Aquaphotomics and its extended water mirror concept...

Aquaphotomics and its extended water mirror concept explain why NIRS can measure low concentration aqueous solutions

George Bázár,1,2,* Zoltán Kovács,1,3 Mariko Tanaka,1 Roumiana Tsenkokva 1,* 1 Biomeasurement Technology Laboratory, Graduate School of Agriculture, Kobe University, Japan

2 Institute of Food and Agricultural Product Qualification, Faculty of Agricultural and Environmental Sciences, Kaposvár University, Hungary 3 Department of Physics and Control, Faculty of Food Science, Corvinus University of Budapest, Hungary

* To whom correspondence should be addressed E-mail: bazar@agrilab.hu (G.B.); rtsen@kobe-u.ac.jp (R.T.)

INTRODUCTION

Low concentration aqueous solutions low spectral intensity of solutes

REFERENCES & ACKNOWLEDGEMENTS [1] Tsenkova, R., 2009. Journal of Near Infrared Spectroscopy, 17, 303-314. [2] Giangiacomo, R., 2006. Food Chemistry, 96, 371-379. [3] Tsenkova, R., 2010. Spectroscopy Europe, 22, 6-10.

http://www.brooklyn.cuny.edu/bc/ahp/SDPS/SD.PS.water.html

http://www1.lsbu.ac.uk/water/inos.html

10-100mM 1-10mM 0.1-1mM 0.02-0.1mM

11

00

-18

00

nm

factor# 3 3 4 1.75±1.5

R2Cal 0.99±0.00 0.99±0.01 0.84±0.12 0.72±0.09

RMSEC 0.99±0.06 0.34±0.06 0.11±0.04 0.02±0.01

R2CV 0.99±0.00 0.97±0.02 0.48±0.27 -1.17±0.46

RMSECV 1.34±0.22 0.48±0.13 0.19±0.05 0.03±0.00

RPDCV 22.63 6.33 1.56 1.05

13

00

-16

00

nm

factor# 3 3 3.75±0.5 1.75±1.5

R2Cal 0.99±0.00 0.99±0.01 0.80±0.15 0.68±0.09

RMSEC 0.99±0.07 0.34±0.07 0.13±0.07 0.02±0.01

R2CV 0.99±0.00 0.97±0.01 0.33±0.33 -0.91±0.70

RMSECV 1.34±0.23 0.48±0.12 0.22±0.05 0.03±0.00

RPDCV 22.59 6.37 1.37 1.07

10-100mM 1-10mM 0.1-1mM 0.02-0.1mM

11

00

-18

00

nm

factor# 3 3 3 1

R2Cal 0.99 0.98 0.35 0.07

RMSEC 1.03 0.40 0.23 0.03

R2CV 0.99 0.98 0.24 -0.1

RMSECV 1.08 0.42 0.25 0.03

RPDCV 27.94 7.19 1.23 1.15

13

00

-16

00

nm

factor# 3 3 3 1

R2Cal 0.99 0.98 0.33 0.05

RMSEC 1.04 0.40 0.23 0.03

R2CV 0.99 0.98 0.23 -0.04

RMSECV 1.08 0.42 0.25 0.03

RPDCV 28.04 7.13 1.22 1.15

The molecular changes of the water solvent caused by the solute can be detected by NIR spectroscopy and used for qualitative and quantitative analyses [1]

Means and standard deviations of PLSR results on lactose concentration in the four replicate solutions (n = ca.30) at the

different concentration ranges, applying different spectral regions

PLSR results on lactose concentration at the different concentration ranges using the four replicate solutions together (n = ca.120), applying different spectral regions and ‘leave one replicate out’ cross-validation

13

90

-14

25

nm

14

40

-14

75

nm

15

80

-16

15

nm

16

80

-17

00

nm

17

20

-17

55

nm

1100 1350 1600 1800 Wavelengths [nm]

10

0

-10

-20

-30

10

-10

-30

50

0

-50 Reg

ress

ion

po

wer

R

egre

ssio

n p

ow

er

Reg

ress

ion

po

wer

Structural changes of water in sugar solutions presented on aquagram

BUT!

Measuring low concentration of sugar in aqueous solutions based on the molecular changes of water [2]

MATERIALS AND METHODS RESULTS

10-100mM

1-10mM

0.1-1mM

- Analytical grade lactose diluted in Milli-Q water 0.02-0.1mM range, with 0.01mM steps 0.1-1mM range, with 0.1mM steps 1mM-10mM range, with 1mM steps 10mM-100mM range, with 10mM steps - Four independent replicates were prepared for each concentration range - FOSS XDS spectrometer (FOSS NIRSystems, Inc., Hoganas, Sweden) with RLA module and 1mm cuvette transmittance spectra (logT-1) at 1100-1800nm with 0.5nm spectral step - R Project (www.r-project.org), The Unscrambler v9.7 (CAMO Software AS, Oslo, Norway), Pirouette 4.0 (Infometrics, Inc., Woodinville, WA, USA)

Characteristic changes at water matrix coordinates

describe the water spectral pattern of lactose.

Visualization on aquagram [3]:

1344nm

1364nm

1412nm

1445nm

1475nm

1506nm

1590nm

1380nm

1400nm

1425nm

1440nm

1455nm A = Aquagram value

a = absorbance after MSC μ = average of all spectra

σ = SD of all spectra

A =a − μ

σ

0

0.5

1.0

1.5

Ab

sorb

ance

(w

ater

)

0

0.5

1.0

1.5

Ab

sorb

ance

(so

luti

on

s)

0

0.125

0.25

1.5 Ab

sorb

ance (lacto

se)

-2

-1

0

1

2n

d d

eriv

. x1

0-4

(wat

er)

2

2

-2

-1

0

1 2

nd

der

iv. x

10

-4 (s

olu

tio

ns)

2

2

-0.5

-0.25

0

0.25

0.5

0.75

1100 1300 1500 1700

1100 1300 1500 1700 1100 1300 1500 1700

1100 1300 1500 1700

11

52

14

12

14

62

13

44

17

80

11

40

1

17

5

12

08

12

76

1

30

2

13

42

1

36

6

13

80

14

50

1

49

0

15

36

15

92

1

61

6

16

46

16

96

1

72

8

17

64

1

79

6

Raw spectra 2nd derivative spectra

2n

d d

eriv. x10

-4 (lacto

se)

water lactose

Aqueous solutions of lactose

(0.02-100mM)

Signals of lactose can hardly be detected in low concentration solutions.

Subtraction of water spectrum from those of the lactose solutions reveals the spectral differences of the different concentrations.

Only water bands dominate

Regression vectors of calibration models

built on the subtracted spectra of

water and lactose solutions show stability among

replicate measurments, and

accentuate the dominant water

regions.

1-10mM 10-100mM

CONCLUSIONS

NIR technique coupled with aquaphotomics concept is useful method for quantification of the investigated carbohydrate solutes at millimolar level. Lactose causes gradual changes in the water molecular matrix, thus, performance of calibration on lactose concentration does not decrease when only the characteristic spectral region of water 1st overtone (1300-1600nm) is applied. In the contrary, it has been demonstrated in the present study that the absorption regions of water provide most useful information on the solutes in case of highly diluted aqueous solutions. Accordingly, the molecular changes of water caused by the solute can be traced and used for describing the amount of dissolved material. NIR technique and aquaphotomics based on the extended water mirror concept provide a quick and accurate alternative for classical analytical measurements even at very low (1-10mM) concentration levels.

Financial support of Japan Society for Promotion of Science (G.B. JSPS P12409) is acknowledged.

Dynamic changes of structure maker and structure breaker characteristics of sugar in

water [2]. Breaker is dominant in low, while maker in high concentrations.

H+·(H2O)4-8

OH-(H2O)1,2,4

H+·(H2O)2

OH-(H2O)1,4

O2-(H2O)4

S0

Free -OH

S0

OH-H bending

H+·(H2O)2 S1

Deionized water

OH-(H2O)4,5

2ν2+ν3

S2, S3

aν1+bν3

(a+b)=2

H+·(H2O)2,6

H+·(H2O)2,6