Analysis of lead in CaCO3 using voltammetry

Calcium compounds are widely distributed in nature occurring as calcium carbonate and include marble, limestone, chalk and dolomite.

Calcium carbonate is a simple compound with the chemical formula CaCO3.

Calcium carbonate has found uses in a whole variety of different industries such as the paint and coatings, paper, plastics, adhesive and building products, and agriculture, as well as being a commonly used raw material that is found for example in household cleaners, cosmetics and toothpaste.

Parameters checked to assess its suitability for use include purity, whiteness, thickness, and homogeneity.

Calcium supplements are tablets, capsules, or liquids containing the mineral calcium from a non-food source and include calcium carbonate, chelated calcium (chemically combined with an other substance) and powdered bone (bonemeal) or dolomite - a mineral. For certain groups of people it may not be possible to get all the calcium that is required from food, especially if that person suffers from a milk allergy, has a lactose intolerance or is currently dieting.

Millions of people around the globe take calcium supplements to reduce the risk of osteoporosis and attain the health benefits of an adequate daily calcium intake.

During recent years, concerns have been issued with regard to the purity of certain calcium supplements and in particular the lead content that they contain.

Lead - a cause for concern? Lead occurs naturally as a mineral and can be found in the environment around us due to its presence in soil, water, and air.

As a consequence lead is found in fruit, dairy, and vegetable products.

In children and babies, low levels of lead can adversely affect neurobehavioral development and cognitive functions.

In adults, lead at high doses can cause an elevated blood pressure, anaemia, and adversely affect the nervous and reproductive systems.

Lead is of particular concern during pregnancy as the mother can pass it on to the unborn baby.

Health concerns were raised a few years ago about the lead content of calcium supplements, particularly from those natural sources such as oyster shell, bonemeal, and dolomite.

The manufacturers of such products have responded by using calcium deposits with lower lead levels, or by chemically refining the calcium carbonate.

Calcium supplements made from bonemeal or dolomite have the highest levels of lead and should be avoided whenever possible.

Limestone or ground calcium carbonate typically contain between 0.6-1.5 parts per million (ppm) of lead, while oyster shells are generally less pure containing approximately 1-5 parts per million of lead.

The United States Pharmacopoeia and Food Chemicals Codex, which establishes standards for food and drug ingredients, both have a tolerance of 3 parts per million of lead for calcium carbonate. The majority of calcium supplements available today in the marketplace contain considerably less lead than the levels set by the Codex, allowing the consumer to buy with confidence. Voltammetry - a brief overview.

Heyrovsky first introduced polarography in 1922.

The term voltammetry is applied to designate the current-voltage measurement obtained at a given electrode.

Polarography is a special case of voltammetry referring to the current-voltage measurement acquired using a dropping mercury electrode with a constant flow of mercury drops. Stripping voltammetry uses the same instrumentation as traditional polarography, but a stationary electrode such as the hanging mercury dropping electrode (HMDE) is used.

The voltammetric measurement is performed on a stationary mercury drop allowing one to achieve considerable increases in sensitivity.

The jump in sensitivity is made possible by electrochemical pre-concentration of the metals in question at the surface of the stationary electrode before the current-voltage curve is recorded.

The recorded current is the redissolution (reoxidation) current of the preconcentrated metal traces.

Voltammetry today represents a refined, clean, simple technique that offers outstanding limits of detection and is now the fastest growing analytical technique for trace analysis.

With the Metrohm Multi Mode Electrode (MME) the mercury is hermetically sealed in the reservoir and suffices for around 200,000 drops, ensuring low laboratory running costs.

The Human need for calcium.

Calcium plays a critical role in building and maintaining strong bones and teeth, and has become one of the most popular dietary supplements over recent years.

During childhood it is necessary to grow a healthy skeleton to support the growing body.

By the time one reaches the age of 20 the bones have usually stopped growing in length, and it is the opinion of medical experts that around this time the bones reach their peak bone mass.

The density of this is partly defined by the extent to which calcium was acquired during the formative childhood stages; the greater the peak bone mass, the less likely one is to suffer from problems associated with fragile bones later in life.

Bone is a living tissue that constantly renews itself and is strong and flexible, but everyday wear and tear causes tiny structural defects.

Specialised cells within the human body are able to remove weakened bone then remodel it by depositing material that calcifies to form new bone.

The process of bone remodelling is a natural one and the cycle is completed every four months in a young, healthy adult.

As humans age the process of bone remodelling becomes less efficient, making calcium nutrition vitally important to avoid a rapid decline in bone mass density. Calcium is imperative to maintain life, and without it we would die.

Almost every cell in the body including those in the heart, nerves, and muscles rely on calcium to function properly.

Calcium is found in the skeleton, in the cells, and in the blood - which transports calcium to the organs and cells where needed.

Calcium is regulated by the body to ensure that a good supply is always available by absorbing calcium directly from the food that has been consumed, and this is the body's preferred method of calcium intake.

Calcium can be also acquired from bones if not enough is available from dietary sources, however the bones become thinner and more fragile as a result.

Calcium leaving the body during the passage of urine can also be slowed down to return some back to the blood stream where it remains available to the organs and cells.

Calcium has been proven to reduce the risk of osteoporosis as well as providing benefits to the cardiovascular system and ensuring that overall health is well established.

Calcium protects the body from lead absorption, as calcium and lead are absorbed at the same site in the intestine - but the site prefers to intake calcium.

The ingested lead passes through the gastrointestinal tract and is excreted from the body. The use of additional calcium supplements has proven to be to be beneficial to menopausal women, because calcium absorption seems to slow down with a decrease in oestrogen.

However it should be stated that an increase in calcium intake is not a substitute for those hormones in preventing the bone loss that can occur during the menopause.

Work carried out by Tel Aviv University suggests that calcium supplements may appear to suppress the localised growth of rectal adenomas in line with appropriate dietary and lifestyle counselling.

These are small benign tumours that are outgrowths of tissue lining the walls of the lower bowel.

Cancer experts are of the opinion that colorectal cancers arise from these non-malignant growths.

The studies conducted suggest that those patients who take calcium supplements showed a reduction in the tissue biopsies measured by pathologists.

This seems to highlight the positive effects of calcium, when used in conjunction with a low fat diet, upon the limited sample of people surveyed.

Calcium is plentiful in milk, cheese, and yoghurt, and it is beneficial to consume these products on a daily basis.

As one ages, calcium becomes less efficiently absorbed so it may be necessary for certain individuals to increase their calcium intake with the use of supplements. Calcium supplements are best taken with meals as the acid secreted by the stomach during digestion enhances their absorption.

Vitamin D helps the human body to use calcium and is made in the skin when one is subjected to sunlight, as well as being found naturally in foods such as seafood, eggs, and liver. Calcium supplements acquired from reputable manufacturers are made with refined, high quality pharmaceutical grade ingredients with trace levels of lead well below the 3 parts per million standard.

As calcium carbonate is more concentrated than other calcium supplements, it contains more of the elemental calcium that the body uses and is less expensive than other types, often being the preferred choice of supplement.

No adverse effects have been observed in people who consume above the recommended daily intake of calcium (2500 milligrams per day).

It was formerly suspected that a high dietary intake of calcium increased the risk of kidney stones, but this is now believed to be an incorrect supposition.

Method for analysis of lead in calcium carbonate.

0.5g of calcium carbonate was weighed into a Pyrex beaker.

2ml of concentrated hydrochloric acid was carefully added, and after the end of carbon dioxide formation, a little deionised water was added to bulk up the solution.

The solution was allowed to cool and the contents transferred quantitatively to a 50ml volumetric flask before being made up to the mark with deionised water.

10ml of deionised water, 1ml of prepared sample, and 1ml of acetate buffer were added to the reaction vessel in the Metrohm 757 VA Computrace.

The role of the electrolyte and additional solutions in voltammetry is crucial.

Many determinations are pH-dependent and the electrolyte can increase the conductivity and selectivity of the solution.

The solution was then degassed with nitrogen for a period of five minutes to remove the electrochemically active oxygen, before the lead content determined with two standard additions using the HMDE. The HMDE is an electrode mode of the MME.

Four mercury drops of a defined size are formed in succession at the MME, and the last drop remains suspended on the end of the capillary.

The entire voltage sweep is then performed on the single stationary drop. The analysis produced a result of approximately 0.8 parts per million of lead present in the sample of calcium carbonate. Conclusion.

It is thought that for many people the benefits of calcium supplements far outweigh any theoretical concerns about the low levels of lead that have been found in certain brands of calcium supplements.

A large proportion of the population does not get enough calcium from their dietary intake, and are recommended to take additional calcium supplements to maintain optimal health.

The levels of lead in calcium supplements have shown a remarkable decline over the past ten years.

A study conducted in 1993 concluded that most of the 70 brands tested had measurable quantities of lead, while a similar survey carried out in 2000 showed that two-thirds of the samples analysed were well below the standard set by the Food and Drug Administration.

It is however recommended that consumers acquire products that are labelled for their lead content, as there is still some variance between the actual quantities of lead present in the different brands commercially available today.

Due to the health concerns that have arisen in the past, it is important to constantly monitor the lead contained within calcium supplements to ensure strict quality control during the manufacturing processes and to maintain public confidence.

Voltammetry is an increasingly popular technique which, in many instances, offers unrivalled detection limits even when compared to vastly more expensive analytical techniques.

Voltammetry uses standard addition as a means of calibration and quantification, and the advantage of doing so is that any matrix effects present in the sample are taken into account.

Voltammetry requires no specialist laboratory infrastructure like expensive fume extraction: all that is required is a sturdy bench top on which to mount the instrument, and a regulated flow of an inert gas.

The running and maintenance costs of voltammetry are minimal, ensuring a cost effective analytical solution to those organisations interested in analysing the lead content contained within calcium carbonate or other calcium supplements.

The following internet sites were used extensively as references and can be used to obtain further information: www.berkeleywellness.com www.calciuminfo.com www.caribvoice.org www.metrohm.ch www.omya.com www.osteoporosis.ca