Inter-laboratory performance of analytical laboratories and process laboratories of the salt

industry in determining the iodine content of iodated table salt

EE StrydomNutritional Intervention Research Unit

Medical Research Council of South Africa

As investigators we wish to express our sincere gratitude towards the participating laboratories

• Process laboratories of table salt producers (11)– Bergpan & Crystal Salt Works in Vivo– National Salt Ltd in Veldrif and Port Elizabeth– Swartskop Sea Salt in Port Elizabeth– Khoisan in Veldrif– Kalkpoort in Upington– Royal salt (Saltcor, Parow and Salpura, Upington)– Oranje Saltworks in Upington– Oranje River Salt works in Kimberley– Swan salt in Alrode

• Analytical laboratories (4)– Pathcare Upington, Forensic DoH CPT– Microchem Laboratory Services CPT, Cameron CPT

• Iodine is essential for the production of thyroid hormones which control cell metabolism, neuromuscular tissue growth and development, especially the fetal perinatal brain.

• Iodine deficiency (ID) is the world’s most prevalent cause of brain damage where serious iodine deficiency during pregnancy may result in stillbirths, abortions, stunting, goitre, mental impairment and cretinism.

• Constant insufficient dietary iodine results in hypothyroidism (elevated TSH and low FT4) and subsequently palpating or visible Goitre.

WHY IS IODINE AN ESSENTIAL MICRONUTRIENT

SALT IODISATION

• Salt iodisation is the most effective vehicle and long-term strategy to ensure adequate iodine nutrition.

• Compulsory iodation of table salt in South Africa– at 40-60 ppm iodine was introduced in 1995– changed to 35-65 ppm in 2006– Salt is fortified with potassium iodate in South Africa

RATIONALE

Under-iodated salt at <20 ppm Over-iodated>80 ppm

2001: 35% 2001: 2%

2005: 13% 2005: 18%

• Table salt producers with poor quantitative monitoring of salt, lack of equipment, training and technical ability were largely responsible.

• RSA is virtually iodine sufficient but pockets exist where inadequately iodated salt is used in households

National surveys shown that iodated salt at production level were not adequately iodised (40-60 ppm)

AIM

A) To strengthen the capacity of salt producers to produce adequate iodated table salt by • providing a standardised

titration method (manual)• Equipment• Chemicals (AR grade) • Skills necessary for reliable

iodine monitoring of iodated salt on a routine basis.

B) To evaluate the performance of laboratories analysing the iodine content of iodised salt through annual inter-laboratory comparisons

ASSESSMENT AND TRAINING

Process labs Analysts Re-visit & re-training labs

7 (New) 20 5

5 (Existing) 4 2

•Assessed 12 salt producers for the

possibility to determine iodine in salt at

the production site

•One laboratory was shared between two

salt producers

•11 laboratories tested salt samples

during assessment or training course

TRAINING COURSE

•Two-day training courses

•Consequences of inadequate iodine nutrition

•National importance of accurate salt iodisation

•Equipment use

•Verification of instruments and balance

•Reagent preparation and storage

•Calculations and expression of results

•Importance of controls

•Accuracy, precision and % deviation

•Contamination and Safety

•Preventive maintenance

EQUIPMENT

Schilling Bach Nalgene Acrylic Balance with SABS weights

Domestic hotplate and labwareSelf Zero Burettes

EQUIPMENT(provided to newly trained process laboratories)

METHODOLOGY Quality control exercise for inter-laboratory comparison

• Homogenously iodated salt pools of increasing concentrations ranging for 10-100ppm were prepared by the MRC and analysed in triplicate by the participating laboratories – 5 salt pools in 2007– 6 salt pools in 2008 – 8 salt pools in 2009

• Results were compare to MRC iodine values.– % deviation to determine accuracy and agreement– % coefficient variation (CV) to determine repeatability

ANALYTICAL METHODS OF CHOICE

• Manual titration method with Burette– 50g, 25g or 10g acidified salt sample titrated with 0.0125N, 0.01N

or 0.005Nsodium thiosulfate in the presence of potassium iodide • WYD Iodine Checker

– Colorimetric measurement of the blue iodine-starch complex at 570nm of a10g salt sample

• Petentiometry– 25g or 10g salt samples titrated with 0.01N or 0.005N sodium

thiosulfate, repectively

• According to RSA legislation and worldwide , manual titration is the method of choice because of its accuracy, ease of operation and low cost.

EQUIPMENT(used by existing process and analytical laboratories

WYD colorimeter

Bottle Top Burettes Petentiometers (ISE)

ACCEPTABLE ALLOWANCE CRITERIA

Iodine range (PPM) Assigned %CV

Assigned %Deviation

<20 =<10% =<20 to 30%

20 to 70 =<5% =<10%

>70 =<5% =<15%

Salt with high alkalinity or uneven distribution of iodine

due to particle dynamics

=<10% =<20% ( lower values)=<10% ( higher values

Laboratory performance satisfactory level: •For moderately and commendable performance, more than 50% to 80% of all samples (e.g. 3 out of 5 QC samples) should be within acceptable allowance criteria •Unsatisfactory (questionable): <50%•Highly – exceptional : 80 to 100%•Results which deviate more than 40% will be excluded from statical analyses for scientific reports

RESPONSE

Process laboratories

Year 2007 2008 2009

Invited 11 11 11

Responded 10 9 (10*) 8

Results acceptable 9 7 (9**) 6

Salt samples re-analysed 1 2 2

*received results of 2008 in 2010, ** after re-analysing results

Analytical laboratories (were recruited via SANAS website and by word of mouth)

Invited 1 1 8

Accepted invitations 1 1 6

Responded 1 1 3

Results acceptable 1 1 2

Salt samples re-analysed 1

PRECISION OF PARTICIPATING LABS

Year N Mean %CV < 5% CV Highest %CV

2007 65 2.20 94% of samples 12.4

2008 70 2.50 87% of samples 23.3

2009 112 3.90 80% of samples 44.11 (24.8*)

ACCURACY: PROCESS LABORATORIES The % deviation from the target value

Accuracy: Analytical Laboratories (AL)The % deviation from the target value (Nov 2009)

POSSIBLE INTERFERING SUBSTANCES

Chlorine compounds in our water and disinfectants could interfere with reaction resulting in elevated results

Cold tap water14-10-2010 Deionised water Cold tap water

5-11-2010

Chlorine 15ppm Chlorine 15ppm

This 15ppm chlorine tested with the iodometric method could have elevated the iodine value approximately 15ppm

(falsely elevated Iodine approx. 5ppm)

SUMMARY OF RESULTS

• Overall a statistical significant overestimation of accuracy was observed in 2007, 2008 and 2009

• Overall 82%, 76% and 63% of iodine values deviated less than 15 % from target value, in 2007, 2008 and 2009 respectively

• In comparison to the process laboratories, the analytical laboratories underestimated the iodine concentration in 2009 (P=0.04)

• Consisting overestimation could lead to under –iodisation of salt and underestimation to over-iodisation

FINDINGS

Decline in accurate measurements which could result in inadequate

salt iodisation

Shortcomings of process laboratories in the salt industry

•Managerial responsibilities and inadequate lab infrastructure

•Lack of technical abilities and staff retention

•Inferior lab instrumentation and inappropriate cleaning

•Expired and contaminated chemicals and reagents

•Insufficient acidifying and Interfering substances

Outcome of results and interaction with analytical laboratories

•Need to standardize methods commonly used in RSA

•Misunderstanding and interpretations of the AOAC methods

•Lack of participation in inter-laboratory comparisons

CONCLUSION

• In view of the effectiveness of the training, three of the newly trained salt producers significantly improved their laboratory infrastructure and management within one year

• This project effectively standardised the titration method for iodated salt and trained analysts in the South African salt industry, but there is a need for long term compliance of process laboratories and analytical laboratories to ensure accurate iodation of salt.