman spectroscopy system. The dichroic beam splitter removed two sources of unwanted light from the optical path: photons Raman scattered by the excitation fiber and photons elastically scattered by the sample. Laser power at the sample was typically 200 mW.

Fig. 2
Fig. 2

(a) Typical unprocessed spectrum of an analyte mixture solution. Spectra such as this were used in the PLS analysis directly without any wavelength correction or background subtraction. (b) Same spectral data as in (a) after background subtraction of a spectrum of pure solvent. The resulting spectrum shows a combination of Raman bands from the three dissolved analytes.

Fig. 3
Fig. 3

PRESS versus number of PLS loading vectors for each analyte. Note that the PRESS is plotted on a logarithmic scale. The PRESS of all three analytes improves most dramatically when the third loading vector is added; see text for discussion.

Fig. 4
Fig. 4

NIR Raman spectra of individual dissolved analytes. As in Fig. 2(b), spectra are background subtracted but not calibrated for wavelength dependence of the spectrograph and CCD. The concentration of each analyte is 100 mM: (a) glucose, (b) lactic acid, (c) creatinine. Creatinine's spectrum exhibits many strong bands that make it the most distinct of the three; see text for discussion.

Fig. 5
Fig. 5

(a) PLS prediction of dissolved glucose concentrations from NIR Raman spectra with six loading vectors. Collection time is 100 s. RMSEP is 1.2 mM. (b) PLS prediction of dissolved lactic acid concentrations from NIR Raman spectra with six loading vectors. Collection time is 100 s. RMSEP is 1.3 mM. (c) PLS prediction of dissolved creatinine concentrations from NIR Raman spectra with three loading vectors. Collection time is 100 s. RMSEP is 1.2 mM.

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