Summary

Food and beverage laboratories have to determine the phosphate (and sometimes citrate) concentration in soft drinks. Because of the large number of samples they have to analyse it is necessary to have a fast analysis. To speed up the elution of the normally late eluting citrate ions, a higher concentration of NaOH in the eluent is used.

Sample

Commercially available soft drink which contained phosphate as well as citrate.

This sample was diluted 10x before injection. This dilution was made 4 consecutive times and injected into the system.

Reagents

Eluent: 25.0mM NaOH / 3.0 mM Na₂CO₃

Suppressor solutions:
Regenerant: 100 mM H₂SO₄
Rinsing solution: UP water (18 MΩ)

Standards (in ppm)

level	1	2	3	4	5
PO43-	10	30	50	70	100
C6H5O73-	10	30	50	70	100

Apparatus and Accessories

881 Compact IC Pro Anions + MCS	2.881.0030
858 ProfIC sample processor – Pump	2.858.0020
METROSEP A supp 15 – 150	6.1030.420
METROSEP A supp 15 guard	6.1030.500

Sample Preparation

• A 20 μL loop was used to pass the standards and samples to the column.
• Calibration standards were prepared with UP water (18 MΩ).
• The calibration standards were made as dilutions from one parent standard. The following dilutions were used: 1:10, 3:10, 1:2, 7:10, 1:1.
• All samples were passed through an ultrafiltration cell (with a 0.2μm filter).
• The sample was diluted 10x to fit it into the calibration range.

Analysis

All samples were injected automaticly with an 858 Professional IC Sample processor with ultrafiltration.

To speed up the elution of the normally late eluting citrate ions, a higher concentration of NaOH in the eluent was used.

Calculation

All calculations were performed using MagIC Net 1.1 software.

Parameters

Data source:	Conductivity detector 1
Channel:	Conductivity
Recording time:	15 min
Flow:	0.8 mL/min
Max. Pressure:	15 MPa
Temp. coefficient:	2.3 %/°C
Column Thermostat:	45°C
Loop:	20μL
Rack:	6.2041.440
Special Position 1:	149
Special Position 2:	150
Special Position 3:	151
Work Position:	125 mm

Calibration results

	Correlation coefficient	% RSD
PO43-	0.999993	0.304
C6H5O73-	0.999532	2.456

Results [ppm]

Sample	Inj. 1	Inj. 2	Inj. 3	Inj. 4
Phosphate	557.3	556.3	549.1	546.5
Citrate	333.4	335.3	333.6	332.5

Comments
Calibration curves and chromatograms with peak tables.

Date
Tuesday, 2008-06-17

Name
Steven Broeckx
Metrohm Belgium

Calibration Info

Function:	A = 3.01930E-3X Q + 3.54739E-7X Q2
Relative standard deviation:	0.304148 %
Correlation coefficient	0.999993

 

Function:	A = 2.47936E-3X Q + 7.52988E-8X Q2
Relative standard deviation:	2.456459 %
Correlation coefficient	0.999532

 

Chromatograms with peak tables

Sample data
Ident	AFSCA Phosphate – Std 3
Sample type	Standard 3
Determination start	2008-06-17 09:26:41 UTC+2
Method	AFSCA 2008 Phosphate
Operator	Steven Broeckx
Sample data
Data source	Conductivity detector 1 (881 Comapact IC)
Channel	Conductivity
Recording Time	15.0 min
Integration	Automatically
Column Type	Metrosep A Supp 15 150/4.0
Eluent composition	AFSCA Test eluent 2 - 25.0mM NaCH, 3.0 mM Na2CO3
Flow	0,800 mL/min
Pressure	10.55 MPa
Temperature	45.0 °C

Peak number	Rentention Time Min	Area (µS/cm) x min	Height µS/cm	Concentration ppm	Component Name
1	3.295	0.0102	0.048	invalid	Chloride
2	6.757	3.3614	7.458	49.830	Phosphate
3	9.617	2.6408	3.745	51.632	Citrate

 

Sample data
Ident	365 Cola light lemon (1:10 verdund)
Sample type	Sample
Determination start	2008-06-17 09:45:05 UTC+2
Method	AFSCA 2008 Phosphate
Operator	Steven Broeckx
Sample data
Data source	Conductivity detector 1 (881 Comapact IC)
Channel	Conductivity
Recording Time	15.0 min
Integration	Automatically
Column Type	Metrosep A Supp 15 150/4.0
Eluent composition	AFSCA Test eluent 2 - 25.0mM NaCH, 3.0 mM Na2CO3
Flow	0,800 mL/min
Pressure	10.33 MPa
Temperature	45.0 ˚C

Peak number	Rentention Time Min	Area (µS/cm) x min	Height µS/cm	Concentration ppm	Component Name
1	2.927	0.1341	0.591	invalid	Fluoride
2	3.300	0.6905	3.979	invalid	Chloride
3	4.082	9.2929	31.461	invalid
4	4.823	0.5541	1.350	invalid	Nitrate
5	6.748	3.7984	8.566	556.305	Phosphate
6	9.683	1.6964	2.538	335.280	Citrate