Urinary fluoride testing is an important means of evaluating human fluoride exposure levels, widely used in occupational health monitoring, screening for endemic fluorosis, and environmental toxicology research. The quality of urine sample collection directly affects the accuracy of test results. This article will systematically explain scientific sample retention methods from the aspects of pre sampling preparation, sample retention standards, storage and transportation.

　　1、 Preparation before sampling: eliminate interference factors

1. Time selection

It is recommended to collect morning urine (first urination in the morning) as its fluoride concentration is stable and can reflect the fluoride metabolism status at night. To evaluate 24-hour fluoride exposure, preservatives (such as toluene) should be used to collect urine throughout the day and record the total urine volume.

2. Container selection

Use polyethylene plastic or glass bottles to avoid fluoride ion adsorption caused by metal containers. The container needs to be cleaned with deionized water in advance and dried at 60 ℃ to ensure no fluoride contamination. Some testing institutions provide dedicated sampling bottles containing preservatives (such as boric acid) that can be used directly.

3. Preparation of subjects

Avoid high fluoride diets (such as tea, seafood, and fluoride toothpaste) 24 hours before sampling.

Occupational exposure groups should be removed from the work environment for at least 12 hours before sampling to eliminate the effects of acute exposure.

Women should avoid menstrual periods to prevent blood contamination of urine.

　　2、 Sample retention standard: Ensure sample representativeness

1. Collection method

After cleaning the external genitalia, discard the anterior segment urine (about 50ml) and collect 10-50ml of middle segment urine (for children, it may be reduced).

If preservatives are used, they should be added in a 1:100 ratio (such as 50ml of urine mixed with 0.5ml of toluene) to prevent bacteria from decomposing urea and causing changes in fluoride concentration.

2. Information recording

On the label of the sampling bottle, indicate the subject's name, gender, age, sampling date, time, and exposure history (such as whether they have been exposed to fluoride industrial raw materials). Occupational exposure groups need to additionally record their job type, length of service, and protective measures.

　　3、 Preservation and transportation: maintaining sample stability

1.短期保存

Immediately seal the bottle cap after collection and store at 4 ℃ for 48 hours. If the storage time needs to be extended, it needs to be frozen (-20 ℃), but repeated freeze-thaw cycles can cause fluoride ion precipitation, affecting the results.

2. Transportation requirements

Use insulated foam box and ice bag for transportation to ensure that the sample temperature is maintained at 2-8 ℃. Avoid direct sunlight or severe vibrations to prevent container rupture or urine leakage.

3. Inspection deadline

It is recommended to deliver the samples to the laboratory within 24 hours after sampling. Samples that are overdue will need to be collected again. Occupational health examination institutions usually provide on-site sampling services to shorten transportation time.

　　4、 Special scenario handling

1. Sampling for infants and young children: Use specialized urine bags to avoid skin contact contamination.

2. Coma patients: Collecting urine through a catheter requires strict aseptic procedures.

3. Batch sampling: For environmental epidemiological investigations, random grouping and blank control should be set up to exclude background fluoride interference.

Scientific sample retention is the cornerstone of urine fluoride detection. By standardizing the sampling process and strict quality control, errors can be minimized to the greatest extent possible, providing reliable basis for fluoride exposure assessment, disease diagnosis, and public health intervention.