上海必优生物科技有限公司

D-Sorbitol/Xylitol
Colorimetric method
for the determination of D-sorbitol and xylitol1 in foodstuffs
and other materials
BOEHRINGER MANNHEIM / R-BIOPHARM
Enzymatic BioAnalysis / Food Analysis
For in vitro use only Store at 2-8°C
Cat. No. 10 670 057 035
Test-Combination for 3 × approx. 12 determinations
Principle (Ref. 1)
D-Sorbitol and xylitol are oxidized by nicotinamide-adenine dinucleotide
(NAD) to D-fructose or D-xylulose, respectively, in the presence of the
enzyme sorbitol dehydrogenase (SDH, also called polyol dehydrogenase)
with the formation of reduced nicotinamide-adenine dinucleotide (NADH)
(1a, 1b).
Under the assay conditions, the equilibrium of the reactions (1a, 1b) lies on
the side of NAD and D-sorbitol or xylitol, respectively. However, they are
favourably displaced as the formed NADH is removed in a subsequent
reaction in which NADH reduces iodonitrotetrazolium chloride (INT) to a
formazan in the presence of diaphorase (2).
The absorbance of the formazan is measured at its maximum at 492 nm.
The Test-Combination contains
1. Bottle 1 with approx. 25 ml solution, consisting of:
potassium phosphate/triethanolamine buffer, pH approx. 8.6; Triton X-100
(trademark of Rohm & Haas, Philadelphia, USA)
2. Three bottles 2 with each approx. 35 mg of lyophilizate, consisting of:
diaphorase, approx. 4 U; NAD, approx. 28 mg
3. Bottle 3 with iodonitrotetrazolium chloride solution, approx. 2.5 ml
4. Three bottles 4, with lyophilizate SDH, approx. 25 U, each
5. Bottle 5 with D-sorbitol assay control solution for assay control purposes
(measurement of the assay control solution is not necessary for calculating
the results.) Use the assay control solution undiluted. (Expiry date:
see pack label)
Preparation of solutions
1. Use contents of bottle 1 undiluted.
2. Dissolve contents of one bottle 2 with 2.5 ml redist. water.
3. Dilute contents of bottle 3 with 6 ml redist. water.
4. Dissolve contents of one bottle 4 with 0.6 ml redist. water. Slight
opalescence of the solution does not interfere with the assay.
Stability of reagents
Solution 1 is stable at 2-8°C (see pack label).
Bring solution 1 to 20-25°C before use.
The contents of the bottles 2 are stable at 2-8°C (see pack label).
Solution 2 is stable for 1 week at 2-8°C.
Bring solution 2 to 20-25°C before use.
The contents of bottle 3 are stable at 2-8°C (see pack label).
Solution 3 is stable for 3 months at 2-8°C, or for 1 month at 20-25°C stored
in the dark.
Bring solution 3 to 20-25°C before use.
The contents of the bottles 4 are stable at 2-8°C (see pack label).
Solution 4 is stable for two weeks at 2-8°C, and for 4 weeks at 15 to
25°C.
Procedure
Wavelength: (Hg) 492 nm
Glass cuvette2: 1.00 cm ligth path
Temperature: 20-25°C
Final volume: 3.050 ml
Read against air (without a cuvette in the light path) against water or blank
Sample solution: 0.4-10 ?g D-sorbitol and/or xylitol/assay3
(in 0.100-2.000 ml sample volume)
1 If D-sorbitol and xylitol are present, the sum of both sugar alcohols is determined.
2 If desired, disposable cuvettes may be used instead of glass cuvettes.
3 See instructions for performance of assay
4 For series analysis, a suitable stock solution may be prepared by mixing solutions 1, 2 and 3.
This stock solution is stable for 1 h when stored in the dark at 20-25°C. Use 1.000 ml for the
assay.
5 INT is sensitive to light. After addition of solution 3, do not store the cuvettes in the
light.
(1a) D-Sorbitol + NAD+ SDH
D-Fructose + NADH + H+
(1b) Xylitol + NAD+ SDH
D-Xylulose + NADH + H+
(2) NADH + INT + H+ diaphorase
NAD+ + formazan
* Rinse the enzyme pipette or the pipette tip of the piston pipette with sample solution before
dispensing the sample solution.
** For example, with a plastic spatula or by gentle swirling after closing the cuvette with
Parafilm (trademark of the American Can Company, Greenwich, Ct., USA)
If the absorbance A2 increases constantly, extrapolate the absorbance to the
time of the addition of solution 4 (SDH).
Determine the absorbance differences (A2-A1) for both, blank and sample.
Subtract the absorbance difference of the blank from the absorbance
difference of the sample.
A = (A2-A1)sample - (A2-A1)blank
The measured absorbance differences should, as a rule, be at least 0.100
absorbance units to achieve sufficiently precise results (see “Instructions for
performance of assay” and “Sensitivity and detection limit”, pt. 4).
Calculation
According to the general equation for calculation the concentration:
V = final volume [ml]
v = sample volume [ml]
MW = molecular weight of the substance to be assayed [g/mol]
d = light path [cm]
? = extinction coefficient of INT-formazan at 492 nm
= 19.9 [l × mmol-1 × cm-1]
It follows for D-sorbitol:
for xylitol:
This calculation is only valid in the case of the presence of either D-sorbitol
 or xylitol in the sample / the assay.
If the sample has been diluted during preparation, the result must be multiplied
by the dilution factor F.
Pipette into cuvettes Blank Sample
solution 14
solution 24
solution 34, 5
sample solution*
redist. water
0.600 ml
0.200 ml
0.200 ml
-
2.000 ml
0.600 ml
0.200 ml
0.200 ml
0.100 ml
1.900 ml
Mix**, after 2 min read absorbances of the solutions (A1). Repeat the
measurement after 2 min.
If a change in absorbance greater than 0.010 is observed, the sample must
be treated according to pt. 7 (removal of reducing substances). However, if
the change in absorbance is less than 0.010, such pre-treatment is not necessary,
providing the reaction is started immediately after the previous measurement
by adding of:
solution 4 0.050 ml 0.050 ml
Mix**, wait until reaction has stopped (approx. 30 min), and read absorbances
of the solutions (A2).
If the reaction has not stopped after 30 min, continue to read the absorbances
at 5 min intervals until the absorbance increases constantly for
5 min.
c =
V × MW
× A [g/l]
? × d × v × 1000
c =
3.050 × 182.17
× A = 0.2792 × AD-sorbitol [g D-sorbitol/l
19.9 × 1.00 × 0.100 × 1000 sample solution]
c =
3.050 × 152.15
× A = 0.2332 × Axylitol[g xylitol/l sample
19.9 × 1.00 × 0.100 × 1000 solution]
For recommendations for methods and standardized procedures see references
(2)
0711.11748335001
2
When analyzing solid and semi-solid samples which are weighed out for
sample preparation, the result is to be calculated from the amount weighed:
1. Instructions for performance of assay
The D-sorbitol content or xylitol content, respectively, present in the assay
has to be between 0.4 and 10 g. In order to obtain a sufficient absorbance
difference the sample solution is diluted to yield a concentration between
0.01 and 0.10 g/l.
Dilution table
If the measured absorbance difference (A) is too low (e.g.  0.100), the
sample solution should be prepared again (weigh out more sample or dilute
less strongly) or the sample volume to be pipetted into the cuvette can be
increased up to 2.000 ml. The volume of water added must then be reduced
so as to obtain the same final volume in the assays for sample and blank.
The new sample volume v must be taken into account in the calculation.
2. Technical information
2.1 For series analysis, a suitable stock solution may be prepared by mixing
solutions 1, 2 and 3. This stock solution is stable for 1 h when stored at
20-25°C in the dark. Use 1.000 ml for each assay.
2.2 The reaction system is sensitive to light (daylight or artificial light) after
the addition of INT (solution 3 or reaction mixture). The incubation has to
be done in the dark:
a) if incubating in the photometer, close cuvette compartment of the
photometer and block out light.
b) Cover the cuvettes or store in a darkened cupboard.
3. Specificity (Ref. 1)
Besides D-sorbitol and xylitol, sorbitol dehydrogenase also oxidizes other
polyols, such as iditol, allitol, ribitol although with lower velocity. Other
polyalcohols such as mannitol, arabitol, dulcitol do not react.
Under the above-mentioned assay conditions, glycerol is practically not
oxidized (less than 0.2 % conversion with 100 g of glycerol/assay. With a
higher enzyme activity a measurable reaction can be observed; see also
Ref. 1).
In the analysis of commercial D-sorbitol and xylitol, results of approx. 100 %
have to be expected.
4. Sensitivity and detection limit (Ref. 1)
The smallest differentiating absorbance for the procedure is 0.005
absorbance units. This corresponds to a maximum sample volume v =
2.000 ml of a D-sorbitol, resp. xylitol concentration of approx. 0.1 mg/l
sample solution (if v = 0.100 ml, this corresponds to approx. 1.2 mg/l sample
solution).
The detection limit of approx. 0.2 mg/l is derived from the absorbance
difference of 0.015 and a maximum sample volume v = 2.000 ml.
5. Linearity
Linearity of the determination exists from 0.4 g D-sorbitol, resp. xylitol/
assay (0.2 mg D-sorbitol, resp. xylitol/l sample solution; sample volume v =
2.000 ml) to 10 g D-sorbitol, resp. xylitol/assay (0.1 g D-sorbitol, resp.
xylitol/l sample solution; sample volume v = 0.100 ml).
6. Precision
In a double determination using one sample solution, a difference of 0.005 to
0.010 absorbance units may occur. With a sample volume of v = 0.100 ml
this corresponds to a D-sorbitol or xylitol concentration of 1.5-3 mg/l. (If the
sample is diluted during sample preparation, the result has to be multiplied
by the dilution factor F. If the sample is weighed in for sample preparation,
e.g. using 1 g sample/100 ml = 10 g/l, a difference of 0.015-0.03 g/100 g can
be expected.)
ContentD-sorbitol =
cD-sorbitol [g/l sample solution]
× 100 [g/100 g]
weightsample in g/l sample solution
Contentxylitol =
cxylitol [g/l sample solution]
× 100 [g/100 g]
weightsample in g/l sample solution
Estimated amount of D-sorbitol
 or xylitol per liter
Dilution
with water
Dilution
factor F
 0.10 g
0.10-1.0 g
1.0-10 g
 10 g
-
1 + 9
1 + 99
1 + 999
1
10
100
1000
The following data have been published in the literature:
D-Sorbitol solutions:
10 g/assay n = 15 CV = 1.6 %
30 g/assay n = 15 CV = 0.6 %
70 g/assay n = 15 CV = 1.0 %
Xylitol solutions:
4 g/assay n = 15 CV = 1.62 %
8 g/assay n = 15 CV = 1.62 % (Ref. 1.3)
Analysis of bakery goods (Ref. 2.1):
x = 4.56 g/100 g n = 10 s = ± 0.149 g/100 g CV = 3.27 %
x = 18.76 g/100 g n = 10 s = ± 0.283 g/100 g CV = 1.51 %
x = 4.66 g/100 g n = 19 r = 0.22 g/100 g R = 0.35 g/100 g
rrel = 4.72 % Rrel = 7.51 %
x = 19.51 g/100 g n = 17 r = 0.64 g/100 g R = 1.28 g/100 g
rrel = 3.28 % Rrel = 6.56 %
7. Interference
High concentrations of reducing substances e.g. L-ascorbic acid in fruit
juices or SO2 in fruit (jam) interfere with the assay since they react with INT,
thus causing a “creep reaction”. Therefore, quantities larger than 5 g of Lascorbic
acid or SO2/assay should be removed by treating the sample with
H2O2 and alkali.
For this purpose weigh (or pipette) sample, diluted, if necessary, containing
approx. up to 5 mg D-sorbitol or xylitol, respectively, into a 50 ml volumetric
flask. Fill up to approx. 40 ml with water, add 1 ml KOH (2 M) and 0.01 ml
H2O2 (30%; w/v). Incubate solution for 10 min at approx. 70°C. After cooling
to 20-25°C adjust to pH 7-8 with sulfuric acid (1 M). Fill up to the mark with
water, mix, filter and use the solution for the assay.
D-Fructose up to 1 mg/assay and butylene glycol up to 500 g/assay do not
interfere with the assay (reaction time: 60 min).
Recognizing interference during the assay procedure
8.1 If the conversion of D-sorbitol and xylitol has been completed according
to the time given under “Procedure”, it can be concluded in general that
no interference has occurred.
8.2 On completion of the reaction, the determination can be restarted by
adding D-sorbitol or xylitol (qualitative or quantitative): if the absorbance
is altered subsequent to the addition of the standard material, this is also
an indication that no interference has occurred.
8.3 Operator error or interference of the determination through the presence
of substances contained in the sample can be recognized by carring out
a double determination using two different sample volumes (e.g.
0.100 ml and 0.200 ml): the measured differences in absorbance should
be proportional to the sample volumes used.
When analyzing solid samples, it is recommended that different
quantities (e.g. 1 g and 2 g) be weighed into 100 ml volumetric flasks.
The absorbance differences measured and the weights of sample used
should be proportional for identical sample volumes.
8.4 Possible interference caused by substances contained in the sample can
be recognized by using an internal standard as a control: in addition to
the sample, blank and standard determinations, a further determination
should be carried out with sample and assay control solution in the
same assay. The recovery can then be calculated from the absorbance
differences measured.
8.5 Possible losses during the determination can be recognized by carrying
out recovery tests: the sample should be prepared and analyzed with
and without added standard material. The additive should be recovered
quantitatively within the error range of the method.
9. Reagent hazard
The reagents used in the determination of D-sorbitol/xylitol contain hazardous
materials in the sense of the Hazardous Substances Regulations, the
Chemicals Law or EC Regulations 67/548 and 99/45 and subsequent alteration,
supplementation and adaptation guidelines. Please refer to the safety
date sheet or the labels of the affected vials for further information.
3
10. General information on sample preparation
In carrying out the assay:
Use clear, colorless or colored and practically neutral liquid samples
directly, or after dilution according to the dilution table, and of a volume up
to 2.000 ml;
Filter turbid solutions;
Degas samples containing carbon dioxide (e.g. by filtration);
Adjust acid samples to approx. pH 8 by adding sodium or potassium
hydroxide solution;
Crush or homogenize solid or semi-solid samples, extract with water or
dissolve in water and filter if necessary; resp. remove turbidities or dyestuffs
by Carrez clarification;
Deproteinize samples containing protein with perchlorid acid; alternatively
clarify with Carrez reagents;
Extract samples containing fat with hot water (extraction temperature
should be above the melting point of the fat involved). Cool to allow the fat
to separate, fill up to the mark, place the volumetric flask in an ice bath for
15 min and filter; alternatively clarify with Carrez-solutions after the extraction
with hot water.
Carrez clarification:
Pipette the liquid sample into a 100 ml volumetric flask which contains
approx. 60 ml redist. water, or weigh sufficient quantity of the sample into a
100 ml volumetric flask and add approx. 60 ml redist water. Subsequently,
carefully add 5 ml Carrez-I-solution (potassium hexacyanoferrate(II) (ferrocyanide),
85 mM = 3.60 g K4[Fe(CN)6] × 3 H2O/100 ml) and 5 ml Carrez-IIsolution
(zinc sulfate, 250 mM = 7.20 g ZnSO4 × 7 H2O/ 100 ml). Adjust to
pH 7.5-8.5 with sodium hydroxide (0.1 M; e.g. 10 ml). Mix after each addition.
Fill the volumetric flask to the mark, mix and filter.
11. Application examples
Determination of D-sorbitol resp. xylitol in fruit juices
Pipette 5.0 ml of black currant juice, resp. 1.0 ml of apple juice (filter turbid
juice before) into a 50 ml volumetric flask. Add successively 30 ml redist.
water, 1 ml KOH (2 M) and 0.05 ml (in the case of apple juice 0.02 ml)
hydrogen peroxide solution (30%; w/v), mix and incubate for 15 min at 20-
25°C. Then adjust pH to approx. 8 by the addition of sulfuric acid (1 M). Add
2600 U catalase6, mix and incubate for 20 min (10 min in the case of apple
juice), fill up the volumetric flask to the mark with water, mix and filter. Use
the filtrate for the assay.
Determination of D-sorbitol or xylitol in diabetic honey
Accurately weigh approx. 5 g of honey into a 100 ml volumetric flask and
add approx. 70 ml water. Incubate for 10 min at approx. 70°C. Allow to cool
and fill up to the mark with water. Dilute solution according to the dilution
table and use it for the assay.
Determination of D-sorbitol or xylitol in diabetic jam
Homogenize approx. 10 g of jam for 2 min in an electric mixer (homogenizer).
Accurately weigh approx. 1 g of the homogeneous material into a
100 ml volumetric flask, add approx. 50 ml water and incubate for 5 min at
approx. 60°C. Allow to cool to 20-25°C, fill up to the mark with water. Mix
and filter. Dilute with water according to the dilution table, if necessary, and
use it for the assay.
Determination of D-sorbitol or xylitol in ice-cream
Accurately weigh approx. 1 g of sample into a 100 ml volumetric flask, add
approx. 60 ml redist. water and incubate for 15 min at approx. 70°C; shake
from time to time. For clarification, add 5 ml Carrez-I-solution (3.60 g
potassium hexacyanoferrate(II), K4[Fe(CN)6] × 3 H2O/100 ml), 5 ml Carrez-
II-solution (7.20 g zinc sulfate, ZnSO4 × 7 H2O/100 ml) and 10 ml NaOH
(0.1 M), mix after each addition, adjust to 20-25°C, fill up to the mark with
water, and filter. Use the clear, possibly slightly turbid solution for the assay,
diluted, if necessary.
Determination of D-sorbitol or xylitol in marzipan and sweets
Accurately weigh approx. 5 g of the homogenized and minced sample into a
100 ml volumetric flask, add. approx. 60 ml water and keep the volumetric
flask for approx. 15 min in a water-bath at approx. 60°C whilst occasionally
shaking. After cooling to 20-25°C fill up to the mark with water. Mix and
filter, centrifuge, if necessary. Dilute the clear solution, if necessary, and use
it for the assay.
Determination of D-sorbitol and xylitol in protein-containing samples
Deproteinize protein-containing sample solutions with ice-cold perchloric
acid (1 M) in a ratio of 1:2 (1 + 1), centrifuge and neutralize the supernatant
with KOH (1 M).
6 from bovine liver (25°C, H2O2 as substrate)
Determination of D-sorbitol or xylitol in diabetic chocolate
Accurately weigh approx. 3 g ground chocolate into a 100 ml volumetric
flask, add 70 ml water and heat to approx. 70°C in water-bath while shaking.
Allow suspension to cool to 20-25°C and fill up to the mark with water. To
obtain separation of fat, place the volumetric flask for 20 min in the
refrigerator. Centrifuge solution (for 5 min at approx. 5000 rpm). Dilute the
clear supernatant solution, if necessary, and use it for the assay.
Determination of D-sorbitol or xylitol in diabetic bakery products
Mince and homogenize approx. 10 g of bakery products in a mortar or
electric mixer. Accurately weigh approx. 3 g of the sample into a 100 ml
volumetric flask and add approx. 70 ml water. Place the volumetric flask for
15 min into a water-bath at approx. 70°C. After cooling to 20-25°C fill up to
the mark with water. Keep for 20 min in a refrigerator for separation of fat.
Centrifuge sample solution for approx. 5 min (at approx. 5000 rpm). Dilute
the clear, or slightly turbid supernatant solution according to the dilution
table and use it for the assay.
Determination of D-sorbitol or xylitol in diabetic pudding mix
Accurately weigh contents of one bag (approx. 10-15 g) into a 1 l Erlenmeyer
flask and add approx. 500 ml water. Bring mixture to boil and let it simmer
for 2 min; allow to cool, transfer quantitatively with water into a 1 l volumetric
flask and fill up to the mark. After mixing, centrifuge part of the mixture (for
approx. 5 min at approx. 5000 rpm). Dilute the clear or slightly turbid
supernatant solution according to the dilution table and use it for the assay.
12. Further applications
The method may also be used in the examination of pharmaceuticals, cosmetics,
paper and in research when analyzing biological samples. For details
of sampling, treatment and stability of the sample see Ref. 1.
Determination of D-sorbitol or xylitol in fermentation samples and cell
culture media
Place the sample (after centrifugation, if necessary) in a water-bath at 80°C
for 15 min to stop enzymatic reactions. Centrifuge and use the supernatant
(diluted according to the dilution table, if necessary) for the assay.
Homogenize gelatinous agar media with water and treat further as
described.
References
1.1 Bergmeyer, H. U., Gruber, W. & Gutmann, I. (1974) in Methoden der enzymatischen
Analyse (Bergmeyer, H. U., Hrsg.) 3. Aufl., Bd. 2, S. 1368-1371, Verlag Chemie,
Weinheim, and (1974) in Methods of Enzymatic Analysis (Bergmeyer, H. U., ed.) 2nd ed.,
vol. 3, p. 1323-1330, Verlag Chemie, Weinheim/Academic Press, Inc., New York, London
1.2 Bässler, K.H. (1974) in Methoden der enzymatischen Analyse (Bergmeyer, H.U., Hrsg.) 3.
Aufl., Bd. 2, S. 1425-1428, Verlag Chemie, Weinheim, and (1974) in Methods of Enzymatic
Analysis (Bergmeyer, H.U., ed., vol. 3, p. 1323-1330, Verlag Chemie, Weinheim/
Academic Press, Inc., New York, London
1.3 Beutler, H. O. & Becker. J. (1977) Enzymatische Bestimmung von D-Sorbit und Xylit in
Lebensmitteln, Deutsche Lebensmittel-Rundschau 6, 182-187
1.4 Beutler, H.-O. (1984) in Methods of Enzymatic Analysis (Bergmeyer, H. U., ed.) 3rd ed.,
vol. VI, pp. 484-490, Verlag Chemie, Weinheim, Deerfield Beach/Florida, Basel
2.1 Beutler, H.-O. & Dresselhaus-Schroebler, M. (1993) Ringversuche zur Bestimmung von
D-Sorbit in diätetischen Backwaren, Deutsche Lebensmittel-Rundschau 89, 349-351
2.2 Amtliche Sammlung von Untersuchungsverfahren nach §35 LMBG; Untersuchung von
Lebensmitteln: Bestimmung von D-Sorbit in Feinen Backwaren, 18.00-14 (Mai 1994)
2.3 International Federation of Fruit Juice Producers (IFU, Methods of Analysis, no. 62-
1995); contained in "Code of Practice for Evaluation of Fruit and Vegetable Juices"
(1996) edited by Association of the Industry of Juices and Nectars from Fruits and Vegetables
of the European Economic Community (A.I.J.N.).
Concentration: see bottle label
D-Sorbitol assay control solution is a stabilized aqueous solution of D-sorbitol.
It serves as an assay control solution for the enzymatic determination of
D-sorbitol in foodstuffs and other materials.
Application:
1. Addition of D-sorbitol assay control solution to the assay mixture:
Instead of sample solution the assay control solution is used for the assay.
2. Restart of the reaction, quantitatively:
After completion of the reaction with sample solution and measuring of A2,
add 0.050 ml assay control solution to the assay mixture. Read absorbance
A3 after the end of the reaction (approx. 30 min). Calculate the concentration
from the difference of (A3-A2) according to the general equation for
calculating the concentration. The altered total volume must be taken into
account. Because of the dilution of the assay mixture by addition of the
assay control solution, the result differs insignificantly from the data stated
on the bottle label.
For further information see instructions of
Test-Combination D-Glucose Cat. No. 10 716 251 035
Test-Combination D-Glucose/D-Fructose Cat. No. 10 139 106 035
Test-Combination Sucrose/D-Glucose Cat. No. 10 139 041 035
Test-Combination Sucrose/ Cat. No. 10 716 260 035
D-Glucose/D-Fructose
Test-Combination Starch Cat. No. 10 207 748 035
3. Internal standard:
The assay control solution can be used as an internal standard in order to
check the determination for correct performance (gross errors) and to see
whether the sample solution is free from interfering substances:
The recovery of the standard is calculated according to the following
formula:
Pipette into
cuvettes
Blank Sample Standard Sample +
Standard
solution 1
solution 2
solution 3
sample solution
assay control sln.
redist. water
0.600 ml
0.200 ml
0.200 ml
--
2.000 ml
0.600 ml
0.200 ml
0.200 ml
0.100 ml
-
1.900 ml
0.600 ml
0.200 ml
0.200 ml
-
0.100 ml
1.900 ml
0.600 ml
0.200 ml
0.200 ml
0.050 ml
0.050 ml
1.900 ml
Mix, and read absorbances of the solutions (A1) after approx. 2 min.
Continue as described in the pipetting scheme under “Procedure”. Follow the
instructions given under “Instructions for performance of assay” and the
footnotes.
recovery =
2 × Asample + standard - Asample × 100 [%]
Astandard
D-Sorbitol assay control solution (Bottle 5)
R-BIOPHARM AG
An der neuen Bergstraße 17
D-64297 Darmstadt
Phone + 49 61 51 / 81 02-0
Fax + 49 61 51 / 81 02-20
www.r-biopharm.com