Study on production and utilization of a reference material for determination of multi-residue pesticides in tomato matrix

doi:10.21203/rs.3.rs-3899330/v1

Controlling pesticide residues in food has been always a concern globally. It is recommended to use certified reference materials (CRM) or reference materials (RM) in pesticide analysis to validate analytical methods and assess the quality of the measurement results. A comprehensive study on production, storage, transportation, and utilization of an RM of pesticide residues (Difenoconazole, Imidacloprid, Acetamiprid, Indoxacarb, Profenofos, Buprofezin) in tomato was conducted. After comparing two production processes of freezing and freeze-drying, the freeze-drying production process was concluded to be superior. The RM production and characterization process is in accordance with ISO 17034:2016 and ISO guide 35:2017-08. The concentrations of 6 pesticides in the RM are around their Codex maximum residue limits. At a storage temperature of 4°C, freeze-dried RM are predicted to be stable for all six pesticides for at least 548 days, while at a temperature of − 20°C, the shelf life was at least 696 days.

Reference material

tomato

pesticide residue

LC-MS/MS

proficiency testing

Pesticides are widely used in agriculture and considered to be the most cost-effective way to prevent or control pests, weeds, other plant pathogens, and maintain high crop yield. However, the pesticide residues in food and environment have raised concerns on human health due to their potential acute and chronic toxicity. On the other hand, tomato is grown and used as food worldwide. Global tomato production has risen from 177.3 million tons in 2016 to 186.8 million tons in 2020 [1]. Given the increasing amount of tomato produced in the global market, there have been groundswell concerns about the pesticide residue. Difenoconazole, Imidacloprid, Acetamiprid, Indoxacarb, Profenofos, Buprofezin are some common plant protection chemicals used in tomato crops, and their maximum residue limits (MRL) have been prescribed. According to European Union, the MRLs of Difenoconazole, Imidacloprid, Indoxacarb, Profenofos, Acetamiprid and Buprofezin are 2, 0.3, 0.5, 10, 0.5, 0.01 mg/kg, respectively. For Codex regulation, the MRLs for pesticides in tomatoes are as follows: Difenoconazole − 2 mg/kg, Imidacloprid − 0.5 mg/kg, Acetamiprid − 0.15 mg/kg, Indoxacarb − 0.5 mg/kg, Profenofos − 10 mg/kg, Buprofezin − 1 mg/kg.

Reliable analytical methods for the identification and quantification of pesticide residues in tomatoes has been developed mainly base on liquid chromatography - mass spectrometry [2–6] and gas chromatography - mass spectrometry [7–11]. The amount of sample for one analysis is from 1,0 to 50,0 g [11–14]. The well-known sample preparation method for pesticide analysis is QuEChERS [3, 5, 6, 11]. To validate analytical methods and assess the quality of the measurement results, it is recommended to use certified reference materials (CRM) or reference materials (RM) in pesticide residues analysis.

Previously, some publications have researched on production of CRM or RM for pesticides in food matrix such as carrot/potato matrix [15], apple [16], cabbage [17], tea [13], olive oil [18], passion-flower fruits [19], grapes [20], cucumber [21], tomato [22, 23]. Storage condition especially temperature is highly affect shelf life the RM. Most vegetables and fruits matrix RM are stored at − 20°C or lower, but olive oil can be stored at 4°C or higher temperature. The RM of pesticides in food are various include frozen [13, 15, 16, 19, 23], freeze dry after spiking pesticide [15, 17, 21], freeze dry before spiking pesticides [21]. These studies mainly focused on production and shelf life of RM or proficiency testing items, while stability of RM in utilization such as transportation and after open the RM bottle has not been pay attention.

The primary aim of this study is to focus on productions of a reference materials for determination of multi-residue pesticides in tomato matrix in accordance with ISO 17034:2016 (1), characterization the RM according to ISO guide 35:2017-08 (2), study stability of the RM (3) in long term stability, transportation and after open the bottle. We had compared two types of RM: frozen tomato and freeze dried tomato. The optimized protocol to produce an RM for pesticide residues in tomato would finally reported in this article.

Chemicals and reagents

Standards of six pesticides Indoxacarb, Difenconozole, Buprofezin, Imidacloprid, Profenofos, Acetamiprid were purchased from LGC standard, Dr.Ehrenstofer (Table 1). Acetonitrile, methanol (gradient grade for liquid chromatography), acetic acid (glacial), magnesium sulfate anhydrous, sodium acetate anhydrous were purchased from Merck, Germany. Primary secondary amine powder (analytical grade) from Agilent and purified water (Milli–Q Integral 3; Millipore, Billerica, MA) was used in this research for sample preparation process.

Table 1

Purity of pesticide standards
No.	Name	Certified Purity % (g/g)	Certified expanded uncertainty % (g/g)
1	Difenoconazole	99.58	0.91
2	Imidacloprid	98.55	1.07
3	Indoxacarb	97.37	1.34
4	Profenofos	95.80	1.97
5	Acetamiprid	99.75	0.91
6	Buprofezin	98.6	1.3

Equipment

A multifunction blender, a small blender, a deep freezer (MDF-U700VX-PB, Panasonic), a fridge, a freeze drier (MODULYOD) with some basic tools of laboratory were used for production of the RM. Pesticide residues analysis was performed by High performance liquid chromatography system 20 AXL of Shimadzu and ABI 5500 QQQ Aplied Biosystem spectrometer. The separation was conducted by Xbrigde C18 (100 mm x 4.6 mm; 2.5 µm) column.

Preparation of tomato reference material candidates

The RM was produced from fresh ripe tomatoes. All of the tools and equipment in the procedure were cleaned and dried before use. Total 25 kg of selected tomatoes were rinsed under distilled water then peeled, chopped, pureed and filtered through a sieve. A mixture of pesticides was prepared at concentration of 1.2 g/L Indoxacarb, 1.4 g/L Difenconozole, 2.0 g/L Buprofezin, 1.0 g/L Imidacloprid, 20.0 g/L Profenofos, 0.4 g/L Acetamiprid in distilled water. Each portion of 0.5 kg tomato puree was added 250 µL mixture of pesticides, then mixed by a blender. The added analyte content was close to the corresponding MRLs of the substances in tomato matrix. After that, all of the spiked tomato puree was gathered and homogenized in a multi-function blender for 20 minutes. The tomato puree candidate material was bottled in 100 mL HDPE jars.

The tomato puree jars were divided into 2 groups: group 1-frozen and group 2-freeze dried tomato. Group 1 was divided into 2 subgroups: group 1–1 was stored at − 20°C, group 1–2 was stored at − 80°C. The group 2-freeze dried was firstly placed in a deep freezer for 2 days at − 80°C, then freeze dried for 2 days at − 40°C. Before and after freeze dry process, six bottles of group 3 were weighed to calculated the mass lost during the freeze dry process. The group 2 freeze dried RM candidate were divided into 2 subgroups: group 2 − 1 was stored at 4°C; group 2–2 was stored at − 20°C. Groups of samples were presented in Fig. 1. All types of tomato bottle were sealed before being stored.

Analytical method for quantification of multi-residues pesticide in tomato

Multi-residues pesticide in tomato was analyzed by a validated LC-MS/MS method that refereed to AOAC Official Method 2007.01 [24] and CEN Method 15662:2018 [25]. This method was conducted at National Institute for Food Control (NIFC, Vietnam) that has been accredited according to ISO/IEC 17025:2017 [26]. Generally, a portion of 10 g homogenized sample was extracted and cleaned by QuEChERS method then analyzed by liquid chromatography tandem mass spectrometer (LC-MS/MS). In this research, the tomato puree was weighed 10.0 g, whereas tomato freeze dried sample was taken 0.5 g and reconstituted with 10 mL of distilled water for each analysis. The extract solutions of samples were diluted 5 times before being analyzed in the LC-MS/MS system.

Homogeneity assessment

CRM or RM are prepared in batches. It is important to assess the homogeneity that refer to variation of property values between separate units and variation within a unit. According to ISO guide 35:2017, the minimum number of samples taken for homogeneity study is given by:

${N}_{min}=\text{max}(10, \sqrt[3]{{N}_{prod}}$ )

In which, ${N}_{prod}$ is the total number of RM candidate products. Therefore, in our case, ten samples were randomly taken for homogeneity study, and they were analyzed in duplicate for each pesticide. Right after being produced, ten bottles of frozen candidate material (group 1) were randomly selected to analyzed in duplicate for homogeneity assessment that was processed according to ISO/IEC 17034:2017 [27] and ISO guide 35:2017-08 [28]. Similarly, for group 2, after freeze dry and sealing process, ten bottles of freeze dried candidate material were randomly selected for homogeneity assessment. Each sample was analyzed concentration of spiked pesticides twice. The data collected was checked for statistically difference by ANOVA-one way at α = 0.05 (Section B.2.4 ISO 13528:2022).

The uncertainty of certified value is included uncertainty of homogeneity assessment. The uncertainty ${u}_{hom}$associated with heterogeneity is given by the formula:

$${u}_{hom}=\sqrt{{u}_{bb}^{2}+{u}_{wb}^{2}}$$

In which, ${u}_{bb}$ is the between unit standard deviation and ${u}_{wb}$ is between sub-unit standard deviation.

Stability assessment

To monitor long term stability, the candidate RM in each group were tested pesticides concentration monthly. Five bottles represented for each group were randomly selected and analyzed in duplicate every month. The data were collected from 6 points: 5, 41, 81, 101, 143, 173 days (from manufacture date), then linear models were fitted:

y = b ₁ t + b ₀.

Where:

$${\varvec{b}}_{1}= \frac{\sum _{\varvec{i}=1}^{\varvec{n}}\left({\varvec{t}}_{\varvec{i}}- \stackrel{-}{\varvec{t}}\right)({\varvec{y}}_{\varvec{i}}- \stackrel{-}{\varvec{y}})}{\sum _{\varvec{i}=1}^{\varvec{n}}{({\varvec{t}}_{\varvec{i}}- \stackrel{-}{\varvec{t}})}^{2}}$$

$${\varvec{b}}_{0}= \stackrel{-}{\varvec{y}}- {\varvec{b}}_{1}\stackrel{-}{\varvec{x}}$$

The acceptable level for 6 pesticides was set at 10% of the assigned value that is the average of 10 bottles taking for homogeneity assessment (the initial point). The lower limit was set at assigned value minus 10%; the upper limit was set at assigned value plus 10%. For estimation shelf life (${\varvec{t}}_{\varvec{s}\varvec{h}\varvec{e}\varvec{l}\varvec{f} \varvec{l}\varvec{i}\varvec{f}\varvec{e}}$), 95% confidence interval for future value is taken account, and choose the shortest time at which one of the confidence limits intersects the upper or lower limit. The uncertainty due to instability during storage (u_lts) was calculated by:

$${\mathbf{u}}_{\mathbf{l}\mathbf{t}\mathbf{s}}= {\mathbf{s}}_{{\mathbf{b}}_{1}}\times {\varvec{t}}_{\varvec{s}\varvec{h}\varvec{e}\varvec{l}\varvec{f} \varvec{l}\varvec{i}\varvec{f}\varvec{e}}$$

$${\varvec{s}}_{{(\varvec{b}}_{1})}= \frac{\varvec{s}}{\sqrt{\sum _{\varvec{i}=1}^{\varvec{n}}{({\varvec{t}}_{\varvec{i}}-\stackrel{-}{\varvec{t}})}^{2}}}$$

RM candidate of group 1–1 (stored at − 20°C) were taken to conduct investigation of transport conditions represented for frozen tomato RM. Three shipping insulated foam boxes were prepared for three conditions: the first box contained 3 frozen tomato samples and 2 kg of dry ice (− 5 ± 5°C), the second one contained 3 frozen tomato samples and 2 kg of gel ice (4 ± 5°C), and the third one contained 3 frozen tomato samples only (20 ± 5°C). All of these boxes were added shockproof material and carefully enclosed. Experimental simulation of transport conditions was carried out for 2 days. The sample temperature was measured at the end of experiment time. After that, these frozen tomato samples were analyzed concentration of spiked pesticides.

Tomato freeze dried group 2–2 (stored at − 20°C) were taken to conduct investigation of transport conditions represented for freeze dried CRM similar to the frozen group. The first shipping insulated foam box was prepared for transport 3 samples with shockproof material at ambient temperature (20 ± 5°C). The second shipping insulated foam box contained 3 sample and 2 kg of gel ice (4 ± 5°C). The samples were analyzed after 2 days of simulation experiment.

Laboratory can use RM few times so the stability after open the bottle should be questioned. Three bottles of sample group 1 stored at − 20°C were taken to perform study stability after open the bottle for reusing frozen tomato RM. The bottle was firstly defrosted at room temperature and taken 10.0 g for pesticide analysis, then closed the cap and stored at − 20°C. The cycle of freeze-thawing and sample taken were repeated 7 times within 2 weeks. Sample was taken to analyze at day 1, 3, 5, 7, 9, 11, 13 (day 1 is the open bottle day). For freeze dried tomato RM candidates, stability after open bottle was assessed similarly.

Certified value and uncertainty

The certified values of 6 pesticides were calculated by the average of 10 bottles at initial point (homogeneity assessment). The uncertainty of certified reference material was square root of the sum of squares of the components: uncertainty of homogeneity (${u}_{hom})$, uncertainty of long term stability (${u}_{stab})$, uncertainty of transportation (${u}_{trans})$, uncertainty of characterization which is included uncertainty of pesticide standards (${u}_{std})$ (Table 1) and uncertainty of the analytical method (${u}_{meth}=$15%):

$${u}_{CRM}=\sqrt{{u}_{hom}^{2}+{u}_{stab}^{2}+{u}_{trans}^{2}+{u}_{std}^{2}+{u}_{meth}^{2}}$$

Proficiency testing scheme

RM or CRM are particularly important for analytical chemistry, the application in quality control purposes is well recognized. Although the RM candidates had not been certified completely, the RM candidate (group 1) after two months of production was proofed to be homogeneous and stable then these samples were utilized as a proficiency testing (PT) item in a PT scheme that was organized by National Institute for Food Control (NIFC) with fourteen participants in the whole country.

Homogeneity assessment

The homogeneity of the batches was assessed by ANOVA one-way. The difference between the samples within a batch of frozen tomato or freeze dried tomato is not statistically significant (Table 2). The data showed that both of the RM candidates: frozen tomato and freeze dried tomato were homogenous, the difference between samples was not significant (P-values were greater than 0.05). The calculated ${u}_{hom}$ of each pesticide were presented in Tables 2 and 3.

Table 2

Result of ANOVA one-way test and uncertainty of homogeneity assessment of frozen tomato
No.	Analytes	Average (mg/kg)	MS_between	MS_within	P-value	${\varvec{u}}_{\varvec{h}\varvec{o}\varvec{m}}$ (mg/kg)
1	Acetamiprid	0.2205	2.22E-05	9.77E-05	0.982	0.00699
2	Buprofezin	1.0135	0.00307	0.001145	0.070	0.02586
3	Difenoconazole	0.5853	2.81E-05	2.43E-05	0.408	0.00351
4	Imidacloprid	0.5363	0.00034	0.000408	0.600	0.01428
5	Indoxacarb	0.5306	0.000168	0.000327	0.834	0.01278
6	Profenofos	8.345	0.130244	0.08855	0.278	0.2153
MS: mean square

Table 3

Result of ANOVA one-way test and uncertainty of homogeneity assessment of freeze dried tomato
No.	Analytes	Average (mg/kg)	MS_between	MS_within	P-value	${\varvec{u}}_{\varvec{h}\varvec{o}\varvec{m}}$ (mg/kg)
1	Acetamiprid	4.798	0.0207	0.010	0,1532	0.0760
2	Buprofezin	15.52	0.0513	0.059	0.5780	0.1718
3	Difenoconazole	11.33	0.0213	0.047	0.8750	0.1533
4	Imidacloprid	10.79	0.9116	0.0745	0.3765	0.1951
5	Indoxacarb	10.81	0.0687	0.066	0.4717	0.1820
6	Profenofos	151.5	11.911	11.5	0.4744	2.4022
MS: mean square

Weighing 6 bottles before and after freeze dry process showed that 94.7% tomato mass was reduced (18.9 times). It indicated that water account for 94.7% and dried material account for 5.3% of tomato. The concentration of pesticides in freeze dried tomato increased 19.2 time (in average) compare to frozen tomato that is mainly due to the water remove. The finding was not in line with conclusion of H. Saldanha et al [29] that abundance of analytes losses due to freeze-dried process. The difference can be in freeze dry technique and inherent nature of our chosen analytes. The results of mass loss due to freeze dry process suggests ratio for reconstitute sample:water (1:20).

Transportation stability assessment

Reference materials can be used as proficiency testing items or quality control samples, so these products have to be transported from producer to laboratories. Practically, shipping condition is not often well control like storage condition. The lower the temperature, the more expensive it is to transport samples. Moreover, transportation may cause change in RM properties. Therefore, it is crucial to study transportation stability of RMs in different temperatures.

Frozen tomato RM candidate

In the group of frozen tomato CRM candidate, three conditions of transport were examined and compared to the initial condition (the homogeneity data). Paired comparison of each pesticide was conducted and presented in Fig. 2.

The data show that within 2 days, transport frozen tomato at a temperature of 4 ± 5°C would not make any significant change in the concentration of 6 spiked pesticides. The statistical decline only observed at the last stimulate condition (20 ± 5°C) for Acetamiprid, Difenoconazole, Indoxacarb. Thus, the uncertainty for transport was calculated by standard deviation of transport data at temperature of 2 ÷ 8°C and homogeneity data (Table 3).

Freeze dried tomato RM candidate

In the group of freeze dried tomato candidates, two conditions of transport were examined and compared to the initial condition (the homogeneity data). Paired comparison of each pesticide was conducted and presented in Fig. 3. The freeze dried tomato candidates were stable for transporting at temperature of 4 ± 5°C. While at 20 ± 5°C, stimulation experiment data showed unstable of Acetamiprid, Difenoconazole, Imidacloprid and Indoxacarb.

It is concluded that if the RM candidates are transported within 2 days, they are stable at temperature at 4 ± 5°C. However, if the transportation time is longer, priority is given to transporting the RM at a lower temperature (-5 ± 5°C). The temperatures of 20 ± 5°C will change the properties of the RM candidates. The uncertainty of transport of 6 pesticides at 4 ± 5°C were presented in Table 3.

Stability after open the bottle

Each bottle of RM candidate contains about 100 g of frozen tomato or 50 g of freeze dried tomato that can be used up to 10 times analysis. Thus, it is necessary to assess stability of the material after open the seal of the RM bottle.

After several times of defrosting, the sample of frozen tomato was likely to separate water from the matrix that lead to inhomogeneity within a bottle. Therefore, it is recommended to shake the bottle well or vortex before taking sample from the bottle. Data analysis (Fig. 4) showed that after 3 cycles of freeze-thawing the frozen RMs were stable. After 4 cycles of freeze-thawing, visibly, the color of frozen tomato pureed became slightly darker, and the concentrations of pesticide reduced. Thus, the frozen tomato material is recommended to be use within a week after open the bottle seal or 3 cycles of freeze-thawing, and the sample bottle should be vortexed well before taking sample. In contrast, the freeze dried RM did not show any significant change in concentration of pesticides as well as physical state after 7 cycles of freeze-thawing. Therefore, it can be concluded that the freeze dried tomato RM is table for use within 2 weeks or 7 cycles of freeze-thawing.

Shelf life estimation and uncertainty

RM candidates of each group were monitor pesticide concentration for 6 months. The data was collected to establish the trend line. In this situation, the change in concentration is small so linearity trend was applied for all pesticides. The acceptable change for analytes to estimate uncertanty of long term stability was 10% of certified value. The uncertainty of the analytical method (15%) was the main component account to the uncertainty of the RM that account for. Certified value, estimated shelf life and uncertainty of 6 pesticides were present in Table 4 and Fig. 5. For frozen tomato at − 20°C, the shelf life of 6 pesticides were similar, from 407 to 455 days. When the storage temperature is lowered to − 80°C, the estimated shelf life of the sample increases by 1.7 to 2 times. With freeze dried samples, the storage time of the sample was different for each substance. Furthermore, freeze-dried samples can be stored at higher temperatures. At 4°C, the freeze-dried RM was estimated to be stable for 548 days; at − 20°C, the estimated shelf live was 696 days.

Proficiency testing result

The group 1 RM candidate after two month of production were used for a proficiency testing (PT) scheme. Most of the participants analyzed pesticides by liquid chromatography – mass spectrometer, and few participants used gas chromatography – mass spectrometer. The results of participants were checked by Grubbs’ test for outlying observation and remove "outliers" according to ISO 5725-2:2019 (E). Assigned value (xpt), standard deviation (σpt) and uncertainty of PT scheme were calculated according to ISO 13528:2015 and AOAC INTERNATIONAL – Appendix F-Table 5. Difenoconazole and Imidacloprid data were statistically analyzed by Algorithm A; the other were processed by Qn method. Z’-score of them were shown in the Fig. 6. It can be seen from Table 5that the assigned values of PT scheme are agree with the certified values including measurement uncertainty of the corresponding pesticide. That proves the reliability of the certified value of our RM candidate.

Table 5

Assigned value (xpt), standard deviation (σpt) and uncertainty of the PT scheme compare with the certified value and uncertainty (k = 2) of RM
No	Analyte	Assigned value (mg/kg)	σ_pt (mg/kg)	u_x (mg/kg)	Certified value (mg/kg)	Uncertainty (mg/kg)
1	Acetamiprid	0.214	0.021	0.008	0.2205	0.072
2	Buprofezin	0.970	0.077	0.029	1.0135	0.320
3	Difenoconazole	0.590	0.071	0.027	0.5853	0.180
4	Imidacloprid	0.532	0.063	0.022	0.5363	0.170
5	Indoxacarb	0.553	0.048	0.020	0.5306	0.166
6	Profenofos	8.32	0.481	0.222	8.345	2.544

Comparison of frozen tomato and freeze dried tomato RM

It is evident that the matrix effect is highly affect result in pesticide residue analysis not only for tomato but only other foodstuffs matrix [2]. Preparation of matrix matched calibration curve and using quality control sample (RM, CRM) are the typical solutions for this problem. This study not only focus on the production and characterization of RMs but also comparison of two RM production processes in term of production, transportation, storage and utilization.

It is obvious that the process of producing freeze dried tomato RM involves more steps than the frozen tomato RM. However, freeze dried tomato can adapt to higher storage temperatures that are easier to conduct and cost-effective.

For transportation, both RMs need to be kept at 4 ± 5°C to be stable for 2 days. Longer time of transportation should be stored at lower temperature.

Regarding the use of RM in analysis, there is no difference between frozen RM or freeze-dried RM after reconstitution with water at the ratio of sample:water 1:20 (w/w). However, when defrosted, frozen RM is susceptible to separate water from the matrix, causing sample inhomogeneity within one RM unit. This problem does not occur with freeze-dried samples. Moreover, the freeze-dried RM was proved to be stable for 2 weeks after opening the bottle or defrosting 7 times, while frozen RM only stable for one week or 3 times defrosting. In sample preparation, the frozen tomato and the reconstitute freeze dried tomato did not show any difference.

This study has successfully procured RM for pesticide residues in tomato. Although both of frozen and freeze dried RM were assessed to be homogeneous and stable for over one year, the freeze-dried RM has more advantages over the frozen one in term of storage, transportation and utilization. At a temperature of 4°C, freeze-dried RM are predicted to be stable for all six pesticides for at least 548 days, while at a temperature of − 20°C, the stability time is at least 696 days. The RM was also confirmed to be reliable and stable when successfully organizing a proficiency testing program with 14 participating laboratories across the country. The assigned values of PT scheme are agree with the certified values including measurement uncertainty of the corresponding pesticide. That proves the reliability of the certified value of our RM candidate.

Acknowledgements

This work was supported by National Institute for Food Control, Vietnam.

Contributors

Nguyen Thi Anh Huong, Le Thi Hong Hao and Nguyen Thi Minh Hoa have framed the concept for this work and carried it out by Nguyen Linh Trang, Tran Thi Thu Trang, Dinh Hoang Anh, Nguyen Thi Thao Nguyen, Le Thi Phuong Thao. The statistical data were analyzed by Nguyen Thi Minh Hoa. The manuscript was written by Nguyen Thi Minh Hoa and approved by all the authors.

Corresponding author

Correspondence to Nguyen Thi Minh Hoa, Email: [email protected] and Thi Anh Huong Nguyen, Email: [email protected].

Conflict of interest

The authors declare that they have no competing interests.

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No competing interests reported.

Study on production and utilization of a reference material for determination of multi-residue pesticides in tomato matrix

Status:

Version 1

Abstract

Figures

Introduction

Materials and methods

Chemicals and reagents

Equipment

Preparation of tomato reference material candidates

Analytical method for quantification of multi-residues pesticide in tomato

Homogeneity assessment

Stability assessment

Certified value and uncertainty

Proficiency testing scheme

Results and discussion

Homogeneity assessment

Transportation stability assessment

Frozen tomato RM candidate

Freeze dried tomato RM candidate

Stability after open the bottle

Shelf life estimation and uncertainty

Proficiency testing result

Comparison of frozen tomato and freeze dried tomato RM

Conclusion

Declarations

References

Additional Declarations

Status:

Version 1