UV-1900i UV-VIS Spectrophotometer

Quantitative Analysis of Hexavalent Chromium in

Application Water Samples with UV-1900i
News
Qi An Tan, Zhen Hao Lee, Ai Ming Chua
Centre for Application Solutions, Shimadzu (Asia Pacific) Pte Ltd, Singapore

User Benefits
 UV-1900i and LabSolutionsTM UV-Vis software with CHEMetrics Chromate analysis test kit enable easy and accurate colorimetric
measurement of hexavalent chromium with minimal sample and reagent preparation.

 Introduction  Experimental
Chromium (Cr) is a group 6 transition metal that could be found Potassium dichromate (K2Cr2O7) from Merck, Germany was used
naturally in rocks, plants, soil etc. There are two common forms to prepare a 1 ppm Cr(VI) standard solution for analysis.
of chromium that could occur in the environment: the trivalent
form, Cr(III), and hexavalent form, Cr(VI). Cr(III) is an essential After preparing the standard solution, the sample cup was filled
nutrient which contributes to macronutrient metabolism [1]. with 20 mL of the Cr(VI) standard solution. The A-2800 Acidifier
However, Cr(VI), which is mainly produced by industrial Solution from the test kit was added and the mixture was stirred
processes such as electroplating and stainless-steel production, in the cup. The tip of the Vacu-vial ampoule was immersed into
is considered a health hazard. Respiratory exposure of Cr(VI) the sample cup and snapped by pressing against the sample
increases the risk of lung and nasal cancer, while dermal contact cup. The ampoule was then inverted several times and wiped
may induce skin irritation and ulceration. Due to its toxicity, dry. It was left to stand for two minutes before measurement
Cr(VI) is classified as a group 1 carcinogen by the International was performed with the spectrophotometer.
Agency for Research on Cancer (IARC). Therefore, it is critical to
monitor its quantity in various sources such as food, water and The UV-1900i UV-VIS spectrophotometer (Fig. 2) was used for
electronics [2]. photometric measurement. Before sample measurement, the
ampoule blank was used to auto-zero the instrument. Table 1
This application news describes the use of Shimadzu’s UV-1900i lists the instrument and analytical conditions.
and LabSolutions UV-Vis software with CHEMetrics Chromate
Vacu-vials kit for the quantitation of Cr(VI) in water samples
according to the American Public Health Association (APHA)
Standard Method [3].

 CHEMetrics Vacu-vials Kit

CHEMetrics Vacu-vials kit shown in Fig.1 was used for this
analysis. It is a simple and convenient method which allows for
colorimetric determination of analytes without tedious reagent
preparations. Each chromate Vacu-vials test kit includes 30
vacuum-sealed testing ampoules, an A-2800 Acidifier Solution, a
Fig. 2 UV-1900i UV-VIS spectrophotometer
25 mL sample cup, an ampoule blank, and instructions. Each
testing ampoule contains a unit dose of pre-formulated Table 1 Measurement conditions
diphenylcarbazide reagent, which selectively reacts with Cr(VI)
in the acidified water sample to form a red-violet colored Instrument : UV-1900i
complex. The concentration of the complex formed is directly Measurement Mode : Absorbance
proportional to the Cr(VI) concentration. During analysis, the tip Measurement Wavelength : 540 nm
of the ampoule is snapped off in the sample solution to draw it Slit Width : 1.0 nm
into the ampoule. After the chromogenic reaction is completed, Accumulation Time : 0.1 s
the sample–reagent mixture is then directly measured in the
ampoule.
Using the formula provided in the test kit instructions, the
concentration of chromate (CrO4) in ppm can be calculated as
follows:

CrO4 (ppm) = 3.58 (A540) – 0.01 (1)

where A540 is the absorbance of the solution measured at 540

nm.

Fig. 1 CHEMetrics Vacu-vials Kit

Application
News

As the concentration value derived from equation (1) represents To determine the limit of detection (LOD) and limit of
CrO4, a conversion factor is required to obtain the concentration quantitation (LOQ) for the method, the ampoule blank was
in terms of Cr(VI). This can be achieved with the following measured ten times. The results and their standard deviation (σ)
equation: are shown in Table 3.

Cr(VI) (ppm) = 0.45 × CrO4 (ppm) (2) Table 3 Ten Replicate Measurements of Ampoule Blank

No Abs at 540 nm (A540)

These calculations can be automatically performed directly from
measured absorbance values using LabSolutions UV-Vis 1 0.00005
software by setting the formula in the Formula window as 2 -0.00034
shown in Fig. 3.
3 -0.00137
4 -0.00041
5 -0.00021
6 0.00818
7 0.00139
8 0.00003
9 -0.00328
10 -0.00052
σ 0.00300

Based on Table 3, low σ of 0.00300 was obtained. To derive the

LOQ and LOD, equation (1) is first rearranged with A540 on the
left-hand side as follows:

A540 = 0.279 × CrO4 (ppm) + 0.003 (3)

Fig. 3 Formula Settings for CrO4 and Cr(VI) calculation The LOD and LOQ for CrO4 and Cr(VI) are then calculated as
follows:

LOD = 3 σ / m = 3 × 0.00300 / 0.279 = 0.032 ppm (CrO4)

 Results and Discussion = 0.014 ppm [(Cr(VI)]
The results of five replicate measurements of the 1 ppm Cr(VI)
standard are shown in Table 2. The Relative Standard Deviation LOQ = 10 σ / m = 10 × 0.00300 / 0.279 = 0.107 ppm (CrO4)
(RSD) is less than 1 %, which shows good precision of the = 0.048 ppm [Cr(VI)]
analysis. The results are also accurate as a recovery of 105 % was
obtained. where m is the slope of the rearranged equation (3).

Table 2 Five Replicate Measurements of 1 ppm Cr(VI) Standard

No Abs at 540 nm (A540) CrO4 (ppm) Cr(VI) (ppm)  Conclusion

1 0.652 2.32 1.05
The Shimadzu UV-1900i and LabSolutions UV-Vis together with
CHEMetrics Chromate Vacu-vials kit can be used to quantify
2 0.653 2.33 1.05 hexavalent chromium in water accurately and with high
3 0.655 2.33 1.05 precision. The operation is also easy as the sample preparation
procedure is simplified.
4 0.653 2.33 1.05

5 0.653 2.33 1.05

Average 0.653 2.33 1.05  Reference

RSD (%) 0.139 0.139 0.139 1. Dept of Health & Human Services (DHHS), Agency for Toxic
Substances & Disease Registry (ATSDR), Division of
Toxicology & Human Health Sciences (DTHHS), Georgia,
USA (2012). Toxicological Profile for Chromium.
2. DHHS, Centers for Disease Control and Prevention (CDC),
National Institute for Occupational Safety and Health
(NIOSH), Washington DC, USA (2013). Criteria for a
Recommended Standard - Occupational Exposure to
LabSolutions is a trademark of Shimadzu Corporation in Japan and/or Hexavalent Chromium. Publication No. 2013–128.
other countries. 3. APHA Standard Methods for the Examination of Water and
Wastewater (23rd ed) (2017). Method 3500-Cr B.

04-AD-0287-EN First Edition: Jan 2023

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