American Journal of Analytical Chemistry, 2013, 4, 653-660
Published Online November 2013 (http://www.scirp.org/journal/ajac)
http://dx.doi.org/10.4236/ajac.2013.411078
Open Access AJAC
Spectrophotometric Determination of Water-Soluble
Hexavalent Chromium and Determination of Total
Hexavalent Chromium Content of Portland Cement in the
Presence of Iron (III) and Titanium (IV) Using Derivative
Ratio Spectrophotometry
K. A. Idriss*, H. Sedaira, S. Dardeery
Chemistry Department, Faculty of Science, Assiut University, Assiut, Egypt
Received September 7, 2013; revised October 8, 2013; accepted October 25, 2013
Copyright © 2013 K. A. Idriss et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
A rapid, reliable and accurate method for the determination of hexavalent chromium in Portland cement is developed.
The proposed method includes direct spectrophotometric determination of Cr (VI) in Portland cement with 1, 2, 5, 8
Tetrahydroxyanthraquinone, (Quinalizarin, QINZ) at pH 1.5. The European Directive (2003/53/EC) limits the use of
cements so that it contains no more than 2 mg·Kg−1 of water-soluble Cr (VI). The absorbance at 565 nm due to Cr
(VI)-QINZ complex is recommended for the determination of water-soluble Cr (VI) in Portland cement. The quantifica-
tion of Cr (VI) released from cement when mixed with water is performed according to TRGS 613 (Technical Rules of
Hazardous Substances). The validity of the method is thoroughly examined and the proposed method gives satisfactory
results. A derivative spectrophotometric method has been developed for the determination of total Cr (VI) in Portland
cement in the presence of Fe (III) and Ti (IV). The hexavalent chromium complex formed at pH 1.5 allows precise and
accurate determination of chromium (VI) over the concentration range 0.05 to 3.0 mg·L−1 of chromium (VI). The valid-
ity of the method was examined by analyzing several Standard Reference Material (SRM) Portland cement samples.
The MDL (at 95% confidence level) was found to be 25 ng/mL for chromium (VI) in National Institute of Standards
and Technology (NIST) cement samples using the proposed method.
Keywords: Chromium (VI) Determination; Quinalizarin; Portland Cement Analysis; Derivative Spectrophotometry
1. Introduction
In cement industry, raw materials are mixed in controlled
proportions and ground to form a fine and homogeneous
mixture called raw meal. The raw meal is burnt in kilns
to the point of partial melting (~1400˚C) where reactions
forming clinker phases take place. Clinker is interground-
ed with gypsum to form the construction product-cement.
Description of cement composition is normally carried
out by chemical analysis to give the contents of major
and minor components expressed as oxides. In a cement
plant, on-line control of the composition of cement is
necessary to maintain the composition of the cement
within strict requirements [1]. The improvement of the
quality is tantamount to the improvement of the chemical
composition.
One of the problems affecting cement companies is the
need to determine and control the content of the hexava-
lent chromium, due to its toxic effects. The hexavalent
chromium is considered an undesirable component of
cement because of its potential health consequences. Cr
(VI) content of Portland cement contributes to the debili-
tating medical condition known as dermatitis [2-7]. Due
to increasing health-related concerns, the amount of Cr
(VI) found in Portland cement is coming under increas-
ing scrutiny [7,8].
European countries have limited the amount of Cr (VI)
allowed in Portland cement; it must be no more than 2
ppm water-soluble chromate relative to the dry cement
mass [9]. The major sources of chromium content of
*Corresponding author.

K. A. IDRISS ET AL. 654
Portland cement are the kiln feed raw materials, refrac-
tory brick, wear metal from grinding media and additives
[7].
The chemical, environmental and medical literatures
describe research and analytical method development for
the determination of Cr (VI) in a broad variety of sample
types, including Portland cement, cement constituents
and concrete/mortar [10]. The US EPA, ASTM, OSHA
and NIOSH and other agencies have established many of
these analytical procedures as required test methods.
These methods include a range of instrumental tech-
niques including UV-Visible spectrophotometry, atomic
absorption spectrophotometry (AAS), ion chromatogram-
phy (IC), capillary electrophoresis (CE), XRF and induc-
tively coupled plasma (ICP) by either emission or mass
spectrometry. The colorimetric method has been widely
used for quantitative analysis of Cr (VI) in cement and its
extraction fluids [11-13].
Derivative spectrophotometry opens up possibilities,
not only for increasing selectivity [14-16], but also for
increasing sensitivity [17,18]. Salinas et al. [19] devel-
oped a spectrophotometric method for resolving ternary
mixtures; the method is based on the simultaneous use of
the first derivative of the ratio spectra and measurements
at zero-crossing wavelengths. Although several methods
have been applied to determine Cr (VI), direct visible
spectrophotometric methods using anthraquinone de-
rivative have not yet been investigated for its determina-
tion in Portland cement. The common availability and the
relatively low cost instrumentation, the stability of the
procedures and the accuracy of the techniques make the
absorption spectrophotometry advantageous for cement
analysis [20-24]. In this work, fundamental study of the
complexation reaction of hexavalent chromium with
QINZ is described, a rapid and sensitive first derivative
ratio spectrum zero-crossing method is undertaken to
determine Cr (VI) in the presence of Fe (III) and Ti (IV)
in mixtures using Quinalizarin as a complexing agent.
Solution spectra of the extracted Cr (VI), as indicated by
the TRGS 613 [25], are also investigated under our opti-
mum conditions. The validity of the method is thor-
oughly examined and its analytical characteristics are
determined and approved to be suitable for the intended
purpose.
2. Experimental
2.1. Chemicals and Solutions
All chemicals used were of analytical reagent grade and
doubly distilled water, were used for the preparation of
aqueous solutions.
A 1.0 × 10−3 mol·L−1 stock standard solution of Qui-
nalizarin was prepared by dissolving an accurately
weighed amount of Sigma (St. Louis, MO, USA) pure
grade reagent in absolute ethanol. A 10−4 mo l · L −1 stock
standard solution of potassium di chromate (or potassium
chromate) and 10−3 mol·L −1 stock standard solution of
ferric chloride were prepared using the AnalaR grade
product. Titanium stock standard solution was prepared
as given elsewhere [20]. The metal content of the solu-
tion was determined by conventional methods [26]. Solu-
tions of perchloric acid, sodium perchlorate and standard
sodium hydroxide solution were all prepared from ana-
lytical-reagent grade reagents. Solutions of diverse ions
used for interference studies were prepared from AnalaR
chloride salts of the metal ions and potassium or sodium
salts of the anions to be tested. The solution spectra were
recorded in water-ethanol containing 50% v/v ethanol.
The acid-base properties of the QINZ were studied under
our experimental conditions and the pKa values of the
reagent were determined.
2.2. Cement Samples
National Institute of Standards and Technology (NIST)
Standard Reference Materials (SRMs) 1880b and 1885a
were used as the Portland cement matrix in this study.
Precautions for handling and use were taken in accor-
dance with the instructions on the NIST data sheet. A
complete composition of SRMs samples according to
NIST certificates of analysis [27] is given in Table 1.
Samples of ordinary Portland cement (OPC) were sup-
plied by Assiut Cement (Cemex, Egypt).
Table 1. Complete composition of SRM(s) samples accord-
ing to the NIST certificate of analysis [27].
Constituent1880b (wt %) 1885a (wt %)
SiO2 20.42 ± 0.36 20.909 ± 0.047
Al2O3 5.183 ± 0.073 4.026 ± 0.032
Fe2O3 3.681 ± 0.023 1.929 ± 0.061
CaO 64.16 ± 0.40 62.390 ± 0.410
MgO 1.176 ± 0.020 4.033 ± 0.033
SO3 (*)2.710 ± 0.099 2.830 ± 0.021
Na2O 0.0914 ± 0.0052 1.068 ± 0.061
K2O 0.646 ± 0.014 0.206 ± 0.011
TiO2 0.236 ± 0.012 0.195 ± 0.014
P2O5 0.2443 ± 0.0027 0.1220 ± 0.0015
Mn2O3 0.1981 ± 0.002 0.0478 ± 0.0015
F 0.0539 ± 0.0012 0.13
Cl 0.0183 ± 0.00057 0.0040 ± 0.0005
ZnO 0.01054 ± 0.00034 0.0029 ± 0.0003
Cr2O3 (*)0.01927 ± 0.00042 0.0195 ± 0.0006
SrO 0.0272±0.0016 0.638±0.026
LOI 1.666±0.011 1.68
Total 100.49 100.18
(*)The uncertainty estimates for SO3 and Cr2O3 include an additional com-
ponent of uncertainty of 2% (relative) to account for greater than expected
heterogeneity observed during testing of the material after packaging.
Open Access AJAC

K. A. IDRISS ET AL. 655
2.2.1. Dissolution of Cement Samples
Weigh accurately 0.5 g of the sample (dried at 110˚C)
into a beaker and dissolve it in the minimum volume of
hydrochloric acid. Heat to dryness, add 10 ml of HCl (6
mol·L−1) to the residue, digest and filter the insoluble
residue into a 25 ml calibrated flask and then dilute to
volume with doubly distilled water.
2.2.2. Cement Extraction Procedure [25]
Aqueous cement extracts were prepared according to the
TRGS 613 procedure; weigh accurately 10.0 g of the
sample in a 250 mL beaker with 40 mL of distilled water.
Stir the mixture for 15 ± 1 minutes intensively at 300
rpm. Immediately filter the suspension without washing,
through a dry glass frit of porosity 3. If the cementitious
preparation contains turbidity, the sample is centrifuged
and then filtered through a narrow-pore filtering medium.
Aliquot of samples were used for the determination of
soluble Cr (VI) in Portland cement.
2.3. Apparatus
A Perkin-Elmer (Norwalk, CT, USA) Lambda 35 double
beam spectrophotometer was used for ordinary and first
derivative spectral measurements using 1 cm matched
quartz cells. The derivative spectra were recorded at a
scan speed of 240 nm·min−1, ∆λ = 5 nm and a slit width
of 2 nm. The smoothing and differentiation calculation
are based on a least-squares polynomial convulation
function using 17 data points.
2.4. Procedures
2.4.1. Ordinary Spectrophotometry
Transfer an aliquot of a sample solution containing
chromium (VI) (1.0 - 75 μg) and/or ferric (III) (12 - 150
μg) and/or titanium (IV) (100 - 200 μg) into 25 mL cali-
brated flasks. Add 12.5 mL of 1.0 × 10−3 mol·L−1 qui-
nalizarin solution and ensure a final ethanol content of 50
% v/v. Adjust the pH to 1.5 using 0.2 M perchloric acid,
while keeping the ionic strength constant at 0.1 (NaClO4).
Dilute to volume with doubly distilled water and record
the normal spectrum from 700 - 500 nm against a reagent
blank as the reference.
2.4.2. Derivative Ratio Spectrum—Zero Crossing
Method
The stored spectra of Cr (VI)-QINZ complex, Fe (III)-
QINZ complex and their ternary mixture with Ti (IV)-
QINZ complex were divided by a standard spectrum of
Ti (IV)-QINZ complex. The first derivative of the ratio
spectra were recorded from 650 - 550 nm. In the ternary
mixture, the concentration of chromium (VI) was propor-
tional to the first derivative divided signals (1DD) at 572
nm (zero crossing point for Fe (III)/Ti (IV).
2.4.3. Colorimetric Determination of Soluble Cr6+ in
Portland Cement
Weigh accurately 10 g of the sample into a beaker and
prepare the sample solution as indicated earlier in Ce-
ment Extraction Procedure [25]. Transfer a 2.0 - 5.0 mL
aliquot of the prepared extracted cement solution into a
25 mL calibrated flask and add 5.0 mL of QINZ (1.0 ×
10−3 M). Adjust the pH to 1.5 by the addition of 0.2 M
perchloric acid, while keeping the ionic strength constant
at 0.1 (NaClO4). Dilute to volume while keeping final
ethanol content of 50% v/v. Record the absorbance of the
solution from 700 - 500 nm against a reagent blank as the
reference. Measure the absorbance value at 565 nm whi-
ch directly proportional to soluble Cr (VI) content in
Portland cement.
2.4.4. Derivative Spectrophotometric Determination
of Total Cr6+ in Portland Cement
Weigh accurately 0.5 g of the sample into a beaker and
prepare the sample solution as indicated earlier in disso-
lution of cement samples. Transfer a 0.5 - 1.0 mL aliquot
of the prepared cement solution into a 25 mL calibrated
flask and add 12.5 mL of QINZ (10−3 M). Adjust the pH
to 1.5 by the addition of 0.2 M perchloric acid, at the
ionic strength of 0.1 (NaClO4). Dilute to volume while
keeping final ethanol content of 50% v/v. Record the
absorbance of the solution from 700 - 500 nm against a
reagent blank. Divide the obtained normal spectrum by a
standard one for Ti(IV)-complex. Record the first de-
rivative of the ratio spectrum and measure the amplitudes
(1DD) at proper zero crossing wavelength as mentioned
above. Total Cr (VI) content in Portland cement is calcu-
lated directly using regression equation.
3. Results and Discussion
3.1. Acid-Base Properties of the Reagent
The QINZ reagent yields five colored acid-base forms in
solutions of pH~2.0 - 11.0: H4L, H3L−, H2L2−, HL3− and
L4−, exhibiting the absorption maxima at 230, 280, 340,
485 and 590 nm, respectively. Distinct isosbestic points
are observed for the particular acid-base equilibrium. The
absorbance versus pH graphs were interpreted assuming
that a particular equilibrium is established under selected
conditions. Under our experimental conditions, pKa1
(H4L/H3L−) = 2.5, pKa2 (H3L−/H2L2−) = 3.1, pKa3
(H2L2−/HL3−) = 5.5 and pKa4 (HL3−/L4−) = 10.5 (I = 0.1,
25˚C).
3.2. Complexation Equilibria of Cr6+ with QINZ
The complexation equilibria of Cr6+ with Quinalizarin
were studied in solutions containing 50% (v/v) ethanol
over the pH range 0.5 - 3.5. The solution spectra were
recorded in solutions containing an excess of the reagent
Open Access AJAC

K. A. IDRISS ET AL. 656
and in solutions containing an excess of the metal. The
absorption spectra reflect the formation of a complex
with a band at 565 nm (where the reagent, Quinalizarin
does not absorb). The complex formation starts at pH 1.0.
The colour development is attained at pH 1.5 - 2.0. At
higher pH values, a decrease of absorbance is ob- served.
The absorbance versus pH graphs for the Cr (VI)-QINZ
system in Figure 1 were interpreted using the relation-
ships reported elsewhere [28,29]. The number of protons
released during complexation (q) and the equilibrium
constant (Keq) were proved graphically from the plots of
solutions investigated.
The logarithmic transformations of equimolar solu-
tions and solutions with an excess of reagent are straight
lines with a slope (q) and intercept including (Keq). By
considering the acid-base equilibria of Quinalizarin in
50% (v/v) ethanol and the distribution ratio of the reagent
species at different pH values, one can assume that the
neutral form of the reagent (H4L) is the prevalent ligand
species in the pH range of complexation. At this pH
range, the graphical analysis of the absorbance versus pH
graphs, for solutions with different component ratios,
indicated the best fit for the formation of complex with
the liberation of two protons according to equilibrium
(A).
64
42
CrLHCrLH2H K

 eq

(A)
3.3. Equilibrium and Stability Constants
The equilibrium constant Keq was determined by consid-
0
0.2
0.4
0.6
0.8
1
00.5 11.522.5 3
pH
Absorbance
1
2
Figure 1. Absorbance vs pH graphs for Cr (VΙ)-QINZ com-
plex. Λ = 565 nm, 50 % ( v/v) ethanol, 0.1 mol·L-1 (NaClO4).
1) CM = 2 × 10−4 mol·L−1; CL = 3 × 10−4 mol·L−1. 2) CM = 2 ×
10−4 mol·L−1; CL = 1.5 × 10−4 mol·L−1.
ering equilibrium (A). The stability constant (β) of chro-
mium-QINZ complex is related to the equilibrium con-
stant (Keq) by the expression β = K eq Ka1
−1 K
a2
−1. The
calculated values of the apparent equilibrium constant
and stability constant at pH 1.5 are 8.8 ×104 and 3.5 ×
1010, respectively.
3.4. Analytical Characteristics of the Method
Under the optimum conditions, a linear calibration graph
for the normal spectrophotometric method was obtained
from 0.05 - 3.0 µg·mL−1 of chromium. The molar ab-
sorptivity of the Cr (VI) complex at 565 nm was 6.0 ×
103 L·mole−1·cm−1 Figure 2. Sandell sensitivity of the
reaction of Cr (VI) was found to be 3.2 ng·cm−2. The
reproducibility of the method was checked by analyzing
a series of five solutions with a Cr (VI) concentration of
1.0 µg·mL−1. The relative standard deviation (RSD) was
found to be 0.96%.
The detection limit (at the 95% confidence level) of
the proposed method for the mean of five analyses was
calculated. The calculated detection limit was found to be
25 ng·mL−1 for the normal spectrophotometric procedure
of certified NIST SRMs. Results obtained for the analy-
sis of cement materials were given in Table 2.
3.5. Effect of Diverse Ions
To assess the usefulness of the proposed method, the
effects of diverse ions that are often exist in Portland
cement were studied. The tolerance of the method to for-
eign ions was investigated with solutions containing 0.02
0
0.03
0.06
0.09
0.12
0.15
0.18
500 550 600 650 700
Wav elength (n m)
Absorbance
1
2
3
4
5
6
7
1`
2`
Figure 2. Absorption spectra of Cr (VI)-QINZ complexes,
[Cr(VI)] = 1) 0.2, 2) 0.416, 3) 0.624, 4) 0.832, 5) 1.04, 6) 1.248,
7) 1.456 mg·L−1, 1`) OPC(a), 2`) OPC(b), [QINZ] = 2 × 10−4
mol·L−1, 50% (v/v) ethanol, 0.1 mol·L−1 (NaClO4), pH 1.5.
Open Access AJAC

K. A. IDRISS ET AL. 657
Table 2. Spectrophotometric determination of soluble Cr
(VI) in some Portland cement materials.
Chromium (VI) determination Cr (VI) Cr (VI)
Material using the proposed method Using Using
DPC AAS
Abs.565nm C
Cr(VI) s C Cr(VI) C Cr(VI)
Cement (OPC)
OPC (a) 0.0039 0.0338 1 × 10−5 0.0375 0.037
OPC (b) 0.0088 0.07622 × 10−5 0.070 0.079
Regression equation r S
Abs.565 = 6.0 × 103CCr(VI) 0.9998 2 × 10−4
Number of determinations for each sample: n = 5. OPC: ordinary Portland
cement, Abs.565 = Absorbance at 565 nm, CCr(VI) = Cr (VI) concentration
(mg·L−1), DPC: diphenylcarbazide, AAS:atomic absorption spectropho-
tometry, r = Regression coefficient, S = Standard deviation. OPC (a): ce-
ment extraction of 10 gm OPC in 80 mL dist. H2O, OPC (b):cement extrac-
tion of 10 gm OPC in 40 mL dist. H2O.
mg of Cr6+ per 25 mL and various amounts of foreign
ions. The tolerance criterion for a given ion was taken to
be the deviation of the absorbance values by more than ±
2% from the expected value. The determination of chro-
mium was possible in the presence of Na+, K+, Ca2+, Sr2+,
Mg2+, Mn2+, Zn2+, Al3+, Cr3+, SO4
2−, SO3 2−, NO3 −, Cl−,
Br−, I− and PO4
3−(10.0 mg). The ions Fe3+ and Ti4+ in-
terfered seriously which was overcome by using deriva-
tive ratio spectra-zero crossing method.
The complexation of the interfering cations, Fe3+ and
Ti4+ with QINZ were studied at the pH 1.5. The absorp-
tion spectra reflect the formation of Fe-QINZ complex
with λmax at 580 nm, and the formation of Ti-QINZ com-
plex with λmax at 575 nm.
3.6. Derivative Ratio Spectrum—Zero Crossing
Method for the Determination of Hexavalent
Chromium in Presence of Ferric (III) and
Titanium (IV)
In order to resolve the ternary mixture, we needed to se-
lect the appropriate zero-crossing wavelengths that per-
mitted the determination of one component in the pres-
ence of the other two [24].
The reproducibility of zero-crossing wavelengths of
derivative ratio spectra was checked by recording the
first derivative ratio spectra of Fe (III)-QINZ system, at
different concentrations of Fe (III) and using a standard
spectrum of Ti (IV)-QINZ complex as a divisor Figure 3.
The zero-crossing wavelengths were obtained at 552 and
572 nm.
Figure 4 shows the derivative ratio spectra of a series
of ternary mixtures containing increasing amounts of
chromium (VI), using Ti-complex as a divisor. Chro-
mium (VI) can be determined using the absolute value of
the total first derivative divided spectrum (1DD) at a
wavelength corresponding to the zero-crossing point of
-1.7
-1.3
-0.9
-0.5
-0.1
0.3
0.7
1.1
525 550 575 600 625
Wavelength (nm)
first d erivati ve o f ratio sp ectr
a
552 nm
1
2
3
4
5
6
7
8
9
Figure 3. First derivative ratio spectra of Fe (III)-QINZ
complex, [Fe (III)] = 1) 1.1, 2) 2.2, 3) 3.3, 4) 4.4, 5) 5.5, 6) 6.6,
7) 7.8, 8) 8.9, 9) 10.0 mol·L−1, [Ti (IV)] = 7.0 mol·L−1 as divi-
sor, [QINZ] =2 × 10−4 mol·L−1, 50 %( v/v) ethanol, 0.1
mol·L−1 (NaClO4), pH 1.5.
-0.015
-0.01
-0.005
0
0.005
0.01
0.015
0.02
560 565570 575 580585 590
Wav eleng th (nm)
F irst d erivative o f ratio sp ectr
a
1
2
3
4
1`
2`
h
572 nm
Figure 4. First derivative ratio spectra of ternary mixtures
of (Cr6+, Fe3+ and Ti4+)-QINZ complexes containing incre-
ment amounts of chromium. [Cr (VI)] = 1) 0.005, 2) 0.312, 3)
0.624, 4) 0.936 mol·L−1, [Fe(III)] = 2.8 mol·L−1 and [Ti(IV)]
= 7.0 mol·L−1, 1`) 1885a SRM, 2`) 1880b SRM, [Ti(IV)] = 7.0
mol·L−1 as divisor, [QINZ] = 4 × 10−4 mol·L−1, 50%(v/v)
ethanol , 0.1 mol·L−1 (NaClO4), pH 1.5.
ferric complex. The height h, corresponding to values
taken at 572 nm (zero-crossing point of ferric complex)
is proportional to chromium (VI) concentration.
Open Access AJAC

K. A. IDRISS ET AL. 658
In order to test the validity of the method, several syn-
th
3.6.1. Effect of Divisor
e three components can be used
3.6.2. Calibration Graphs and Statistical Analysis of
The cph, prepared by plotting the first de-
able 3. Results of analyzing synthetic mixtures containing
) 7.0 mg·L−1 Ti (IV) (divisor)
etic mixtures of chromium (VI), ferric (III) and tita-
nium (IV) were prepared and tested up to 3.0 mg·L−1 for
chromium (VI), 3.0 mg·L−1 for ferric (III) and 7.0 mg·L−1
for titanium (IV) in the ternary mixture Table 3. Mean
recoveries and the relative standard deviations were
found to be 101 and 0.96 for chromium, using Ti-QINZ
as a divisor.
The standard spectra of th
as divisor; but we found that the most favorable results
were obtained using the standard spectrum of titanium
(IV) (7.0 mg·L−1).
the Results
alibration gra
rivative divided value, 1DD, (h) versus hexavalent chro-
mium concentration gave a straight line passing through
the origin confirming the mutual independence of the
derivative signals of the three complexes. The calibration
graph obtained was linear over a range of 0.0 - 3 mg·L−1
of chromium. A critical evaluation of the proposed
method as obtained by statistical analysis of the experi-
mental results is given in Table 4. The detection limits
(at the 95% confidence level) of the proposed method for
the mean of five analyses were determined. The calcu-
lated detection limit is 25 ng/mL for chomium using Ti-
complex as a divisor.
T
varying amounts of Cr (VI), Fe (III) and Ti (IV) using the
proposed method and determination of Cr (VI) in some
Portland cement materials.
Composition of mixture (mg·L−1
1DD572 nm
Cr (VI) Fe (II) Ti (IV) Cr (VI), founy
0.005 2.8 7.0 0
SRCium (VIation sing
d Recover
(mg·L−1) (%)
0.005 100.0
0.312 2.8 7.0 0.3130 100.3
0.624 2.8 7.0 0.6233 99.88
0.936 2.8 7.0 0.9345 99.83
NISTM hrom) determinCr (VI) u
Cement using the proposed method diphenyl
Material carbazide
x s 95% CI x
1885a 0.0093 2.0 × 10−6x ± 0.0001 0.0096
1880b 0.0243 1.0 × 10−5x ± 0.0002 0.0234
Nf detns fmple: n umber oerminatioor each sa= 5. x: mean rs:
id
1
S
b
ecovery;
standard deviation, 1DD = the first derivative dived signal. Certified
amounts (mg·L−1), total Cr: SRM 1885a, 0.0806; SRM880b, 0.079.
Table 4. Statistical data for calibration graphs.
Regression equations r Sm
A)
0.9998 2 4 -bs.565 = 6.0 × 103 CCr(VI ×10−------
Stand
0.9999 2 × 10−3 1 × 10−3
ard divisor 7.0 mg·L−1 Ti(IV)
1DD572 = 450 CCr(VI) + 9.0 × 10 -4
Ab = Terid
C), r ssion ffici=
Z as a reagent for the direct spec-
nclusion
nalizarin spectrophotometric method
REFERENCES
[1] H. Sedaira, K. and M. S. Abdel-
s.565= Absorbance at 565 nm, 1DD
= Cr(VI) concentration (m−1
he first d
= Regre
vative divi
coe
ed signal,
ent, S
Cr(VI) g·L m
Standard deviation of slope and Sb= Standard deviation of intercept.
4. Applications
The potential of QIN
trophotometric determination of hexavalent chromium
prompted us to explore the applicability of the method
for determination of soluble hexavalent chromium con-
tent in Portland cement according to TRGS 613 extrac-
tion procedure and the determination of total hexavalent
chromium content in Portland cement in presence of
Fe2O3 and TiO2. The validity of direct spectrophotometry
and first derivative ratio spectra-zero crossing methods
were thoroughly examined. Replicate analysis of ordi-
nary Portland and NIST cement samples SRM 1880b and
1885a were performed (representative spectra are shown
in Figures 2 and 4). Soluble hexavalent chromium con-
centration in direct spectrophotometry was determined
by measuring the absorbance at 565 nm. The total
hexavalent chromium concentration was determined by
measuring 1DD signals at appropriate wavelength. Using
Ti (IV)-QINZ complex as a divisor, Cr (VI) concentra-
tion determined by measuring 1DD signals at 572 nm
(zero-crossing point for ferric complex).
The obtained values for Cr (VI) concentrations in or-
dinary Portland and NIST cement materials by using the
proposed method were found to be in a good agreement
with those obtained by using diphenylcarbazide method
(Tables 2 and 3). In the precision study, five determina-
tions were carried out for each sample. A good precision
of the proposed method was obtained, which allow the
application of the method to the routine analysis of ce-
ment.
5. Co
The proposed qui
for the determination of Cr (VI) content of Portland ce-
ment has proved to be reliable, rapid and accurate. The
method is efficient and precise enough and has the po-
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