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Determination of Arsenic Species in Apple Juice by
LC-ICP-MS Analysis
Arsenic species can be analyzed using an LC-ICP-MS system.
Enables the safety level of arsenic in food to be evaluated.
Using a method package for analyzing arsenic species eliminates the need to register analytical conditions, etc.
Sachiko Wakasugi and Tadashi Taniguchi
Inductively Coupled Plasma Mass Spectrometer ICPMS-2030
Introduction
The natural environment contains many kinds of substances.
These include hazardous substances such as arsenic. However,
arsenic exists in a variety of forms, and the toxicity differs
depending on the form. Generally, arsenite is more toxic than
arsenate, and organic arsenic is less toxic than inorganic arsenic.
It is difficult to completely avoid arsenic in the natural
environment since it is also contained in drinking water and
agricultural/livestock products. The foods we eat also might
contain various types of arsenic. U.S. Food and Drug
Administration (FDA) sets action levels when a level of a
contaminant is unavoidable, to inform industry on the level of
contamination above which the FDA may regard certain foods
as adulterated.
1)
For these reasons, various surveys and studies
on arsenic in food products are being conducted around the
world.
One method for analyzing trace quantities of arsenic with high
sensitivity is ICP-MS. However, although ICP-MS can measure
the total concentration of arsenic, it cannot discriminate
between different forms of the element. While determining the
total concentration of arsenic is important, it is also important
to determine the concentrations of specific forms.
The arsenic species can be separated using a liquid
chromatograph (LC). By connecting the LC unit to an ICP-MS on-
line, the arsenic species can be analyzed with high sensitivity.
This article describes an example of analyzing the arsenic
species contained in apple juice using an LC-ICP-MS.
Sample
Commercially available apple juice
Sample Pretreatment
A 2 mL sample was measured, 0.1 mL of 100 mmol/L phosphoric
acid was added, and the mixture was diluted with 0.15 mol/L
nitric acid solution to make 10 mL.
Calibration Curve Sample
0.1 mL of 100 mmol/L phosphoric acid was added to accurately
measure standard samples of arsenite (As III), arsenate (As V),
monomethylarsonic acid (MMA), and dimethylarsinic acid
(DMA) and the mixtures were diluted with 0.15 mol/L nitric acid
solution to make 10 mL.
Mobile Phase Preparation
10 g of methanol was measured and placed in a 1-L bottle. Then
about 900 mL of purified water, 1 mL of 98 wt% formic acid, and
1 mL of a 25 % tetramethylammonium hydroxide solution were
added and diluted with purified water to make 1 L.
Column Stabilizer Solution
About 900 mL of purified water was added to a 1-L bottle, and
then 0.85 mL of 98 wt% formic acid was added. 0.115 mL of
85 wt% phosphoric acid was added, and the mixture was
diluted with purified water to make 1 L.
Analytical Conditions
Samples were analyzed with an LC-ICP-MS system, which
consisted of an ICPMS-2030 inductively coupled plasma mass
spectrometer connected to a Nexera series HPLC system (Fig. 1).
Using LabSolutions™ ICPMS TRM software, the ICPMS-2030
system can control Shimadzu LC units. This enables everything
from sample injection to chromatogram analysis to be
performed via a single software program.
The analytical conditions used for analysis were those included
in the LC-ICP-MS Method Package for Arsenic Speciation
Analysis Type 2.
For new columns, stable analysis is enabled by introducing a
column stabilizer solution through the column for at least 2
hours.
Table 1 shows the analytical conditions for LC, and Table 2
shows the analytical conditions for ICP-MS.
Fig. 1 LC-ICP-MS System Components
Instrument: ICPMS-2030
RF Power: 1.2 kW
Plasma Gas Flowrate: 9 L/min
Auxiliary Gas Flowrate: 1.1 L/min
Carrier Gas Flowrate: 0.7 L/min
Nebulizer: Nebulizer 07
Chamber: Cyclone Chamber (electronically cooled)
Plasma Torch: Mini-Torch
Collision Gas: He
Instrument: Nexera Series
Column: Sigma-Aldrich Discovery HS F5
(250 mm × 4.6 mm I.D., 5 µm)
Guard Column: Shim-pack™ GIST (G) [Metal free]
(10 mm × 3.0 mm I.D., 5 µm)
Mobile Phase: 0.1 % Formic acid
(including 1 % methanol and 0.025 %
tetramethylammonium hydroxide solutions)
Mobile Phase Flowrate: 0.75 mL/min
Column Oven Temp.: 40 °C
Injection Volume: 10 µL
Analysis Time per Sample: 6 min
Table 1 LC Analytical Conditions
Table 2 ICP-MS Analytical Conditions
ICPMS-2030 Nexera™ Series
