EXPERIMENTAL
NOTES
FIAS 100 with PinAAcle™ 900T AAS
AAS-PHARMA
Author
Dr. Pravin Konde
Technical Specialist – Inorganic
Customer Knowledge Centre for Analytical Sciences
PerkinElmer (India) Pvt. Ltd.
Thane – 400 615 India.
Email: [email protected]
Analysis of the “Big Four”- toxic elements,
Pb, Cd, Hg and As in the Ayurvedic
Herbal Tonic - Chyawanprash using FIAS
100 coupled to a PinAAcle™ 900T AAS
Abstract
Chyawanprash is a comprehensive herbal tonic with multiple health benefits, prepared
according to an ancient Ayurvedic formula. It is used by people around the world today,
and especially in India, it is a proven energizer, immunity booster and pre-emptive tonic.
As per USP and other regulatory bodies, such products needs to be monitored for heavy
metals like Arsenic, Mercury, Lead and Cadmium which are considered as the most toxic
elemental impurities in such medicines. The analysis of these elements in this matrix is
considered challenging due to the stringent low limits set by the regulations and the
volatile nature of some of these elements.
The determination of As and Hg was perfomed using HG-AAS with a PerkinElmer FIAS-100
system connected to a Perkinelmer PinAAcleTM 900T Atomic Absorption Spectrophotometer
(AAS). On the other hand, the analyses of Cd and Pb were carried out using GFAAS. tIn
this case the same PinAAcle 900T AAS was utilised in the graphite furnance mode using
a transversly heated graphite furnace atomizer (THGA) equipped with a longitudanal
Zeeman background correction and a tube view colour furnace-camera which eases the
auto sampler tip allignment. Both systems are controlled by the intuitive WinLab32TM for
AA software, which features all the tools to analyze samples, report and archive data and
ensure regulatory compliance. PerkinElmer high-energy electrodeless discharge lamps (EDL)
were used as the light sources for all four elements analyzed.
Sample digestion
0.2 g of a Chyawanprash sample was treated with mixture
of 5 ml HNO3, 2 ml HCl and 1 ml 30% H2O2 in a PerkinElmer
Multiwave-3000TM microwave digestion system (MWDS). All
acids and reagents used for digestion were of SuprapurTM grade
(Merck). The digestion program for this sample is given below.
After digestion, the solution was made up to 25 ml in a graduated
plastic bottle with 18 MΩ deionised water.
Microwave Digestion Program
Instrumental Conditions (Cd and Pb by Graphite AAS)
Optimized Experimental Conditions for PinAAcle TM 900T
Element
Cd
Pb
Wavelength (nm)
228.80
283.31
Slit Width (nm)
0.7
Signal Type
AA-BG
Measurement
Peak Area
Lamp Type
EDL
*Matrix Modifier
Pd + Mg-Nitrate
Injection volume (µL)
20
Step
Power (W)
Ramp (Min)
Hold (Min)
Fan
Gas
Argon
1
600
10
10
1
Graphite Tube
Std THGA
2
1200
10
10
1
Calibration Equation
Linear, through zero
3
0
-
15
3
No of Standards
3
Standards Used
0.5, 1, 2 µg/L
P-ramp: 0.5 bar/s, IR : 220°C, P: 60 bar
Standard and sample preparation for Cd and Pb
For the analysis of Cd, calibration standards of 0.5, 1 and 2 ppb
were prepared from a 1000 ppm Cd standard. Whereas for Pb
analysis, 12.5, 25 and 50 ppb calibration standards were prepared
from a 1000 ppm Pb standard. All above dilutions were carried
out with 2% Suprapure grade HNO3 solution in deionized water,
which was also used as a calibration blank.
A duplicate of the final sample solution was spiked with 0.5 ppb
(for Cd) and 25 ppb (for Pb) using respective standards to check
the accuracy of the methods.
Standard and sample preparation for As and Hg
For analysis of Hg and As, a common stock solution of 500 ppb
concentration for both elements was prepared from PerkinElmer
1000 ppm respective element standards.
For preparation of calibration blank and standards, 0, 0.5, 1 and
1.5 ml of the 500 ppb stock solution were taken in four different
50 ml plastic vials to which 5 ml Conc. HCl (30%, AR grade) and
5 ml of mixture (3% KI - 5% Ascorbic acid, Both AR grade) were
added. Subsequently, the flasks contaning these mixtures were
allowed to stand for 30 minutes, to ensure complete reduction
of As+5 species (if present) to As+3 species. Finally all flasks were
filled up to the mark with deionized water. This gave calibration
standards of 0, 5, 10 and 15 ppb respectively for both elements.
For the sample, 10 ml of the sample solution was taken in a 50
ml volumetric flask and the same reduction step as above was
followed before dilution. The sample was then analysed under the
experimental conditions shown in the table below.
In similar way a spiked sample (5 ppb of both, As and Hg) was
also prepared and checked for spike recovery.
12.5, 25 and 50 µg/L
*Matrix modifier was prepared by diluting mixture of 0.2 ml of stock solution (PE
part number B0190634) and 0.2 ml of stock solution (PE part number B0190635)
to 10 ml with deionised water. 5 µL of this solution was added in the blank, standards
and samples.
The furnace temperature programs used for Cd and Pb analysis were as follows in the
table below:
Step
1
Temp (°C )
For ‘Cd’
For ‘Pb’
Ramp
Time
(sec)
110
110
1
Hold
Time
(sec)
Internal
Flow (ml/
min)
Gas type
30
250
Normal
2
130
130
15
30
250
Normal
3
500
850
10
20
250
Normal
4
1500
1600
0
5
0
Normal
5
2450
2450
1
3
250
Normal
Read step – 4, Injection temp – 20°C
Instrumental Conditions (As and Hg by FIAS-Flame AAS)
Optimized Experimental Conditions for FIAS 100 and PinAAcle TM 900T
Element
As
Hg
Wavelength (nm)
193.70
253.65
Slit Width (nm)
0.7
Signal Type
AA
Measurement
Peak Height
Read Time
30 seconds
Replicates
2
Air Flow (L/min)
7
0
Acetylene Flow (L/min)
1.8
0
Lamp Type
EDL
Standard/Sample volume in reaction flask (µL)
500
Reductant solution used
0.2% (W/V) NaBH4
Carrier Solution
3% (V/V) HCl
Carrier Gas
Argon
Carrier Gas – Flow rate
2.5-3.5 bar
Calibration Equation
Linear, through zero
No. of Standards
3
Standards Used
5, 10,15 µg/L
Analytical Results & Conclusions
Note:
1. 0.2% (W/V) NaBH4 was prepared in 0.05% (W/V) NaOH.
2. For the analysis of mercury (Hg), flame is not required.
3. Mercury sample and standard solutions were stabilized by
addition of 1-2 drops of 5% KMnO4 solution.
The flow injection program with FIAS 100 used for As and Hg
analysis is as follows:
Step Prefill
Time (sec)
Pump 1 Speed (rpm)
Valve
15
120
Fill
1
10
120
Fill
2
15
120
Inject, Read
3
0
0
Fill
Calibrations graphs: Calibration graphs obtained for all four
elements are shown below. Correlation coefficients obtained for
Cd, Pb, As and Hg were 0.9999 and 0.9995, 0.9991 and 0.9996
respectively showing excellent linearity.
Sr.
No
Element
Results (ppb)
Spike
results
(ppb)
% Recovery
Sample Results
ppm or (µg/g)
1
Cd
0.001
0.515
102.8
ND
2
Pb
0.004
24.825
99.29
ND
3
As
0.028
4.855
96.54
ND
4
Hg
0.176
5.103
98.54
0.114
Conclusions
This results confirmed that the determination of Cd, Pb,
As and Hg after acid solubilisation of Chyawanprash by
microwave digestion can be performed by Graphite Furnace
AAS and Flow Injection-Hydride Generation AAS. PinAAcle™
900T AAS with FIAS 100 is suitable for such applications
involving measurements of these elements at trace levels.